ManeuversFlight Notes

ManeuversFlight Notes
Maneuvers and Flight Notes
Copyright Flight Emergency & Advanced Maneuvers Training, Inc. dba Flightlab, 2009. All rights reserved.
For Training Purposes Only
General Briefing
Anxiety!!!
If you’ve never flown aerobatics (or have had
some bad experiences in the past), anxiety is
natural. Sometimes people are anxious about
safety, sometimes about how well they’ll
respond when the instructor places the aircraft in
an upset condition. Anxiety disappears as you
learn to control the aircraft. We won’t take you
by surprise (well, not immediately). We’ll teach
you how to follow events so that surprises
become manageable.
Even so, there may be times when you feel that
too much is happening too fast. That’s not
entirely bad: it shows that you’re pushing the
boundaries of your previous training. As you
gain practice you’ll find that the aircraft’s
motions become easier to follow and tracking the
horizon becomes less difficult. Your comfort
level then quickly rises.
But if you feel confused or unsafe at any time, let
us know.
Airsick?
The same goes if you begin to feel airsick. You
probably don’t learn well with your head in a
bag, so don’t hesitate. Let us know immediately
so that we can modify the program and flight
schedule for your comfort. If you’re new to
aerobatics, you’ll discover that airsickness has
nothing to do with the previous number of
trouble-free hours in your flying career.
Resistance—or “habituation,” depending on your
theory—usually arrives, but it takes time.
Most of our maneuver sets call for repetitions,
but we can easily stretch those out over several
flights, if you prefer. That’s easier on the
instructor, as well. If you’re concerned about
airsickness, a good resistance-building technique
is to fly somewhat aggressive lazy-eights (which
you might remember from the Commercial
Flight Test) in a light aircraft a few days before
you fly with us. Lazy-eights supply the pitching
and rolling motions and variations in g force
your body must adjust to. But stop at the first
feelings of discomfort. Becoming sick does not
help you adapt faster.
Don’t fly aerobatics on an empty stomach. Eat!
You look thin! Drink plenty of water, especially
when the outside temperature is high.
Dehydration reduces g tolerance.
Research done with persons subject to motion
sickness suggests what you’ve perhaps already
observed: People who report that they’ve
recovered from feelings of nausea can remain
highly sensitized to vestibular disturbance for
hours afterwards. That’s why those airsick
passengers who announce with relief that they’re
now feeling much better often spontaneously reerupt as you start to maneuver into the traffic
pattern. The temporary disappearance of
symptoms doesn’t necessarily mean the battle is
over.
What to Read: Ground School Texts
The texts you’ll receive (or download) along
with the Maneuvers and Flight Notes cover a
wide range of subjects, giving background
material you can go into, more or less deeply,
according to your interests. Our program is best
for pilots who not only want to gain aerobatic
and upset recovery skills but who also have a
broader curiosity about the principles of aircraft
response. Skills can be learned quickly, but
satisfying curiosity takes time—because, ideally,
curiosity grows. (And the subject of airplanes is
vast.) You may find it helpful to read at least the
ground school selections “Axes and Derivatives”
and “Two-Dimensional Aerodynamics” before
the first flight—don’t worry if you don’t have a
technical background; they’re not as nerdy as
they sound. Treat the ground school texts as a
long-term resource, not a short-term burden.
What to Think About
Think about searching out the basic relationships
that determine aircraft behavior. At very least,
you need to examine two areas. The two ground
Maneuvers and Flight Notes
school selections mentioned above provide an
introduction.
You need to understand how an aircraft
responds to its own velocity vector, and to its lift
vector. If you know where the velocity vector is
pointed (relative to the aircraft’s fixed axes), and
where the lift vector is pointed (relative to the
horizon), you know how a stable aircraft is likely
to behave. This is the core of our presentation of
stability and control.
You also need to understand the nature of the
pressure patterns over the surface of the wing:
how those patterns originate and how they
migrate as angle of attack changes. This is
especially important as the aircraft approaches
the stall, because pressure patterns determine the
availability of control.
Where to Look
Unusual-attitude training should take both
outside and inside attitude references into
account. Aerobatic pilots look outside first. We
fly in reference to the real horizon, not the
artificial one. Of course, that’s because we fly
aerobatics only in VFR conditions; but even if
we have an aerobatic-friendly attitude indicator,
the real horizon provides much better
information.
Unlike aerobatic pilots, many IFR pilots tend to
look inside first, even in good weather. If control
of aircraft attitude is a reflexive, heads-in activity
for you, you may need to reacquaint yourself
with the information out the window. Partly
because of the essential role peripheral visual
cues play in spatial awareness, that’s where the
information is best during unusual attitudes.
Physiological correlation between what your
body feels and what your eyes see also happens
much faster when you’re looking outside. Then
begin to connect what you’ve learned about
aircraft behavior from looking out with the
symbolic attitude information available within
the cockpit. You’ll find that the symbolic
information—which unfortunately lacks the
peripheral cues we primarily rely on to perceive
our motion within the world—becomes easier to
interpret when you can associate it with attitudes
and flight behaviors you’ve already seen outside.
valuable building block, outside/inside-learning
process may not occur with sufficient repetition
for the benefits to sink in. Pilots might
demonstrate maneuvering proficiency in specific,
directed tasks, but still have limited attitude
awareness.
Rudder Use
We want you to experience and understand the
effects of rudder deflection on aircraft response
at high angles of attack. While the same basic
aerodynamic principles apply in swept-wing
aircraft as in our straight-wing propeller-driven
trainers, in practice large aircraft and swept-wing
dynamics are different, and more limited rudder
use is recommended. On matters concerning
rudders, search the Internet for Boeing
Commercial Airplane Group Flight Operations
Bulletin, May 13, 2002. Also Airbus FCOM
Bulletin, Use of Rudders on Transport Category
Airplanes, March 2002.
Standard Procedures
•
Clear the airspace before each
maneuver.
•
Acknowledge transfer of control.
•
Don’t hesitate to apply your own CRM
procedures and call-outs as you think
appropriate to the safety of the flight.
•
Don’t fret about your mistakes.
Mistakes are your best source of
information. Bracket your responses
until you zero-in on the correct
procedure.
One of the drawbacks of simulator training
programs for unusual attitudes is that this
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Maneuvers and Flight Notes
2.
Maneuver Sets and Lesson Plan
Because certain maneuvers use up motion
tolerance more rapidly than others, and personal
tolerance varies, your maneuver sequence might
be different than the standard schedule. You’ll
also repeat some maneuvers when you fly the
second aircraft.
The core lesson is upset recovery, but we teach
much more than recovery procedures, as you’ll
see when you begin reading. The Flight Notes
below each maneuver description cover
fundamental aerodynamic principles. Together
with the ground school presentations and
supporting texts, they describe aircraft
characteristics you’ll observe and techniques
you’ll learn. They attempt to expand your frame
of reference with examples drawn from different
aircraft types. They’re part narrative, part
explanation, and sometimes a warning.
The information in the Flight Notes is obviously
more than an instructor could give during a
flight, and much more than a student could be
expected to take in. Chances are we won’t have
time to cover every detail, nor will every detail
apply to your type of flying. Don’t let the
material overwhelm you. Familiarize yourself
with the relevant Flight Notes before each sortie,
as you think best. When you review the notes
after the flight, you’ll find them much easier to
absorb, because you can connect them with what
you’ve just done. The ground school texts
reinforce the Flight Notes and add further
information.
We use boldface italics to emphasize important
concepts. (Boldface in the procedure description
reminds instructors of points to emphasize in
setting up and carrying out maneuvers.)
Steady-Heading Sideslip: Dihedral Effect &
Roll Control
High Angle of Attack (Alpha):
3.
4.
5.
6.
7.
Stall: Separation & Planform Flow (Wing tuft
observation)
Accelerated Stalls: G Loads & Buffet
Boundary, Maneuvering Stability
Nose High Full Stalls & Rolling Recoveries
Roll Authority: Adverse Yaw & Angle of
Attack, Lateral Divergence
Flap-Induced Non-convergent Phugoid
Roll Dynamics:
8.
Nose-Level Aileron Roll: Rolling Flight
Dynamics, Free Response
9. Slow Roll Flight Dynamics: Controlled
Response
10. Sustained Inverted Flight
11. Inverted Recoveries
12. Rudder Roll: Yaw to Roll Coupling
Refinements and Aerodynamics:
13.
14.
15.
16.
17.
Rudder & Aileron Hardovers
Lateral/Directional Effects of Flaps
Dutch Roll Characteristics
CRM Issues: Pilot Flying/Pilot Monitoring
Primary Control Failures
High-Alpha/Beta Departures:
18. Spins
Additional Basic Aerobatic Maneuvers:
Loop, Cuban Eight, Immelman, Hammerhead,
Slow Roll, Point Roll
Here’s how the maneuvers break down into
general categories:
Natural Aircraft Stability Modes, Yaw/Roll
Couple:
1.
Longitudinal & Directional Stability, Spiral
Divergence, Phugoid
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3
Maneuvers and Flight Notes
First Flight
Second Flight
Third Flight
1. Longitudinal & Directional
Stability, Spiral Divergence,
Phugoid
9. Slow Roll Flight Dynamics:
Controlled Response
Review Maneuver Sets 9-12
10. Sustained Inverted Flight
16. CRM Issues: Pilot
Flying/Pilot-Not-Flying
2. Steady-Heading Sideslip:
Dihedral Effect & Roll Control
11. Inverted Recoveries
18. Spins
3. Stall: Separation & Planform
Flow (Wing tuft observation)
12. Rudder Roll: Yaw to Roll
Coupling
Basic Aerobatic Maneuvers
4. Accelerated Stalls: G Loads &
Buffet Boundary, Maneuvering
Stability
13. Rudder & Aileron Hardovers
5. Nose High Full Stalls &
Rolling Recoveries
15. Dutch Roll Characteristics
6. Roll Authority: Adverse Yaw
& Angle of Attack, Lateral
Divergence
Possible:
7. Flap-Induced Non-convergent
Phugoid
Basic Aerobatic Maneuvers
8. Nose-Level Aileron Roll:
Rolling Flight Dynamics, Free
Response
On Return:
On Return:
14. Lateral Effects of Flaps
19. Spins
17. Primary Control Failures (as
necessary)
Fourth Flight
Review and additional aerobatic
maneuvers to be determined.
17. Primary Control Failures
Possible:
9. Slow Roll Flight Dynamics:
Controlled Response
On Return:
17. Primary Control Failures
These maneuvers are for training purposes in appropriate aircraft
only. Follow the procedures and obey the restrictions listed in
your pilot’s operating handbook or aircraft flight manual.
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Maneuvers and Flight Notes
Trimming for Airspeed in Level Flight
We usually trim an aircraft in climb for VY, best rate of climb, or perhaps a bit faster to preserve the view over
the nose and to keep engine temperatures from rising. In descending from altitude for landing, we might trim
for a comfortable descent rate. In the pattern we trim for pattern speed based on habitual power settings, and
then for our landing reference speed.
But we usually don’t trim for a particular airspeed in cruise. Instead, we level off at a certain altitude,
accelerate a little while nudging the trim forward, and then pull back the power to cruise setting. Last, we
final-trim to zero out the control force necessary to maintain level flight. Then we take the airspeed we get.
Sometimes in flight-testing, or in our program, you’ll want to start a maneuver from a specific, trimmed,
level-flight airspeed. Here’s what you do:
•
Bring the aircraft to the required altitude
•
Set the power to the approximate value dictated by experience. Of course, don’t chase airspeed with
large power changes. Just get close.
•
Use pitch control to bring the aircraft to the desired airspeed.
•
While holding airspeed constant, use power to center the VSI at zero climb/descent rate.
•
Trim out the control force.
Note that pitch controls airspeed, power controls the aircraft’s flight path angle relative to the horizon.
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5
Maneuvers and Flight Notes
1. Longitudinal & Directional Stability, Spiral Divergence, Phugoid
Flight Condition: Upright, free response in roll/pitch/yaw.
Lesson: Aircraft behavior when disturbed from equilibrium flight.
Procedures:
Longitudinal Stability: Stick force, Phugoid
Static stability: On the climb to the practice area, trim for VY. Observe longitudinal (pitch axis) stick
forces needed to fly at airspeeds greater than or less than trim. Assess force gradient. Look for
characteristics due to friction.
Simulate the effect on longitudinal stability of moving center of gravity aft: Trim, pitch up to fly 10
knots slower than trim, hold speed while instructor slowly trims nose up. Note how stick force
decreases (simulating a decrease in stability), disappears (simulating neutral stability), and then
reverses (simulating static instability).
Dynamic stability: Use pitch up and stick release to demonstrate phugoid. Observe period, amplitude,
damping.
Directional Stability:
Low cruise power, airspeed white arc.
Enter flat turn with rudder, while keeping wings level with aileron. Observe build up of pedal forces
to full deflection.
Quickly return pedals and ailerons to neutral; observe overshoots and damping.
Look for characteristics due to friction.
Lateral Stability: Spiral Mode
Power and trim for low cruise.
Enter a 10-degree bank angle, return controls to neutral and observe response in roll. Note appearance
of phugoid. Repeat bank with additional 10-degree increments until onset of spiral departure.
Look for asymmetries by repeating to the opposite side.
Allow spiral mode to develop as consistent with comfort and safety.
Roll wings level; release controls; observe recovery phugoid.
Reduce entry airspeed and observe the increase in roll amplitude versus time.
Knife-edge recovery:
Low cruise power, airspeed white arc.
Roll knife-edge.
Immediately release controls and observe response.
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Maneuvers and Flight Notes
Flight Notes
We’ll start by exploring how an aircraft’s inherent stability determines its free response when disturbed
from equilibrium. Free response is what happens when the pilot stays out of the control loop. It’s easier to
understand the sources of an aircraft’s complex, self-generated motions when you can break them down
into simpler, free response “modes” around each axis. Usually, a moment generated around one axis
produces some form of response around another. From the standpoint of unusual-attitude training, if you
understand and can anticipate an aircraft’s “basic moves,” managing the control loop properly to maintain
or to re-establish control becomes closer to second nature.
In aircraft with basic cable-and-pushrod reversible controls, like our trainers, free response can depend on
whether the stick and rudder pedals are held fixed or literally left free so that the control surfaces are
allowed to streamline themselves to changes in airflow. Irreversible, hydraulically powered controls are
always effectively fixed. See FAR Parts 23 & 25.171-181 for stability requirements.
Longitudinal Static and Dynamic Stability
flight test procedures to look at basic aircraft
characteristics. We’re going to adapt the
procedures to our own purposes, take a general
approach, have fun, and not worry about always
doing things with the real precision that’s
required to gain accurate data points in actual
flight test. A rough narrative follows.
•Here’s the deal on longitudinal static stability,
as required by Part 23.173: “… with the airplane
trimmed … the characteristics of the elevator
control forces and the friction within the control
system must be as follows: (a) A pull must be
required to obtain and maintain speeds below the
specified trim speed and a push required to
obtain and maintain speeds above the specified
trim speed.’’
•On the way to the practice area we’ll observe
the Part 23.173 requirement. We’ll trim the
aircraft and then observe the stick forces
necessary to fly at slower and faster airspeeds
(a.k.a. angles of attack) without retrimming.
When we release the force, the nose initially
pitches toward the trim angle of attack. This
initial tendency is what we mean by positive
static stability (static refers to the initial
tendency, dynamic refers to the tendency over
time). The more force we have to apply to
deviate from trim, the greater the stability. We
can increase static stability (and thus the stick
forces needed to deviate from trim) by moving
the center of gravity forward. We decrease
stability (and decrease the forces) by moving it
aft. We can fake the effect using trim, as
described in the Procedures, above.
• You’ll observe that the push force required to
hold the aircraft 10 knots, say, faster than trim is
noticeably greater than the pull force needed to
hold it 10 knots slower. That’s because the
dynamic pressure generated by the airflow
you’re holding against is a function of velocity
squared, V2. The illustration below suggests how
stick forces vary with speed. The force is zero at
trim speed.
Stick Force
Gradient
Pull
Control Force, FS
•We’ll use some maneuvers borrowed from
Trim Speed
0
Airspeed
Push
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7
Maneuvers and Flight Notes
•Phugoid: Next, we’ll pitch up about 45 degrees
Positive Longitudinal
Dynamic Stability
Period
Displacement
or more, slow down and nibble at the stall, then
return the stick to its trim position and let go.
