Its been covered in several threads, from Duma:
'The speeds given in the Typhoon's table (of 'limiting indicated airspeeds against height bands') were, after allowing for position error, equivalent to a Mach number of 0.79, which was higher than for any contemporary piston-engined fighter except the Spitfire IX. Our job at RAE Farnborough was to determine how critical this limiting Mach number was if taken to the ultimate loss of control. These tests were normally started at the highest possible altitude, so that if loss of control did occur in the dive the Mach number would automatically reduce as height was lost, provided the dive angle was kept constant, and thus allow control to be regained.
The aircraft to be used for the compressibility dive tests was Typhoon IB EK154, fitted with a Machmeter and powered by a 2,200hp Sabre IIA. THe aircraft was climbed to 32,000 ft and after a 3 min level run at full throttle at that height was half rolled and the nose allowed to drop 30 degrees before half rolling again to maintain that dive angle. The indicated Mach number (IMN) had built up to 0.82 by 27,000ft, with moderate buffeting, then at 0.83 a noticeable nose-down change of trim occurred and at the same time the buffeting inceased. Finally at IMN=0.84, the nose-down trim change increased dramatically and even a two-handed pull on the stick could not effect recovery. I could just manage to keep the dive from steepening, and held on with considerable effort until, at 20,000ft, the nose began slowly to rise; by 18,000ft recovery was complete. From these tests it was clear that the true limiting Mach number of the Typhoon was 0.79 and the true critical Mach number was 0.81.'
...in any case if somebody has any hard data they can send it to HTC.
