> -----Original Message----- Jim Wilson wrote:
> 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 > These data seem fairly authoritative P51D Mustang 7125lbs W_gross= 10,100 W_max(with 489 gals of fuel)= 11,600lb Performance: max = 437mph at combat emergency power at 25000ft, 413mph at 15000ft, 395mph at 5000ft, cruising speed 362mph, climb rate 3475 ft/min. Service ceiling 41,900ft. (source:Profile Pub No 8 P51D Mustang) Typhoon Ib W_empty = 8840 W_gross = 13,250lbs Performance: max = 412 mph at 18,000ft. Service ceiling 35200ft (source: Aeroplane June 2004) Hope this helps Vivian _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