(This is a more aggressive entry than actually
required to provoke a phugoid, but it’s a good
attention-getter during unusual-attitude training.)
The nose will start down, again indicating
positive static stability, but then go below the
horizon. Velocity will increase past trim speed,
and the nose will begin to rise. Although the
aircraft’s attitude varies, its angle of attack
remains essentially constant. The aircraft will
pitch up, slow, pitch down again, speed up, and
then repeat this up-and-down phugoid cycle a
number of times. It will gradually converge back
to its original trimmed state. (Had we simply let
go of the stick instead of carefully returning it to
the original trimmed position, control system
friction might have produced a different elevator
angle and a different trim. That, in turn, could
superimpose a climb or a dive over the phugoid
motion.) Your instructor will point out that the
amplitude of each pitch excursion from level
decreases (indicating positive damping and thus
positive dynamic stability) while the period (time
to complete one cycle) remains constant at a
given trim speed. The period is quite long, so the
phugoid is also referred to as the ‘long period”
mode—and the faster you fly the longer the
period. Damping in the phugoid comes from the
combined effects of thrust change and drag
change as the aircraft alternately decelerates and
accelerates as it climbs and descends.
Time →
Equilibrium
Amplitude
Time to subside
Period/Time to subside = damping ratio, ζ
•You’ll need right rudder at the top of the
phugoid to counter the slipstream and p-factor
and keep the nose from yawing, and maybe some
left rudder at the bottom. You might need aileron
to keep wings-level, as well—but don’t
contaminate the phugoid with inadvertent
elevator inputs.
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Maneuvers and Flight Notes
Directional Stability
• Notice that the aircraft tries to roll in the
•Flat Turn: The next maneuver is the basic
flight test for static directional (z-axis) stability.
When you depress and hold a rudder pedal,
causing the nose to yaw along the horizon, you
generate a sideslip angle, β. Sideslip creates a
side force and an opposing moment. Notice the
increased pedal force necessary as rudder
deflection increases. For certification purposes,
rudder pedal force may begin to grow less
rapidly as deflection increases, but must not
reverse, and increased rudder deflection must
produce increased angles of sideslip. The rudder
must not have a tendency to float to and lock in
the fully deflected position due to a decrease in
aircraft directional stability at high sideslip
angles as the fin begins to stall. If it did, the
aircraft would stay in the sideslip even with feet
off the pedals. (Things could be dicey if the
pedal force needed to return a big rudder
exceeded the pilot’s strength. Many well-known
aircraft had rudder lock problems during their
early careers, including the DC-3 and the early
Boeing 707, and the B-24 Liberator bomber.)
direction of the deflected rudder, and that you
have to apply opposite aileron to keep the wings
level. This is caused by a combination of
dihedral effect (an aircraft’s tendency to roll
away from a sideslip angle, β, a response we’ll
examine presently), and roll due to yaw rate—in
which one wing moves faster than the other and
produces more lift. An aircraft with reduced
directional stability may yaw faster in response
to rudder deflection than will a more stable type,
and go to a higher β, and consequently need
more opposite aileron. (You’ll see a difference
between the Zlin and the SF 260 in this regard.)
•Finally, note that when you apply aileron
against the roll, you’re also applying an
additional “pro-rudder” yaw moment, this time
caused by the adverse yaw that occurs when the
into-the-turn aileron goes down. (There’re other
moments in the mix we won’t worry about.)
•A given rudder deflection produces a given
sideslip angle, but the force required rises with
the square of airspeed. So we won’t have to work
as hard if we pull the power back to keep the
speed down.
Directional Stability
X
v
β
V
v is the Y-axis component
of the aircraft’s velocity
vector, V.
v = V sin β
•When you release or quickly center the pedals,
the now unopposed side force causes the aircraft
to yaw (weathervane) into the relative wind. In
our jargon, the directionally stable aircraft yaws
its plane of symmetry back into alignment with
the velocity vector. This initial tendency
demonstrates positive static directional stability.
We’ve entered a dynamic state, as well.
Momentum takes the nose past center, which
generates an opposing side force that pushes it
back the other way. The nose keeps
overshooting, but the amplitude of the
divergence decreases each time. This time
history indicates positive dynamic directional
stability. You might notice an increase in
damping when you return the rudders positively
to neutral and hold them fixed, instead of letting
them float free. However, this behavior also
depends on the amount of friction in the rudder
control circuit.
Bill Crawford: WWW.FLIGHTLAB.NET
Stabilizing yaw
moment.
9
Maneuvers and Flight Notes
Spiral Mode
•When you enter a shallow bank and positively
return the controls back to neutral (so that
unintended deflections or control system friction
don’t taint the result) the aircraft should slowly
start to roll level after a few moments. The
aircraft’s velocity vector (for a definition, see
ground school text “Axes and Derivatives”) has a
component of motion (sideslip) toward the low
wing, which leads to a wings-level rolling
moment due to dihedral effect—a response
referred to as lateral stability. The aircraft’s
lateral stability provides positive spiral stability.
Sideslip also produces a yawing tendency, but
dihedral effect predominates at smaller bank
angles.
Sideslip Becomes a Spiral Dive
When Dihedral Effect x Yaw Damping <
Directional Stability x Roll Due to Yaw Rate
Lβ.
Z axis
Resulting yaw rate, r.
Roll moment due to
yaw rate, Lr, greater
than opposite roll
moment due to
sideslip, Lβ.
•The outside wing in the turn is moving faster
than the inside wing—that’s a yaw rate. As you
add bank increments you’ll find a point—if the
atmosphere’s not too turbulent—where bank
angle remains constant (neutral spiral stability).
The rolling moments produced by dihedral effect
and roll due to yaw rate are now equal and
opposite. (Again, there’re other moments in the
mix, but their contribution is minor.)
• At some point the aircraft will likely begin a
banked phugoid, just like the phugoids we’ve
observed, but tipped on its side. The aircraft will
bring its nose up and down as it turns. Hands off,
the aircraft retains a constant angle of attack,
according to trim, regardless of pitch attitude or
bank angle.
•When we raise the bank angle further, but don’t
increase lift by adding back stick, the aircraft
slips increasingly toward the low wing. The yaw
rate builds due to the greater side force against
the tail. Directional (z-axis) stability causes the
nose to weathervane earthward in a descending
arc. Now roll due to yaw rate predominates over
the opposite rolling moments, and sends the
aircraft into the unstable spiral mode
•Test pilots typically place an aircraft in a given
bank angle, center the ailerons (or bank the
aircraft with rudder while holding the ailerons
fixed), and then time the interval required to
reach half the bank angle for the spirally stable
condition, or double the bank angle for the
unstable. It’s important that control surfaces are
10
Lr
v
Effective lift less than weight
results in a sideslip velocity
component, v, and sideslip
angle, β.
positively centered during these tests, because
any residual deflection caused by control system
friction can create an apparent difference in
spiral characteristics. (Friction confuses the
picture when you’re trying to figure out how an
aircraft behaves. Friction in the elevator system
makes you think longitudinal stability is different
than it is; friction in the ailerons that prevents
them from returning to center automatically
when released gives you a roll rate that shouldn’t
be there. Normally, you’d accommodate to such
things without really being aware of the extra
control input—but here we’re paying attention!)
•The coefficient of roll moment due to yaw rate,
Clr, goes up with coefficient of lift, CL, so it’s
more pronounced at low speeds, where α and
coefficient of lift are high. And for a given bank
angle, yaw rate goes up as airspeed goes down.
So you’ll double your spiral bank angle more
quickly at lower entry speeds.
•Finally, note that the ball stays essentially
centered during a spiral departure. That’s
directional stability doing its job, unto the last.
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
Phugoid Again
•The phugoid shows us how a trimmed,
•Recover from spiral dives by first rolling the
wings level with the horizon. Now we’re back in
the more familiar wings-level phugoid. Notice
how the aircraft’s positive static longitudinal (yaxis) stability initially brings the nose back to
level flight. You’d normally push to suppress the
phugoid as the nose comes level with the
horizon, but we’ll again allow the aircraft to go
past level and progress through the first cycles of
the phugoid mode.
•Again, you’ll need right rudder at the top of the
phugoid to counteract the slipstream and p-factor
and keep the nose from yawing, and some left
rudder at the bottom. Jets and counter-rotating
twins don’t have this problem.
•An aircraft’s longitudinal stability comes from
its tendency to maintain a trimmed angle of
attack. As you ride through it, the attitudes,
altitudes, and airspeeds change, but in a phugoid
the angle of attack, α, remains basically
constant. The attitude excursions of our
constant-α phugoid remind us again that an
aircraft’s angle of attack and its attitude are two
different things. When displaced, aircraft return
to their trimmed attitude and airspeed by virtue
of maintaining their trim angle of attack
throughout a cycle of phugoid motions. In
essence, pilots keep altitude pegged by keeping
ahead of the phugoid and damping its cycle
themselves. A power change provokes a
phugoid, unless the pilot intervenes to smooth
out the transition.
longitudinally stable aircraft normally maintains
its speed if left to its own devices. After a
disturbance, it puts its nose up or down, trading
between kinetic and potential energy, until it
eventually oscillates its way back to trim speed
(or to its trim speed band if control friction is
evident). But the trade becomes solely potential
to kinetic when a bank degenerates into a spiral
and, as we’ve seen, the bank angle becomes too
steep for the phugoid to overcome. Think of a
spiral departure as a “failed” phugoid, in which
the nose can’t get back up to the horizon because
the lift vector is tilted too far over.
•What if an aircraft trimmed for cruise rolls
inverted for some reason and the befuddled pilot
just lets go? Left unattended, the inverted aircraft
will pursue its trim by dropping its nose and
“reverse-phugoiding” itself around in a rapidly
accelerating back half of a loop (a “split-s”).
Speed will rise until the structure maybe quits, or
the dirt arrives. Inverted, hands-off survival
prospects improve in the unlikely situation that
the aircraft is at altitude but trimmed for slow
flight. Trimmed for 70 knots with power for
level flight, and then rolled inverted while the
nose is allowed to fall, the Zlin will pull a 4-g
split-s, hands-off on its trim state alone, using up
some 1,300 feet of altitude. Then it will playfully
zoom right back up into a normal but initially
high-amplitude phugoid.
•We’ll experience an increased g load as
airspeed exceeds trim speed at the bottom of the
phugoid. At a constant angle of attack, lift goes
up as the square of the increase in airspeed. If we
trim for 100 knots in level flight (1 g) and
manage things so as to reach 200 knots (which
we won’t!), airspeed will be doubled and load
factor will hit a theoretical 4 g. If we accelerate
to 140 knots, that’s a 1.4 increase in speed. 1.42
= 2; thus a load factor of 2 g. (The actual factor
can be affected by the mass balance of the
elevator, or the presence of springs or bob
weights.) We’ll experience less than 1 g over the
top.
Bill Crawford: WWW.FLIGHTLAB.NET
11
Maneuvers and Flight Notes
Knife-edge Free Response
•After you’ve observed spiral characteristics,
and learned to expect divergence following a
high bank angle, knife-edge behavior might
surprise you. Starting at knife-edge with the nose
on the horizon, when the controls are released an
aircraft with positive dihedral effect will
generally roll upright and pitch nose-down (and
then eventually pitch up into a phugoid if you
don’t touch the elevator). The roll response has
been associated with the amount of “keel” area
above the aircraft’s c.g. Acting at different
locations and in opposite directions,
aerodynamic side force and gravity produce a
roll couple. This wings-leveling couple, added to
that generated by dihedral effect, overcomes the
opposing spiral tendencies caused by directional
stability and roll due to yaw rate.
•If you enter knife-edge flight, or even just a
steep bank angle, in a nose-high attitude,
however, spiral tendencies will often dominate.
It’s fun to examine this by flying aggressive
lazy-eights (linked wingovers) and observing
12
Keel Effect
Resulting roll.
Side force produces
both wings-level roll
moment and nosedown yaw moment.
Gravity acting
through
aircraft c.g.
which moments win out when you let go of the
stick and/or rudder at various points. Note the
phugoid embedded in the maneuver as the
aircraft climbs and descends.
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
2. Steady-Heading Sideslip: Dihedral Effect & Roll Control
Flight Condition: Upright, crossed controls, high β.
Lesson: Lateral behavior during sideslips.
Procedures:
Power for speed in the white arc.
Apply simultaneous aileron and opposite rudder to rudder stop.
Aileron as necessary to maintain steady heading with no yaw rate.
Maintain approximate trim speed. Aircraft will descend.
Hold rudder/ release stick.
Repeat in opposite direction.
Hold stick/ release rudder. Observe sequence of yaw and roll.
Hold sideslip. Pitch up and down to demonstrate y-wind-axis pitch/roll couple.
Possible Maneuver: Hold the sideslip and demonstrate “over the top” spin entry, with immediate, controls
neutral recovery.
Flight Notes
A directionally and laterally stable aircraft yaws toward but rolls away from its velocity vector when
the vector is off the plane of symmetry. Those characteristics are the “ basic moves” of directional and
lateral behavior. In our steady-heading sideslips, we’ll apply cross-controls—rudder in one direction and
aileron in the other—causing the aircraft to fly with its velocity vector displaced from symmetry. The
control forces necessary to prevent the aircraft from yawing and rolling in response to that displacement are
the reflection of its inherent stability. They tend to change with angle of attack, especially in the buffet
boundary, where aileron effectiveness often deteriorates and the rudder takes on increasing importance for
lateral control. In that regime, a pilot often displaces the velocity vector on purpose, to assist roll control.
(He may not know that’s what he’s doing, but nevertheless...)
Pilots of flapless (usually aerobatic) aircraft are accustomed to using sideslips to control the descent to
landing. It’s how they show off in front of the aircraft waiting at the hold line. If you rely on flaps for
descent, you may be rusty on aggressive cross-control slips. A little practice with them will improve your
ability to respond to control system failures. You counter the rolling moment generated by an
uncommanded rudder or aileron deflection by entering an opposing sideslip, modifying the sideslip as
necessary for turns.
•Test pilots use steady-heading sideslips to
evaluate an aircraft’s lateral stability. That means
its tendency to roll away from the direction of a
sideslip—in other words, to roll away from the
direction the velocity vector is pointed when the
velocity vector is not on the plane of symmetry.
(The mechanics of lateral stability, or dihedral
effect, are explained in more detail in the ground
Bill Crawford: WWW.FLIGHTLAB.NET
13
Maneuvers and Flight Notes
school text “Lateral-Directional Stability.”)
Steady-heading sideslips are also used to assess
directional stability and rudder effectiveness by
measuring the rudder deflection and pedal force
needed to produce a given sideslip angle, β.
They can also be used to evaluate control
harmony and to set up the conditions for
observing Dutch roll. Wing-low crosswind
landings are steady-heading sideslips, so an
aircraft’s behavior in sideslips can limit
crosswind capability.
•Pressing the rudder and yawing the aircraft
•Do you notice any differences sideslipping to
the left or right, possibly caused by p-factor or
slipstream?
•Dihedral effect can depend on aircraft
configuration. It can diminish with flap
extension. This is important in connection with
rudder hard-overs, because flaps lower
“crossover” speed, as you’ll see later.
•When you release the stick while holding
creates a sideslip angle between the aircraft’s
velocity vector and its x-axis plane of symmetry,
as illustrated to the right, below. This in turn
produces a rolling moment due to dihedral effect.
We’ll evaluate the strength of this yaw/roll
couple at various sideslip angles by observing
the aileron deflection needed to counteract the
roll and fly the aircraft at a constant, steady
heading, although sideways and wing-low.
rudder, the low wing rises due to dihedral effect
and to roll due to yaw rate. Dihedral effect,
strongest at first, decreases as the sideslip angle
goes to zero. Roll due to yaw rate, weak at first,
increases as the yaw rate rises; then suddenly
disappears when the yaw damps out. The
capacity to raise a wing with rudder alone, in
case ailerons fail, is a certification requirement
for non-aerobatic aircraft, and this stick release is
a standard flight-test procedure.
