Effect of boost control cutout prior to +12 psi boost modifications

[=XIII=Wedge]

Originally Posted by Viper2000

It's not "my conclusion"; I haven't tested it at all. It's just what I've picked up from the forums.

In any case, it's beside the point, and arguments about it (legitimate though the are, since the whole point of the Merlin XII was to increase the FTH at +12 psi boost) belong elsewhere.

This thread is about the correct behaviour of the boost control cutout in aeroplanes that haven't been modified for +12 psi boost, my contention being that operating the cutout with the power lever fully forward should produce approximately +17 psi boost leading to rapid engine damage, based upon the sources I have cited in the original post.

Therefore I conclude that the original purpose of the boost control cutout was to act as a safety feature to guard against failure of the ABC fully closing the throttle and effectively failing an otherwise functional engine, and that combat power for an 87 octane Merlin III would be reached simply by advancing the power lever to give +6¼ psi boost and 3000 rpm.

I read it as +17 psi boost would only occur in a unmodified boost control with 100 octane fuel. I understood it that 87 octane fuel had a maximum boost pressure of 6.25 psi on the Merlin II/III.

I thought the whole reason for the automatic boost control was to reduce the burden on the pilot who could set an engine regime using the throttle\propellor and mixture levers and the boost would remain at that setting rather than keep needing to be altered due to changes in altitude.