A Collection of R-C Hints - RC WORLD Australia Phone

A Collection of R-C Hints - RC WORLD Australia Phone
A Collection of R/C Modelling Tips
This information has not been tested nor confirmed – Use
at your own risk..
How do I make a canopy ?
make a master
make a plaster mould
make a plaster plug
heat some thermo-plastic (0.020" polycarbonate.)
lay the floppy sheet over the mould
form piece by mating the plug to the mould
cool, trim & enjoy...
I suggest you make a plaster mould of the canopy before you start trimming it.
(-: Think ahead " Gravity Works " :-)
Mounting ailerons on hard wood ?
You're inviting flutter with hardwood ailerons. Once that mass starts
oscillating, your wing will disintegrate. Light balsa damps much better,
and is much less destructive if it should flutter.
I am building my first war bird (Top Flite Spitfire), and am now ready to cover. How do I get that nice camouflage
effect, where the 2 colours (olive drab & dove grey) seem to blend into each other?
I cut paper to the camo pattern and lay it on the model. Do not use tape at the edges but rather only in the middle
of the paper to hold it in place. When spraying make sure the spray is 90 degrees to the surface. What happens is
since the paper is not taped down at the edge, the force of the spray causes a little over spray to slip under the
edge of the paper. Takes a little practice but works well. The speed of your pass and distance from the work also
play into it so try to be as
consistent as possible. Instead of paper you can also use construction paper. Just make sure the paper lies
against the surface as tight as possible without taping it.
Another way is with a good airbrush. You can control those patterns
down to a fraction of an inch. However, with a big model you could be
painting all week.
How do get my plain to knife edge ?
If your control lines are in the innermost holes on the servo arm,
and the outermost holes on the rudder horns, that will give you the
least amount of rudder throw. Moving the wires outboard on the servo arm
and / or inboard on the rudder horn will give you more throw. A standard
servo should have the torque to move the rudder far enough to hold knife
edge flight.
Moving the CG aft, within reason, can help knife edge. An easy way
to test CG is to trim the plane for level flight at about 1/2 throttle,
and roll the plane inverted. If the plane pitches down (toward the
ground) significantly, you should be able to move the CG aft. It's best
to move it in small amounts, otherwise the plane could get very
sensitive in pitch (sensitive to elevator movement).
I don't know what prop you're using but a prop smaller in diameter
and larger in pitch will also help. For example, a 13-8 will yield more
control from the rudder and elevator than a 14-6 (the air column from
the prop moves faster over the control surfaces).
With a few adjustments, that plane and engine should be capable of
knife edge flight. It may take full throttle, but it should hold at
least level flight in the knife.
I've heard you can dye canopies with Rit dye. I had some black liquid Rit laying around and had no success with it.
I washed the canopy thoroughly, heated the dye, and left it in for a long time, but it came out clear. Does it have to
be the powdered type to work?
No, it doesn't have to be powdered. I've used both with success!
Your problem is the canopy material. Some plastics used for canopies
will NOT take a tint, no matter how long you soak it in Rit dye, others
will take a tint but will warp badly... ask me how I know! ;-)
By the way, I've discovered that if you add about a teaspoon of table
salt to the water/dye mixture, it seems to help the plastic take the
tint quicker... assuming it will take the tint at all. It's definitely
best to test a scrap of the canopy plastic (that which is left over
after trimming) to see if it will dye or not, and also whether it will
warp in the hot water.
My servo is buzzing why ?
I would test by figuring out which servo(s) are buzzing, then work the
control surfaces with the radio and by hand to see if I could make the
servo stop buzzing. If you can make the servo stop buzzing by simply
supporting the weight of the control surface, you might want a more
powerful servo. If that doesn't help, pull the control horn(s) off the
servo(s) and see if they still buzz. Replace them if they do. There's
internal binding that might cause premature airframe death should the
servo fail.
Measuring Washout
Washout, the downward twist in wingtips that improves low-speed flight, is sometimes used in airplanes with flatbottom wings. A good way to make sure each wingtip has the same amount of washout (or any at all) is to get two
straight wood dowels or carbon rods. Tape each to the bottom of the wing near the tips. Set the wing on something
so you can see both rods, and sight down the wing so you can see each rod in relation to the other. The rods
magnify any angle that might be present in the wing. Correct the wing twist until you have the angle you want. This
doesn't work too well with wings that are rounded on the bottom, but is an excellent way of making sure flat-bottom
wings are true.
4 Tips about Epoxy
1. Wax Paper: Take a sheet of wax paper, and mix your epoxy on half of the sheet. Then when done, fold the wax
paper in half, trapping the epoxy residue inside. This way you can fold it up with no mess and throw it away, and it
won't stick to the inside of the trash can.
2. Foam: When epoxying to styrofoam, such as attaching leading or trailing edges to a foam-core wing, once the
parts are coated well with epoxy and put together, wiggle them around some to work the epoxy into the pores of the
foam. Then let it dry normally. This results in a stronger bond.
3. Bed-Buddy: Ever been caught with cold epoxy? It's much more workable and mixes better when its just above
room temperature (about 80-85 F). I use a "Bed-Buddy" to warm it and keep it warm. A Bed-Buddy is like a long
sock with some kind of granular chemical in it that stays warm for hours after you microwave it for two minutes.
They're designed to keep your feet warm at night, and you can wrap it around your epoxy bottles too between each
use. You can also put the epoxy bottles directly in the microwave oven for a short time, but be careful doing it.
4. Inverter: When your epoxy bottles start getting low, it can take a while to get it out, especially when cold. Build a
simple wooden "inverter" to hold both bottles upside down, and keep them in it between each use. This way your
epoxy will always be ready for use.
Servo Blanks
Here's an easy way to make sure your servos will fit in your plane properly, especially helpful with scratch-built
designs: Take the measurements of your servos, and make a few from wood, identical to the real ones. This may
be easy if the manufacturer supplies full-size drawings of the servos. I made my servo blanks from pine blocks, a
little plywood for the mounting hole piece, and a dowel for the motor shaft. These servo blanks will not only help in
drilling the holes to mount servos, but will assure adequate clearance on all sides. In addition, the dowel is the
correct size to press on an actual servo arm, which will help in aligning pushrods or cables. Using this method will
help keep your real servos safe and clean during the building process.
Vertical Fin Alignment
To get a fin in correct alignment with a fuselage, try using thread. Make sure you have an accurate center mark
near the top-front of the fuselage, and tack-glue a long piece of thread to the top near the nose, a distance from the
centerline equal to half the thickness of the fin. Run the thread back to the tail, and hold it against the side of the fin.
The thread should touch the side of the fin evenly overall. If it doesn't, then rotate the fin until it does, then tack glue
the fin into place, reinforcing it later. Last, remove the thread you tack-glued.
Keeping Knives and Blades Safe in Storage
Get a small block of styrofoam and stick your hobby knife in it. This way the blade won't be exposed, and you won't
cut your hand if you reach into a drawer or box for it. Always keep new blades in their original container, and throw
away used blades into a closed can with a slot cut in the top, don't just throw them into the trash can by
Sharp Props
Most propellers have very sharp edges when new, especially at the trailing edge, which can cut your fingers.
Always sand the edges smooth with fine sandpaper as soon as you buy them. Be extra careful when turning over
someone else's motors by hand, because they might not have sanded the edges of their props.
Extra-Long Screws
If you need an extra-long screw or bolt for something, such as a wing tank or mid-mounted wing, make one by
cutting the correct size threaded rod you need, then solder a wheel collar on one end. Next, using a cut-off wheel,
cut a slot in the wheel collar for a screwdriver.
Engine Mount/Nosegear
If you have a small plane with a very tight engine installation (usually resulting from a very streamlined cowl), often
there's no room for a nose gear assembly. Try drilling holes through the engine mount to accept the nose gear
wire, and hold it in place with wheel collars. The steering arm can be placed below the engine, even on the outside
of the plane. This will work with most engine mounts, even the two-piece ones as long as the engine is rotated 90
Setscrew Gripping
Ever have wheel collars not hold on axles? Or maybe that nose gear keeps twisting because the steering arm won't
tighten? Try grinding or filing a flat spot on the wire where the setscrew will go. This provides a better surface for
the screw to tighten against. Better yet, grind a flat spot with a small diameter (worn out) cut-off wheel. The small
diameter causes the flat spot to actually be concave, which helps the setscrew grip even more.
Parts From Plastic Soda Bottles
Several things for RC airplanes can be made from 1, 2, or 3-liter soda bottles.
Use the colored base that come with some bottles for cowls. They're sized about right for .15 to .25
On bottles that have the base molded into the bottom, cut the bottom off, and this can become a "standway-off" 5-cylinder radial dummy engine when painted properly.
The cylinder that's left after cutting off the top and bottom of bottles can be used to form canopies and
other parts. This plastic shrinks easily with a heat gun and can be molded around wooden forms.
Take the colored base off of a 1-liter bottle, which should leave a hemisphere at the end. Glue fins on the
other end, paint it, and you have a bomb for a large airplane. And if you want to drop it, it probably won't
Curving Balsa
Get some ammonia, found in the household section of the supermarket. Put some in a spray bottle, and spray both
sides of balsa sheet liberally. Carefully bend the sheet to the right shape. You can even tape it to a form, such as
aluminum soda cans, and let it dry. Once dry, it may be used as turtle-decks, etc.
Wing-Tail Alignment
Get an old (but straight) telescopic antenna, the same type as on transmitters. Use it as an adjustable-length
measuring rod to compare critical measurements on planes during construction. I use this idea to compare the
distance from one wingtip to the stabilizer, and to make sure this distance is equal on both sides of the plane. This
ensures that the stabilizer is parallel to the wing.
