ORIGINAL: Malcolm H
Being an F3A aerobatic flyer, correcting the track of the model over the ground is second nature but I was shocked to discover that this particular airframe has so much yaw/roll couple that rudder is totally useless for this purpose.
Also has anyone tried heading hold mode on roll?
To be fair to the model Malcolm, you should never use rudder to adjust your heading. Turning by banking is the only proper method. Yawing it is a trick used in competition aerobatics to try to fool the judges so that they don't see the bank and don't realise you are adjusting course! I gather that the full-size F-18 has some nasty yaw characteristics and particularly on approach to land the computer has to keep it within a very narrow yaw envelope otherwise things become unpleasant.
As to heading hold, the advice is not to use it on fixed wing models. Rate mode which damps out disturbances works well enough for us, and HH mode can have unexpected consequences. It works fine on helis which have very light tail inertia and fast servos and very fast yaw response that can keep up with where the gyro thinks you are adjusting your heading to. It's a different matter with the inertias and roll rates of fixed wing which will lag some way behind where the gyro thinks the wing should be.
H