3D Harrier: Throttle Technique DAS PARKFLY The high alpha “harrier” pass is the corner stone of 3D flying. A harrier pass consists of flying an airplane at a very high angle of attack and a very low airspeed. In this position, it can be said that the plane is flying on the prop instead of on the wing. Control during a harrier is primarily maintained by propwash over the tail surfaces. Thus, as a 3D pilot, you must start thinking of throttle as equating to “control”. However, if you tried to maximize control by maintaining a higher throttle position, the airplane might climb or accelerate. On the other hand, if you waited until the controls were no longer effective to start adding power, you may not recover control in time to save the maneuver. Therefore, a 3D pilot smoothly pumps the throttle when flying on the prop in order to maintain propwash over the tail surfaces without holding the higher throttle positions long enough to cause the airplane to accelerate. The objective is to pump the throttle throughout the harrier to maintain the same height, while adjusting the elevator to maintain a very high angle of attack. At the instant the controls become ineffective or the plane starts to descend, give the throttle a little extra boost. You will find that you are able to respond to moments when more control is needed much faster when continually pumping the throttle, than if the throttle had been stationary. Throttle Boost control or climb Mean average to maintain same altitude Effect descent To maintain the same height during a harrier, the amplitude or range of the throttle movements is usually between 1/4 and 1/2 throttle with an airplane capable of hovering at half throttle. Note: if you lose complete control at these very low airspeeds, often the only way to regain control and recover is to quickly go to full power. C-89 KPTR: Pump the throttle to maintain control authority without accelerating. Vary the amplitude or range that you pump the throttle to control altitude. 3D Harrier Pass: Elevator Technique DAS The simplest way to enter a harrier is to slow down near stall speed. Then smoothly pull the nose up to establish a very high angle of attack while simultaneously adding power to maintain the same height. PARKFLY Every airplane has a certain fuselage angle or “sweet spot” during the harrier that results in the least amount of wing rocking. That angle is usually close to 45 degrees, and it usually takes about half elevator to achieve that angle. You will then find that it takes constant elevator adjustments to maintain that angle due to the fact that airplanes are not designed to fly this way. Note: If you are late with any of your elevator adjustments, it will take a much larger input to recover, thus increasing the potential for over-controlling. Therefore, 3D pilots smoothly pump the elevator throughout the harrier to keep their fingers nimble and ready to instantly respond to the needs of the moment. Inputting a series of smaller adjustments, rather than waiting to respond with larger adjustments, also reduces the potential for over-controlling. 45N Seeking the sweet spot.... Lower nose Mean average to maintain 45N attitude Raise nose KPTR: Seek to maintain an approx. 45 degree fuselage angle during the harrier by smoothly pumping the elevator. C-90 DAS PARKFLY 3D Harrier Pass: Rudder and Aileron Applications Rudder is used throughout the harrier to correct left and right deviations and to steer the airplane. Coordinated aileron and rudder inputs are used to keep the wings level and prevent adverse yaw. Airplanes are typically very unstable during high alpha flight, making it very easy to over-control. Therefore, you must keep your rudder and aileron inputs very small and brief to avoid causing the wings to rock uncontrollably. Conventional flying experience teaches us to relax the elevator and lower the nose when the wings start to rock during a stall. However, one must resist the urge to relax the elevator when the wings start rocking during a harrier. Maintaining a high angle of attack can actually work to lessen wing rocking by keeping both wings deeply stalled and therefore having as little aerodynamic influence on the maneuver as possible. Put another way, when the wings start rocking, sometimes pulling more elevator will lead to less wing rocking. You can also reduce wing rocking slightly by programming both ailerons to deflect up 5-10N with up elevator. C-91 KPTR: Use rudder to keep the fuselage pointed in the same direction, and coordinate tiny aileron-rudder inputs to keep the wings level during a harrier. 