New Pilot Tip
Something to pay attention to when learning to fly is control reversal. Control reversal is when the inputs on the
transmitter sticks must be reversed when your plane is flying toward you, rather than away from you.
When flying away from you, there is no problem, just move the stick in the direction you want to turn.
Many new pilots become disoriented when their plane is approaching them. To help with this, move the stick in
towards the low wingtip. This will level the wing when your plane is coming toward you, avoiding a sharp bank, and
possibly a crash.
Example: Say your plane is coming toward you, and the right wingtip is low, as if banked to the right. Move the stick
to your left, toward the low wingtip. This will bring the plane's right wingtip up, and level the wing.
Installing Triangle Stock
For me, triangle reinforcements have always been difficult to handle due to their shape, especially if they're coated
with epoxy.
Try sticking your Xacto knife loosely into one end of the triangle. Then lay it on the bench so that the wide part of
the triangle (the hypotenuse) is against the bench top. Now apply the epoxy or other adhesive to the sides that will
contact the airframe.
Next, by using the knife handle, insert the triangle into position in the airframe. Press down with your finger onto the
wide side that has no glue, and carefully slide the knife out of the piece.
This way you can cleanly install triangle stock, and not get any glue on your fingers.
Ralph's Rib Maker
Here's what Ralph did to make all those wing ribs for the Joker's Wild planes:
Cut two ribs from 1/16-inch steel. Drill two holes along the center line, one near the leading edge, one near the
trailing edge, for 1/4-inch bolts to pass through. Make sure both steel ribs are identical.
Use a steel rib as a template to draw ribs onto balsa sheet. Leave room around each rib. Cut each rib "block" out of
the sheeting, and drill the holes in each.
Assemble all ribs on the correct length bolts, and sandwich all between the steel ribs. Using nuts, tighten the
assembly down, making sure it's straight.
Now, using a belt sander (a disk sander will work too), remove the extra wood around the ribs down to when the
steel begins touching the sander. Cut out the spar notches with a hand saw, and clean them out with a file.
This will make all the ribs for a wing at once, and they'll all be identical, resulting in a straight, uniform wing. It can
also be used for a tapered wing (with all the ribs of different size), and bulkheads and formers can be made using
this method too.
Sandbag Weights
Fill plastic zip-lock bags of various sizes about 3/4 full of fine sand, and seal each well.
Use these to hold down large parts while building, such as wings. The sand will conform to the shape of parts well.
They also work good when gluing sheeting to foam.
Air-Bleed Screws
When adjusting air-bleed carburetors (the ones with the little hole in the front), a good rule to remember is the word
“richen”. Split this word in half (rich-en), and when you want the carburetor rich, turn the screw in. Of course
leaning the carburetor would be turning the screw out.
Measuring Balsa Density
Knowing the density or weight of balsa pieces can be important. It's especially useful when making ailerons or
wingtips, because you want the pieces to be "matched", which will result in a better balanced and better flying
airplane. To do this, choose balsa that is similar in weight by weighing them on a gram scale. If you don't have a
gram scale, use the deflection method: Take the balsa pieces, and using heavy weights or sandbags, hold down a
few inches of one end of each balsa piece onto the edge of a table. Make sure that equal amounts of each piece of
balsa overhang the edge. Place a smaller weight onto the other end of each piece, and measure how far each one
bends from the floor. The one that bends the most generally is the lighter piece. Using this method, you can choose
balsa that is similar in density. Keep in mind that if you build from kits, you don't have to use the supplied wood if
you don't like it!
Transmitter Neck Straps
If you use a neck strap on your transmitter, beware of getting it caught in a rotating propeller! Some people leave
the strap around their neck and detach the transmitter while starting engines. This is a perfect way for it to get
caught in the prop, especially if you start your planes on the ground rather than a stand or table. Also, having the
transmitter nearby while starting an engine is potentially a hazard. When you pick up the transmitter make sure the
strap doesn't swing into the prop.
3-Blade Props
3-blade propellers are useful when you have a scale plane that's modeled after a plane that uses them. However,
since the engine has more mass to turn, the maximum RPM is lower. The general rule is to use a 3-bladed prop
one inch smaller in diameter than the 2-blade you would normally use. This will allow close to the same maximum
RPM as you would have with a 2-bladed prop. You may also increase the pitch by one inch, but experiment and
see what works best with your engine and plane.
Firewall Fuelproofing
Firewalls of planes are normally coated with epoxy to help prevent fuel and oil damage to the wood. On planes with
no cowling, apply a coat of epoxy on the firewall after you cover the plane with film covering. Make sure the film
overlaps a little onto the firewall. This way the epoxy seals the edges of the film covering. Besides, most film
adheres better to wood than epoxy, so that's another plus.
Ultracote Printing
Goldberg Ultracote film covering has a paper backing that you can print on. Cut a 8.5 X 11 inch sheet, put it in an
inkjet printer, and print your design on the paper backing (don't use a laser printer or anything that uses heat - it'll
destroy your covering). This works well for large lettering. Make sure your image is reversed, so that when it's
printed on the backing you can cut it out and it'll be correct when ironed on your plane. If you want to use a piece of
covering that's smaller, print the design onto paper first. Then carefully tape the Ultracote to the paper over the
design. Then run the whole thing through your printer, and the design should print in the same place.
Cutting Dowels Straight
When cutting a dowel, it's easy to make the cut crooked. To help ensure a nice 90-degree end, especially on larger
diameters, try rolling the dowel into the band saw or scroll saw blade.
Picking up Glass Safely
After sweeping up broken glass off your shop floor, it's difficult to pick up tiny fragments. Try making a loop of duct
tape, adhesive side out. Place the loop over your hand, and pat the fragments carefully so they stick to the tape.
Then just throw the tape loop in the trash.
Antenna Holder
Here's a way to attach a receiver antenna to the back of your plane after it exits the fuselage. Take a short length of
fuel tubing and make two cuts into it, dividing it into thirds, but make the cuts go through the tubing only halfway.
Then pin the tubing to the top of the plane's fin. Thread the antenna through the tubing, lacing it through the cuts.
This will keep the antenna somewhat taught and out of the way of control surfaces.
Converting Cubic Inches to cc's
Sometimes there's a need to convert cubic inches to cubic centimeters (cc) or vice-versa where engine
displacement is concerned. One cubic inch is equivalent to 16.39 cubic centimeters. So to convert from in3 to cc's,
just multiply the in3 by 16.39 to get cc's. To convert cc's to in3, divide the cc's by 16.39 to get in3. And remember, a
7.5cc engine is the same as a .46 (pretty close).
Repairing Dings & Dents
Have you ever had a dent in a balsa leading edge? Try fixing it with water! Get a small diabetic syringe and put
water in it. Inject a little water into the balsa into and around the dent in the leading edge. Heat the area with your
covering iron. When the water starts boiling, it will build pressure and push the balsa out to its original shape.
(Courtesy Victor A.)
Film Covering Degreaser
Have you ever wanted to add more film covering (Monokote, Ultracote)to a plane you've already flown? It's difficult
to get all the oil exhaust off the plane so the film will stick. Try using Cyanoacrylate (CA or superglue) kicker
(catalyst). Just spray it on and wipe it off. I've been told it's a very good degreaser. (Courtesy Vince R.)
Pull Oil out of Wood
Sometimes firewalls and engine areas of older planes get soaked with oil from the fuel. This weakens glue joints to
the point where a plane could fall apart in midair. Try using Cyanoacrylate (CA or superglue) kicker (catalyst). Just
spray it on and wipe it off. I've been told it pulls the oil right out of the wood. Several treatments may be necessary.
This also works if a fuel tank develops a leak and the fuselage gets soaked with fuel. (Courtesy Jevan F.)
Balancing Planes
Here's a good way to balance airplanes. While building your plane, insert a half-inch square piece of plywood
where the balance point should be. For a low wing, this should be on the bottom of the wing, and for a high wing
this would be on top of the wing (Note: sometimes something will be in the way, like a canopy, and you can't use
this technique). When the plane is finished, put a small hook into the plywood and suspend the plane with wire or
string. This way you can check the fore-aft balance AND the lateral balance at the same time (Note: a low wing will
be suspended inverted).
Fiberglassing Wing Centers
Whenever I fiberglass a wing center section, I've found it's difficult to get the fiberglass cloth to lay flat after it's been
folded in a bag. Here's two ways to make this easier: (1)Use thin CA to tack it down. You may saturate the whole
cloth with thin CA, or apply epoxy. On foam wings, make sure you use CA safe for foam. (2)Give the cloth a light
spraying of 3M Spray Adhesive, then apply it to the wing. I've found this method to work extremely well, and it's
safe for foam. Then apply the epoxy as usual.
Control Horn Installation
When installing control horns onto control surfaces the screwdriver invariably slips. The result is a hole poked into
the covering material or a gouge in the balsa. There is a simple tool you can make that will eliminate this damage.
Take a small piece of thin plywood and cut a rectangular opening in it just slightly larger than the base of the control
horn. Place this opening around the control horn base before tightening the mounting screws. Now when the
screwdriver slips there will be no damage to your new aircraft! (Courtesy Fred H., Derby Radio Control Club, Derby
Turning Wing Bolts
If you use nylon wing bolts on your plane that take a slot screwdriver, and you forget your screwdriver, try using a
quarter. A quarter is actually easier to use than a screwdriver, since it won't slip off the bolt and damage your wing.
What if you forget your quarter too? Usually you can get a quarter from loose change in your pocket, or your car.
