Mike,

Ailerons - especially if the plane uses 2 aileron servos. Any servo will have some amount of play in the geartrain, and some amount of blowback (which is all but eliminated with a good digital servo). Aileron servos are working the hardest during high G pulls / pushes, and if they are not maintaining center equally, it will be very difficult to get the plane to loop track properly. I agree with the 821 recommendation for this application.

Regards,

Dave L
Team JR