Vivian Meazza wrote:
> However (and there's always a however), I can't land the
> thing. Closing the throttle and pulling back the propeller pitch
> control doesn't reduce the power enough. I reasoned that there was too
> much boost with the throttle closed, (currently set at 10%,
> AFAICS). 10% of the supercharger output at sea level before the
> wastegate is a big number

Yeah, that's a good point.  The idle tuning of the engine was done
before turbocharging was added, and doesn't really map well to the new
regime.  As a near-term workaround, you can always pull the mixture
way back to reduce power to near-zero.

I'm wary of adding a magic number to the configuration files for this,
though.  I wonder if there's a saner way of calculating an appropriate
idle power dynamically from the input values...

A related issue that stands to be fixed is that the current code
doesn't really model a gear-driven supercharger properly.  With a
centrifugal compressor like this, the output pressure gain is a direct
funcition of RPM.  The existing code tries to model an exhaust-driven
turbo charger by simply multiplying the input MP by the turbo-mul
factor, which isn't the same thing.  The behavior will match at
maximum power output, but be off in the middle and at the low end.

> One other 'however': the property mp-inhg seems to be bound to the
> supercharger output before the wastegate is applied.

Really?  PistonEngine.cpp:112 looks like it is setting the current MP
based on the turbo output.  Maybe there's a different bug somewhere
(units conversion, maybe?)


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