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.
I didn’t know about this incident but whilst in YugoSlavia with two Gnats in 1958 I had exactly the same thing happen. The temperature probe was mounted on the top of the windscreen frame. I too experienced an alarming yaw oscillation at around M 1
It was the summer of 1958 I was a flight test engineer at Chilbolton airfield where I met ‘Bob’ Dey who at that time was flight testing the GNAT. I owe him a drink as I was unable to see him in the hospital after the mishap since I had to leave for India in a hurry. Hope I can get in touch with him to reminisce about the times with him and then Sqdn Ldr Das.