•You’ll enter a steady-heading sideslip by
•Aerobatic aircraft without much dihedral effect
applying crossed controls: deflecting the rudder
while adding opposite aileron to keep the aircraft
from turning. Notice how the forces and
deflections increase as you move the controls
toward the stops. Under FAR 23.177(d), “the
aileron and rudder control movements and forces
must increase steadily, but not necessarily in
constant proportion, as the angle of sideslip is
increased up to the maximum appropriate to the
type of airplane…. the aileron and rudder control
movements and forces must not reverse as the
angle of sideslip is increased.”
Velocity vector, V, and
sideslip angle, β. Sideslip
to the right.
Angle of Attack (α) and Sideslip Angle (β)
X-Z plane
(such as the Great Lakes, or the Yak-52) often
tend not to roll toward level but to pitch down at
stick release. An aircraft’s pitching moment due
to sideslip may be nose-up or down, minimal or
pronounced, different left or right—depending
on how propeller slipstream, fuselage wake, and
the downwash generated by the wing and flaps
affect the horizontal stabilizer. The combination
of longitudinal (pitch) and lateral (roll) forces
you find yourself holding helps you anticipate
how aggressively the aircraft will respond on
release. The Zlin is a great trainer in this respect.
Lift vector
V
X body axis
β
α
V
Angle of velocity vector, V, to x
body axis gives aircraft angle of
attack. Angle of velocity vector to
wing cord gives wing angle of
attack.
14
Y body
axis
X body
axis
Z body axis
Bill Crawford: WWW.FLIGHTLAB.NET
Left rudder
produces right
sideslip.
Maneuvers and Flight Notes
When the stick is released in a sideslip to the left
(right rudder down, left aileron), the Zlin can
aggressively pitch-up and roll right, the
combined motions leading to a sudden increase
in the angle of attack of the right wingtip, and a
possible tip stall. Much fun!
•Swept-wing aircraft can build up large rolling
moments during sideslips, and mishandling can
put even a large aircraft on its back. Sideslip
angles are generally restricted to around 15
degrees during flight test for transport aircraft.
FAR 23.177(d) says that a “Rapid entry into,
and recovery from, a maximum sideslip
considered appropriate for the airplane must not
result in uncontrollable flight characteristics.”
“Rapid” is a key word here, since a slow entry to
and recovery from a sideslip keeps the aircraft’s
angular momentum under control.
•Things get a little complicated now, and we
apologize. Notice that when you first release the
rudder, while holding aileron deflection
constant, the aircraft doesn’t respond to the
ailerons and immediately start rolling. Watch
how the nose yaws and reduces the sideslip
before the roll begins. The vertical stabilizer’s
center of lift is above the aircraft’s center of
gravity. As a result, the rudder deflection in a
steady-heading sideslip actually produces an
added roll moment in the same direction as the
ailerons. (See Figure 17 in the ground school text
“Lateral-Directional Stability.”) Releasing just
the rudder eliminates this rolling moment
contribution, but replaces it briefly by a rolling
moment due to yaw rate as the aircraft
straightens out. (Did you get that?) The
important point is that only after the aircraft’s
directional stability substantially eliminates the
sideslip will the ailerons start to dominate and
the aircraft roll. This really is less confusing with
a hand-held model for demonstration, or in the
aircraft where you can see things unfold.
•Our trick of holding the ailerons in place while
releasing the rudder allows us to keep the roll
moment due to aileron deflection fixed. We can
then observe the yaw as the aircraft’s directional
stability realigns the nose with the velocity
vector. We can observe the ramp-up in roll
response and properly attribute it to the
vanishing sideslip. This gives us a way to use a
steady-heading sideslip to demonstrate the
relationship between sideslip and aileron
effectiveness. A sideslip can either work for a
roll rate, or against it. For a given aileron
deflection, in an aircraft with dihedral effect,
roll rate goes down when rolling into a sideslip
(right stick, right velocity vector, say, as in the
sideslip seen from above, illustrated on the
previous page). Such an “adverse” sideslip could
typically happen in an aircraft with adverse yaw
and not enough coordinated rudder deflection
when beginning the roll. On the other hand,
stomping on the rudder too hard while rolling
with aileron will skid the airplane and
demonstrate that a proverse sideslip, opposite
the direction of applied aileron, increases roll
rate—in addition to sliding your butt across the
seat. That stomp could be a useful trick for
accelerating roll response in an emergency, but
in swept-wing aircraft could lead to a severe
Dutch roll oscillation. The fundamental
relationship between sideslip angle (angle of the
velocity vector versus plane of symmetry) and
roll rate is something many pilots never really
get—maybe because instructors think that the
rudder affects only yaw. But in a laterally stable
aircraft, yaw just about always provokes a rolling
moment.
•Roll couple for a given sideslip angle, β, and
aircraft configuration varies in direct
proportion to the coefficient of lift, CL. That’s
certainly the case with swept-wing aircraft, and
at least apparently the case with straight-wing,
although not to the same degree. (See ground
school text “Lateral-Directional Stability.”)
•Roll due to yaw rate also varies directly with
CL, as noted when we observed the spiral mode.
When we fly steady-heading sideslips, we try to
isolate dihedral effect by keeping the heading
steady and eliminating yaw rate. But there’s
always a yaw rate when we enter and leave the
maneuver, and of course sideslips and yaw rates
occur together in turbulence. Their individual
contributions at a given moment can be difficult
to sort out.
•You can think of the deflected rudder (or an
existing sideslip) as setting the direction and
initial rolling tendency, and of the elevator as
modulating the rate through its control of CL.
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15
Maneuvers and Flight Notes
This is easy to remember, because when you
raise CL by pulling back on the stick, toward the
rudder, roll moment produced through dihedral
effect and roll due to yaw rate increases. When
you lower CL by pushing, the contribution
decreases. This relationship holds for both
straight and especially for swept wings, although
the mechanisms and some details are different,
as the ground school illustrates. It also works
upside-down; as long as you have positive g.
You will see this when we do rudder rolls.
•Or, if you prefer a more visceral terminology,
put it this way: Hauling back and “loading” an
aircraft increases yaw/roll couple; “unloading”
decreases it. And that’s not all unloading does,
as we’ll note more than once. Imagine that
you’re operating at an angle of attack high
enough to reduce aileron effectiveness through
airflow separation, and high enough to disrupt
flow over the tail such that yaw-axis stability is
reduced and a sideslip develops. Putting the stick
forward and unloading will reattach the flow,
bringing the ailerons back while also reducing
the sideslip-generated roll couple by reducing
coefficient of lift, CL. (Examples might be during
an immediate recovery from an initial stall/spin
departure—developed spins are handled with
rudder first—or during a recovery from a rudder
hardover.)
• With a swept wing, the dihedral effect derived
specifically from sweep actually disappears at
zero CL. A sideslip then no longer produces a
rolling moment, unless the wing also has
geometrical dihedral (tips higher than roots),
which does work at zero CL. (Again, see ground
school text “Lateral-Directional Stability.”)
Aircraft Pitch Around Y Wind Axis
x body
axis
V
β
y body axis
y wind
axis
The y wind axis remains perpendicular to and moves with
the velocity vector, V. The aircraft pitches around the y
wind axis. Geometrically, this also produces a roll. So in a
sideslip to the right, as above, pulling the control back
causes a roll to the left; pushing forward causes a roll to the
right.
rolling moment toward the vector. This is
another effect that’s tough to visualize, but if you
spend a few minutes fiddling with a small
aircraft model you just might have a revelation.
•Wind-Axis: In this maneuver set we pushed
and pulled on the on the stick while sidesliping.
We watched the motion of the nose relative to
the horizon, and discovered that the aircraft was
pitching about its y wind axis, not its y body
axis. Because of the displacement of the y wind
axis from the body axis, a pitching moment also
produces a rolling moment, as described in the
illustration to the right. This geometrical effect
works in the same direction as the CL effect
described above. In other words, pulling will
geometrically produce a rolling moment opposite
the velocity vector; pushing will produce a
16
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
•Steady-Heading Sideslip Spin Departure:
More confusing stuff, sorry again: Here’s what
happens when we stall the aircraft during a
steady-heading sideslip, by holding crossed
rudder and aileron while increasing aft stick. In a
steady-heading sideslip to the aircraft’s left, as
illustrated here, right rudder is deflected; ailerons
are left. The horizontal component of lift created
by the bank angle pulls the aircraft to its left and
thus generates a nose-left aerodynamic force
against the tail. We counter the resulting left yaw
moment with right rudder to maintain our steady
heading. At the stall, as lift goes down so does its
horizontal component and the resulting yawing
moment to the left. This allows the rightward
yaw moment generated by right rudder to
dominate. If we hold control positions the
aircraft yaws and rolls to the right in an “over the
top” entry into a spin.
• Going over the top is the most congenial way
for the aircraft to behave, because the wings first
roll toward level and there’s more time for
recovery. Bringing the stick forward and
neutralizing the other controls should keep the
aircraft from entering a spin. Opposite rudder
might also help. Remember that aircraft always
depart toward the deflected rudder (opposite the
displaced velocity vector). So you won’t break
toward the low wing in a sideslip—it just feels
like you might because that’s the direction in
which you’re sliding off your seat.
•Note that in a side-slipping spin departure to the
Steady-heading
Sideslip Spin
Departure
The horizontal component of lift
increases as the stick is pulled back
and CL rises. This component rapidly
decreases at stall, as lift drops
(dashed arrow).
aircraft’s right, for illustration, the left aileron we
originally hold to maintain a steady heading, and
then for demonstration keep in at the stall,
doesn’t arrest the rightward roll off. There’s too
much airflow separation by that point for the
ailerons to generate much opposite roll. But the
down aileron still produces lots of adverse yaw,
which pulls the right wing back and encourages a
spin entry.
Roll moment due to
sideslip/dihedral effect
L
φ
Y
W sin φ
W
Roll moment due to ailerons,
here shown in equilibrium with
the opposing moment due to
sideslip, quickly drops off as
the aircraft stalls and airflow
separates over the ailerons. But
adverse yaw increases and
helps drive the aircraft into a
spin to its right.
Bill Crawford: WWW.FLIGHTLAB.NET
17
Maneuvers and Flight Notes
3. Stall: Separation & Planform Flow (Wing tuft observation)
Flight Condition: Upright, power-off 1 g stall, high α.
Lesson: Stall anatomy.
Procedures:
Clearing turns.
Power idle.
Trim for 1.5 times anticipated stall speed.
1-knot-per-second deceleration below 70 knots.
Note buffet onset airspeed and stall speed.
Full stall before power-off recovery.
Power as required for recovery and climb.
Repeat with 5-knot-per-second deceleration below 70 knots.
Stalls while watching the wing tufts.
Provoke secondary stall in recovery.
Repeat with flaps. (Is there a difference in “break?”)
Flight Notes
We’ll cover boundary layers, adverse pressure gradients, and wing planform effects in the ground school
and supporting texts. Then, as an accomplished aerodynamicist, you’ll be able to interpret the sometimessurprising motions of the wing tufts and the accompanying separation of the airflow from the wing as α
rises or the aircraft’s configuration changes. FAR Parts 23 & 25.201-207 cover stall requirements.
•On the way to the practice area, note the
turbulence in the boundary layer as shown by the
movement of the wing tufts. Note the increased
movement as the turbulent layer thickens
downstream.
•Don’t make our stalls a minimum-altitude-loss,
flight-check-style exercise. Give yourself time to
observe the full aerodynamic progression. Play
around. But remember: This is not procedure
training. Follow the recovery techniques in
your aircraft’s AFM or POH.
18
•For FAR Part 23 and 25 certification, stall
speeds are determined for the aircraft configured
for the highest stall speed likely to be seen in
service. In part, this means at maximum takeoff
weight and forward center of gravity limit, trim
set for 1.5 anticipated stall speed, and using an
airspeed deceleration rate of 1 knot-per-second
starting at least 10 knots above stall. We’ll try to
maintain this deceleration rate for later
comparison to a 5 knot-per-second deceleration
entry. Up to a point, increasing the deceleration
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
rate beyond 1 knot-per-second usually drives
down the stall speed, but then the load factor
starts to rise and stall speed increases. The
decrease in stall speed that comes with a
somewhat increased deceleration occurs because
of the delay in pressure redistribution as α rises.
This delays separation and allows the wing to
function briefly at a higher angle of attack and
coefficient of lift than normal, a phenomenon
called dynamic lift to differentiate it from the lift
conditions at static angles of attack measured in
a wind tunnel. Lift normally creates a downwash
over the horizontal stabilizer, and thus a nose-up
pitching moment. The nose pitches down when
the downwash disappears at the stall. Dynamic
lift delays this to a higher angle of attack.
Location of minimum static pressure
Favorable
pressure
gradient
Adverse pressure
gradient resists airflow.
Adverse pressure begins
earlier as α increases.
•It’s important that a rapid deceleration produced
by a high pitch rate doesn’t compromise control
authority. That’s not an issue with our aircraft,
but can be with large aircraft in which pitching
momentum can carry and momentarily hold the
aircraft past stall angle of attack, with
insufficient airflow available for positive control.
On the other hand, a deceleration rate below 1
knot-per-second may not produce maximum α.
Favorable
pressure
Adverse
pressure strips
the airflow from
the wing.
Boundary layer separation at stall
•Watch the tufts. The trainer has the root-first
stall progression typical of its wing shape. In
contrast, swept wings naturally stall first at the
tips. They’re coerced to behave more in a rootfirst manner by the use of stall fences, vortilons,
vortex generators, and changes in airfoil from
root to tip.
•Notice the definite relationship between airflow
separation at the wing root, as evidenced by the
tufts, and the buffet onset in our training aircraft.
Do you feel the buffet in the airframe, mostly in
the stick (as in the L-39 jet trainer), or in both?
In our aircraft the buffet provides plenty of
aerodynamic stall warning. Compare this to a Ttail design where the turbulent flow largely
passes beneath the stabilizer and stall warning
has to be augmented by a mechanical stick
shaker, or to planform designs where the wing
root separation happens too late to provide much
aerodynamic warning. In the MiG-15, for
example, there’s no real buffet—the stick gets
light and lateral control goes to mush.
•You might want to do a couple of stalls with the
instructor assisting in directional control while
you concentrate on the wing and play the stick to
modulate the full tuft stall progression from root
to tip. If you’ve done the relevant ground school,
visualize and manipulate the adverse pressure
gradient in the chordwise direction, and the
change in local coefficient of lift in the spanwise
direction. Note the change in airflow over their
surfaces (as shown by the tufts) when the flaps
or ailerons go down. When the flaps go down,
note the vortex that forms on the outboard tip.
Acting on the tail, the increased downwash from
this vortex causes the pitch-up that follows flap
deployment.
•The secondary stall we provoked on purpose,
by pulling too hard on recovery, reminds us of
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19
Maneuvers and Flight Notes
the absence of positive (nose-up) pitch authority
at maximum lift coefficient, CLmax, regardless of
aircraft attitude. We can run out of elevator
(and aileron!) authority in any attitude when
there’s no angle of attack in reserve. The
absence of positive pitch authority, in the form
of an “uncontrollable downward pitching
moment” is one of the ways the FAA defines a
stall for certification purposes under FAR Part
23.201(b). We’ll revisit this loss of pitch
authority when we fly loops, and during the pullup recovering from spins.
•Part 23.201(d) states, “During the entry into and
the recovery from the [stall] maneuver, it must
be possible to prevent more than 15 degrees of
roll or yaw by the normal use of the controls.” In
coordinated flight, our trainers tend to stall
straight ahead, without dropping a wing—at least
not initially. If you hold the stick back during the
stall oscillation, a wing may drop. Many aircraft,
like the sultry Siai Marchetti SF260, will
announce a stall more by a wing drop than by a
nose-down pitch-break (also called a g-break).
Some airfoil and planform arrangements can be
demanding, no matter how carefully the pilot
keeps the ball centered. A venerable T-6 Texan
or SNJ will generally drop to the right. The right
wing stalls first, reportedly, because it’s set at a
higher incidence. Our ground school video of a
T-6 wing shows how the stall pattern leads to
early flow separation in the aileron region. Our
video of the Giles G-200 aerobatic aircraft shows
a rapid trailing-to-leading-edge stall, which gives
20
no buffet warning, and in this particular aircraft
produces a sudden drop to the left.
