Bug 174 on 12lbs boost. Review please.

[camber]

Originally Posted by Kurfürst

There's a logical failure in your assumption that the boost cut-out would increase boost beyond +9 lbs. Its quite likely in fact that the pilots obtained +9 by using the boost cut-out, as on the Spitfire I.

This is contradicted by the July 1940 Spit II manual which you are quoting. 30 minute climb rating is +9psi, 30 minutes, 2850rpm. The boost cutout description is listed as EMERGENCY override of automatic boost control, sealed against inadvertant use. 30 minute climb is not an emergency, thus clearly +9psi is available on normal throttle operation (also +9psi is typically referred to as rated boost in Spit II publications).

It does beg the question, what kind of boost control override installation is being described in the July 1940 Spit II manual? An original type, which gives full throttle plate control in the event of controller failure and is unsuitable as a combat boost? Or the modified type, which is not really a cutout but an increment for the boost control setpoint (to +12psi)?. The July 1940 manual does not let us know.

It seems commonsense that the Spit II boost cutout was the +12psi type, and use of it as combat boost was approved and occurred during the BoB (although not in the July 1940 manual). This is considering the use of +12psi Spit I's during the same period and combat reports as above. But specific documents appear to be lacking.

camber