First step is to check your stick.
go to "map controllers". Select your joystick from the top drop down box. Look at the numbers on the "axis" rows. Are they steady? or do they jump all around? If they are steady, thats good, if not you can adjust them by clicking on one of the axis rows, then click on the "advance" button just above the list of axis and buttons. This swings out another panel with sliders to adjust the stick sensitivity.
To adjust the stick sensitivity, first you want to get the numbers to stop bouncing around. Adjust the "dead band" sldier up a small bit at a time. Flick your stick and let it recenter. Check the numbers and see if they stay steady. If so, move on, if not move the slider up a bit and test again.
Once the dead band is adjusted (adjusting the dead band removes the slop your stick might have and helps keep your auto pilot on) you can use the other sliders to adjust how sensitive the stick movement is in game. This is a very personal setting as some guys have zero adjustment and are very good at keeping their hand movement small and smooth and others like me jerk their stick all over the place. Animal has a great write up on how to adjust your stick setting on his site.
Animals Flight Controls setupChallengers flight control YouTube videoOnce you have things working right again, make a copy of the "setting" folder in the Aces High game folder and save it someplace where you can find it. This way if you have to delete and reinstall the game you can just swap the settings folder and you will have all your old settings back.
