On Tuesday 18 May 2004 16:45, 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
Production Typhoons could exceed 530 mph in dives, with bombs/RPs, and Tempests could overhaul V1s. I thought the Sea Fury was even faster, but I don't have a figure off-hand. LeeE _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
