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Jim Sower <canarder@frontiernet.net> wrote:
<... That ambient pressure outside certainly needs to be accounted for ...>
OTOH, the back-and-forth between Rusty and I and others seems to indicate that 5 or
6 psi (or 10-12 in Hg) is all the boost anyone will reasonably need. So a popoff
valve set for 5 psi and forgotten would allow us to take off with 35" (in the
unlikely event we needed that much power) and turbo normalize to 15 k ft so it
would seem that a really dumb popoff valve would work OK.<<<
That's true provided you don't have a problem with the potential 40" MAP you could get on a std sea level day... the popoff's whole purpose is to limit MAP to some reasonable MAP redline. If the possibility of hitting 40" is acceptable to you I suppose it would be ok. Alternatively, I also like the idea of using a simple pressure switch to sense MAP, set to go off an inch or two MAP less than your redline... hooked to big red light on the panel when you see it you ease back on the throttle. The set-and-forget throttles we have on the big Continentals and Lycomings incur all the expense and complication of a slope controller and an oil-pressure-driven wastegate actuator. If you're willing to live with a little more workload and the responsibility of maintaining MAP below redline through diligent piloting, you could probably do away with the wastegate and popoff entirely. Run all the exhaust through the turbo, be gentle with the throttle, pay attention during descents to maintain your chosen MAP and you would be just fine. Just another thought.
<Marv>
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