Air Marshal PK (Babi) Dey
During the Gnat development programme at Folland’s airfield at Chilbolton, we were having trouble with accurate measurements of free air temperature in flight. So one fine morning I found a small probe on top of the canopy when programmed to carry out high Mach dives.
As the speed built up in a steep 60° dive from 45,000ft, and approached 0.9M, the aircraft suddenly went into a violent lateral oscillation. I could do nothing to control it and expected the fin to break off any moment. Instinctively, I had ‘closed throttle and was trying to ease out of the dive. I took my feet off the rudder pedals which were also moving viciously. As suddenly as they had started, the oscillations stopped, and I gently returned to base, very shaken and relieved that the aircraft was still in one piece.
Investigations proved that the tiny probe on top of the canopy was the villain, creating shock waves that hit the fin and started the oscillations as the aircraft speed went past 0.94M. It was a lesson I never forgot, and always thereafter I treated any projections that the ‘boffins’ wanted to stick onto an airframe with the greatest suspicion.