Speed graphs for Spitfire and Hurricane

[camber]

Hi Sutts,

I agree with you but would state it slightly differently:

Although manifold pressure ("boost") and rpm are linked in a physical sense, the Merlin boost controller manipulates the throttle valve to maintain a boost pressure setpoint. It will compensate for rpm and height changes within it's mechanical limits, and thus keep boost pressure constant.

IvanK:

Very interesting report. It does make sense that the airscrew efficiency curve could cause a reduction in thrust with increasing rpm. But I think you are right that this is an unusual finding in a specific case that requires investigation. There is not much point giving 3000 rpm availability on the CSP control generally (as was ubiquitous on Hurris and Spits) if this represents a thrust reduction due going past an optimum on a prop efficiency curve.