Arnt Karlsen wrote > > > 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?
If we knew the static idle thrust that would be a good way to go. I was considering solving for idle rpm, which we do know. If I can't, Andy will come up with a way, I'm sure. > > 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 > Luftwaffe fighters. Surprised me too. Seems unlikely: the Spitfire had a manual mixture lever. I'm going by the Pilot's Notes para 19: "Throttle. The throttle lever works is a slot in the decking shelf on the left-hand side of the cockpit. The take-off position is gated. There is a friction adjuster on the inboard end of the lever spindle. The mixture control is fully automatic and there is no pilot's control lever." I can't identify a lever in any of the contemporary photos that I have access to, but I can't be absolutely certain - they are pretty blurred. Wishful thinking by the author of the Notes? Possibly, but I'm going to stick with the reference, unless anyone can come up with an amended version. > > > 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 > > number' > > > > > 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 > > compressor. > > ..this is the big ass clutch-housing-and-gearbox like thing down the > rear end of the Merlins? Yes > ..ahem; http://www.enginehistory.org/merlin_xx.htm , specificly > http://www.enginehistory.org/ModelEngines/Hares/Merlin XX/2i.jpg > http://www.enginehistory.org/ModelEngines/Hares/Merlin XX/2j.jpg > http://www.enginehistory.org/ModelEngines/Hares/Merlin XX/2k.jpg > > ..looks centrifugal, no? ;o) Yes - bit of brain fade there - I interpreted one of my references incorrectly, but on closer reading I was quite wrong. I read " 2 impellors" and assumed that meant Roots type, which has 2, but of course they are on the same shaft and centrifugal, giving 2 compressor stages. (And 2 speed, but that's another story) Thank you for pointing it out. Regards, Vivian _______________________________________________ Flightgear-devel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
