On Thu, 7 Apr 2005 19:16:08 +0100, Vivian wrote in message
> Andy Ross wrote
> > 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.
..how about solving for idle static thrust?
> Unfortunately, the Hurricane had/has automatic mixture control!
..??? The only ones I'm aware of had such fancy gear, is the Axis side,
look for "kommandogerat", was used in all frontline piston powered WWII
> > 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...
> That would be good ... if we knew or could deduce the HP. Meanwhile,
> it's quite easy to tune the minimum output using the so called 'magic
> > 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.
> Working on it right now. BTW the Merlin had a Roots type displacement
..this is the big ass clutch-housing-and-gearbox like thing down the
rear end of the Merlins?
..ahem; http://www.enginehistory.org/merlin_xx.htm , specificly
..looks centrifugal, no? ;o)
> I'm looking at some representative pressure ratio curves
> wrt rpm. I'm testing out a supercharger which varies output with
> engine rpm, modified by throttle.
> > > 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?)
> The property is bound to the variable _mp, while the wastegate is
> applied to the variable mp. If the property is bound to mp, it gives
> the right output. The problem is entirely in the binding - the turbo
> code works correctly.
..med vennlig hilsen = with Kind Regards from Arnt... ;o)
...with a number of polar bear hunters in his ancestry...
Scenarios always come in sets of three:
best case, worst case, and just in case.
Flightgear-devel mailing list