3D Harrier Turns DAS Turning while in a harrier attitude consists of steering with the rudder, using the ailerons to keep the wings level, and pumping the elevator and throttle to maintain the same fuselage angle and altitude. PARKFLY As unstable as an airplane is during a harrier, in order to turn without over-controlling you must limit your rudder inputs to brief nudges every few moments. Note: Turning with rudder alone at this angle of attack would lower the wing on the inside of the turn. Lowering a wing at such a low airspeed could cause the airplane to drop sharply! Therefore, you’ll need to apply opposite aileron throughout the turn to keep the wings level. Once the turn is finished, continue using the rudder to steer, but switch to coordinating aileron and rudder in the same direction to keep the wings level. Remember, if the wing on the inside of the turn drops, the plane can fall sharply toward the ground, so be ready during a harrier to punch the throttle to full to help with the recovery. Apply opposite aileron (cross-control) throughout the turn to keep the wings level. Rudder alone! Side note: If the plane behaves strangely, as if it was responding to alien control inputs, most likely the mix percentages you’re using are far too highCwhich probably explains why odd things happen during other maneuvers as well. KPTR: Gently nudge the plane around the turn with rudder while applying opposite aileron to keep the wings level. C-92 3D Rolling Harrier Rudder Warmup The next featured maneuver is the awesome rolling harrier pass. The first phase of learning a rolling harrier is practicing consecutive rolls using only the rudder to maintain altitude. The objective during this exercise is to apply top rudder only during the segments of the rolls when it is most effective at keeping the nose up, i.e., starting approx 45 degrees before knife edge, through knife-edge and up to 45 degrees past knife edge. PARKFLY There won’t be enough time to try to manage the rudder by watching the airplane. Instead, each time the wings approach knife-edge, commit to a steady “in-out” rudder control input. Then quickly reflect on the result and determine whether you need to change the size or pace of the subsequent rudder inputs to effect better results. For example: Start by positioning the throttle to approx. half. Pull the nose up slightly and start rolling. If you are rolling to the right, smoothly input top left rudder “in-out” when the wings approach knife-edge. If the result is a heading change because the rudder input was too slow, i.e., held in too long, determine to speed up the pace of the subsequent top right rudder input. Or, if your first rudder input proved too small to prevent a loss of altitude, increase the size of all subsequent rudder inputs. Note: The most common rudder mistake during rolls is a weak “opposite” rudder, i.e., when rolling right, pilots tend to input a deliberate left rudder input, but the subsequent opposite right rudder inputs tend to be much smaller. Therefore, determine to input the same amount of rudder in both directions. Left C-93 Each control input during rolls can be broken down into size and duration: Duration (elapsed time) In-out Size Rudder input Maximum rudder Start rudder KNIFE EDGE DAS In-out Right KPTR: Commit to deliberate “in-out” rudder inputs, triggered by seeing the wings approaching knife-edge, then quickly reflect on the result and apply what you learned to the next rudder input. Neutral rudder 3D Rolling Harrier Elevator Technique Duration (elapsed time) Size In-out Elevator input Push elevator INVERTED Using rudder alone during the rolling harrier warmup may have PARKFLY only raised the nose up about 20 degrees. During the second phase of learning a rolling harrier, elevator will be added to help raise the nose higher. The objective is to continue making the rudder inputs as before while pulling and pushing the nose up during the upright and inverted segments of the rolls. Once again, there won’t be enough time to try to manage the elevator by watching the plane. Instead, each time the wings approach level, commit to a steady “in-out” elevator input. Then quickly reflect and apply what you learned to the subsequent elevator inputs. Start by positioning the throttle to approx. half. Pull the nose up slightly and start rolling. If you’re rolling right, apply top left rudder when the wings approach knife-edge. When the plane approaches inverted, push down elevator (in-out). When the plane approaches knife-edge, input top right rudder. And when the plane approaches upright, pull up elevator. Repeat as many times as you can, and control your altitude at this stage by varying the size of your elevator and rudder inputs. Maximum elevator Neutral elevator Approaching 45N Approaching 45N In-out Left.... In-out push.... Approaching 45N Approaching upright Approaching inverted Pull the nose up and start rolling DAS In-out In-out right.... pull.... In-out Left.... KPTR: Start rolling and think “left, push, right, pull (upright), left, push, right, pull (upright), etc., etc..” C-94 Advanced 3D Rolling Harrier DAS Significant control deflections and the high angle of attack during a rolling harrier create a lot of drag, thus, you will have to start pumping the throttle to maintain altitude and optimal control: Start rolling with the throttle near half. Adjust the rudder and elevator to maintain an approx. 