Tail Wheel Strengthening
Tail wheels and their associated parts take a lot of punishment, especially on rough fields. Sometimes the "tiller"
part of the wire that goes into the rudder breaks out. Here's two ways to strengthen it: 1. Put hardwood or plywood
into the part of the rudder that the tiller goes into, a piece about half an inch square by the rudder thickness should
do for most planes. 2. Position the tiller so that it goes in-between the rudder control horn.
Deburring Brass Tubes
I use 1/8" brass tubing for fuel lines through firewalls. Silicone fuel tubing is connected to the brass on both sides of
the firewall. To provide a better fit and extend the life of the silicone fuel tubing, carefully debur the ends of the
brass by running a hobby knife along the inside edge of the brass. Then use fine sandpaper to smooth the outside
edges. Since brass is a soft metal, the fine sandpaper (about 220 grit) works very well.
Needle Valve Modification
On planes with cowlings, I modify the engine's needle valve so it can be adjusted inside while the engine is
running. I grind the outside end of the needle valve flat. Then I cut off the head of a hex bolt (either size 6 or 8), and
solder the head onto the end of the needle valve. Then you can stick a hex wrench through a small hole in the
cowling to adjust the valve.
Foam Cutting
When I buy a large (4 x 8 ft.) piece of foam, I like to cut a smaller piece off before using the hot wire. My hot wire
isn't big enough to use on a full sheet, so I use a reciprocating electric knife, the kind used for meat and bread. It
works pretty well for cutting off a usable piece.
Wheel Axle Bushings
If you have a wheel that's too big for the axle, make bushings from brass or aluminum tubing to make up the space.
If you get tubing of the correct size, you can also make multiple bushings that fit inside each other, if that is
required. Don't let wheels wobble! They'll wear out quicker, and make ground handling difficult.
Cleaning Airplanes Well
If you have an airplane that you really want to take care of and look good for a long time, you have to occasionally
clean it really well. Do this by disassembling what you can (remove the wing and landing gear) and wipe it down
with alcohol from the drug store. This will remove fuel oil residue well. This is also a good cleaning for film covering
when you have to apply new film over old.
Empty Fuel Bottles
If you purchase fuel in plastic bottles, when they're empty, put it in an out of the way place with the cap off for about
a day. This will allow the residual fuel to evaporate. If you place the cap on without airing it out, you have a potential
bomb if an ignition source should ever penetrate the bottle. After the bottle is aired out, crush it, then replace the
cap. Then recycle the plastic if you can at a recycling center. Many places don't take plastic, so if it does end up in
a landfill, at least it will take up less space by being crushed. You should air out and crush metal fuel cans too.
Wheel Collar Tightening
If you use wheel collars with the tiny hex setscrews (I think most of us do), sometimes while tightening them the
hex wrench rounds off a little, causing it to stick in the setscrew. So you end up turning the hex wrench to loosen
the wheel collar just to get the wrench out. But now the setscrew may not be tight anymore. To check it, just turn it
with your fingers. If it doesn't turn, it's tight enough. If you can turn it, try to tighten it more.
Q. How do I make a V-Tail work ?
If you have room in the fuselage an old trick is to use a sliding tray. The
"rudder" servo sits in the sliding tray and is moved fore and aft by the
"elevator" servo. Result: mechanical mixing of rudder and elevator (which is
what a v-tail gives you). If you're interested in this idea (I've used it
with good success several times) let me know and I'll draw up a sketch. It's
really quite easy to build but it does require some room in the fuse.
The other suggestion would be to use one of the commercially available
v-tail mixers.
Along with undercarriages, flaps can be quite a challenge to rig in an appropriate and reliable manner. A review of
possible configurations might be a good way to start.
Plain flaps - hinged in a similar war to ailerons. These are the simplest to set up. Hinges can be of the flat plastic
with the metal pin variety, Robart Hinge Points, or plastic covering material on small powered models or gliders.
Spotted flaps - more complicated, but can be more effective than plain flaps. The hinge line is below the wing so
that as the flap goes back and down a slot opens up between it and the wing. Some of the airflow goes through the
slot producing more lift than does the plain flap. Hinges can be made from two control horns with 8 BA bolts as the
hinge point ( as shown below). Robart Hinge Points can be also be used as flap hinges.
The most common effect of flap operation commented on ( complained about ) is the pitch up usually experienced
on deployment. Flaps are fitted to enhance low speed handling so throttling back and slowing down before lowering
the flaps may reduce the pitch up. Radios with flap/elevator mixing almost completely eliminate this problem. Flaps
increase lift and therefor drag, making them useful for short, steep approaches. Airspeed need to be watched to
prevent overly high rates of descent leading to heavy landings.
Flap Linkages
The simplest flap mechanism is flaperons which require an aileron servo in each wing mixed electronically to
function as flaps as well. This set-up is commonly seen in fun fly machines, but any plane with strip ailerons can be
set-up this way
The two cases below show the conventional inboard flap/outboard aileron set-up. Set-up such as these
allow flaps with broader chords. I have read that flaps ( 25 - 30 % of wing cord ) produce smaller pitch ups
than narrower ones. Only driving the flaps via a torque tube. Air loads on flap surfaces can be quite high
requiring push rods to be straight and rigid. Ball joints can be used to minimize the "slop" that sometimes
occur with push rod end fittings.
These are but a few thoughts on the subject. Its an area where a great deal of experimentation can be
carried out. Basic trainers lend themselves to this admirable and successful ideas can be used in scale
Parallel Operation = Reliability & More Flight Time
The use of redundant parallel fight packs (packs may be of different capacity but MUST be of an equal number of
cells) is an excellent way to increase the available flight time and significantly improve the reliability of the on power
system. The simplest means is to run two complete wiring harness, switches and charge jacks from each pack and
plug one into the normal battery port and the other into an extra channel on the receiver. No diodes or isolation is
required (see below). This is simpler and more reliable than some of the complex battery backup systems being
offered on the market. Whether you are using 4 or 5 cells is your option, remembering that a 5 cell pack will provide
more power to the servos but at the same time discharge faster giving you less flight time.
Parallel charging of Ni-Cds is not recommended due to the tendency of the cells to have the voltage drop off after
they reach full charge. Should one pack have a slightly different capacity than the other then it will reach full charge
sooner and the voltage will start to drop off allowing more current to flow into this pack. The other pack may not
then reach a full state of charge. Repeated charge/discharge cycles under this parallel arrangement causes
additional charge unbalance. While you may experiment and find that you get what appears to be both packs
charged you will eventually run into problems with this arrangement. As an extreme, take the case of two packs,
one having 250 mAh capacity and one having 600. The smaller capacity pack will reach full charge much sooner
assuming that there is at least an equal "sharing" of charge current. As it peaks and the voltage declines slightly
due to the heating of the battery as the oxygen is recombined it will begin to take more and more current to
maintain a voltage equal to the as yet uncharged pack and the voltage tries to drop further and demands even
more current to keep it up. This pack will then be taking nearly all the charge current leaving the larger pack
woefully short during what would be perceived as a normal charge time like 16 hours.
Many pseudo battery "experts" put forth the argument that plugging two battery packs into the same receiver with
out blocking diodes is NOT a good thing, claiming that his creates a host of problems and the two packs will end up
fighting each other or "cross charging".
These concerns show a lack in the understanding of the charge and discharge potentials involved in Ni-Cd cells.
One pack cannot charge the another (equal number of cells) as the discharge voltage of a pack can never be as
high as the voltage required to charge the other pack. For the doubters here is an experiment: completely
discharged one pack to 4.0 volts and then connected to a fully charged pack having an equal number of cells.
There will be less than a 10% transfer of charge in a 24 hour period. Since shorts rarely occur in fully charged
packs the risk of one pack "dumping" into one with a shorted cell are insignificant. A simple ESE preflight test would
detect a pack with a shorted cell.
While it is a fact that the typical failure mode of a battery is for a cell to fail shorted there are some subtleties here
that escape many people. First one of the major causes of "battery" failure has nothing to do with the batteries
themselves but rather with a switch or connector in the battery circuit. The dual redundancy concept is to protect
against the failure having the highest probability - that being the circuit path from the battery to the power buss in
the receiver. Adding more components to this path, like regulators and/or diodes isn't going to help the matter but
rather adds to the probability of failure.
Perhaps the following discussion on the nature of shorts will better help the modeler understand.
While it is agreed that shorts are the failure mode in Ni-Cds batteries one has to look further into the "when" of the
A short develops in a Ni-Cd when conductive particulate bridge the separator or the separator itself deteriorates to
the point where it allows the positive and negative plates to touch. Rarely does the short occur all at once but rather
building up a very small conductance path termed "soft shorts". In a charged cell the energy in the cell will blow
away any short as it tries to develop. You've heard about "zapping" cells. The cell actually zaps itself before the
short can develop. Only in cases of severe overcharge at high rates can the separator melt down to the point where
the plates contact each other (hard short). In this case the energy in the cell then dumps and we have what is
referred to as a hot steamer, the electrolyte boils, nylon in the separator melts down and is forced by the steam
through the vent. On some occasions the vent is clogged by the molten nylon separator and becomes inoperative
causing the cell to rapidly disassemble. So under normal circumstances a cell maintained at some state of charge
is much less likely to short than a cell that is completely discharged. It should be noted however that the self
discharge increases rapidly in cells where there is a short building (high resistance -soft short) due to separator
deterioration and/or cadmium migration. One other shorting mechanism is a manufacturing defect where the
positive or negative collector tab bridges the opposite plate. These usually fall out before the cells are shipped or
assembled into batteries.
Preflight procedure should involve checking each battery separately. First check each with ESV through charge
jack. You should get nearly identical readings, then switch one on, check controls, switch off and then switch on the
other battery, check controls again, then turn both systems on and fly with confidence.
