Make sure that you have calibrated your joystick in Windows first, and then in Aces High. 

Also, make sure that you have updated your joystick drivers when necessary.

If your joystick(s) connects to your computer using a USB port, and you have Windows XP (or later) installed, it is not neccessary to load any additional drivers in order for the joystick(s) to be used in Aces High. You still need to calibrate the stick in Windows first though.