•Stall separation can also begin at the leading
edge, and aircraft with leading-edge stalls
typically misbehave. The stall break, perhaps
caused by the sudden bursting of the laminar
separation bubble, is abrupt and usually happens
asymmetrically due to physical differences
between the leading-edge spans. A wing drop is
likely. On various Lear models, if the leading
edge has been removed for repair, a test pilot
will come out from the factory to do a stall test
before the aircraft goes back in service.
•Even if meant to be, aircraft often aren’t
aerodynamically symmetrical in behavior. In
practice, manufacturing tolerances simply aren’t
that tight; and a life of airborne adventure takes
its toll. The PA-38 Piper Tomahawk became a
particular offender when the production aircraft
were built with fewer wing ribs than the
prototype used for certification tests. This
allowed the wing skins to deform—or
“oilcan”—under changing air loads.
Unfortunately, the performance of its GA(W)-1
wing is very sensitive to airfoil profile. The
deformations led to rapid and unpredictable wing
drop at stall. Prompt, proper recovery inputs
were necessary. The Tomahawk has about twice
the stall/spin accident rate per flight hours as the
Cessna 150/152.
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
4. Accelerated Stall: G Loads & Buffet Boundary, Maneuvering Stability
Flight Condition: Banked, high α.
Lesson: Flight behavior under turning loads.
Procedures:
Power low cruise.
Trim.
Using instrument or outside reference, roll to bank angle specified by instructor.
Keep the ball centered with rudder.
Apply stick-back pressure to buffet, reducing power or increasing bank angle as necessary.
Note buffet speed, stall speed, buffet margin as compared to 1-g stall.
Repeat at higher bank angles. Note exponential rise in buffet speeds and stick force.
Explore aileron effectiveness in buffet by rocking wings 15 degrees left and right.
Flight Notes
Earlier, we increased the airspeed deceleration rate to lower the “book” stall speed. Here we use load factor
to raise it.
•Stall speed goes up by the square root of the
load factor, n. (n = Lift/Weight).
•Induced drag goes up by the square of the load
factor.
•Thus whenever you raise the load factor (pull
“g”), stall speed and drag also rise. You can’t
feel the latter two directly; you have to learn the
association. The increasing stick force is one cue
that the numbers are ascending. The force
driving you into your seat is another.
• Of course, hangar wisdom holds that a wing’s
stalling angle of attack remains constant for a
given configuration (high-lift devices in or out).
That’s a small fiction, but also a profound
working “truth” because it emphasizes angle of
attack as the essential stall determinant, not just a
number on the airspeed dial—a number that
itself changes with weight and load factor for a
given configuration. If you want to be picky,
stalling angle of attack depends on Reynolds
Number, which is the ratio between inertia forces
and viscous forces in the boundary layer on the
surface of the wing. For a given airfoil, stall
angle of attack rises with Reynolds Number.
•Notice the increased buffet intensity in the
accelerated stalls compared to those at 1 g.
There’s more energy in the turbulent airflow
shed by the wing at this higher buffet speed (the
inboard wing tufts tend to capitulate and blow
off after repeated accelerated stalls), and more
energy in the surrounding free stream flow.
Bill Crawford: WWW.FLIGHTLAB.NET
21
Maneuvers and Flight Notes
Pitch Damping
• At higher g, does the buffet margin change
compared to a 1-g stall? The comparison should
be made at the same knots-per-second airspeed
deceleration rate to be valid. Often stall warning
varies inversely with knots-per-second, more
rapid entry producing less warning. A rapid entry
is probably typical of pilot technique in an
accelerated stall.
VT
Tail’s
aerodynamic
center
Tail arm, lT
•The accelerated stall and the 1-g stall both
occur at the same angle of attack, but the
accelerated stall requires a heftier pull. The
aircraft exhibits an increase in pitch stability as
the g load rises (meaning a stronger tendency to
return to trim speed, which is the tendency
you’re pulling so hard against). That’s because
the angular velocity of the tail, caused by the
pitch rate in the turn, produces a change in tail
angle of attack, as illustrated to the right, and
thus an opposing damping moment. Increasing
the g load means increasing the pitch rate, and
ups the damping. The additional elevator
deflection needed to overcome more damping
requires more force. This effect leads to what’s
called maneuvering stability (which we cover in
the ground school text “Longitudinal
Maneuvering Stability”). Damping is a function
of air density, and goes down as you climb.
•The geometry is such that, for a given g, an
aircraft has a higher pitch rate (thus higher
damping) in a turn than it does in a wings-level
pull up. As a result, you’ll pull harder in a 2-g
turn than in a 2-g pull up, for example.
•At a given density altitude, in aircraft with
reversible control systems, like ours, the
necessary stick-force-per-g is independent of
airspeed (although Mach effects may increase
forces at higher speeds). In other words, the
force required to pull a given g doesn’t increase
with airspeed, as you might naturally think. (Of
course, it’s a bit more complicated. See ground
school text “Longitudinal Maneuvering
Stability.”)
•The table farther on shows how load factor
cg.
Pitch rate, q
VT
qlT
(pitch rate
times arm)
also increase exponentially, rather than
uniformly, with bank angle. A pilot banking into
a steep turn has to increase his pull force at a
faster and faster rate. Stick force rises slowly at
lesser bank angles. Past 40 degrees or so, the
increasing force gradient starts becoming more
apparent. There’s a surprising difference in the
force necessary for a 55-degree versus a 60degree bank. Steep turns might get a little easier
(maybe) once you figure this out.
•Notice the instant transformation in control
authority at recovery due to the increased
airspeed in the accelerated stall. Watch the wing
tufts to see how quickly the airflow reattaches
when you release some aft pressure. The
damping you generate in the turn pushes the nose
right down. At 2 g’s there’s a 40 percent increase
in stall speed. Because dynamic pressure goes up
as the square of the airspeed increase, that means
double the dynamic pressure (1.42 = 2) available
for flight control compared to a recovery from a
stall near 1 g. More dynamic pressure means
more control response for a given deflection.
You can recover from an accelerated stall while
the wing is still loaded (pulling more than 1 g).
You only have to release enough g to get the stall
speed back down.
increases exponentially with bank angle in a
constant-altitude turn. It follows that stick forces
22
ΔαΤ, Change in tail angle
of attack
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
Deg.
bank
30o
Load factor
required for
constant-altitude
turn
1.15
Stall speed
factor
increase
over 1-g Vs
1.07
60 kt
stall
times
increase
64.3
35o
1.22
1.10
66.3
40o
1.30
1.14
68.4
45o
1.41
1.19
71.2
50o
1.55
1.24
74.7
55o
1.74
1.32
79.1
60o
2.00
1.41
84.8
65o
2.37
1.54
92.4
70o
2.92
1.71
102.5
75o
3.86
1.96
117.9
80o
5.76
2.40
144
•But releasing g may not always be equivalent to
releasing your aft pressure on the stick. In some
aircraft (often former military) you may have to
push to expedite things. You may find that the
gradient of stick force rises more slowly as g
increases, as it does in the L-39 jet trainer
because of the bungee cord “boost” within the
elevator circuit. Or the aircraft may have an aft
c.g., which increases maneuverability at the
expense of stability, and thus reduces the
tendency to pitch the nose down when aft
pressure is released. Early swept-wing fighters
had a tendency to stall at the tips first. Because
of the sweep, a loss of lift at the tips shifted the
center of lift forward and caused the aircraft to
pitch nose-up and “dig in” during accelerated
stalls.
•The higher dynamic pressure while
maneuvering can lead to higher rolling moments
if the wings stall asymmetrically. Any wingdropping obstreperousness an aircraft might hint
at during 1-g stalls can intensify at the higher
airspeeds of an accelerated stall. Our rectangularwing trainers stall root-first, and resist roll-off if
flown in a coordinated, ball-centered manner.
But accelerated stalls in other aircraft can be
defined more by a wing drop than by a pitch
break or a stolid, straight-ahead mush.
•As the load factor increases, the stall speed
starts coming up to meet your airspeed. At the
same time, if you didn’t or can’t increase power
(“thrust-limited”), your airspeed starts heading
down because of the increased induced drag.
Eventually, if you pull hard enough, the two
speeds converge. If an aircraft is thrust-limited,
test pilots will perform descending, wind-up
turns to explore its behavior at higher g, by
turning altitude into the increasing airspeed
necessary to attain increasing g levels.
•Because stall speed rises in a turn, your
calibrated airspeed above 1-g stall dictates your
bank-angle maneuvering envelope. The closer
you are to the 1-g (wings-level) stall speed in a
given configuration, the less aggressively you
can bank and turn an aircraft while keeping
out of buffet and maintaining altitude. You can
certainly enter a steep bank without stalling
while flying slowly, since stall speed is not
directly related to bank angle. Stall speed
depends on load factor—in this case on the load
factor required to make a turn happen at a given
bank angle without altitude loss. For a constantaltitude turn, load factor goes up exponentially
with bank angle, as the table illustrates. You
can’t generate the necessary load factor unless
you’re going fast enough for your bank angle. If
you’re too slow, but nevertheless try to arrest a
descent by hauling back on the stick, you’ll stall.
Level the wings first. If you have excess
airspeed, you can haul back and turn and climb.
The relationship between airspeed, attainable
load factor, and turning performance is discussed
in the ground school text “Maneuvering Loads,
High-G Maneuvers.”
•Pilots have it drilled into them that an aircraft
can stall at any attitude. Stall speed is also
independent of attitude. At a given weight and
configuration, an aircraft pulling two g, for
Bill Crawford: WWW.FLIGHTLAB.NET
23
Maneuvers and Flight Notes
example, has the same stall speed regardless of
its attitude relative to the horizon.
•An aircraft constantly rolls toward the outside
of a climbing turn. It constantly rolls toward the
inside of a descending turn. (You’re right. This is
difficult to visualize.) The rolling motion creates
a difference in angle of attack between the
wings, with the down-going wing operating at a
higher angle of attack. As a result, climbing
aircraft tend to roll away from the direction of
the turn at stall break. This is favorable because
it decreases the bank angle. When descending,
they tend to roll into the direction of the turn at
stall break. But propeller effects, rigging, and
poor coordination can gum this up. Watch where
the skid/slip ball is and see what happens.
•Prop-induced gyroscopic precession can affect
control forces in turns. Precession creates a
moment that’s always parallel to the axis of the
turn—the axis typically being perpendicular to
the horizon. On aircraft with clockwise-rotating
propellers, as seen from the cockpit, precession
pulls the nose to the dirt in a turn to the right,
and to the sky in a turn to the left. If the forces
generated are large enough (heavy prop, high
rpm, high turn rate, long moment arm from prop
to aircraft c.g.) more up-elevator will be needed
24
when turning to the right. And the rudder
becomes more involved as the bank angle
increases and precession moves closer into
alignment with the aircraft’s y axis. Greater
rudder deflection may then be needed for
coordination. The WW-I pursuits equipped with
rotary engines (engine and prop turned together)
were famous for their gyroscopic
behaviors—quick turning to the left but awkward
and vulnerable to the right. If the nose pitched
down gyroscopically in a right turn, the pilot
could spin out trying to counter with opposite
rudder and up elevator.
•Finally, notice the greater rudder force
necessary to stop or reverse a steep turn,
compared to the coordinating rudder force
necessary when beginning the turn. One reason
is the higher angle of attack in the turn and thus
the greater adverse yaw accompanying aileron
deflection. Also, the aircraft has picked up
angular momentum, which the rudder has to help
oppose. So more rudder deflection is required for
coordination coming out.
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
Stick-force-per-g test procedure: wind-up turn.
Fly the test at a constant, trimmed airspeed. Airspeed variations introduce additional forces, as described
in the ground school “Longitudinal Maneuvering Stability.” At a constant airspeed and power setting, you
will descend during the maneuver as bank angle increases.
Establish trim speed in level flight at test altitude. Record pressure altitude, temperature, and power setting.
Climb with increased power to 1,000 above test altitude. Reset trim power.
Bank as required to obtain desired load while descending as necessary to remain at trim speed.
If equipped, measure stick force when airspeed and g-meter readings stabilize. Establishing a stable state,
even briefly, isn’t always easy— it takes practice, especially as bank angle increases! If you’re not
equipped for measuring, a subjective assessment of stick force and gradient is still a useful exercise.
If the aircraft does not have a g-meter, use bank angles to establish approximate load factors. As 60o
approaches, you might find it easier to control airspeed with your feet: for example, top rudder if speed
exceeds trim.
Trim speed:
Pressure altitude:
Bank angle
30o
1.15-g
Temp:
45o
Power setting:
1.41-g
60o
2-g
Actual g-meter
reading
Stick force
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25
Maneuvers and Flight Notes
5. Nose-High Full Stalls, Lateral Control Loss & Rolling Recoveries
Flight Condition: Wings level, high α, nose-high, limited lateral control.
Lesson: Exposure to nose-high attitudes, limited visual references, lateral control loss.
Procedures:
Full Stall: Nose-High Pitch Break
25”/2,500 rpm.
Clearing turns.
Pitch up + 60 degrees (use wingtip reference).
Power idle.
Hold wings-level attitude as possible, keeping the ball centered with rudder.
Allow full stall with stick held back.
Pitch up + 60 degrees.
Hold necessary power, with stick back, aileron neutral and feet off the rudder pedals.
Allow a yaw rate to develop (aircraft will yaw left due to prop effects).
Observe lateral control divergence.
Recover aileron effectiveness with nose down pitch input.
Recover aileron effectiveness with opposite rudder.
Rolling Recovery from Nose High
Recover nose-below-the-horizon.
Recover nose-to-the- horizon.
Flight Notes
Nose-high recoveries are practiced in simulators as a standard element in upset training. The Airplane
Upset Recovery Training Aid gives a procedure based on a push—followed by a roll, as required to get the
nose back down. We’ll explore the dynamics of recoveries done badly. We want you to lose lateral control,
see why, and see what it takes to get it back.
•The first maneuver gets you familiar with nosehigh attitudes and pitch breaks. The pitch break
(or g-break) in a 1-g nose-high stall is much
more pronounced than in the 1-g stalls done from
close to normal pitch attitudes. The aircraft
rapidly sinks and the nose will swing well below
the horizon before it’s possible to recover a
26
flyable angle of attack. The initial nose-up
attitude will block the horizon ahead and force
you to use the wingtips for roll, pitch, and yaw
reference. (The attitude indicator will be off,
unless we forget.) Don’t just stare at one
wingtip. We have two! Compare them.
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Maneuvers and Flight Notes
•We want you to experience lateral control
divergence and loss of roll damping. We set this
up by holding a nose-high attitude with power
on, stick back, feet off the rudders, and ailerons
initially neutral. We let the aircraft’s natural
tendencies in this configuration take over. Pfactor and slipstream will yaw the aircraft to the
left. We’ll try to recover from the resulting
coupled roll with ailerons alone (stick still held
back). Lateral control will be lost.
•Notice that, while you can retain some aileron
effectiveness into a stall buffet and break, at
highα, aileron effectiveness disappears if the
airplane starts to yaw opposite the direction of
intended roll, as we let it do above. Instead of
rolling the aircraft as we intend, the ailerons
generate more adverse yaw than lift, which
simply makes things worse. Once the stick goes
forward, however, or the pilot uses rudder to stop
the yaw, the ailerons regain authority.
•The Airplane Upset Recovery Training Aid
recommends recovery from a nose-high attitude
with a push, followed by a roll if necessary
(2.6.3.2-5). Pushing starts the nose in the right
direction and unloads the wing so that the
aircraft accelerates and the ailerons retain
effectiveness. Rolling tilts the lift vector and
allows the aircraft’s z-axis directional stability to
assist in bringing the nose down. Confining the
roll to less than approximately 60 degrees keeps
the wing lift vector above the horizon and makes
pitch control easier in the recovery back to level
flight. During the time it takes to roll the lift
vector back to vertical, the buildup in angular
momentum in a heavy aircraft can carry the nose
unnecessarily below the horizon if the initial
bank angle is too steep.
•In a delayed rolling recovery, if you hold the
nose in the buffet and apply ailerons, you won’t
have much roll authority. The reduced roll
control at low airspeeds and high angles of attack
can increase the difficulty of a rolling recovery
from a nose-high attitude. This underscores the
need to push and unload the airplane if the
ailerons aren’t working.
