PPRuNe Forums - View Single Post - SR71 Lecture – Colonel Richard Graham – RAF Museum Cosford
Old 20th Sep 2016, 12:13
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megan
 
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suffered serious 'engine unstart' consequences that led to the loss of a sizeable proportion of the fleet, and to the deaths of many crews.
SSD has little knowledge as to the aircraft, there any number of good books available detailing the aircraft should he wish to educate himself. While unstarts were a feature of the aircrafts operation, there was only one crash and one death in which an unstart had a role to play.

That was 64-17952 on a test flight to establish, among other things, improving high Mach cruise performance by reducing trim drag. This entailed having the CoG further aft than normal to compensate for the rear ward movement of the CoP at high Mach. An unstart always produced a high pitching moment, and the pilot had to be right on top of it before the AoA exceeded a critical value where control would be lost, and be unrecoverable. Controlling the pitch rate proved not a great problem, as years of trouble free service proved. However in this particular case with an unstart, with the CoG so far aft it was not controllable, and control was lost, with the entire forebody breaking away from the main body.

The solution to reducing the trim drag was to move the CoL forward, so reducing the static margin and trim drag. This was achieved by inserting a wedge between the nose section and the forward fuselage, giving the nose a 2° tilt up.
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