I just point and shoot on auto!
plane http://i279.photobucket.com/albums/kk134/redgrittybrick/DSC_6297.jpg (Gloster Gladiator I, Nikon D50, 18-200 VR, Program mode, 200mm, f5.6, 1/800, ISO 200, unprocessed JPEG from camera, resized for web in Picasa)
plane http://i279.photobucket.com/albums/kk134/redgrittybrick/DSC_6308.jpg (EXIF data says 95mm(!?), f6.3, 1/640, ISO 200, I cropped it a little then resized for web)
plane http://i279.photobucket.com/albums/kk134/redgrittybrick/DSC_6208.jpg (Barnstormer picking up a ribbon with his wingtip - I zoomed out to get a better chance of catching the moment. Uncropped. 95 mm, f5.3, 1/400, ISO 200)
I try to find a good place to stand, watch how the planes use the airspace, consider what sort of angles I want to shoot. Hope for good weather. Pan with the plane.
I'm happy with these but I'm sure you could do a lot better with some care. Photographing planes at airshows is a zillion times easier than photographing wild songbirds in my garden.