Summary: Diodes are not required. Packs must be of the same number of cells. Packs may be of different
capacities. Individual charge jacks must be provided for each pack (and not interconnected). Total capacity
available will be the sum of the individual capacities. Specialized chargers are not required since standard packs
(600-800 mAh AA packs)can be charged employing regular system wall chargers (1200 to 1600 mAh should cover
most giant size projects).
Taipan Glow Plugs
An article from Brain Gardiner
How does a glow plug work ?
Contrary to what many have previously been lead to believe the following is an explanation of how a glow plug
functions in a motor. The plug is initially heated by applying a voltage ( Typically 1.5 Volts ) to it. This is to cause it
to glow so as to ignite the fuel at compression and start the internal combustion cycle. Once the cycle has started ,
the power source can be disconnected, as with the heat generated at combustion the CATALYTIC reaction
generated between the methanol and platinum in the plug coils becomes sufficient to keep the process going.
The catalytic reaction is a reaction whereby platinum will glow in the presence of methyl alcohol vapour. This will
happen without any external source being applied.
How do you select the Correct plug for your application, and Why.
To do this you need to understand a little more of the theory behind the process. In glow flue the catalytic reaction
is generated between the methanol and platinum only. Castor oil, synthetic oil, nitro methane etc. do not generate a
catalytic with the platinum.
Next you need to understand that a certain surface area of platinum is required to generate a sufficient catalytic
reaction to keep the internal combustion process going. Also it is necessary to allow extra surface area for the
reaction to be great enough when it diminishes with the available methanol dropping as in the case at motor idle.
Simply put, cold plugs are manufactured using a thicker wire to give greater surface area to facilitate a greater and
thus the required catalytic reaction where less methanol is present in the fuel mixture.
So! More nitro means less methanol which in turn means a greater surface area to platinum ill be required to
generate a sufficient catalytic reaction.
Suddenly it all makes sense! To work out which temperature plug to use, you need to know how much methanol is
in your fuel, Not how much nitro or oil. As a rough rule of thumb, 80% methanol or above, use a hot plug. 70% 75% use a medium plug. 60% - 75% use a cold plug. 65% or less use a very cold plug.
Idle Bars and Other Stuff
Again, contrary to what many believe, the idle bar on a glow plug is not necessarily what its name would suggest. It
is in fact to stop any fuel not vaporized from dousing the platinum coil of the glow plug by dispersing it away from
the coil. Why are plated coils not as good as platinum alloy coils? Plated coils suffer from very quick degeneration
as the plating breaks down under operation conditions. As bits of plating come off, the plug is effectively becoming
a hotter and hotter until in a comparatively short time it is no longer able to perform its function.
Conversely, a platinum alloy coil will still degenerate, but as it is platinum alloy throughout, the surface remains as
platinum alloy and the plug continues giving much the same characteristics for quite a long time.
Plated coils are very poor value when compared to platinum alloy coiled glow plugs.
Disassembling a Model Aircraft Glow Engine
There is nothing magical about model airplane engines. The tolerances aren't even too critical, except on a few
models that beginners don't use. If you have an OS40FP and are curious about the insides, by all means, talk to an
instructor about it, maybe have him there watching you, and have a look inside. Again, there's nothing magical in
there, or even particularly delicate.
I will say this. If you are afraid of engines and refuse to learn about them, you will be missing a large part of
modeling, will make a lousy instructor (imo), and waste a LOT of money and flying time waiting for someone else to
clean out your motor after a small crash. Well after you get the plane back together, you will still be looking in the
mail everyday, waiting for them to finish doing to your motor what you could have accomplished yourself in ten
To take a typical model engine apart:
1. Remove the glow plug.
2. Remove the muffler.
3. Remove the engine backplate. Save the gasket if there is one.
4. Remove the cylinder head. Loose the screws in a criss-cross pattern. Save the gasket if there is one.
5. Turn over the motor until the cylinder is down as far as it goes. Place a hardwood dowel or servo rail or such in
the exhaust port, so that it protrudes into the cylinder above the piston. Turn over the motor, and the piston should
push the sleeve up so that you can get a grip on it. Don't touch the sleeve with pliers, please. Remove the stick, but
leave the sleeve sticking up out of the bore for now.
5a. Note the orientation of the piston. There is often an arrow or some other mark on the piston face. Notice this
and remember it, or if you have to, use a grease pencil on the piston face to mark the position. You'll want to wipe
this off just before final reassembly, though.
6a. If the engine has a separate front and rear crankcase, separate them. Save the gasket. The crank will stay with
the front half, and the connecting rod should now be free.
6b. If the engine does not have a separate front and rear crankcase, and if it has rings, you should be able to slip
the connecting rod off of the crankpin with the piston all the way down. If it doesn't have rings, you can pull the
sleeve out, leaving the piston in the motor, then slip the rod off the pin and remove the piston. When pulling out the
sleeve, notice which way the ports are pointed. (This will be important for reassembly.) Don't use tools on the
7. Remove the carburetor from the engine.
8. If you remove the prop nut and washer, the prop thrust washer (the knurled thing behind the prop) sometimes
just slips off. On other engines you have to get a three-pronged gear-puller to get it off. When it does come off, be
careful not to lose the woodruff key that sometimes comes out with it, and the brass bearing washer if it's there.
9. At this point, the crankshaft will often just slip out. If not, it is a press fit, and is more difficult, and I don't suggest
you attempt it unless you have a hydraulic press. If you have a motor like this and need to replace the bearings,
just send this assembly in for servicing.
10. If it does come out, the next thing is the bearings, if you motor has ball bearings. The rear bearing comes out by
heating the case in a 350degree oven for fifteen minutes, removing it with a pot holder, and rapping it on a piece of
wood, rear of the motor down, and the bearing should just pop out. Careful not to burn yourself. Let it cool. You
should then be able to use a steel rod or drift punch and tap out the front bearing from the rear of the motor.
11. The piston comes off of the rod by slipping the wrist pin out. That has probably slipped out by itself already,
though. :-)
Bearings should have no rough spots, and no visible damage. This is a common malady. Also, you should feel no
play in them.
Look for cracks anywhere, and replace the part if you find them. This is rarely necessary.
Look carefully at the connecting rod. Look at the bearing surfaces at the end, and fit them on their respective pins
to look for play. This is common with older engines.
The piston should have no scratches, only polished areas. Same for the inside of the sleeve. This would indicate
dirt ingestion, and the piston and sleeve should be replaced.
If the piston has a ring, it should be polished, with no nicks, and obviously be unbroken. If you replace the ring, it's
a good idea to replace the sleeve, too, and vice-versa.
The back plate will have marks from the crankpin. That's okay, as long as they are not deep scratches. This would
indicate bad bearings or a torqued crank. Rare.
Clean any crap out of the inside of the motor. Don't worry too much about the castor varnish--just use a
castor/synth blend for a while. The motor should be spotlessly clean inside before reassembly.
1. Heat the case again (not the bearings). Push the bearings into their bores using a wood-padded vise and just
enough pressure to move them, and no more. Oil them with castor or 3-in-1.
2. Drop the crankshaft in. Oil. Hold it on there with the thrust washer, a prop hub, nut washer and nut.
3. If you have a ringed engine, oil the piston, ring, and inside of sleeve. Find the pin in the ring slot, and place the
ring gap there. (That is the only way you can compress the ring all the way around. Press the ring in with your
fingers and slip the piston into the bottom of the sleeve. There should be a shoulder on the inside of the bottom
edge of the sleeve to help you with this. Be gentle, it doesn't take force, and you can easily break the ring. Get the
orientation right, same as you noted earlier.
4a. If you had to remove the sleeve (6b, above) before the piston, just reverse the process. The sleeve will go in
easier if you oil the outside.
4b. Otherwise, slip the sleeve in there (pay attention to orientation) and put the connecting rod on the crank pin.
Make sure the ports all line up just perfectly. Push the sleeve up using the wood in the port and turn it if you have
(Oh, you needed to reattach the front and back crankcase halves in here somewhere. :-)
5. Install back plate.
6. Install cylinder head, criss-cross pattern on the screws. If there was a piston fence (a raised ridge on the piston
face), get the orientation of the head so the slot matches up to it.
7. Install the carb. Push pretty hard when seating it; you don't want air leaks there.
8. Glow plug.
And there you have it. Maybe an hour, assuming you need to replace the bearings. Don't kill the screws, and use
non-permanent locktite if you are worried about them backing out.
Dave Svoboda, Palatine, IL
Storage of your Ni-Cd R/C Packs
"How should I store my batteries at the end of the season? What should I do to them when I put them back in
The batteries should be removed from the transmitter and plane for longer term storage. Here in the south where a
lot of us work out of our garage work shops I recommend putting them in the refrigerator (not the freezer) during the
off season. While not so important where your workshop rarely gets above 23 degrees C (74 F) the refrigerator is
still a good bet. Why? The failure mode of Ni-Cds is separator failure, this is the material that keeps the plates from
touching each other. When it fails the cell shorts. At higher temperatures it oxidizes faster. In fact, the rate doubles
for every 10 degrees C increase.
"Should I store my batteries charged or discharged?" It doesn't really matter, they will self discharge in a few
months stored at room temperature. If you are going to store them in the refrigerator the charge will remain for a lot
longer so I would discharge them first to 4.4 volts and them put them away. Good cells will just set there in the
discharged condition (the voltage can vary considerably but is usually above 1 volt). In a battery with damaged
"worn out" separator in the cells, the cells are apt to short if left in a discharged condition. This is actually good
since it is the first indication of a cell that's going bad and it is best to replace the pack. A battery left on trickle
charge will seldom short out since it is in the charged condition and any short that tries to develop will be zapped by
the charge in the cell. Partial shorts (those having fairly high resistance) can be developing that can cause the cells
to self discharge at a higher rate than normal and possibly leave you short in the middle of a flight after you just
measured the cell when it came off charge with your ESV and everything looked OK.
