Black 6 Thu 19th Apr update re Spit II

[camber]

Hi all,

This previous thread has a lot of hashing out of the mechanics of boost control in Merlins:

http://forum.1cpublishing.eu/showthread.php?t=29031

A quick summary of what I concluded from the discussion:

* The Merlin (e.g. III) has a mechanical supercharger, which can deliver about 20psi boost at sea level (predetonation, power loss and engine damage will result even if 100 octane fuel was used)

* The early boost controller limits boost to +6 1/4 psi, by altering the mechanical relationship between the pilot's throttle handle and the actual throttle plate just before the supercharger. The original red tab pulls a cable which alters air channels in the controller and gives full throttle control back to the pilot, in case of controller malfunction.

A careful pilot could pull the red cutout, get full throttle control and manually "sneak" the throttle up to true maximum power (i.e just before predetonation drops it again), at some risk to the engine.

* With 100 octane the boost control system was modified with extra drilled air channels that made the red tab not a true boost cutout, but instead increased the boost pressure setpoint to +12psi when activated.

There is a second method of boost override possible, the gate system which appears in the Spit II. Instead of a pressure setpoint increment, this gives a maximum throttle position. (E.g you can have 75% throttle even if the resulting boost is greater than the controller setpoint). So it is useful to give a set higher boost at sea level which will decay as altitude increases (i.e "take off boost")

There is no problem with having both systems at once, I did not understand the system well enough to work out effects of activating both at once!

camber