Lane, that is a nice diagram showing the cable connection from red tab to the boost cutout override (no wonder it is invisible in flight sim cockpits considering where it sits!) The mechanical connections go to the control bar on the other side of the firewall that connects to the differential gear (and then on to the real carby throttle) but this is not shown.
Sutts, I would think that on the Merlin XII in Spit II rated for 100 octane, the highest boost allowed by the boost regulator setup (boost cut off red tab = OFF) would be +9psi. But with the variable aneroid in the boost controller (an improvement available by the Merlin III), the pilot can advance throttle to any boost under +9psi and the system will maintain it there as you climb. So if you have filled up with 87 fuel after landing at a station without 100 octane, you must be careful only to pull 7psi on the hand throttle. Otherwise the engine will probably let you know!
If you push the red tab (boost cut off = ON) you have access to +12psi (provided altitude is low enough that the supercharger can actually achieve it). With 87 fuel this would also be a very bad idea but nothing would stop you from doing it (except a desire to keep being a fighter pilot).
The thing that still confuses me is that the Spit II also has a throttle gate that allows "take off boost" of +12.5psi that is only supposed to be for taking off from small fields or overloaded. I'm not sure why both systems (boost cut-off red tab, throttle gate) need to be there at the same time.
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01-16-2012, 11:48 AM
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