•The “nose below horizon” and “nose to the
horizon” rolling recoveries demonstrate the
problem of flight path control at high angles of
attack. Because nose-up authority disappears at
high α, stopping the nose on the horizon is
difficult without encountering a buffet.
•In a jet, power application in a nose-high
recovery will depend on the aircraft’s thrust line
and the resulting pitching moment when power
is applied. Aircraft with engines mounted on
pylons below the wings can pitch up in a manner
possibly difficult to control when thrust is
increased at low airspeed. In addition, a jet has to
accelerate and build up speed before control
surfaces regain authority. With a prop, horizontal
and vertical stabilizers start to regain authority
once the slipstream returns. But ailerons still
require airspeed. In an extreme case, if you slam
the power forward on a go-around in a P-51 or
similar warbird while flying slowly, the torque
effect can be more than the ailerons can handle.
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27
Maneuvers and Flight Notes
6. Roll Authority: Adverse Yaw & Angle of Attack, Lateral Divergence
Flight Condition: Upright, power-off 1g stall, high α, varying β, pro-spin.
Lesson: Lateral/directional control at increasing α.
Procedures:
Spin recovery briefing as required.
Power idle.
1-knot-per-second deceleration below 70 knots.
Instructor demonstrates initial task.
Sample aileron authority: Decelerate toward stall while rolling 15 degrees left and right at a constant roll rate.
Alternate between rudder free and coordinated rudder as necessary to hold nose on point.
Note: 1. Change in aileron deflection needed to maintain roll rate.
2. Change in aileron forces.
3. Increase in adverse yaw.
4. Contribution of coordinated rudder to roll rate.
5. Lowest speed for aileron authority.
Continue rolling inputs through stall break. At wing drop, hold opposite aileron. Observe aileron reversal.
Hold aileron deflection and recover using forward stick to demonstrate return of aileron authority. Instructor
will demonstrate if required.
Sample rudder authority: (Instructor demonstrates initial task.) Establish constant rate left/right yaw tempo
sufficient to assess rudder authority during stall entry.
Note: 1. Change in required rudder deflection.
2. Change in rudder forces.
3. Lowest speed for rudder authority.
Observe lowest speed for lateral control using coordinated aileron and rudder.
Flight Notes
In the previous maneuver set we observed the loss of aileron effectiveness during delayed nose-high rolling
recoveries. In this set we’ll continue to examine changes in lateral control. We won’t intentionally spin the
aircraft at this point in the program, but the aircraft will be bopping around pretty aggressively, with the
velocity vector wagging left and right, and these are potential spin entries (high angle of attack plus sideslip
and yaw rate). Just centering the rudder and ailerons and releasing aft pressure is enough for recovery
from an incipient spin departure in our aircraft. (As the spin develops, however, recovery technique
becomes more critical, for reasons we’ll cover in spin training.). That said—don’t be timid. Challenge the
aircraft to the point where lateral control is lost, and then get it back.
28
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
The subject of this maneuver set is mostly the rudder. Rudder-induced sideslips can accelerate a rolling
maneuver and contribute to maximum-performance upset recoveries. Proper rudder use is essential for
coordination at high α: but misuse of the rudder at high α can also cause spin departure, or severe yaw/roll
oscillation (Dutch roll), especially in swept-wing aircraft. Following the November 12, 2001 vertical
stabilizer failure and crash of American Airlines Flight 587, an Airbus A300-605R, attention has focused
on the structural loads generated on a vertical stabilizer when the rudder is deflected to opposite sides in
rapid succession. Rapid rudder reversals, even below maneuvering speed, VA, and even with rudder
limiters, can result in loads in excess of certification requirements. FAR Part 25.351 rudder and fin load
requirements are based on the demonstration of a sudden full rudder deflection (either to the stop or until a
specified pedal force is reached) at speeds between VMC and VD (design dive speed) in non-accelerated
flight. This is followed by a stabilized sideslip angle, and then the sudden return of the rudder to neutral,
not to a deflection in the opposite direction.
The American Flight 587 accident also raised fears that unusual-attitude training that overemphasizes
rudder can in fact provoke an upset if a pilot overreacts with rudder to an otherwise non-critical event, or
uses it at the wrong time. Although we’ll demonstrate the effects of rudder and sideslip on rolling moments
as α increases, for all the reasons above we won’t define the rudder as the primary high-α roll control,
especially not for swept-wing transport aircraft (historical jet fighters are a separate issue). Reduce the
angle of attack if necessary to regain lateral authority, and use ailerons or spoilers for unusual-attitude
roll recoveries, along with the rudder required for coordination, not roll acceleration. This is consistent
with both Boeing and Airbus philosophy, but can be applied to any aircraft. Aggressive rudder use is an
important part of aerobatic training, and of course aerobatic training is the basis of unusual-attitude
training. But aggressive rudder use doesn’t always carry over—partly because of concern the rudder will be
used at the wrong moment and partly because, even with an experienced aerobatic pilot at the controls, the
dynamics following a nominally correct aerobatic input may be different in a swept-wing aircraft than in a
straight-wing trainer.
•In the golden days, when tail-wheel aircraft
with lots of adverse yaw were standard, and
pilots could still be seen wearing jodhpurs, flight
instructors often had students perform back and
forth rolls-on-point, which instructors in jeans
today often mistakenly call “Dutch rolls.” (In a
real Dutch roll the nose wanders.) The idea was
to wake up the feet for directional control during
takeoffs and landings, and especially to teach the
rudder coordination necessary to counteract
adverse yaw. This maneuver set is similar, but
the dynamics are more complex and revealing
because we roll the aircraft while simultaneously
increasing its angle of attack (and thus its
coefficient of lift, CL).
•Pay attention to how control authority
deteriorates: You’ll need to increase your control
deflections to maintain rolling and yawing
moments as airspeed (dynamic pressure)
diminishes. The down aileron will begin
producing proportionally less roll control and
more induced drag as the angle of attack rises
(induced drag increases directly as the square of
lift), and therefore more adverse yaw. You’ll see
the result in the movement of the nose. Keeping
the nose on point with rudder will demonstrate
how the rudder becomes increasingly necessary
for directional control when using ailerons for
roll control at higher angles of attack, and then
increasingly dominant for roll control as the
ailerons lose authority and roll damping begins
to disappear.
•Rudder-induced roll control doesn’t decline as
much as aileron control typically does, because
the yaw/roll couple that the rudder provokes goes
up in proportion to coefficient of lift. Aileron
authority, however, goes down as airspeed
diminishes and as flow separation begins to
affect the outboard wing sections.
•Ultimately, at aircraft stalling angle of attack
the ailerons can (legally, see below) begin to
“reverse” (not to be confused with wing twisting,
“aeroelastic reversal”). This happens when
adverse yaw begins to dominate, and the
opposing roll moment the yaw produces (through
Bill Crawford: WWW.FLIGHTLAB.NET
29
Maneuvers and Flight Notes
sideslip and yaw rate) overcomes the roll
moment generated by the ailerons. The airplane
then rolls toward the down aileron. This is called
lateral control divergence. Its natural prey is an
airplane with lots of adverse yaw and lots of
dihedral effect, when flown at high angle of
attack by pilots who don’t use their feet to keep
yaw under control (and thus the velocity vector
on the plane of symmetry).
•Adverse yaw goes down and aileron
effectiveness returns when you apply forward
pressure to reduce α: Push to recover aileron
effectiveness. As in the nose-high stalls done
earlier, you’ll see how quickly a “reversed”
aileron regains its appropriate authority once the
nose comes down.
•After the flight, compare the trainer’s stall
behavior to the requirements in FAR Part
23.201-203 (for aircraft under 12,500 pounds)
and to the requirements for transport certification
under FAR Part 25.201-203. (See the Summary
of Certification Requirements.) The wording is
different, but 23.201(a) and 25.203(a) say the
same thing. According to the latter: “It must be
possible to produce and to correct roll and yaw
by unreversed use of the aileron and rudder
controls, up to the time the airplane is stalled.”
[Italics ours] Did we demonstrate capabilities at
stall α beyond those explicitly required?
30
•We’ve demonstrated the continuing authority of
rudder, compared to aileron, for roll control in
the high-α region of the envelope. Nevertheless,
in general, don’t rely on the rudder for primary
roll authority at high α, if you can avoid it. The
best course is to push the stick forward and cause
normal control authority to return. Certification
requirements assume a pilot will do just that. We
don’t want our demonstrations to turn into what
the airlines call negative learning, so remember:
These lateral and directional control exercises
are not procedure training. Recover roll control
at high α by pushing to reattach airflow and to
restore aileron effectiveness as required. Use
coordinated, ball-centered rudder to enhance
roll rate by checking adverse yaw. This is
correct for any aircraft, but particularly so for
swept-wing—in which yaw/roll couple is more
pronounced than for straight-wing aircraft and
the gyrations of the real Dutch roll are more
severe, and in which the high-α/β corners of the
envelope may not have been explored during
flight test because operational encounter was
never intended.
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
The illustration below puts things in velocity
vector terms.
Velocity vector projected
onto the x-y plane gives
sideslip angle, β.
Velocity Vector, V
Y-axis
Lift vector
X body axis
x body axis
α
V
V
α
β
Velocity vector, V,
projected onto x-z
plane gives aircraft
angle of attack, α.
X-Z plane of symmetry
Z body axis
X-axis
β
z body
axis
Velocity
vector
X-Y plane
A directionally stable aircraft yaws in the direction the velocity vector is pointed, returning the vector to the x-z plane of symmetry as
it does. A laterally stable aircraft rolls away from the velocity vector when the vector becomes displaced from the plane of symmetry.
In the illustration, the second aircraft wants to yaw right but roll left.
As an aircraft slows, and angle of attack and thus adverse yaw increase, aileron deflection will increasingly shift the velocity vector
off the plane of symmetry, unless the pilot uses “coordinated” rudder deflection to counter the yaw. If present, P-factor and
slipstream will also increase, tending to shift the velocity vector to the right unless the pilot compensates with right rudder.
So as speed goes down, the tendency of the velocity vector to wander goes up. The resulting rolling moments away from the velocity
vector increase with β, and also increase with angle of attack.
Rolling an aircraft with rudder is a matter of pointing the velocity vector to generate a rolling moment in the desired direction. The
dangers of aggressive rudder use at high angle of attack are that the aircraft enters a spin, or enters a Dutch roll oscillation the pilot
inadvertently reinforces while trying to correct.
Bill Crawford: WWW.FLIGHTLAB.NET
31
Maneuvers and Flight Notes
7. Flap-Induced Phugoid
Flight Condition: Longitudinally unstable, varying lateral/directional control.
Lesson: Downwash/horizontal stabilizer interaction, control practice.
Procedures:
Speed for white arc in level flight.
Student’s hands in “prayer” position (palms facing inward but not touching stick, rudder/aileron control only).
Instructor lowers flaps approximately 15 degrees.
Student maintains directional and lateral control. No pitch input.
Instructor manipulates flaps as required, monitors flaps-extended speed.
Observe the effect of lowering the landing gear.
Flight Notes
A dynamically stable phugoid motion is convergent. We can produce a non-convergent phugoid by
lowering the flaps, but we don’t retrim. The flaps increase the downwash angle over the horizontal
stabilizer and, with the stick free, the nose pitches up in response. As the wing roots stall and the downwash
disappears, the nose pitches down. When lift then returns, the downwash reappears, driving the nose back
up for the next stall. Your job, during this stall-and-recovery roller coaster, is to keep the aircraft under
directional and lateral control, using aileron and rudder only.
•The center of lift moves rearward along the
wing chord when you lower the flaps. This
produces a nose-down pitch moment. (The drag
you create below the aircraft’s center of gravity
also contributes.) But watch the tufts when the
flaps go down and note the vortices that form
around the flaps’ outboard tips. These vortices
increase the angle of the downwash affecting the
horizontal stabilizer. This down flow produces a
nose-up pitch moment. The pitch-up from the
downwash on the stabilizer is greater than the
pitch-down from the reward shift in lift. As a
result, the aircraft pitches up at flap deployment.
angle reinforces rather than opposes a change in
wing angle of attack, flaps generally reduce
longitudinal (pitch axis) stability. One reason for
T-tails is to raise the stabilizer out of the area of
downwash (and propwash) influence.
•As the aircraft stalls and recovers, you’ll
experience changes in lateral and directional
control, already familiar from earlier nose-high
maneuvers. Propeller and slipstream effects will
be more pronounced, however, because of the
need to maintain power to keep the maneuver
going.
• Anytime you (or a gust) raise the angle of
attack of a wing you also increase the downwash
angle. Typically, the downwash angle changes
more rapidly with AOA when the flaps are
deployed. Because the change in downwash
32
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
8. Nose-Level Aileron Roll: Rolling Flight Dynamics, Free Response
Flight Condition: Knife-edge & inverted, free yaw/pitch response.
Lesson: Free response behavior in rolling flight, attitude familiarization.
Procedures:
Check: Seat belt, cockpit, instruments, altitude, outside.
About 23”/2,300 rpm.
From level flight with elevator and rudder neutral throughout.
360-degree roll with full aileron.
Recover from dive (instructor notes g’s pulled in recovery).
If motion sickness is not a concern, repeat the same as above but use partial aileron deflection to
decrease roll rate and allow the nose to fall farther below the horizon.
Flight Notes
We teach you to roll an aircraft through 360 degrees before we tackle emergency upset roll scenarios. This
is less demanding on your motion tolerance at the start of training because the flying is smoother and you
remain in control. You’ll begin by observing how the aircraft responds in pitch and yaw to changes in bank
angle during a 360-degree rolling maneuver. Then you’ll learn to control that response.
•You’ll end up losing altitude, with the nose well
below the horizon at the completion of these
introductory rolls. They’re not the way an
experienced aerobatic pilot rolls an aircraft—but
we start with this ailerons-only, nose-in-levelflight technique to demonstrate the airmanship
problems that an actual unusual-attitude rolling
departure would involve. You’ll gain more
sophisticated, aerobatic control inputs as we fly.
•The aircraft’s free-response directional and
•Because the aircraft rolls, pitches, and yaws in a
• Notice the important relationship between roll
relatively extreme manner with respect to the
horizon, pilots new to aerobatics usually have a
difficult time tracking attitude. In the second roll,
with reduced aileron, the horizon will certainly
disappear behind the nose as the aircraft rolls
through inverted. At this point untrained pilots
have the famous tendency to release aileron and
pull into a split-s. Don’t worry. This you will
never do!
rate and pitch attitude at roll completion. The
slower the roll rate the steeper the final pitchdown attitude. The aircraft’s free response has
more time to bring the nose down. Larger
passenger aircraft roll far more slowly than
aerobatic trainers. As a result, a badly executed
maneuver for a trainer might actually simulate a
best-case controlled-response outcome for a less
longitudinal stability characteristics are designed
for upright flight. They produce nose-down
moments (with respect to the horizon) during a
roll. Directional stability drives the nose down at
each knife-edge, and longitudinal stability does
the same at inverted. The more stable the
aircraft, the more adverse the result.
Bill Crawford: WWW.FLIGHTLAB.NET
33
Maneuvers and Flight Notes
responsive aircraft. So, keep the roll going at the
highest possible rate.
certification, which we operate under, FAR Part
23.337(a)(3) requires a positive limit load of 6 g.
• While we want you to understand the
•Remember that for a given g load the radius of
a turn (or of a pull-up at the completion of a roll,
as is the case here) at any instant varies directly
with the square of the true airspeed. Double the
speed means four times the altitude consumed. A
recovery in a piston aerobatic trainer’s lowairspeed/high-g envelope consumes much less
altitude than recovery in a jet operating at higher
speeds and lower limit loads.
Roll Rates Depend on
Airspeed and Control
System Design
Symbol ∼ means
proportional.
Control Force, Fa
importance of holding full aileron deflection to
achieve maximum-rate recoveries, the idea of
keeping the roll going needs qualification when
we think about vortex encounters, and for the
sake of primacy we should state it right off. By
the time a pilot reacts to a vortex with opposite
aileron the aircraft probably has already been
tossed to a different part of the paired vortex
flow field (and/or the individual vortex has
snaked around to a different part of the aircraft)
and the imposed rolling moment has changed.