The reason I recommend removing the batteries from the transmitter and plane is to protect against "black wire"
disease. Should a cell short while in storage there is a high probability that there will be some leakage that can lead
ultimately to the "black wire" problem.
Now when your batteries are coming out of storage, before charging, check the voltage without a load on the
battery. It should read well over 4.0 volts even if it has not been charged all winter. They should be essentially fully
discharged, flat as we say in the business. In this condition if the battery is going bad it will probably have shorted
and you will read zero volts on that cell. It may be a soft short, one that could be blown away merely by the simple
action of slow charging. Don't do it! It is just lying there waiting to bite you. Replace the pack. Cut out the "good"
cells if you want and use them in something less critical than your model. If you have access to a cycler running
though a couple of charge/discharge cycles is a good idea just to make sure you are getting the capacity you are
suppose to. Anything less than 80% of rated is suspect. Once at the field, pre-flight battery checks are in order,
particularly at the beginning of the season. Since those that religiously check their flight packs with an expanded
scale volt meter seem to crash less (due to battery failure) one must assume that the ritual is smiled upon by the
R/C Gods.
Now, back by popular demand, the pattern trimming chart:
This chart was set up for trimming a pattern plane. However, there are quite a few sport aerobatic planes that
would fly better if they were set up like pattern planes. It's a lot easier to fly a plane that's properly set up than a
plane with all kinds of perverse mixing. I also must give credit where credit is due, this chart comes from the
NSRCA (National Society of Radio Controlled Aerobatics) newsletter and was submitted by Mike Chipchase of
Australia. Some of this information is repeated from the last article on trimming for aerobatics.
First let's talk about basic airplane setup. The latest pattern designs are set up with 2.5 degrees of right thrust, 0
degrees down thrust, .5 degrees positive incidence on the wing (root and tip, no washout), and 0 incidence on the
stab. Or, .5 ~ 1 degree down thrust and 0 incidence on the wing. Use an incidence meter to check this, or block the
plane up on a big flat table and use a scale accurate to 1/32nd of an inch. If the plans show this information use
that as a starting point.
Control throws should be set up as shown on the plans. It's very important each aileron to have the same throw.
This should be setup mechanically. The aileron throws should be set up the same up and down. If the plane has
split elevators make sure that each elevator half has the same throw as the other half. I usually set the plane up
with more down elevator than up elevator. That way I'll have the same control authority for up or down elevator. Set
up the rudder with about 30 ~ 35 degrees of throw. Of course the ailerons and the elevator need to be gap sealed.
To start out, the CG should be placed as shown on the plans, or about 30% of the average chord. The CG can be
adjusted later. Use the placement of the radio to place or move the CG if possible. This is better than adding
unnecessary weight because light airplanes fly better than heavy ones. Since the battery pack is the heaviest part
of the radio, its placement will have the biggest affect on the CG. Also, laterally balance the plane. Pick it up
underneath the center of the spinner and underneath the center of the tail. Place weight on the light wing tip until
the plane balances. Embed the weight in the wing tip.
With all that in mind here’s the chart.
----------------------------------------------------------------------To test for | Test procedure
----------------------------------------------------------------------Observations | Adjustments
----------------------------------------------------------------------Control Neutrals | Fly model straight and level
----------------------------------------------------------------------Trim for straight and level | Adjust clevices to center transmitter
| trims.
----------------------------------------------------------------------Control throws | Fly model and apply full deflection
| of each control in turn.
----------------------------------------------------------------------Check the response of each | Aileron Hi-rate 3 rolls in 4 sec.
control | Lo-rate 3 rolls -n 6 sec. Elevator
| Hi-rate to give a smooth square
| corner. Lo-rate for a loop of 130 ft.
| diameter. Rudder Hi-rate for stall
| Lo-rate to maintain Knife edge
| flight.
----------------------------------------------------------------------Decalage (incidence) | Power off vertical dive, cross wind
| any. Release controls when model
| vertical.
----------------------------------------------------------------------A. Does model continue straight | A. No adjustments
down |
B. Does model start to pull out | B. Reduce incidence
(nose up) |
C. Does model tuck in (nose | C. Increase incidence
down) |
----------------------------------------------------------------------Center of gravity | Roll model inverted
----------------------------------------------------------------------A. Lots of down elevator | A. Add weight to tail.
required to maintain level |
flight. |
B. No down elevator required to | B. Add weight to nose.
maintain level flight or |
model climbs. |
----------------------------------------------------------------------Tip weight, course adjustment | Fly model straight and level upright
| Check aileron trim maintains wing
| level. Roll model inverted, wings
| level. Release aileron stick.
----------------------------------------------------------------------A. Model does not drop a wing | A. No adjustment needed.
B. Left wing drops | B. Add weight to right tip.
C. Right wing drops | C. Add weight to left tip.
----------------------------------------------------------------------Side thrust | Fly model away from you into any wind
| Pull into a vertical climb (watch as
| the plane slows down.)
----------------------------------------------------------------------A. Model continues straight up | A. No adjustment needed.
B. Model veers left | B. Add right thrust.
C. Model veers right | C. Reduce right thrust.
----------------------------------------------------------------------Up/Down Thrust | Fly model on normal path into any
| wind. When model is straight out from
| you about 100 meters away, pull into
| a vertical climb and release the
| elevator.
----------------------------------------------------------------------A. Model continues straight up | A. No adjustment needed.
B. Model pulls to canopy (up) | B. Add down thrust.
C. Model pulls to belly (down) | C. Reduce down thrust.
----------------------------------------------------------------------Tip weight, fine adjustment | Fly the model away from you into any
| wind and pull into a small diameter
| loop.
----------------------------------------------------------------------A. Model comes out wings level | A. No adjustment needed.
B. Right wing low | B. Add weight to left tip.
C. Left wing low | C. Add weight to right tip of remove
| from left tip.
----------------------------------------------------------------------Aileron differential | Fly model on a normal pass and do 3
| or more rolls.
----------------------------------------------------------------------A. Roll axis on model | A. Differential OK
centerline |
B. Roll axis off to the same | B. Increase Differential
side of model as roll |
command. |
C. Roll axis off to opposite | C. Decrease Differential
side of model as roll cmd. |
----------------------------------------------------------------------Dihedral | Fly model on normal pass and roll
| into knife edge flight. Maintain
| with top rudder (do this test to the
| right and left sides)
----------------------------------------------------------------------A. Model does not roll out of | A. Dihedral OK.
knife edge. |
B. Model rolls in direction of | B. Reduce Dihedral
applied rudder. |
C. Model rolls opposite the | C. Increase Dihedral
rudder in both tests. |
----------------------------------------------------------------------Elevator Alignment. | Fly model straight away into any
| wind. Pull into an inside loop.
| Roll inverted and push into an
| outside loop.
----------------------------------------------------------------------A. No rolling when elevator | A. Elevators correctly aligned.
applied. |
B. Model rolls in same direction | B. Elevator half misaligned. Raise
in both tests. | half or lower the other.
C. Model rolls in opposite | C. One elevator half has more throw
directions in both tests | then the other. (Model rolls to
| the side with the most throw.)
| Reduce the throw on one side or
| increase it on the other side.
----------------------------------------------------------------------Pitching in knife edge flight | Same as dihedral test.
----------------------------------------------------------------------A. No pitch up or down | A. No adjustment needed.
B. Model pitches up (to canopy) | B. Alternate cures.
| 1. Move the CG aft.
| 2. Increase the wing incidence.
| 3. Drop the ailerons.
C. Model pitches down (to belly) | C. Reverse the above
----------------------------------------------------------------------Notes: Trimming must be down in calm conditions. Make multiple tests before making any adjustments. If any
changes are made go back over the previous steps and readjust as necessary.
Well, there it is. For the purists out there you might note that none of these adjustments require the use of a
computer radio. A well designed, well built aerobatic plane can be set up very close to perfect without any mixing.
In fact that is one measure of a well designed pattern plane.
I hope this helps any one out there that is interested learning advanced aerobatics.
Aileron Differential
The primary effect of aileron deflection is roll. The secondary effect is yaw, and it is yaw that can cause problems
with tracking in rolling maneuvers. How is it minimized, or better sill, eliminated ?
It is the down going aileron that causes the problem. While increasing lift on that portion of the wing it increases
induced drag, yawing the plane in that direction, usually the wrong direction which is why it is called adverse yaw.
So it would seem that decreasing movement in the down going aileron relative to that of the up-going one would be
the solution.
Aileron differential - Move up than than down, usually. ( Fig.3 )
Modern computer radios have the facility to adjust differential electronically, but it is possible to achieve the same
result mechanically using the rotary output of the servo arms.
Both these arrangements will produce differential movement of the pushrods.
The relative lengths of the arrows shows the direction and magnitude of the
Fig 1.
The set up shown above in Fig.1 would suit high wing trainers and low wing planes with aileron servos installed
outboard the wings. Fig.2 shows the set up for low wing planes with one aileron servo sitting upright in the centre
RCAS Newsletter 213 March 1999
Who do I make a fiberglass cowl for my plane?
This brings up many Questions on my Part.. :-) I will break up the Answer in several parts.
Making your template for the mold of a cowl. There are several materials you could use to do the job.
Molding Putty
Play doe
1. I would go for the Molding putty of Play doe ( A smooth finish will be left )
2. I would cover the front of the fuselage with ether glad rap or if it is a finished surface with
solar film ( or your choice of covering ). If you wish to leave the Motor on the fuse, cover
that as well ( only with Glad rap )
3. Apply the putty to the front of the fuse. remember that there must be no part of the plane
showing where the putty is places.
