Beginning in late 1943, high-speed diving trials were undertaken at Farnborough to investigate the handling characteristics of aircraft travelling at speeds near the
sound barrier (i.e., the onset of compressibility effects). Because it had the highest
limiting Mach number of any aircraft at that time, a Spitfire XI was chosen to take part in these trials. Due to the high altitudes necessary for these dives, a fully feathering
Rotol propeller was fitted to prevent
overspeeding. It was during these trials that
EN409, flown by Squadron Leader J. R. Tobin, reached 606 mph (975 km/h) (Mach 0.891) in a 45° dive.
In April 1944, the same aircraft suffered engine failure in another dive while being flown by Squadron Leader Anthony F. Martindale,
Royal Air Force Volunteer Reserve (RAFVR), when the propeller and reduction gear broke off. The dive put the aircraft to Mach 0.92, the fastest ever recorded in a piston-engined aircraft, but when the propeller came off the Spitfire, now tail-heavy, zoom-climbed back to altitude. Martindale blacked out under the 11 g loading, but when he resumed consciousness he found the aircraft at about 40,000 feet with its (originally straight) wings now slightly swept back.
[125] Martindale successfully glided the Spitfire 20 mi (32 km) back to the airfield and landed safely.
[126] Martindale was awarded the
Air Force Cross for his exploits.
[
not bad for a fragile, one trick pony !