Excellent! Two references which really clarify the Spit II boost operation:
Quote:
Originally Posted by 41Sqn_Banks
I've found a description of the "Gate Control":
http://www.enginehistory.org/Piston/...erlinABC.shtml
According to this description the boost obtained by the gate control may vary depending on atmospheric pressure, this would explain why the maximum take-off boost is given as +12.5 in the later manual, as this would possibly be achieved on days with high atmospheric pressure.
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This is a great explanation of the "take off boost" gate. Because the gate represents not an automatically controlled boost level, but an ability to reach a given throttle valve opening without boost control, this override throttle valve opening % must be calibrated for a typical atmospheric pressure at sea level (to give +12.5). So the boost level of +12.5 psi is approximate, under sea level it would get higher
Lane:
Those are very useful combat reports. Even though it contradicts my idea that the +12psi was delivered through main throttle operation

Clearly the Spit II red tab IS used in combat, logically it was to deliver +12psi as per Banks post (although this is not stated explicitly).
Although the gate can only give any benefit at low level, the second report re-inforces my idea that pilots might use it "just in case" at any level. In this case the pilot pulled his boost tab, gated the throttle at maximum rpm, and felt re-assured that he was getting maximum performance!
Very interesting that a Spit pilot would refer to pushing the red boost override tab as "pressing the tit" (second report). Although the Hurricane boost cutout is much more, err, breast like I guess it was just too enjoyable a reference for Spit pilots to not take up too. It starts to explain how those terms get so jumbled up in combat reports.
Lastly, the second report suggests that he can only just keep up with his leader using all boost enhancements available in his MkII. What is blue leader flying if Blue 2 is writing "performance notes on the MkII" and suggesting he had to go all out to keep up? A MkI +12psi? This seems rather intriguing to me!
Cheers, camber