4. Mold the Putty to the shape that you desire
5. Smoothen the surface as throw it is the finished product
o Remember that any imperfections that you leave on this Putty Cowl will be there in the finished
fiberglass cowl.
blocks of Balsa wood
o I this type of Molding you have to be good with wood.
1. Find a Big enough peace of Polystyrene and Glue the Polystyrene to the Fire wall. same
goes with the Balsa wood but that is hard to find so glue scraps to gather to shape a cowl
out of. ( Use you imagination a bit )
2. Sand the surface to the shape that you desire
3. Smoothen the surface as throw it is the finished product.
4. With Polystyrene , cover it with a thin layer of epoxy and then sand that so it to is with out
fault. ( All we are doing that for is to get rid of the imperfections inherit with Polystyrene )
5. As for the Balsa wood I would go for dope.
o Remember that any imperfections that you leave on this Putty Cowl will be there in the finished
fiberglass cowl.
Now that is dune you must have a Backing plate or Flange that comes out about an inch directly behind the surface
you just molded into place. This will be used for the Mold that we are just about to make. This will become the rim
of the mold. It gives it strength and also a great place to have splash over of the resin.
Now we have a Fuselage with a fake cowl on the front of it. NOW is the time we start to make a Mold for
the real fiberglass cowl. This also has steps you must follow.
1. You must get a Releasing agent. this comes in two types a wax and a type of paint on film. They
both act as a separating film between the Hardened surface and the Resin you are about to apply.
( A type of condom if you wish to see it that way :-) No surface should not be with out this film
because if there is no film the resin will stick to it like :-) Glue. To get the releasing agent go to your
fiberglass supplier and ask there. As for the wax, do not leave big lumps of wax on the surface.... it
is a thin film....
2. it is best to have apposing reasons when designing a mold. You have to make a decision. Do you
want the cowl to be made of Epoxy or Polyester fiberglass ? if you want an Epoxy Cowl you make
the mold of Polyester and Visa-Versa.
3. Make the first batch of resin to cover the howl surface ( Don’t be bashful use a lot ) and wait till it
just gets that stage before it is take to touch( If you wish use a heat gun to spread it up a bit ). Now
mix the reason ( Same type ) to layer on with the fiberglass.
4. Leave to set .... There you are you have a Mold.... Just take it of and remove the back Cowl from
within it.
Now we have a mold what about the Cowl that we want to make ? it is exactly the same...
Coat the mold with the releasing agent just like above.
Cut the fiberglass to a pattern so it will lay in the mold nicely.
If you made the mold out of Polyester reason the cowl will be of Epoxy. and just like above.
Make the first batch of resin to cover the howl surface ( Don’t be bashful use a lot ) and wait till it
just gets that stage before it is take to touch( If you wish use a heat gun to spread it up a bit ). Now
mix the reason ( Same type ) to layer on with the fiberglass.
9. and now put the fiberglass and reason around the sides.
10. Once it is dry and has hardened simply take the cowl out of the mold. it might be hard at first but it
will separate.
Why Down Thrust ?
Lift is proportional to velocity square. For airplane with non-symmetrical
airfoil, say, the Clark Y, will going up too much with power up (even
with zero angle-of-attack) if no down thrust, so you need some down
thrust to compensate this. Not only Eagle2, many other trainers also need
down thrust. Hope this helps.
The reason:
Since it is a flat bottom airfoil with a lot of positive incidence, the
faster it goes, the more (LOT more) lift it generates. The down thrust
tries to compensate for this by pulling the nose back down as throttle
(and speed) increase. It would be a lot better to design trainers with a
lot less positive incidence in the wings and make it fly more neutral.
If the down thrust was lessened on the Eaglet, the plane could do loops
just by application of throttle.
Or rather, the difference in incidence angle between the wing and tail
on this type of airplane is high. True incidence should be measured
based on the zero lift datum line (i.e. the datum line that defines
zero lift when it is parallel with the direction of flight). Flat
bottom airfoils have to point significantly nose down to generate no
lift, but are typically mounted with the flat bottom surface parallel
to the tail's centerline.
Such airplanes have to be trimmed nose heavy, and are more pitch
sensitive to changes in airspeed than would one with a symmetrical
airfoil (with the wing mounted at zero incidence to the tail). Which
makes me wonder why more people don't build trainers with big, fat
symmetrical wings. They'd be easier to land, at least - less
susceptible to gusts near the ground.
Airfoil and center of gravity placement are independent. Most flat
bottom airfoils are probably used because they produce lift at a slower
airspeed, and they're easier to build (you don't need a wing jig).
There's no reason you couldn’t move the center of gravity back and adjust
the incidence to trim a plane with a flat bottom airfoil so it had
neutral stability. Note that even with neutral pitch stability, it
still wouldn't fly that well inverted (at slow speeds), because a
typical flat bottom airfoil needs a large negative angle of attack
(or a lot of speed) to produce "inverted lift".
It's probably desirable for a trainer to have positive pitch stability
(nose heavy) as well as slow speed flight, and be easy to build
(unless it's an ARF).
Gyros on Aircraft ?
Gyros are great to help stabilize a plane when "external factors" are
interfering....On landings, the external factor is the pilot, I am not sure
gyros would do that great..... <g> Unless we are talking about windy
landings, where they might help.
I saw a test on a small slope soaring glider, with 3 gyros ( one for each
axe ), it was very surprising to see that small thing on rails, like a 4 or
5 meters...!
In my experience and opinion unless you're flying a helicopter gyro's are
something you don't need. Usually they are used where practicing the
maneuver (landing, torque rolling) would be a better choice. If you use a
gyro you will probably become dependant on it and that’s usually not a good thing.
Glow engine to Gas ?
I've heard that if you convert a glow engine to gas, you need to have
roller bearings on the rod or run rich with the oil. Running too much
oil kind of defeats the purpose, in my opinion, as the beauty of gas is
the cleanliness. I would think that you'd want to use the spark with the
glow so you can get more power if you are going to have that much oil on
your plane...or is the gas oil that much cleaner?
Anyway, that's not my question--somebody's sidetracking me, and I think
it's the guy on the keyboard here. I have a friend who wanted to convert
his Ryobi to glow fuel for extra power and low weight. (The flywheel and
coil alone weight over 19 oz.) So, I guess I was wondering...if you go
the other way, from gas to glow, and you already have roller bearings,
can you run the glow fuel with very little oil, say 32:1 or even
thinner, like a normal gas mix?
What is this fuel crossover like? Can you keep the ignition and get even
more power? Are you still going to have that nasty goo all over your
plane when you are done, even with the roller bearings?
Many times you can't directly convert gas engines to glow because the carbs
aren't compatible. They don't flow enough fuel (it takes nearly twice as
much alcohol as gasoline) and some parts in the carb aren't compatible with
glow fuels. You will also find that gas engines are considerably heavier
than equivalent glow engines. I'm not saying don't experiment, just don't
expect too much.
Glow ignition is very imprecise in its timing, unlike spark ignition
(generalization). Without having the ignition timing locked in, more oil is
needed to remove more heat for those times when the effective ignition
timing is too far advanced, not necessarily for more lubrication.
It is easy to forget that our glow engines are air and liquid cooled, the
liquid being the oil in our fuel, hence the extra mess.
Notice the difference in cylinder fin area and crankcase bulk between
gasoline/spark engines versus glow engines. It is not practical to utilize
the same cooling methods with gasoline/spark engines, i.e., liquid cooling
by expelling heated, spent oil, hence larger surface areas are required.
The few high performance gasoline/spark engines that are available in the
smaller sizes are very expensive, as I am sure you have noticed. The BME 2.7
being a fine engine, but not inexpensive, relatively speaking.
Metal on Metal PROBLEMS ?
... on a trainer airplane (my first one with my brother) every time i was
doing/practicing a loop, the plane goes crazy so i landed and, after
crushing my mind seen that all was correct but on full down elevator the
ailerons were crazy as hell, i finally realize that one tiny little end of
the "Z" bended elevator pushrod was rubbing against the throttle metal
cable i used, and at that point ... i just cut 1/2 centimeter of the end
at the elevator pushrod, reacomodate the servo throw and repeated checking
YES!!! metal on metal can generate tremendous EMF spikes. I have had
several planes where the metal clevis on a metal throttle arm had driven
the receiver nuts at certain RPMs. the only way to stop or prevent this
is to use nylon clevises or ball joints on these high vibration areas.
I even saw metal to metal EMF generated that was visible as arching at
If you absolutely must have a loose metal to metal contact, one possible
way to get around the RF interference is to "ground" one part to the other
(ie- for a metal z bend on a metal throttle arm, solder a cable to the
cable/z bend and ground the cable to the throttle, possibly by passing it
thru one of the engine mounting bolts). I am not sure if this is sound
theory as I haven't tried it myself.
You bet. I am not sure about planes but on R/C helicopters it is a major
concern. On a helicopter there are many metal parts that are moving very
fast. If the parts are not moving properly they can definitely cause
problems. There are numerous stories where a high speed bearing goes bad
it stops running smoothly) and causes a PCM lockout and a subsequent crash.
Loose screws and vibrating washers also need to be taken care of.
The only counter measures that I can suggest would be to make sure that any
metal to metal connections are snug.
