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Rudder is usually used to maintain coordinated flight. When banking to one side to begin a turn, the rudder is usually pushed towards that side. I guess this is still valid in inverted flight: in normal flight, if the pilot bank the plane to the right, it also push the right pedal (to conteract adverse yaw); in inverted flight, if the pilot bank to the right, the plane will turn to the right seen from the ground, i.e. the left seen from the pilot. The pilot should apply left rudder to keep coordinated flight.

If the pilot want to make a aileron roll, what will be the general action on rudder given the flight goes quickly from normal to inverted and back to normal, and the pilot don't want to initiate a turn?

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The key in flying a good roll is to keep the aircraft's nose up in anticipation of the lift requirement when flying in knife-edge or inverted flight. Since in knife-edge the elevator and rudder will assume each others function, you will need rudder as well as elevator for directional and pitch control. Also, depending on adverse yaw, some rudder is required to hold yaw to zero when applying ailerons. The procedure is as follows:

  1. Speed up, so you are fast enough for roll maneuvering and inverted flight.
  2. Pitch up a few degrees. How much depends on wing incidence and zero-lift angle of attack. Look out for some feature on the horizon: This will help you to keep your direction constant.
  3. Stop the pitching motion, then apply full ailerons. Correct the aileron-induced yawing motion by applying gentle rudder (trailing edge in the direction of the up-going aileron). Your goal is to keep the fuselage pointing at the chosen feature throughout the maneuver.
  4. With increasing roll angle, apply rudder to keep the nose up. At the same time, push the stick gently to avoid course deviation. At 90° roll angle, both elevator and rudder have changed their function: The elevator will now control direction, and the rudder will control pitch.
  5. Keep the rotation rate and push the stick more when changing from 90° to 180° roll angle. In inverted flight you need to keep the aircraft trimmed, and depending on the static stability and speed this can require considerable negative elevator deflections. At the same time reduce rudder deflection such that the fuselage will still point into the initial direction. At 180° roll angle both elevator and rudder have returned to their old function, but pulling will now start a dive.
  6. On the way to 270° you will again need to add some rudder, now in the opposite direction, to keep the nose up. Again, elevator and rudder will exchange their functions.
  7. Once you return back to normal flight attitude, stop the rolling motion and reduce rudder deflection back to zero.
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    $\begingroup$ Wow, that's a lot of work! $\endgroup$ – FreeMan Jul 7 '15 at 13:35
  • $\begingroup$ @FreeMan: It becomes less if you fly an aircraft with symmetric airfoil and zero incidence. An aerobatic aircraft, in other words. $\endgroup$ – Peter Kämpf Jul 7 '15 at 16:05
  • $\begingroup$ Also flying is not too different from driving. Bet you can parallel park without thinking too hard about it. $\endgroup$ – Dave Kanter Jul 7 '15 at 16:58
  • $\begingroup$ Aileron rolls are really easy, even if they do have 7 steps! Falling Leaf and Dutch Rolls are great coordination exercises for the loop. $\endgroup$ – rbp Jul 7 '15 at 17:04
  • $\begingroup$ @rbp your comment just make me even more curious about aerobatics. I may ask other questions in few days (after reading about falling leaf and other aerobatics yet unknown to me) $\endgroup$ – Manu H Jul 10 '15 at 10:08
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Well first, by barrel roll do you mean a true barrel roll which is a combination loop and roll, or do you mean a tighter maneuver like an aileron roll or slow roll accomplished mainly with ailerons but which can still result in a rotation around a point above the plane?

The answer in all three cases is that rudder is used to help maintain stability in the roll. A little rudder at just the right time can help keep the nose up in a slow roll or even an aileron roll, as the plane rotates through the sideways portions of the roll when gravity is otherwise not countered. Counter-rudder (applying rudder opposite to a bank) can also help to start a "wide" roll by kicking the plane into an initial yaw that counters the tendency of the plane to turn into the initial bank. Finally, first a hard left yaw and then a hard right yaw is used to execute a "true" barrel roll where the plane rolls in a circle roughly perpendicular to its original path.

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  • $\begingroup$ I meant aileron roll. Question edited accordingly. $\endgroup$ – Manu H Jul 7 '15 at 15:59
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As an aerobatic pilot, it's pretty simple. The aircraft will lose lift as you roll through 90 and 270 degrees - knife edge flight. Obviously this will cause loss of normal level flight pitch. So, you have to compensate for that pitch loss you start by adding the pitch you will lose (depending on speed and roll rate of the aircraft) as you start the roll. How much? Start by fairly quickly pitching up about 40 degrees and adjust from there each time you do a roll until you start and end at the same altitude. Rudder? If you roll left, slowly add right rudder topping out at 90 degrees. Reduce rudder to zero at 180 degrees and push the stick gently forward to zero g's. If you go negative, reduce pressure so you float gently through 180 degrees. Reduce that forward pressure to neutral as you come through 270 degrees and simultaneously add left rudder. At 270 degrees continue reducing left rudder to neutral as you come to level flight. Once you master a left roll, just reverse rudder procedure for a right roll. Be gentle with the plane as this should be done with very little stress on the airframe... if it does, you are doing it wrong. Learn how on a plane certified for aerobatics before you try it on the company A380.

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There are 2 types of rolling maneuvers used in aerobatic competition, a slow roll and an aileron roll. First the easy one, an aileron roll. Simply raise the nose above the horizon, apply slight rudder in direction of roll initially to counter adverse yaw, stick in direction of roll. You can do multiple rolls, the limitation being that you must stop once the nose has fallen about 30 degrees below the horizon. A beginner can accomplish this maneuver with minimal instruction. The slow roll has nothing to do with the rate of roll, a high level aerobatic plane can slow roll or aileron roll at 420 degrees per second. The slow roll requires a bit of coordination in that the plane rolls about it's longitudinal axis, pitch not changing during the maneuver, as stated previously, rudder is used at 90 and 270 degrees, and forward elevator at inverted, to keep the plane at constant pitch and the nose not yawing left or right. Of course no one should ever try to teach themselves aerobatics. Get a good instructor and a good aerobatic plane.

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