Too real to be a game!™ 

Flying the Hangar 9 Alpha 40, at 1/2 throttle it climbs out, turns left without any stick input. Why?

Versions: V1 and V2

  • This is all expected. “Welcome to the real world”. It’s aerodynamics.
  • What’s happening is that the propeller is trying to turn one way and that results in turning (rolling) the rest of the airplane the other way. The airframe tends to roll left due to this shaft torque. Then the propeller aerodynamics results in some swirl that hits the left side of the vertical tail. This results in a left sideslip (flow “hitting your right ear”). With dihedral in the wings, the left sideslip produces a left rolling moment which adds to the propeller torque rolling moment. So the end result is that the plane does roll left and turn left. With the throttle up past 1/2, the airplane will get into a porpoise. The ParkZone electric J-3 Cub does the same thing, but to a lesser extent because the propeller has a bigger diameter and this produces less swirl to push the tail around into sideslip.
  • With a real airplane, when it’s taken out to the field, the surfaces are not set exactly to zero deflections like in the sim. So things are a little bit out of alignment and this is OK. Things are close enough to zero that planes climb out OK. Once in the air, the trims are used to make the plane fly straight.
  • So in the sim the trims on the controller can be used to compensate for these aero effects outlined above.
  • Finally, if you climb and cut the throttle and glide, the airplane will fly straight if the surfaces are all ZERO exactly. It flies straight because the propeller swirl and torque go away.
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