Tinting Canopies
This is probably "more than you ever wanted to know" about dyeing canopies, but it was an easy cut'n'paste from
an RC club newsletter, so what the heck, here it is in its entirety. Apologies for the length to those who aren't
interested, but I'm too lazy to edit it down :-)
Ever wonder how those great looking tinted canopies got that way? In many cases, the builder dyed the canopy
using dyes intended for tinting clothing! The process is actually quite easy, and the dye itself is easily obtained and
quite cheap. I've found that Ritt powdered dyes are quite effective in tinting the plastic canopies found in most
model kits, and are available in most drugstores, priced around $2 per package. When using powdered dye to tint
plastic canopies, here are some tips to consider:
Make sure that the canopy is squeaky clean before dyeing. Washing in mild dishwashing detergent is
effective here, and will avoid unsightly fingerprints in the final work. Dry using a soft cloth (not paper
tooling, which is almost always abrasive to some degree).
The container used for dyeing must be clean as well. Stainless steel or glass containers are the best for
this process. Use a container that is just large enough to allow the canopy to be fully immersed in the dye
Wear something appropriate for working with dye. It is also a good idea to place the dyeing container within
a stainless sink and to clear any items from the working area. If you do splash some dye on a hard surface
in your work area, some diluted bleach will take the stain out (rinse the area thoroughly with water after
using bleach!).
A meat thermometer is perfect for measuring the working temperature of the dye solution. Also, a pair of
cheap wood or plastic tongs are handy for handling the canopy while it's in the dye bath.
Fill the container with hot water first, then pour in the dye (this will help avoid splashing dye around). Mix
thoroughly but avoid splashing. Remember to use only enough water to fully immerse the canopy. The
object is to create as strong a dye solution as possible to speed up the tinting process.
Always test the dye bath using the scraps of plastic remaining after trimming the canopy from its "as
shipped" form, principally to determine if the solution is too hot. I've found that an optimal working
temperature is 150-160 degrees F, but you should immerse a scrap for a few minutes to determine if there
is any chance of deformation at these temperatures.
Place the canopy upside down in the dye bath to avoid trapping air bubbles. To remove any bubbles and to
ensure consistent tinting, periodically shake the canopy gently within the dye bath using the tongs. Avoid
scuffing the sides of the container with the canopy.
Periodically remove the canopy and observe the level of tinting. Some plastics take dye more readily than
others, and the level of tinting you desire may vary, so you have to give it an "eyeball" every few minutes.
If you desire a really opaque level of tint, or if the plastic takes dye slowly, it may be necessary to reheat
the dye bath. This is where a stainless steel container comes in handy: remove the canopy, rinse it in tepid
water, and set aside. Place the dye container on the range and use LOW heat to gently bring it back up to
working temperature, checking with the thermometer. Don't overheat! Then remove from the range, and re
immerse the canopy.
Once the canopy has reached the desired shade of tint, remove from the dye bath and rinse thoroughly
with tepid water, then dry using a soft cloth.
Voila! A professionally tinted canopy!
Ni-Cd Life - or why is down so quick?
C. Scholefield
While volumes have been written on this subject I would like to relate it to the specific application of R/C ,
separating fact from fiction and enabling the R/C fraternity to focus on more serious issues of the day, like
convincing your wife it's too foggy to clean the pool so you're going flying while the field is not so crowded.
The primary failure mode of Ni-Cd cells (outside of user abuse) is separator deterioration. This will occur in all NiCd batteries as they age. The separator breaks down allowing the plates (electrodes) to touch and short out the
battery. Millions of testing hours on thousands of cells has established the mean time to failure of a single cell to be
8 years for cells/batteries maintained at 25C (77F). Higher temperatures will significantly reduce these numbers.
Mean time to failure means the time that it takes for half the cells in a given population to fail. As the cells are built
into packs the mean time to failure decreases. For a 4 cell receiver pack the mean time to failure comes out to be
5.7 years while an 8 cell transmitter pack falls to 4.8 years. Now it is completely possible that the average R/C
modeler doesn't want to tempt statistics to the point where half of his battery packs should have failed. A more
reasonable number would be the expected time for 0.1% of his batteries to fail. The number comes out to 58 weeks
for a receiver pack and 49 weeks for a transmitter pack. For the more adventurous willing to live with 1 failure in a
hundred, he can stretch his receiver pack to 103 weeks and his transmitter to 87 weeks. Does this mean that he
should rush out and buy new packs at these intervals? Not really. Proper battery monitoring, while it may not
significantly increase life, will give you ample warning that your pack should be considered for replacement.
Remember, normal failure is the deterioration of the separator system. As the separator deteriorates (oxidizes) self
discharge rate of the battery increases significantly. A pack that looses 15% or more capacity over a week of open
circuit stand is at risk. A pack that looses 10% overnight should be used for ballast only. Check your pack with a
cycler or some technique that gives you the amount of capacity available immediately after charge and then (after
fully charging again) after a rest period of 5 to 7 days.(NO, this isn't MEMORY!). Doing this at least quarterly (if you
are fortunate enough to live where you have a flying season longer than 3 months) will greatly increase your odds
of crashing by some other defect than battery failure.
The number of cycles you put on your battery is secondary in the life equation, again, assuming you don't abuse
them by high rate over charge, vibration or exposure to high temperature. I know of very few people that totally
exhaust their battery packs while flying (at least not as a matter of course) so the packs seldom see a full discharge
and the risk of cell reversal is nil. Test have demonstrated that hundreds of cycles of reversal where 140% of the
rated capacity is taken out in a driven discharge resulted in a capacity loss that was barely measurable. Many multi
speed power tools use the technique of tapping the battery for speed control with no adverse effects on the battery.
A single cell can be discharged through a load to zero volts without damage. In fact this is a good way to determine
if a cell has suffered from separator deterioration. A cell discharged to zero volts will recover to over 1 volt open
circuit if left to stand. Those that will not are approaching the steep part of the failure curve and could be a crash
waiting to happen. Bottom line: the number of full charge/discharge cycles that can be accumulated by today's NiCd technology is in the 400 to 500 cycle range. Of course partial discharges seen in the R/C application can extend
the use cycles to significantly more than this. It doesn't take a battery expert to figure out the amount of flying time
you can accumulate on 500 full discharges. We are talking in excess of 1000 hours. If you put in a full two hours a
week in the air every week year round, you would be well into the next century before you reached 500 cycles.
Separator failure or old age will probably do you in before you run up 500 cycles. Meticulously recording the
number of discharge cycles to establish a replacement schedule can be a study in futility and should be left to the
electric R/C indoor microfilm pylon set. Don't worry about reversal. If you have left your switch on overnight or for
even a couple of days, just give the pack a good long slow charge using your regular charger supplied with the
system for 48 hours and you will probably be OK. It would be prudent to run a capacity check cycle after such an
incident just to make sure.
Long term overcharge, leaving your packs plugged in to the charger supplied with the system, while considered an
acceptable practice for many consumer applications can contribute to a reduction in battery life. First, as a battery
goes into overcharge, oxygen is generated on the positive electrode and then recombined on the negative
electrode. This oxygen rich atmosphere only accelerates the oxidation of the separator. As the oxygen is
recombined on the negative it generates heat. We all know how to make a chemical reaction speed up, turn up the
One further phenomena recently brought to light after years of testing is that of cadmium migration. This is a
transfer of cadmium metal through the porous separator structure to form a conductive bridge between the
electrodes. In simple terms a high resistance short which causes the cell to self discharge, shunts charging current
to where the cell takes longer to charge and ultimately, if left of continue, become a hard short which, if happens
during a period when batteries are part of, or contributing to the direction of an airborne operation, result in a rapid
depletion of model resources. The same testing reference also confirms that the same amount of charge put into
the battery in a short period significantly reduces the cadmium migration. Therefore using a simple appliance timer
to switch your charger on for about an hour a day minimizes the overcharge and yet maintains the packs at peak
charge should an airborne operation be called for at any time. For the experimenter, a charger designed to charge
the battery at C rate (1 hour rate) run at a 10 to one duty cycle (on 0.1 second, off 1 second) is more effective than
charging continuously at the C/10 (10 hour rate common to most system chargers) and will enhance battery life.
For a maintenance charge a 25 to 1 duty cycle is recommended. This pulse charge is better than even a very low
trickle charge for maintaining the battery as cadmium migration is driven by passing current through the separator
(charging) over a period of time. The rate of cadmium migration does not seem to increase proportionally to the
current density, leaving us with the conclusion that getting the job done (replacing charge loss through inherent self
discharge) quickly by a pulse of charge current is better than dragging it out with a long sustained overcharge.
While this gives battery a break it will probably give rise to a new generation of exotic (expensive) chargers
focusing on the dreaded cadmium migration phenomena (hereafter referred to as CMP, people only take three
letter problems seriously) and leave the dreaded memory effect (DME) alone for awhile. Just remember that you
can do the same thing with a $5.00 timer and spend the savings on a subscription to your favorite R/C magazine,
Storing the battery is no big deal. Living in Florida where there are no cool (damp, dark, moldy) basement work
shops, I store my batteries in the refrigerator on off flying season (July 3rd 9:30 AM to July 4th 7:00 AM). Those
living in Northern climates don't really have anything to worry about (there must be some advantage) but should
remember about the trunks of cars and what happens to batteries you leave them in there when you are visiting us
for a winter flying vacation.
Looking at the battery voltage after several months of storage is an excellent way to pick out a weak cell (use
straight pins to probe each cell). If a cell voltage after several months drops noticeably below any of the others,
beware. You have a potential problem and the pack should be relegated to some benign surface application. While
we are on the subject of measuring battery voltage, consider getting one of the little digital voltmeters available
through electronic hobby outlets. They give you a precise reading and are well worth the modest investment.
Second piece of advice. don't listen to the R/C car guys when it comes to batteries, they have never experienced
the thrill of real rip roaring, crank shaft bending, dirt in the transmitter, kind of crash and as a consequence take
liberties with batteries that would make Leclanche and Volta turn over in their graves to say nothing about causing
me just a little heart burn when they get me cornered in "technical" conversations.
