Bob Grimstead practices Derry turns at Serpentine in his Fournier RF4 motor glider, powered by a 30HP Volkswagen engine re-engineered for airwork as the Rectimo.

The Fournier is of timber and fabric clad construction but do not be deceived that this is a fragile piece of work.

This aircraft is quite capable of breaking the man before breaking itself from positive G forces.

Common sense dictates that with any ageing airframe, manouvres be enacted with a little more restraint than when the aircraft was brand new and Bob operates the aircraft within a conservative performance envelope.

The propellor noise evident is caused by the blade tips exceeding the speed of sound as engine rpm increases during descents. The "silent" prop which was fitted to this aircraft was taken to the UK and fitted on another Fournier aircraft which Bob used to fly his display at the London Red Bull Air Race. So until another is found, the noisy prop is back on this aircraft.