Black 6 Thu 19th Apr update re Spit II

[41Sqn_Banks]

Originally Posted by camber

Hi Banks,

I was hoping you would pop up.

Point taken on variable datum controller.

Rereading the Spit II manual AP1565B I still think that rated boost (highest boost without cutout pulled and not using the gate) is +9psi, and hence a 100 octane only condition.

Yes. AP1565B states for the actions after takeoff that the throttle should be move back to the rated +9. The 87 octane limits were not part of the initial manual and were added later. It's save to assume that the pilot had to maintain these lower limits himself in case 87 octane was used.

I admit I am on less certain ground with the hypothesis that the +12psi (when approved) was not delivered for the Spit II via the cutout as per Spit I, but by making it available in normal throttle operation. AP1565B states that Spit II boost cutout is emergency use only (and does not give a boost pressure) which muddies the water a bit. I guess it could be "emergency" combat use or "emergency" boost controller failure (original purpose of the MkI cutout).

However the pilot's notes general link you posted suggest that the red tab WAS used in the Spit II for combat boost. Of course the system could just as easily be set up either way in theory.

I don't have any reference that shows a difference between take-off and cut-out. Both disabled the boost control. Maybe the take-off didn't gave control over the throttle valve but simply opened it completely so the boost jumped directly from +9 to +12 and the cut-out gave direct control over throttle valve to regulate the boost also between +9 and +12.

The bit about the gate during combat is pure speculation based on the original hypothesis If the highest useable boost is available on the normal throttle handle traverse and there is a gate, pilots would tend to go through the gate to ensure they have the maximum available, even if their height meant that the post gate throttle traverse had no effect. Subsequently they would refer to "going through the gate" to get combat boost, which does crop up in combat reports.

Cheers, camber

I'm wonder as well why some pilots called it "going through the gate". If my theory above is correct the pilots could use both methods if they simply wanted maximum boost but had to used the cut-out if they wanted +10 or +11 boost.

Or maybe this is simply referring to earlier engines and it had became a common sentence that was used even if it was technically wrong.