30-45 degree fuselage angle while pumping the throttle to maintain the same height. Note: The best time to pump up the throttle is when the plane rolls through knife-edge, or roughly corresponding with each left rudder input, for example. PARKFLY Prolong top rudder to prevent adverse yaw Rudder input KNIFE EDGE Maximum rudder Start rudder Approx. neutral rudder Approaching 45N Approaching 45N Approaching inverted Left.... C-95 There tends to be significant adverse yaw at the start of a rolling harrier. Here are two ways to initiate a rolling harrier without veering off course: Option 1. Skip altogether or use very little top rudder through the first knifeedge and let adverse yaw raise the nose through the start of the first roll. Option 2. If you are agile, briefly coordinate rudder in the same direction as the aileron to prevent adverse yaw at the start of the roll, then quickly switch to top rudder when the wings approach knife-edge. Note: The down aileron will create so much drag that you’ll have to prolong your top rudder inputs well past knife-edge and up to or slightly past wings level to prevent adverse yaw. Finally, to stay on heading, make sure that you apply deliberate rudder inputs in both directions! push.... Approaching 45N Approaching upright right.... pull.... Approaching 45N Approaching inverted Left.... push.... Approaching upright right.... KPTR: Use very little top rudder at the start, and prolong your top rudder inputs up to or slightly past wings level. pull.... 3D High Alpha Rolling Turns High alpha rolling turns are arguably the most impressive 3D maneuvers. The version featured here is an “outside” roller, where the plane rolls right while turning or circling left. Think of the mechanics of a high alpha rolling turn as similar to a rolling harrier pass, except the rudder and elevator are applied a little earlier to induce a turn as well as raise the nose. A left to right “outside” roller starts with the throttle near half. The nose is pulled up slightly, then right aileron and left rudder are applied to simultaneously start rolling and turning. When the wings near knife-edge, down elevator is applied to push the nose into the turn. Right rudder is applied when the plane is inverted, and then up elevator is applied near knife-edge to pull the nose into the turn. Start: Pull up slightly and simultaneously roll right while applying left rudder. Upright “Left.... push.... right.... pull.... left.... push.... Even tempo.... Upright Knife edge In-out Left.... Inverted In-out push.... right... On high rates, things will happen much too fast to try to base your inputs strictly on watching the wings. Instead, the objective is to commit to a steady drum-beat of “left, push, right, pull, left, push, right, pull, etc..” If the tempo is correct, you will be initiating left rudder at the same time the wings roll through level to start another roll. If your tempo is too fast, the premature inputs will force the plane into a descent. If too slow or late, the plane will roll without turning. Altitude, fuselage angle, and rate of turn are controlled by varying the size of your rudder and elevator inputs and pumping the throttle. For example, if you want to tighten the turn or raise the nose, increase the size of your pushes and pulls. The best time to pump up the throttle is during a knife-edge segment, or corresponding to each left rudder input, for example. Things happen fast, so be ready to boost the throttle at the instant the controls become ineffective or the airplane descends. Note: The most common mistake is weak “opposite” inputs, i.e, the initial rudder and push tend to be deliberate, but subsequent opposite rudder and pulls tend to be much smallerCthus, determine to apply deliberate rudder and elevator inputs in both directions! KPTR: Look to initiate each “left, push, right, pull” sequence as the wings are rolling through upright. C-96 DAS PARKFLY 3D Knife-edge A maneuver that is not difficult, but always seems to impress spectators, is the slow speed knife-edge pass at low altitude: Start with the throttle near half and roll into knife-edge while raising the nose up to 45 degrees. Adjust the rudder to maintain that angle and pump the throttle to hold the same altitude. (Note: While mixes can help make knife-edge flying easier, due to the ever changing aerodynamic, propeller and wind effects, you’ll still need to constantly correct roll and pitch deviations.) Sink = Boost throttle Adjust the rudder to maintain a 45 degree fuselage angle and pump the throttle to maintain altitude. Knife-edge Loop A variation on the knife-edge theme is the knife-edge loop. First, establish knife-edge flight, then hold in full top rudder while gradually applying full throttle to execute the knife-edge loop. To exit, quickly throttle back and/or reduce rudder. Note: The airplane will most likely try to roll upright during the last quarter of the loop, therefore, be prepared to input opposite aileron nearing the bottom of the loop to keep the wings vertical. Also, if a lot of up elevator is mixed with the rudder, the plane will tend to pitch toward the canopy as it picks up speed coming down, thus be prepared to input down elevator to correct. Opp. aileron and push? It’s easy to get confused or unnerved at the bottom of a knifeedge loop, so it’s important to initially practice this stunt high. C-97 KPTR: Even with mixing, don’t be surprised when you have to keep making corrections to maintain knife edge.