I'm a new-comer to RC, and have a few questions about assembling my
sailplane. I have a Hobby Lobby "Skimmer". The instructions assume
that you know a lot of model assembly, and in my case, that's a big
Here's my problem. I'm given some stiff white plastic-like rectangles
that I'm pretty sure are supposed to be the hinges for the elevator and
rudder. My instructions don't tell whether the hinges are to be applied
to the balsa first, then cover the elevator with Monokote, or whether I
cover the surfaces, then affix the hinges.
Which order do I apply hinges and covering?
Are these hinges heat applied, or glued?
You wont likes this.....ya have to cut slots in rudder and elevators on the
edges of the balsa.
do you have the "plastic" ones with little holes in it, and a center pivot,
(epoxy these in) or R they flexible plastic with a "fuzzy" covering in them?
(CA Hinges)?
either way, you have to cut slots.
A One Part Play:
(YOU) Hello, hobby store, I cut my finger off(almost)using my knife to
hinge , do you have a hinge slotting tool?
(Hobby Store) : It's a RC store ain't it? Ya got a credit card number or you
want I stand here all day?
Signed, the guy who has a nice deep slice in his finger RIGHT NOW.
And welcome to the "hobby".
Those are CA hinges. You can cut the hinge slots before or after you finish
covering, but don't glue the hinges in until after. The slots can be cut with
a hobby knife with a #11 blade, or a TY1 Hinge slotting tool. They should
only be the thickness of the #11 blade. After slitting the covering, put a pin
through the center of the hinge, insert the hinge into the wing (or whatever),
slide on the control surface up against the pin (this keeps em centered), flex
the surface as far as it will go, and put 2 drops on each hinge. Now, turn the
wing over and flex the other way, and put 2 more drops on each hinge. They
should be flexed about 50 times after gluing, and that's it! Be sure to pull
the pins out. Good Luck!!
The hinges go into slots that you cut into the surfaces with an X-Acto
knife. The slots are centered on the hinge line of the surfaces. You
can cover the plane first, then cut the slots. After getting the hinges
and control surfaces aligned, just a couple drops of thin CA on each
side of the hinges and you are set. Use a piece of paper towel to wick
any excess glue out of the joints.
Hi Lee, lets see if I can help. The white plastic-like thingies are
your hinges. ( If your using C/A hinges see bottom ) Before you cover
your model you need to cut a slots in the trailing edge of the stab and
fin (attached to the fuselage, you'll picture it in a minute). I assume
your not using ailerons. To do this use a ball point pin and draw a line
down the center of each. Yep! I know that 3/16" or 1/4" is tough to get
a centerline on but if you hold the point of the pen against the wood
and using your fingers as a break you should be able to draw a straight
line down the center. You should be able to eye-ball it when your in
the center. Note that there are tools that will help you draw a perfect
line down the center but I doubt this was included in your kit.
OK, using the plans as a guild, locate where the hinge is positioned on
the wood with a small pencil mark. This is where it gets fun if your
using the regular plastic hinges. You need to first use you x-acto #11
blade to cut a slot on the center line just big enough for each hinge.
Then you need to enlarge the slots so that the hinges will push into the
slots. After this is done you will need to do the same on the rudder
and elevator using the hinges as a guild. I tape them to the stab and
fin and then us a pencil to mark the locations.
Finally, remove all the hinges and cover the model. You will be able to
find the slots by sticking an x-acto knife through the covering. After
the model is covered you need to epoxy the hinges in place. So, using
15 minute epoxy bind the hinge and at the center place a small dab or
dish washing liquid soap. This will prevent the epoxy from sticking to
the hinge point. Now, place a small amount epoxy to the end of the
hinge that will be inserted into the stab or fin. Do the same for all
the hinges on the stab and fin. Let the epoxy setup. OK, with the
epoxy set its time to attach the rudder and the elevator. I usually do
the elevator first as there a more hinges there then the rudder. Just
apply a small dab or epoxy to each hinge, line up the elevator or rudder
and push in the hinges. Again let it set just flex it back and forth
several times as the epoxy sets.
Your Done.
Now if your using C/A hinges do the same as above except just use the
#11 x-acto knife to cut a slit in the stab, fin, rudder, and elevator.
Cover the model, locate the hinge slits, slip in a hinge, push on the
elevator and rudder. Use a drop of C/A on each side of the hinge ( Top
and bottom, left side, right side) and your done.
Well I hope this mess above helps and if I can answer anymore of your
questions please feel free to email me and time.
You are correct. First, I'd throw those away. They're hard to get lined up
properly. Get some CA or "Easy" hinges. After covering, cut a slot at each
hinge location, using ONLY a #11 blade. Don't dig the slot out, the blade cut
will be plenty wide. Slide the hinge about halfway into
the slot and slide the control surface onto the other half. Push the surfaces
tight against each other. Flex the control each way to create the proper gap.
Using ONLY thin CA, place 2-3 drops on each side of each hinge. When it dries,
flex the control both ways and there you are! Strong, easy, and reliable.
May be this will also help.
Draw a pencil line halfway across the "easy hinge".
Drive a dressmaker pin through the hinge on the line
on both ends of the line (about 1/8" from the border)
Insert the hinge in the slot in the stab until both pins
touch it. Then slide the elevator, also against the
pins. That will ensure that the hinge is about halfway in both
For the proper gap, I slide small pieces of 1/16" balsa
between the surfaces which create a uniform gap.
(place them far from the hinges to avoid gluing them.
Once satisfied, place 2-3 drops of thin CA on each side.
Have a paper towel ready to suck any excess glue.
Re I'm building a delta wing and am baffled on the current step in the
The skeleton frame work of the plane and airfoil is there and now the
plan tells me to glue these 2in x 1/16in x 3feet strips of balsa to the
upper and lower leading edges of the air foil. Well these 4 balsa strips
are flat and brittle but the airfoil is nicely curved.
I have to 'wrap' this flat wood around this curved airfoil?
The plan gives no hints on how to do this. Any great ideas?
You can soak the wood and it will bend easier, but softer balsa is
better. If you do the soak method, find some plastic pipe that is about
the same radius as the ribs. Wet the balsa and hold it on the pipe to
perform the shape. I use a layer of paper towel under the balsa and a
bunch of rubber bands and sticks to hold the balsa down. Let it sit
overnight and you will have some nice, preformed balsa sheets that are
much easier to glue on.
The main difference between this method and just soaking and gluing down
is shrinkage. Wetting and gluing will cause a lot of dips between the
ribs as the glue dries. Performing makes the wing much smoother.
Use this same technique on rounded turtle decking.
And if you will mix in household ammonia with the water (no more than equal
parts), then the wood will soften up nicely and form to the pipe easily.
Use a small brush to soak the outside of the wood with vinegar. Let it sit for
a while and it will be easier to bend. It's also possible that the wood is
simply too hard, replace it.
Put the 2"x1/16x3' strips in warm water and soak then for about 20min. then
if the are soft and then you put them over the air foil and clamp them there
till they
dry then you will be able to glue them down works for me.
Don't worry, it's very easy.
Glue the sheet *just* to the leading edge. I typically use aliphatic
resin for this, since you often have to sand the LE joint, especially
if the sheeting goes OVER the LE stock rather than butting up to it.
(Rigid aliphatic glues sand nicer than CA, IMO).
Once that join has dried *completely*, use a spray bottle (such as a
Windex / 409 bottle) on it's wide-fan setting and spray the entire
surface of the sheet with water (and optionally some ammonia). Leave
it for 10 or 15 minutes. With softer balsa, the weight of the balsa and
water alone will already have begun to form the wood around the ribs;
for harder balsa you may need to repeat the process a few times, and
you may want to lie a long straightedge (I use a 48" x 1 1/2" steel
rule) along the "free" edge of the sheeting. This will provide a small
amount of force uniformly along the sheet, to curve it.
Once the LE is curved "close" to the shape you want, just flip the
wing over and run thin beads of thin CA along the rib <-> sheeting
join while gently rolling the wing such that the work surface presses
the sheeting gently against the ribs as you go.
Believe me, it's much easier to do than to describe, so don't be put
off if the above seems complex - it's not.
Of course, you can always go & buy softer balsa to help make the
process even easier.
In addition, and when using thicker balsa, using a really hot iron on the
wet balsa will make it accept almost any curve without cracking. If needed,
use a wet cloth for extra steam. I tape it tight after forming and leave it
to dry before final bonding is done.
An earlier question I gather that there is still some mis-information out
there regarding the best number of blades for a prop. The best number of
blades for a prop is always the fewest number that will fit the particular
situation. The only reason to go to a three or four bladed prop is to clear
the ground or the aircraft structure. If single blade props were more
practical for general use they would be best, but these days you only find them
in special high performance application. The major model prop makers want
nothing to do with a single bladed prop and its counterbalance. The reasons
for not using three or four blades have nothing to do with one blade ruining
the air for the next, this effect is so small as to be completely unimportant.
The reasons that fewer is better stem from the fact that to properly load the
engine with fewer blades you must make them longer. A prop can only use the
air that flows through its "disk" , the circular area it sweeps out while
turning. The larger the disk the greater the available air to move. Also, and
perhaps just as important, the blades will have a higher aspect ration. The
blades will be longer and so have the same performance advantage that
sailplanes use. It is why helicopters work so well. The tip losses will be a
much lower percentage of the total energy output of the blade. If there was a
way to build props with thinner, longer blades without any flexing or fatigue
problems we could get even more out of our engines. The constraint of keeping
the tips slower than the onset of compressibility is also a reason we do not
have long thin blades for our two strokes.
Set the pitch to match the RPM and speed the model is operated at, then get to
that RPM by adjusting the diameter. Add diameter not blades. the scrap balsa pieces.
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