Andy Ross said: > Jim Wilson wrote: > > It'd be great if someone else could look at the P51D fdm. I'm > > lost. Flight dynamics is neither my area of expertise or > > interest. The only reason I did it in the first place is I had a > > 3D model that Jon supposedly had a JSBsim config for that never > > materialized. > > > > In short, the major issues are with the propeller rpm (as Vivian > > noted) and probably more significant, the thing still flys like > > it has the glide ration of a 30m soaring plane. Any help is > > appreciated. > > OK, I'll give it a shot. Most of your problems are due, I > suspect, to the manual propeller stuff. This gets tricky: I > notice you used a "maximum/fast" propeller pitch for the cruise > solution, which is presumably a maximum level speed value. But > 380 knots at ~1300 RPM is actually a very *low* advance ratio, > and requires a coarse pitch, not a fine one. Add that to the > fact that YASim allows for a non-physically large range of pitch > travel and things can get wacky. > > An automatic pitch governor takes care of this for you, but for a > manual lever you're stuck doing all the tuning. Maybe a good > idea would be to export the equivalent manual settings as a > property from a governor, so you could lift values from there... > > The issue with the glide ratio may be due to bad data. You have > the cruise value at 380 (195.5 m/s) ktas and ~1300 > horsepower (968500 W). With those values, the Mustang is being > forced by fundamental physics to cruise on just 1100 pounds of > thrust (4953 N). For an aircraft with an weight of 8000 pounds, > that's *really* slick. > > Could a production mustang really cruise at 380 knots with 50% > fuel, or is that more of a theoretical maximum and/or record > attempt made with a stripped aircraft? (To the peanut gallery: > please don't tell us all about the oil cooler again. :)) > > I played with Vivian's number for the spitfire, and they came out much > saner; with about double the drag coefficient. >
You can see that I was pretty much fumbling around with this one! Anyway, I'm not sure if this is where I got the numbers or not: http://aeroweb.brooklyn.cuny.edu/specs/northam/p-51d.htm That 380kt figure is probably with the manifold pressure set to "war emergency"...everything maxed out for up to 7 minutes. What is more of an issue I think is operating ceiling (which is probably what prompted me to put some of those whacky values in). The 43,000 ft is a bit suspect, for anyone sane that is, but AFAIK 30,000ft at somewhere around 400mph (not knots) should be expected. To the best of my knowledge, there is no production propeller aircraft (turbine or piston) that is faster than the P51D. Also note that the cockpit indicator on this model is in MPH not kts. Best, Jim _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