The compilation of NASA vortex encounter
videos you’ll see in ground school will
demonstrate how an aircraft is dispelled from a
vortex core. You’ll see why you shouldn’t
assume that even a violent initial roll
acceleration caused by a vortex encounter is
handled best by keeping the vortex-induced roll
going through 360 degrees. That being said, note
that The National Test Pilot School, in Mojave,
California, does recommend using the aircraft’s
existing rolling momentum, if advantageous, and
continuing a roll once past 160 degrees.
roll allows you to experience sensations typically
past the minimum 2.5-g positive limit load
allowable for an aircraft certified under FAR Part
25.337(b). (Unfortunately a 360-degree roll
followed by high g can trigger motion sickness
in some, so let’s be cautious.) For aerobatic
34
Aileron Deflection, δa
Pilot maintains max force but
deflection starts going down as
airspeed increases.
Dashed line for
powered controls.
Airspeed
Roll Rate, p, deg/s
• A recovery at higher g after a partial-deflection
Solid line for muscle
powered reversible
controls.
Airspeed
•For a given control deflection, roll rate varies
directly with airspeed. In aircraft with reversible
controls, like our trainers, for a given deflection,
aileron stick force goes up as the square of
airspeed. Assuming no aeroelastic reversal,
you’ll roll faster when flying faster, although
you’ll have to push the ailerons harder and
harder, and eventually will come to a point
where the stick force is too much to handle and
roll rate starts back down. The problem for us is
at the low-speed end, where low roll rates going
into the maneuver permit the nose more leisure
to fall below the horizon if the pilot allows, and
rolling recoveries back to upright take more
time.
Fa ∼ EAS2
Max force pilot can sustain
with reversible controls.
Roll rate decreases for
reversible controls because
pilot can’t hold deflection.
p ∼ TAS
P∼ 1/TAS
Airspeed
Bill Crawford: WWW.FLIGHTLAB.NET
Airspeed for max roll rate
with reversible controls.
Maneuvers and Flight Notes
9. Slow Roll Flight Dynamics: Controlled Response
Flight Condition: Knife-edge & inverted, controlled yaw/pitch response.
Lesson: Control in rolling flight.
Procedures:
Task: Complete the roll with the nose on or near the horizon, not in a dive.
Check: Seat belt, cockpit, instruments, altitude, outside.
Roll 1: 25”/2,500 rpm.
Airspeed at instructor’s discretion.
Raise the nose 20-30 degrees.
Release aft pressure/ rudder neutral.
Full aileron.
Roll 2: Raise the nose as instructor directs.
Top rudder at second knife-edge.
Roll 3: Raise the nose as instructor directs.
Forward pressure at inverted.
Top rudder at second knife-edge.
Roll 4: Raise the nose as instructor directs.
Top rudder at first knife-edge.
Forward pressure inverted.
Top rudder at second knife-edge.
Roll 5: Roll in the opposite direction.
Flight Notes
There’re three standard aerobatic rolls (and one weird one). The first exercise in this sequence is an aileron
roll, so named because the ailerons do all the work. The next exercises introduce the slow roll—an
aerobatic competition maneuver that uses help from rudder and elevator to keep the center of gravity of the
aircraft moving in a straight line (as opposed to the climb and descent of the aileron roll). Slow rolls give
you the tools to handle roll emergences with minimum altitude loss. The third standard roll is the barrel
roll, which is actually a combination loop/roll that takes a path through the sky as if the aircraft were
following the outline of a barrel laid on its side. The idea behind the barrel roll is to keep the aircraft at
positive g for the sake of fuel flow and lubrication if it lacks inverted systems. It also keeps the occupants
more confidently in their seats and permits the trick of pouring coffee from thermos to mug while upside
down. We won’t do barrel rolls as part of your standard training sequence (although we can toss some in)
but the rudder roll (the weird one), which we will do, is fairly similar.
Bill Crawford: WWW.FLIGHTLAB.NET
35
Maneuvers and Flight Notes
Learning to slow roll is actually easier—and the exercise is more informative—when you take it as a
problem to be solved by experimentation, and not as a textbook set of sequenced control inputs. Then, to
make it easier still, you learn the rudder and elevator skills in reverse.
•In Roll 1, raising the nose high enough at the
beginning of the maneuver and then rolling fast
enough solves the procedure task by default.
Start high and the nose simply falls through to
meet the horizon at the end. (Of course, this
doesn’t represent a typical nose-down unusualattitude scenario.)
• In Roll 2, the rudder helps hold the nose up at
the second knife-edge. The resulting sideslip can
accelerate the roll rate through dihedral effect
and roll due to yaw rate. Your instructor will
make sure you experience this acceleration,
because—with certain reservations—it’s an
important emergency skill. As you gain
experience, you’ll learn to amplify the effect by
aft pressure on the stick. (The ultimate
amplification becomes a snap roll, an aerobatic
rather than emergency maneuver. Aerobatic
pilots, especially competition pilots, actually
avoid accelerating aileron rolls with rudder and
elevator, since it leads to a sloppy-looking and
physically unpleasant maneuver. But fighter
pilots have used snapping roll entries since the
First World War to quickly reverse direction and
shake an attacker from their tail, especially at
low speeds where aircraft usually snap roll faster
than aileron roll.)
• Roll 3 uses forward pressure at inverted to
keep the nose up. Remember that the necessary
stick pressure and movement is much less in an
aerobatic trainer, and the response much greater,
than in an aircraft with more longitudinal
stability.
• Roll 4 begins to approximate the technique
used in competition slow rolls: initial top rudder
at the first knife-edge, transitioning to forward
elevator and back to the opposite top rudder at
the second knife-edge. This produces a constant
nose up (with respect to the horizon)
yawing/pitching/yawing moment throughout the
roll, working in opposition to the aircraft’s
natural stability tendencies.
36
Sideslip Enhances Roll Rate
Top rudder causes a sideslip-induced roll
moment, in addition to the aileron roll
moment. This increases roll rate.
Roll moment from
ailerons.
Roll moment from
sideslip (plus roll
due to yaw rate).
Sideslip, v.
•The roll sequence is done first in one direction
to ease the development of perceptual and motor
skills. Roll 5, done in the opposite direction, is
often confusing for the beginner because the now
expected motor sequence is reversed. That’s why
we do it! Here, your confusion makes us happy.
Consider it a memorable training opportunity.
Don’t freeze! Keep the roll going with full
aileron deflection—rudder and elevator are
secondary to aileron when you are learning to
roll.
•Don’t expect to fly rolling maneuvers step-bystep using a memorized formula. The maneuver
can break down dramatically if the aircraft’s
attitude falls out of phase with your programmed
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
Combined elevator and rudder deflection keep tailforce-vector pointing toward the Earth
Top rudder shifting
to forward stick.
Forward stick.
inputs and expectations. Instead of trying to
establish a sequential muscle-motor program at
the start, concentrate on reacting to the aircraft’s
attitude with the correct muscle-motor
response—your muscles will then program
themselves. These rolls are building your
perceptual familiarity with unusual attitudes
along with the motor habits needed to respond as
required. Learn to fly in response to what you
see.
•On the subject of “flying what you see,” you
can tell that we’re suspicious of applying
memorized, step-by-step control sequences, or
“mantras” at the initial stages of unusual-attitude
recovery training. We’d rather try to help you to
discover the correct inputs—under
guidance—yourself. They’ll stick that way, and
you’ll develop the necessary coordination and
harmony. Memorized sequences are most
appropriate when a pilot can’t figure out what’s
happening and sequenced inputs are the only
way to catch up and get things under control. In
aerobatics, that kind of situation is most likely to
occur when spins accelerate or change modes
and the pilot loses visual tracking. Mantras are
only safe when the initial input can be inserted at
any time in the departure: otherwise out-of-phase
inputs can actually make things worse. You may
feel differently about this. It’s worth talking
over.
Forward stick
shifting to top
rudder.
•Once you’ve done a few rolls and experimented
with control inputs and their results, the notion
of tail-force vector will help you understand
what you’ve in fact already begun to practice.
You’re familiar with an aircraft’s lift vector from
the standard illustrations of lift, weight, thrust,
and drag. The tail-force vector is our term for the
sum and direction of the “lift” produced by the
rudder and elevator together. In coordinated,
upright flight the tail-force vector comes entirely
from the elevator/horizontal stabilizer (we’re
neglecting any directional trim forces the
rudder/fin might be producing). It usually points
earthward, normal to the relative wind over the
tail, and balances the nose-down pitching
moment that results when an aircraft’s center of
gravity is forward of the neutral point (see
ground school text “Longitudinal Static
Stability”). When flying inverted, forward stick
is necessary to produce the same balancing,
earthward tail-force vector. Otherwise, the nose
heads downhill. In knife-edge flight, top rudder
replaces elevator in keeping the tail-force vector
pointed down, and the nose (as much as
possible) up.
•To prevent the nose from falling, to delay the
onset, or to reduce the rate at which the nose
falls in a roll, we keep the tail-force vector
pointed toward the Earth—using whatever
Bill Crawford: WWW.FLIGHTLAB.NET
37
Maneuvers and Flight Notes
changing combination of elevator and rudder
the current bank angle requires. Note that, in
using the elevator and rudder in this way, we’re
keeping the aircraft’s total lift vector pointed
roughly heavenward. See “Axes and
Derivatives” in the ground school texts.
•But here come the caveats: In non-aerobatic
aircraft the effectiveness of these control inputs
depends on the effectiveness of the control
surfaces in flight attitudes neither they nor the
rest of the aircraft were specifically designed to
experience! Jet transports typically have a
trimmable horizontal stabilizer with an attached
elevator. The design facilitates wide c.g. and
airspeed range, but pitch authority is limited by
the position of the stabilizer. Even if the
elevators are effective enough to slow the rate
the nose drops while inverted, the resulting
decrease in positive g may lead to fuel flow,
lubrication, or hydraulic system failure. In the
unlikely event the elevators are effective enough
to actually push the nose up inverted, the
resulting negative g may be insupportable
structurally.
•There’s more to worry about: In an aerobatic
aircraft, rudder forces are usually well
harmonized with elevator and aileron. Dutch roll
is usually well damped. But that may not be the
case in a jet, especially swept-wing. In
transports, rudder breakout forces can be
high—and in some designs at certain speeds can
be close to the force required for full deflection,
a situation that can lead to over control. Because
the sideslip angle has to build up before the
resulting rolling moment appears, and because of
roll inertia, there may also be a time lag between
the rudder input and the roll response. Such
factors make it difficult to achieve the rudder-
38
input harmony and timing possible in an
aerobatic trainer. The result of overzealous
rudder use can be the build up of such a large
sideslip angle and consequent roll moment that
the recovering aircraft continues rolling past
wings level. If the pilot reacts to the ensuing
Dutch roll by deflecting the rudder against the
sideslip (left sideslip, left rudder, say), the
moments generated by the sideslip angle and the
rudder together can “over yaw” the aircraft to the
opposite side, causing it temporarily to reach an
extreme, overswing sideslip angle. Suddenly
reversing the rudder against the swing can set up
the forces necessary to damage, or destroy, the
vertical tail. Always use the rudder cautiously in
a swept-wing aircraft.
•Concerning rudders, review the Boeing
Commercial Airplane Group Flight Operations
Bulletin, May 13, 2002, at:
http://www.ntsb.gov/Events/2001/AA587/exhibit
s/240009.pdf
•As we’ve shown, in an intentional roll you can
finesse with top rudder at knife-edge and with
forward stick through inverted in order to keep
the nose up. You can use top rudder and slight
aft pressure to accelerate the roll rate after
passing from knife-edge back toward upright (as
long as the wing isn’t too near stall and rudder
likely to cause a departure). You can apply the
same finesse to emergency recoveries as
appropriate to your aircraft type, but don’t forget
the most important control. In a recovery from a
roll upset, use full aileron. It’s easy to relax
aileron pressure inadvertently. Every student
does it. Learn not to!
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
10. Sustained Inverted Flight
Flight Condition: Inverted, -1g.
Lesson: Situational awareness, trim forces, AI interpretation.
Procedures:
Instructor:
Check: Seat belt, cockpit, instruments, altitude, outside.
Cruise power.
Fly a cardinal heading.
Instructor asks student to point quickly to cockpit instruments and outside cardinal headings.
Instructor rolls aircraft inverted and maintains control.
Instructor asks student to point quickly to cockpit instruments and outside cardinal headings
while inverted.
Student takes control and rolls upright.
Student:
Raise nose about 20 degrees.
Roll inverted.
Forward pressure as required to maintain level flight.
Rock wings approximately 15-20 degrees left and right (note any sensation of adverse yaw).
Roll upright.
Flight Notes
We teach full, 360 degree rolls before we teach half rolls to inverted because the distracting physiological
effects of negative-g inverted flight are easier on the student when encountered later in training. Negative
1-g level inverted flight is an interesting training experience, but it’s actually more an aerobatic than an
emergency skill. In reality, unless you assert yourself with forward pressure, and the aircraft has sufficient
elevator power, you’re not going to experience sustained negative-g during an upset emergency short of an
inverted spin (nor would you want to in an aircraft without proper fuel and lubrication systems). The
aircraft will assert its longitudinal stability and start pitching toward positive g, as this maneuver illustrates.
•Reference points are hard to retain when you’re
hanging upside-down. Students who can respond
quickly to the instructor’s request to point out an
instrument inside or a cardinal direction outside
the cockpit when right-side-up often have trouble
doing the same thing when inverted under actual
negative g. There’s a tendency to tense the body
and stare at a point, and just turning the head and
looking around can require real effort. Flight
skills don’t come naturally under these
conditions, especially when you just discovered
that your seat belt wasn’t as tight as you thought.
•When the instructor rolls inverted and transfers
control and asks you to roll upright, you’ll be
surprised at the amount of forward pressure he or
she was holding. Don’t let up and let the nose
fall too far. When you roll the aircraft from
upright to inverted, remember how that push
force felt and blend it in as you complete the half
Bill Crawford: WWW.FLIGHTLAB.NET
39
Maneuvers and Flight Notes
roll. Notice inverted that the junk that was on the
floor or loose in your pockets is now on the
canopy. A little dust is inevitable, but anything
that could jam the control system requires
immediate recapture and a better preflight next
time around.
•On rolling upright from inverted: If you’ve
flown or read about aerobatics, you might know
that strict procedure often requires rudder input
opposite to aileron, followed by rudder input
with aileron, when rolling upright from negativeg inverted flight. That’s because inverted adverse
40
aileron yaw calls for some rudder deflection
opposite to stick deflection. Such cross-control
technique is usually confusing to the student at
first, and tends to delay recovery actions. It’s
important in precision roll training with aerobatic
aircraft equipped with inverted oil and fuel
systems. But it creates unnecessary confusion in
unusual-attitude training for pilots who will fly
non-aerobatic aircraft with conventional systems
and much heavier control forces in pitch. Even if
the pilot pushes as the aircraft rolls through
inverted, the load will probably remain positive
and inverted adverse yaw won’t occur.
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
11. Inverted Recoveries
Flight Condition: Inverted, high & low kinetic energy states.
Lesson: Attitude recognition and recovery practice.
Procedures:
Instructor:
Check: Seat belt, cockpit, instruments, altitude, outside.
23”/2,300 rpm.
Pitch up to about 45 degrees.
Student closes eyes.
Roll inverted; decelerate on ascent.
Idle power.
Gently pull nose below horizon.
Student:
Opens eyes on instructor’s command.
Rolls upright to recover.
Repeat from different inverted bank angles.
Student pitches up, closes eyes, rolls inverted, opens eyes and recovers on instructor’s command.
Instructor transfers control to the student inverted at a nose-high, low-kinetic-energy state.
To prevent excess airspeed during inverted recoveries, the instructor will normally close the throttle
before the student takes control. In that case the student should simulate proper throttle use.
Flight Notes
Identify the Nearest Horizon (fewest degrees away): Push & Roll, Top Rudder, Pull
When using the AI, roll toward the sky pointer, or roll the lift vector toward the sky.
