Andy Ross wrote: > > I wrote: > > Jim Wilson wrote: > > > 4) Fixed rpm/power numbers under the prop tags. They need to be > > > scaled back according to the gear ratio. Someone with a better > > > understanding of mech engineering might be able to explain why the > > > BHP on the prop shaft is reduced by a factor of 0.35 when that's > > > the gear ratio, or maybe that is wrong and there is something going > > > on in the YASim calcs. > > > > Yeah, that's a bug. Power is power. If the prop wants to sync X > > horsepower at Y RPM, then the engine ought to be defined as producing > > the same X hp at Y/gear-ratio RPM. > > > > Let me take a look. > > Indeed, there was yet another spot I missed when adding the gear-ratio > stuff. The torque conversion from "propeller side" to "engine side" > worked correctly during solution, but not at runtime. This is fixed > now, so you should be able to use real numbers in your propeller tags. > > FWIW, I also took the opportunity to re-visit the P-51D configuration > that I promised (long ago) to hack at. Attached is a version that > should perform more realistically. The biggest change is that I > reduced the cruise speed (360->310) to represent what a typical > aircraft "should" be able to achieve with 50% fuel. The resulting > aircraft is a *lot* less slick (it produces almost three times as much > parasite drag), and should perform more realistically at low > altitudes. You should still be able to hit the textbook numbers with > a stripped aircraft and empty tanks. > > Also, there is a syntax fix: the <piston-engine> tag should be a > subtag of the <propeller> tag. Putting it immediately after the > propeller definition works only due to a lucky interaction with the > way the parser stores its "current object" pointer. It doesn't clear > the value when it sees </propeller>, so you can get away with putting > the engine at any point in the file before the next tag that sets a > current object. > > I haven't flown this enough to say whether it's worth checking in. > Let me know if anyone tries it and likes it. >
I'm currently developing the YASim config for the Hawker Hurricane model. I took the P51d config and plugged in some authoritative numbers for the Merlin XX. Mirabile dictu, it worked right out of the box. The model takes off and flies well (very well, I think), with the performance closely matching the published figures. It can't quite reach the service ceiling, but perhaps the standard atmosphere ain't quite what it was in 1941, or perhaps I need to pump up the supercharger a bit :-). The wastegate opens and closes when it should, and the 2 speed supercharger works correctly. Good work, Andy. 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 - I set it 3% (based on nothing more than a WAG) and it works well. Perhaps we can make this parameter settable with a default value of 10%? One other 'however': the property mp-inhg seems to be bound to the supercharger output before the wastegate is applied. Useful for development, but not for the input to the manifold pressure gauge. Locally, I've added a parameter for manifold pressure after the wastegate. If no one objects, I can send Erik the required changes in the next week or so. Regards Vivian _______________________________________________ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
