Aerobatic Maneuvers
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IMAC
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Immelmann Turn
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Immelman Turn

Here's the description of the Immelmann Turn directly from the Competition Regulations.

Immelmann Turn The model starts the Immelmann flying straight and level, pulls up into one-half (1/2) loop immediately followed by one-half (1/2) roll and finishes flying straight and level and exactly 180 degrees from the heading at entry. Downgrades:
  1. Model not level at start.
  2. Model deviates left or right during half loop.
  3. Half loop not completed exactly above point of commencement of half loop.
  4. Half roll does not commence immediately after half loop.
  5. Plane deviates from a straight line during roll.
  6. Model does not finish in level flight.
  7. Model heading does not finish exactly opposite the direction of entry.
  8. Half loop not round.
  9. In Novice and Sportsman class, maneuver does not start at center line.

Next we come to the Immelmann Turn. This is a relatively simple maneuver, but there are many opportunities to mess it up. Read the description above, then let's look at the downgrades and see how it's supposed to be done.

  1. Model not level at start. Here we go again - same song, 53rd verse! Straight and level flight is absolutely the single MOST IMPORTANT thing you can do to improve your scores.
  2. Model deviates left or right during half loop. Again, entering the maneuver without having the wings level is one of the primary culprits here. If you do enter with your wings level, any cross wind will require you to make corrections with the RUDDER. Make them as soon as you detect ANY change from the desired heading so that only small corrections are necessary. Use as much rudder as required to correct the problem.
  3. Half loop not completed exactly above point of commencement of half loop. If the loop is not round (see #8 below), the 180 degree point will not be exactly above the 0 degree (entry) point of the loop. It will vary to the left or right of the entry point. This requires varying the amount of elevator applied throughout the maneuver to achieve a round loop. Wind speed will cause the amount of elevator required to vary dramatically. Additionally, if a deviation as described in #2 above is not corrected, the exit of the half loop will be displaced either in toward the pilot or out away from the pilot from the entry point.
  4. Half roll does not commence immediately after half loop. Here's an area that separates the men from the boys on the Immelmann Turn. The roll must begin immediately after the end of the half loop. That means absolutely NO straight inverted flight before the roll starts. This will cost you at least one point and often more depending on the length of the straight inverted portion. You must be aligned with the entry flight path and ready to roll when the half loop is completed.
  5. Plane deviates from a straight line during roll. This should be self-explanatory. However, getting your plane to roll axially (around the center line of the fuselage) requires some trimming of the ailerons. Differential throw will be required to optimize axial roll characteristics. That means you need more UP aileron travel than DOWN aileron travel on each side. This can be dialed in if you have a computer radio, but what if you don't? The pushrod must be attached to the servo arm behind (toward the rear of the plane) the center of servo rotation if the aileron servo is mounted on the top of the wing, as on an Ultra Sport, Kaos, or Escape with a single servo. If the servo is on the bottom of the wing (as on high wing plane or with a servo for each aileron mounted on the bottom of each wing panel), the attachment point must be forward of the servo's center of rotation. The amount of offset determines the amount of differential - finding the right amount is a trial and error process.
  6. Model does not finish in level flight. This can happen in several different ways. You will end up diving after the roll if you over-loop (loop more than 180 degrees). Conversely, you climb if you loop less than 180 degrees. Even if your loop is correct, you can still mess things up by not rolling exactly 180 degrees to upright, level flight. Practice, Practice, Practice - with a coach!
  7. Model heading does not finish exactly opposite the direction of entry. This happens primarily when the aircraft won't roll axially. IF the airplane has too little aileron differential (for example, the same amount of up and down travel), the plane to yaw (pivot as if moved by the rudder) in the direction of the roll, creating a barrel roll. Yaw in the direction opposite the roll will occur if too much differential (for example, if only up aileron and no down aileron) is used. Either of these will cause problems on rolls and cost you points.
  8. Half loop not round. See #3 above.
  9. In Novice and Sportsman class, maneuver does not start at center line. I can't stress the importance of this highly enough. Most beginners want to let the plane get well past the center line before starting the half loop. It's easier to see that way, but will cost you a bunch of points. The maneuver must start on center!.
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Updated December 1, 2000