At an airshow I use a monopod occasionally to be able to use slower shutter speeds to prevent completely freezing the movement of propellors. This works quite good with even long lenses (I often use a Nikkor AF-S 4/300 mm with a 1.4 dedicated converter), but mainly for shooting taxiing aircraft.

Using a monopod or tripod for ground to air shots usually isn’t very practical. The “secrets” of obtaining sharp photo’s with long lenses are: use a fast (F 2.8 or 4) high quality lens with or without an equally high quality converter, use a fast shutter speed of at least the reciprocal of the focal length (e.i. 1/500 with a focal length of 500 mm), accurate focussing and accurate panning including follow through after making the exposure.

Quality wise, I would advise against the use of slow zoom lenses combined with a converter. With a converter, much better results would be obtained by using a fast prime (non-zoom) lens. With the quality standard of today’s films, especially colour negative, a faster film up to ISO 400 or even 800 will enable you to use very fast shutter speeds without sacrificing much in picture quality. In this way you should be able to practically eliminate camera shake.