In this maneuver set we’ll apply the lessons learned in slow-roll flight dynamics to a more challenging
attitude environment. Your instructor will fly the maneuvers to the descent line at the start, allowing you to
recover. The initial goal is to get you going downhill, upside-down, horizon obscured, at as slow a speed as
possible, with as gentle an entry as possible. This makes the fewest demands on your motion tolerance, and
keeping the speed down allows you time to discover what the world looks like when you’re descending
inverted. We may use rudder to accelerate the roll recovery, but we’ll take note of the caution required.
Bill Crawford: WWW.FLIGHTLAB.NET
41
Maneuvers and Flight Notes
•In the first maneuvers, you’ll already know that
you’re pointing down and accelerating. In that
case, it’s correct to Push to keep the nose from
falling farther. In subsequent nose-high transfers
of control you’ll be very slow. You’ll be able to
see the horizon, but will need to allow the nose
to come down below it to let gravity help
accelerate the aircraft so that control authority
returns. Don’t reflexively push. If the aircraft
somehow picks up a yaw rate, pushing while
inverted at low speed could lead to an inverted
spin.
•Roll to the nearest horizon with full aileron.
The nearest horizon is the fewest degrees away.
On instruments, that means rolling toward the
sky pointer, or rolling the lift vector toward the
sky.
•As the aircraft rolls upright from inverted to
knife-edge, start applying Top Rudder and
release the forward pressure. If you hold forward
pressure past knife-edge you’ll sacrifice some of
the dihedral effect necessary to assist the roll,
and you’ll push the nose down and yourself out
of the seat. Top rudder holds the nose up through
knife-edge and starts a sideslip that accelerates
the roll.
•Begin your Pull as the aircraft rolls through
roughly 45 degrees. Come off the rudder as you
near upright. Ailerons are primary, but past
knife-edge combining top rudder and elevator
can bring the nose up to the horizon following
the shortest line.
•The top-rudder deflection accelerates the roll
and also keeps the airplane from turning when
you begin your pull. As you roll upright, rudder
and elevator work together to keep the tail-force
vector pointing roughly earthward, so that the
nose comes up to the horizon in a direct vertical
path and sideslip assists roll rate.
trainers and swept-wing aircraft in their Dutch
roll response to rudder deflection. Now worry
about this: If you pull an aircraft to limit load
while rolling with aileron and/or rudder (a
rolling pull-up) the asymmetrical load generated
across the span can take the up-going wing past
structural limits. This could occur from the
rolling moment generated by modest rudder
application alone, since even a small moment
applied at limit load would cause the wing to
exceed that limit. This wrecks airplanes. See
“Maneuvering Loads, High-G Maneuvers” in the
ground school text.
•Any general statement about handling an
aircraft in an upset emergency has to balance the
risks of misunderstanding against the rewards of
airmanship. A given control input or
combination could either get you into trouble or
else help you out of it…depending. So what’s
best to say? A general statement also has to
avoid optimistic assumptions concerning both a
pilot’s ability and the unknown areas of an
aircraft’s response. It has to assume that the
expertise shown in training will deteriorate and
that a pilot will become confused if too many
half-remembered nuances exist in his mind.
Aerobatic instructors know this from the
experience of watching students fumble through
roll recoveries as they try to remember what to
do with the rudder and elevator. In light of the
above, here’s a general, baseline, “I’m out of
practice so what do I do now?” statement that
applies to aircraft with standard flight controls
and flying qualities. Embed this in your mind as
the primary response: In a roll-upset emergency,
go to the ailerons first. Unless you initially need
them to lower the nose to regain airspeed for
aileron authority, rudder and elevator are
secondary. So much the better if you’re more
expert than that!
•You’re using rudder and elevator in an expert
way in these recoveries. Just remember that the
rudder and the elevator can cause trouble. We’ve
already worried about misapplication of or
inappropriate reliance on rudder at high α,
because of possible stall/spin departure. We’ve
worried about differences between aerobatic
42
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
Roll toward the Sky Pointer
Roll the Lift Vector toward the sky
Lift Vector
Earth
Sky
Sky Pointer
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43
Maneuvers and Flight Notes
12. Rudder Roll: Yaw to Roll Coupling
Flight Condition: High α, high β, upright & inverted.
Lesson: Roll control by means of sideslip, yaw rate, and angle of attack.
Procedures:
Check: Seat belt, cockpit, instruments, altitude, outside.
25”/2,500 rpm.
Pitch up to 45 degrees.
Full rudder deflection.
Ailerons remain neutral.
Hold aft pressure.
Full rudder throughout.
Repeat as above with temporary forward pressure at inverted to observe decrease in roll rate; restore
aft pressure to completion.
Flight Notes
The rudder roll is similar to the old-fashioned barrel roll in terms of the flight path the aircraft follows
through the sky, except the ailerons remain neutral and the heading changes are not as great. It’s also a kind
of slow-motion snap roll, although the aircraft doesn’t go all the way into autorotation. It’s not often taught
in civilian aerobatics, but has a history in the military as a way of rapidly reversing bank angle in a high-g
turn. We fly rudder rolls to underscore yaw/roll couple, and to add their more complex motions to your
unusual-attitude experience. The rudder roll also demonstrates that yaw/roll couple responds the same to
longitudinal stick position whether the aircraft is inverted or upright (or in any other attitude), as long as
the wing is at a positive angle of attack. Caution: Rudder rolls can rapidly erode motion tolerance.
• The aircraft will roll 360 degrees on dihedral
effect, roll due to yaw rate, and y-wind-axis
pitch/roll couple. Constant pitching, yawing, and
sideslip drive the maneuver. Unlike the slow
rolls we’ve been working on, where we try to
keep the tail-force vector pointing earthward, in
the rudder roll (and barrel roll) the tail-force
vector rolls with the airplane.
•Notice how reducing the angle of attack with
•If you pull too hard the aircraft can snap roll
suddenly (high angle of attack + sideslip and
yaw rate = departure!). Release aft pressure and
rudder if you feel the roll begin to accelerate too
quickly. (A snap roll at the top of a loop is called
an “avalanche”—which is nicely expressive of
the tumbling feeling it produces. A snap
departure out of a rudder roll feels the same, and
causes the same spatial confusion on first
encounters.)
forward stick (unloading) while inverted reduces
the roll rate. If you relax the stick (or rudder) too
much the roll rate will really decrease and the
nose will just head downhill. If necessary,
recover with full aileron in the normal way.
44
Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
13. Rudder & Aileron Hardovers
Flight Condition: Uncommanded rolls.
Lesson: Effects of pitch inputs during uncommanded rolls.
Procedures:
Demonstrate effect of pitch input during normal spiral, rudder neutral.
Power for low cruise.
Enter spiral mode.
At 45-degree bank, observe response to stick-back pitch input.
Release and recover.
Demonstrate effect of pitch input during rudder hardover spiral, rudder deflected.
Aileron neutral.
Roll 30 degrees with rudder only.
Hold rudder input.
Hold aileron neutral.
Aft pressure to accelerate roll.
Release and recover.
Alternate aft pressure and forward pressure while holding rudder input and observe roll response.
Demonstrate recovery from rudder hardover below crossover speed.
Begin rolling the aircraft with rudder, then apply a partial aileron deflection using too little aileron to stop
the roll. (The aircraft is below crossover speed for the partial aileron deflection.)
As the aircraft rolls, hold rudder and aileron fixed, pitch down for speed to regain aileron effectiveness.
Add power in the recovery as necessary to remain above crossover speed.
Demonstrate recovery from uncommanded aileron deflection, showing the effect of rudder and aft stick.
Partial aileron deflection.
Apply rudder sufficient to slow but not stop the roll.
Stick back (or nose-up trim) to increase α/CL.
Flight Notes
Concerns about rudder hardovers, and the development of the concept of crossover speed, stem directly
from accidents involving Boeing 737s, which were caused or complicated by uncommanded rudder
deflection. (See http://www.ntsb.gov/publictn/2001/aar0101.htm) Here we start by observing that in a
rudder-neutral spiral attitude, back stick gives you a pure pitch response. But during a rudder-deflected
spiral attitude, as produced by an uncommanded rudder hardover, back stick accelerates the roll.
Although aircraft attitude relative to the horizon might appear identical to the pilot, in the rudder-deflected
Bill Crawford: WWW.FLIGHTLAB.NET
45
Maneuvers and Flight Notes
case the aircraft is in a sideslip toward the high wing. Pitch will couple to roll in the presence of a sideslip.
While the hardover issue may not affect all planes and pilots, it’s difficult to confirm one’s immunity, and
the exercise does provide more evidence for flying’s least instinctive but most encompassing maxim:
Sometimes you have to aim for the ground to keep from hitting the ground! In the uncommanded rudder
deflection case, you aim for the ground to regain aileron effectiveness.
•Here’s an official definition, evidently approved
by the attorneys, from The Airplane Upset
Recovery Training Aid. At a given rudder
deflection, crossover speed is “the minimum
airspeed (weight and configuration dependent) in
a 1-g flight, where maximum aileron/spoiler
input (against the stops) is reached and the wings
are still level or at an angle to maintain
directional control.” (2.5.5.4.3)
begin to fall through the horizon. Since roll
couple for a given sideslip angle and aircraft
configuration varies directly with coefficient of
lift (with α), as does roll due to yaw rate, the
rudder-induced roll rate will increase if you try
to raise the nose with aft pressure. This just tilts
the lift vector more toward the horizon and
makes the nose fall even faster (as we
demonstrate in this maneuver set).
• In other (if only slightly more digestible)
•In an emergency, if the hardover roll
words, rudder deflection produces a rolling
moment, in the direction of deflection, due to
sideslip and yaw rate. You can counter an
uncommanded rudder deflection with opposite
aileron, just as you do in a steady-heading
sideslip, but only if you’re going fast enough to
generate a sufficient opposing moment—that is,
if you’re going above the speed where excess
roll power crosses over from rudder to aileron.
The more rudder deflection, the greater the
corresponding rolling moment and therefore the
higher the crossover speed. If you fly below
crossover speed the aileron/spoilers can’t supply
a sufficient opposing roll moment against the
rudder, and an uncommanded roll in the rudder
direction results. Wing-mounted multi-engine
aircraft need powerful rudders to overcome
asymmetric thrust conditions during engine
failures. Uncommanded rudder deflections can
produce powerful roll moments, especially in
swept-wing aircraft.
•You’re familiar with cross-controlled
maneuvers from our earlier steady-heading
sideslips, and noticed (maybe) that we reached
the rudder stops before reaching the aileron
stops. To simulate a crossover problem at a
reasonable angle of attack, we simply limit our
aileron deflection and pretended we’re “against
the aileron stops.”
•When an uncommanded rudder deflection
continues despite full opposite aileron, lower
the nose to regain aileron effectiveness. Diving
even more to regain bank control is not intuitive
if the nose is already coming down in an
unwelcome manner! But reducing the angle of
attack will reduce yaw/roll couple, which in turn
reduces crossover speed. Meanwhile, the airflow
picks up the dynamic pressure necessary for
aileron authority. As you raise the nose, set the
power as required for flight above crossover
speed. Then take a breath and pull out the
Emergency Checklist for the recommended
rudder hardover flap setting, if there is such a
thing. (Maneuver set 14 demonstrated how flap
deployment reduces a sideslip-induced yaw/roll
couple, and thus would reduce crossover speed.)
•In an aileron hardover, you’d obviously try
opposite rudder. Then if necessary you’d raise
the nose to increase the CL and increase the
yaw/roll couple the rudder provides. Flaps would
probably stay up, or go up if that were an option,
again to increase yaw/roll couple as necessary to
combat the ailerons.
•Remember that the basic relationship between
what you do in pitch and what happens in roll
remains constant. Pushing forward reduces
rudder/sideslip-coupling effects and increases
aileron authority, pulling back (literally toward
the rudder) decreases aileron authority and
increases rudder/sideslip-coupling effects.
creates a rolling moment, the aircraft’s nose will
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Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
14. Lateral Effects of Flap Deployment
Flight Condition: Changing β & spanwise lift distribution.
Lesson: Lateral lift distribution and lateral stability.
Procedures:
Power as required for speed in white arc.
Enter steady-heading sideslip.
Hold rudder and aileron fixed.
Lower and raise flaps and observe lateral response.
Observe pitch response due to the changes in downwash angle.
With the flaps down in a sideslip and the aircraft trimmed, hold the rudder and release the stick:
Compare the roll rate with the flaps-up condition explored in maneuver set No 2.
If desired, repeat at idle power, maintaining airspeed in descent, to assess the contribution of propeller
slipstream effects.
In the Zlin, full flaps, wings level, apply full rudder.
Observe pitch change with downwash/propwash shift.
Flight Notes
Here we’ll alter the rolling moments in a sideslipping aircraft by changing flap position. This ties into the
concept of crossover speed during rudder hardovers. Crossover speed may go down in a flaps-down
configuration because of the phenomena we’ll observe here.
•Putting the flaps down increases the lift
generated at the wing roots and thus shifts the lift
distribution inboard. This is partly because of the
increased camber inboard, and partly because,
after we’ve re-trimmed, the wingtips operate at a
lower angle of attack. In effect, we’ve increased
their washout. The inboard shift in center of lift
reduces the effective moment arm and therefore
the rolling moment that results from the sideslip.
Accordingly, when you lower the flaps in a
steady-heading sideslip, the ailerons will have
less to fight against and the aircraft will roll in
the pro-aileron direction.
Flap Effects
Lift
Distribution
Total lift is the same
(lift=weight), but shifts
inboard.
•Because of this inboard shift in lift, an aircraft’s
lateral stability (its tendency to roll away from
the sideslip caused when a wing goes down) is
typically reduced with flaps deployed. Its roll
due to yaw rate may also decrease because of the
washout effect. We’ve already noted the
Wing center of lift
Wing is in a
sideslip to the
right.
Resulting roll
moments
v
v
Centers of lift move inboard with flaps during a
sideslip, reducing the moment arm through which
dihedral effect operates. Roll moment decreases.
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47
Maneuvers and Flight Notes
•In some aircraft, flaps can decrease aileron
reduction in longitudinal stability with flap
deployment caused by downwash effects.
authority. This is one reason why using only
partial flaps during a gusty, crosswind landing is
a good idea. (The other, of course, is that a
higher landing speed increases overall control
effectiveness and leaves the aircraft vulnerable
for less time.)
•The flap effect you’re seeing is magnified in
propeller airplanes by the shifting of the
slipstream over the wings toward the side
opposite the sideslip, as the illustration shows.
This means that the flaps on the high side during
our steady heading sideslip work in an area of
higher dynamic pressure. This increases the lift
on the high wing, reduces it on the low wing, and
produces a rolling moment in the same direction
as the ailerons. With the power at idle, you’ll
need more flap deflection to get the same roll
response you got when lowering the flaps with
power on.
•The last maneuver in the set demonstrates how
a sideslip combined with flaps can cause a
sudden change in the downwash/propwash over
the horizontal stabilizer. The nose may suddenly
pitch in response. Unless you really know how it
will behave, don’t aggressively slip an aircraft
with full flaps on final.
β
Sideslip Shifts
Propwash
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Maneuvers and Flight Notes
15. Dutch Roll Characteristics
Flight Condition: Coupled yaw/roll.
Lesson: How directional and lateral stability interact dynamically.
Procedures:
About 23”/2,300 rpm.
Trim.
Instructor performs sinusoidal rudder inputs.
Observe roll/yaw ratio at wingtip.
Release rudder and observe rudder-free damping and overshoots.
Compare with rudder fixed damping and overshoots.
Flight Notes
Your instructor will probably want to do this demonstration on the return from the practice area. Dutch
rolls can erode motion tolerance rapidly, and that’s best saved for other things. FAR Parts 23.181 & 25.181
cover the requirements for Dutch roll characteristics. (Note: Our sinusoidal rudder inputs are consistent
with FAR Part 25.351 yaw maneuver load requirements.) The Dutch roll is the natural outcome of
aerodynamic stability: an aircraft’s tendency to yaw toward but roll away from its velocity vector.
•As already mentioned, the term Dutch roll is
often misused. The real Dutch roll is not an
exercise in rolling on point, but a coupled
combination of yaw rate, sideslip, and roll. You
can think of it as a rough marriage between an
aircraft’s roll axis (lateral) stability and its yaw
axis (directional) stability. In the Dutch roll, a
disturbance in either axis, whether pilot-induced,
as here, or caused by turbulence, creates a
sideslip. A sideslip that sends the velocity vector
to the left, for example, leads to an opposite
rolling moment to the right (through dihedral
effect and roll due to yaw rate). At the same time
the aircraft’s directional stability works to
eliminate the sideslip by causing the nose to yaw
to the left. However, momentum causes the nose
to yaw past center (past zero β), and this sets up
a sideslip in the opposite direction, which in turn
sets up an opposite roll. The resulting out-ofphase yawing and rolling motions would damp
out more quickly if they occurred independently.
Instead, each motion drives the other. Part 23
aircraft are required to damp to 1/10 amplitude in
7 cycles. Part 25 requires only positive damping.
•Aircraft with lots of lateral stability (the
tendency to roll away from a deflected velocity
vector), compared to their directional stability,
tend to Dutch roll. Reducing dihedral effect will
ease the Dutch roll problem, but at the expense
of reduced lateral stability. Without a yaw
damper to do it for them, it’s difficult for pilots
to use the rudder to control a persistent Dutch
rolling tendency because the period is short. It’s
hard to “jump in” with the correct rudder input at
the right time. (Failure of a yaw damper can also
cause fin overstress if Dutch roll develops.)
Swept-wing aircraft are inherently vulnerable to
Dutch roll. Pilots of swept-wing transports are
frequently trained to damp the rolling motion
with quick, temporary applications of aileron
against the prevailing roll. Temporary
applications prevent the pilot from inadvertently
driving the rolling motion. An aircraft with lots
of lateral stability may also require lots of aileron
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49
Maneuvers and Flight Notes
deflection to hold the upwind wing down during
crosswind landings.
•Aircraft with greater directional than lateral
stability tend to be spirally unstable.
Traditionally, the design compromise between
Dutch roll and spiral instability suppresses the
former and allows the latter, because spiral dives
begin slowly and are normally easier to control
than Dutch rolls. And Dutch rolls make people
airsick. (Which sounds like the dealmaker until
you realize that spiral instability can kill you if
you lose or misinterpret your instruments in
clouds, or in poor visibility at night.)
•Watch the wingtip while driving the Dutch roll
with continuous, uniform, opposite sinusoidal
rudder inputs. Observe if its motion pattern is
circular or elliptical. An ellipse lying on its side
(1.) means more yaw than roll—in other words a
low roll-to-yaw ratio. This is typical of aerobatic
and tactical aircraft required to have fast roll
Velocity vector
rates. A circular wingtip motion (2.) indicates
equal amounts of roll and yaw, as might be
typical of a general aviation aircraft, in which a
pilot can use the rudder for bank control.
•An upright ellipse (3.) would indicate more roll
than yaw—a high roll-to-yaw ratio. That’s
typical of a sailplane and indicates that roll
performance will require good rudder
coordination during roll maneuvering. Any
uncorrected adverse yaw will generate an
opposing sideslip and large roll moments
opposite the intended roll direction. (The long
wings of high-performance sailplanes produce
substantial adverse yaw due to roll rate, so
footwork is essential.)
•The tendency to Dutch roll increases at higher
CL, because increasing the coefficient of lift
increases both dihedral effect (especially with
swept-wings) and roll due to yaw rate. Dutch roll
tendency also increases at higher altitudes, where
damping effects diminish. Since aircraft fly at
high CL at high altitudes, the problem
compounds.
After initial disturbance,
aircraft wants to yaw to
right but roll to left.
Yaws past center
and now wants to
yaw left but roll
right.
Yaw overshoot
decreases as motion
damps out.
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Bill Crawford: WWW.FLIGHTLAB.NET
Maneuvers and Flight Notes
16. CRM Issues: Pilot Flying/Pilot Monitoring
Flight Condition: Various.
Lesson: Upset recovery and the two-person cockpit.
Procedures:
Ground Briefing: Students formulate a plan of response, listing potential unusual attitudes and potential
control errors, plus appropriate pilot monitoring actions.
Instructor:
Check: Seat belt, cockpit, instruments, altitude, outside.
Places aircraft in an unusual attitude.
Announces: “Now recovering.”
Begins recovery.
Student:
Monitors instructor’s recovery technique.
Guards controls with hands against improper deflections.
Verbally coaches best recovery.
Takes control as required.
Flight Notes
“Pilot monitoring” has replaced the earlier term “pilot not flying.” The change keeps both pilots in the loop,
at least rhetorically. As pilot monitoring, your ability to coach your instructor and respond as necessary will
confirm your understanding of recovery techniques. And you’ll be exposed to potential conflicts in
CRM—in this case, recovery management.
•Your instructor may initiate recovery with the
proper control inputs, but with inadequate
control deflection. In that case you might coach,
“More aileron,” then push the aileron if he
doesn’t respond. Or your instructor may call out
“Vertigo!” or initiate an incorrect recovery, in
either case requiring rapid intervention on your
part. One example might be a pull when
inverted.
changes or additions you might make to your
CRM procedures.
•If relevant, it’s important that all pilots in your
flight department discuss the results of this drill
at the completion of the course, and the possible
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51
Maneuvers and Flight Notes
17. Primary Control Failures
Flight Condition: Stick failure/loss of elevator, elevator trim, aileron.
Lesson: Re-establishing and evaluating control.
Procedures:
Fly parallel to a ground reference line (simulated runway).
.
Instructor places aircraft in nose-high or nose-low bank angle.
Student recovers and maintains control with rudder, elevator trim, and throttle only.
Turn 180 degrees and descend over reference line.
Establish landing attitude and a zero rate of descent at an altitude the instructor specifies.
Repeat without elevator trim.
Flight Notes
This maneuver set assumes the loss of both primary longitudinal (elevator) and lateral (aileron) control
systems. Below are the FAR Part 23 requirements concerning loss of primary controls. In this maneuver set
you’ll conduct, in essence, a FAR Part 23.145(e) and Part 23.147(c) flight test. The initial recovery from a
nose-high or nose-low bank angle would not be part of such a test. That’s ours. Attempting the procedure
without elevator or trim is also ours.
FAR Part 23.145(e) By using normal flight and power controls, except as otherwise noted in paragraphs
(e)(1) and (e)(2) of this section, it must be possible to establish a zero rate of descent at an attitude suitable
for a controlled landing without exceeding the operational and structural limitations of the airplane, as
follows:
(1) For single-engine and multiengine airplanes, without the use of the primary longitudinal control system.
(2) For multiengine airplanes -(i) Without the use of the primary directional control; and
(ii) If a single failure of any one connecting or transmitting link would affect both the longitudinal and
directional primary control system, without the primary longitudinal and directional control system.
FAR Part 23.147(c) For all airplanes, it must be shown that the airplane is safely controllable without the
use of the primary lateral control system in any all-engine configuration(s) and at any speed or altitude
within the approved operating envelope. It must also be shown that the airplane's flight characteristics are
not impaired below a level needed to permit continued safe flight and the ability to maintain attitudes
suitable for a controlled landing without exceeding the operational and structural limitations of the airplane.
If a single failure of any one connecting or transmitting link in the lateral control system would also cause
the loss of additional control system(s), compliance with the above requirement must be shown with those
additional systems also assumed to be inoperative.
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Maneuvers and Flight Notes
Observations:
1. Using rudder, how aggressively should you bank the aircraft?
Does a phugoid appear during the turn?
How much altitude is lost after turning if you can’t trim?
2. Do the flaps produce a pitching moment that can be easily trimmed?
3. Do flaps affect the ability to turn using rudder (diminished dihedral effect)?
4. With the aircraft at a given trim state, gear down, what power settings are necessary for:
Level flight?
Positive rate of climb at moderate pitch attitude?
Controlled descent along a standard glide path?
5. Without trim available, can you achieve a landing attitude using power and/or flap deployment?
•FAR Part 23.145(e) assumes that the power and
•Without primary controls, a long, stabilized
trim systems are available. It doesn’t require the
test pilot to complete an actual landing. Flying
without elevator but with trim in a more-or-less
normal fashion presupposes that the elevator
floats free, as it might with a broken cable. A
jammed elevator is rotten news, even if it jams at
a favorable angle. With the elevator frozen and
trim tabs operating, trim input will reverse (noseup trim will produce a nose-down pitch moment,
for example). But don’t expect a trim tab to be an
effective longitudinal control under these
conditions. They’re designed to generate enough
moment to deflect the elevator, not pitch the
aircraft.
final approach is absolutely essential. Without
primary longitudinal and trim control, you’re
stuck with an approach speed according to the
aircraft’s trim state. Manipulate the glide path
with power. Find a long runway, into the wind!
•Without the stick for primary longitudinal and
lateral control, and without elevator trim, the
phugoid suddenly becomes your constant pal.
You’ll provoke a phugoid every time you bank
using rudder. It’s difficult to damp a phugoid
with power, but you should try during this
exercise, just to see. Without trim control, your
best policy is to ride the phugoid out. An aircraft
at an aft c.g. may have a neutral or a divergent
phugoid, however.
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53
Maneuvers and Flight Notes
18. Spins
Flight Condition: High angle of attack plus roll due to sideslip and yaw rate.
(α + Clβ + Clr)
Lesson: Departures and recoveries.
Entry Procedures:
1. Basic spin entry:
4,000 feet agl.
Rudder and elevator trim to neutral.
Mixture rich.
Power idle.
Back stick for standard 1-knot-per-second deceleration.
Ailerons neutral.
Full rudder in desired spin direction at buffet onset.
Stick full back.
2. Nose-high, yaw-rate entry:
4,000 agl.
Cruise power.
Hold steep climb attitude, rudder free.
Allow propeller effects to yaw aircraft to the left.
Back stick until stall/spin break.
3. Skidding-turn-to-final entry:
4,000 feet agl.
Rudder and elevator trim to neutral.
Mixture rich.
12 inches manifold pressure or as required.
Begin skidding turn with rudder.
Hold wings level with aileron.
Apply back stick until stall/spin break.
Experiment with power to determine propeller effects.
Apply sudden aileron toward the direction of the turn while holding rudder and elevator.
4. “Lazy-eight” departure/recovery drill:
Linked opposite-side half-turn spin departures and recoveries.
PARE Recovery Procedure:
Power as spin state requires.
Ailerons neutral.
Rudder full opposite rotation.
Elevator forward to neutral or past neutral according to AFM or POH.
Recover from dive with rudder neutral.
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Maneuvers and Flight Notes
Flight Notes
Spins have become a culminating skill in wide-envelope stick-and-rudder airmanship. In earlier days, under
a different training philosophy, they were a pre-solo foundation skill. Pilots—and also aircraft—are
different today as a result of this fundamental shift. The ground school text contains extensive material on
spin procedures and theory. We review the PARE recovery technique here.
Power to idle. (Reduces propeller gyroscopic
effects and slipstream-induced yaw.)
Recovery inputs immediately following the
break may be less critical (but not always).
Ailerons neutral. (Removes any inadvertent
deflection that may delay recovery. In a
fuselage-loaded aircraft the ailerons go toward
the spin direction to produce an anti-spin inertia
moment in yaw.)
•Note that in the PARE sequence, opposite
Rudder opposite yaw direction. (Provides antispin aerodynamic yaw moment.)
Elevator forward to neutral or past neutral.
(Unstalls the wings; for wing-loaded aircraft
generates anti-spin inertia moment in yaw.)
When the spin stops, pull out with the rudder
neutral. (If recovery rudder is still deflected and
you pull too hard, the aircraft can snap roll into a
spin going the opposite way. Holding recovery
rudder is a common mistake.)
•Power to idle depends on spin state. It’s already
at idle in a practice spin. For an immediate
recovery from a stall/spin break, power can
usually be left on in a single-engine training
aircraft, and brought back as necessary for speed
control in the pull out from the dive. (A prop
twin on one engine requires immediate power to
idle on the operating engine, since the slipstream
produces both rolling and yawing moments in
the direction of the dead engine. Most bets are
off in twins, however, because no spin testing is
required for certification.)
•The PARE sequence comes from certification
demonstration requirements that assume spin
recovery will only begin after a certain time or
number of turns, depending on aircraft category,
and not immediately after the stall/spin break.
rudder precedes forward stick. Forward stick
applied before opposite rudder can accelerate the
spin through aircraft gyroscopic effects, and can
also cause the elevator to block the airflow to the
rudder in some aircraft, each of which delays
recovery. The acceleration isn’t necessarily the
case in an immediate recovery right after
departure, however, as we’ll demonstrate and
discuss. In our trainers the roll acceleration on
departure is initially high; then the yaw rate
picks up. As a result, angular momentum is
greater in roll initially than in yaw. Pushing the
stick forward causes gyroscopic precession
around the roll axis that leads to an anti-spin
moment in yaw. Plus, pushing gets the angle of
attack back down. But once the aircraft’s yaw
rate and angular momentum about the yaw axis
have begun to build, forward stick will cause
momentary gyroscopic acceleration in roll, even
when it follows the rudder in proper sequence.
Our introductory spins will go at least to the
point where you can begin to feel the “push
back”—the increase in pressure needed to bring
the stick forward for recovery as angular
momentum picks up in yaw and the aircraft
becomes increasingly resistant to displacement,
and also experience the momentary roll
acceleration. It’s important to observe these
characteristics and to recognize them as normal.
One to one-and-a-half turns before initiating
recovery will accomplish this in our aircraft.
Multiple-turn spins beyond that have dubious
value in introductory training. In the beginning
it’s better to go for lots of entries and recoveries,
do a careful analysis each time, and not waste
training time recovering large chunks of altitude.
• As part of the analysis, after each spin try to
describe the aircraft’s motions to your instructor.
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55
Maneuvers and Flight Notes
You may find post-stall spin behavior difficult to
follow at first, especially if your attention is
occupied with remembering the recovery steps
and wondering if they’ll actually work. But
report each time. The task helps build tracking
skills and confidence, and keeps the instructor
updated on your progress.
•The infamous skidding-turn-to-final spin (spin
entry 3) will produce a departure in some
aircraft, while others are resistant (too much
directional stability for the available rudder
power; too little elevator power). Some will do it
engine power off; some need a boost in yaw and
pitch from the slipstream hitting the stabilizer
and tail. The slipstream increases the upwash on
the left wing, which then operates at a higher
angle of attack and in a left turn stalls first.
Spiraling slipstream also encourages a departure
to the left. Frankly, a high-α skidding turn is
hard to imagine from a properly trained
pilot—the necessary control forces ought to warn
the pilot off. But what about after an engine
failure in an aircraft with a departure-prone
wing, or when some other distraction arises? At
low altitude and low speed, no matter how good
the pilot, if obstacles are approaching it will be
hard to resist the impulse to rudder rather than
bank the airplane. If the pilot then pulls up the
nose—there’s your spin.
of the aircraft to do the maneuver smoothly. If
you can do all this, you’re definitely a hot stick!
•The pull up when the spin stops is full of
important lessons. Depending on when in the
spin the recovery was introduced, and whether
the pilot as forgotten to neutralize the rudder
(holding recovery rudder too long is a universal
beginner’s mistake), the aircraft may end up in a
sideslip, and may roll rather than raise its nose
when the pilot applies back stick. Or, even if the
pilot uses the rudder correctly, but pulls too hard
before the aircraft has gained sufficient speed,
the aircraft may enter the buffet and lose nose-up
pitch authority. Remember this: When you see a
substantial increase in pitch rate at low speed,
the buffet won’t be far behind. If you penetrate
the buffet too far, nose-up pitch authority may
largely disappear! Ease off.
•In the Zlin, and quite probably in many other
aircraft, a rapid reversal of the ailerons toward
the turn direction, while in-turn rudder and back
stick are still being held, can cause a departure.
When the opposite aileron is removed, the
aircraft rolls and yaws suddenly in the direction
of the skidding turn, and enters a spin. This may
in fact be the true cause of many skidding-turnto-final accidents. The pilot suddenly realized his
error, but corrected with aileron alone.
•The fourth spin exercise is based on the lazyeight. It’s done back and forth across a reference
line on the ground. Each reversal of direction is
accomplished as a spin departure, followed by a
recovery to the half-turn point. Then you add
power and pull up across the line, then cut power
and spin a half turn to the opposite side. Next, go
the other way. Your feet and hands are busy
departing and recovering; you have to maintain
orientation with the ground and stay well ahead
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