On Fri, 2002-04-12 at 12:08, Michael Selig wrote: > At 4/12/02, you wrote: > >Michael Selig writes: > > > > > OK, I think I am just getting confused trying to decipher *all* parts of > > > what you are doing in those files. It's like a puzzle to me. > > > >The JSBSim files can be overwhelming -- they were far worse for me, > >with no background in aerodynamics (or even physics, for that matter) > >-- but the top-level arrangement is very simple and similar to UIUC's. > >There are six top-level sections: > > > >1. METRICS (= UIUC "geometry" and "mass") > >2. UNDERCARRIAGE (= UIUC "gear" ??) > >3. PROPULSION (= UIUC "engine") > >4. FLIGHT_CONTROL (= UIUC "controlSurface") > >5. AERODYNAMICS (= UIUC "CL", "CD", etc.) > >6. OUTPUT (= UIUC "record") > > > >The AERODYNAMICS section contains six AXIS subsections: LIFT, DRAG, > >SIDE, ROLL, PITCH, and YAW. Inside each of those subsections are > >definitions for all the coefficients that act on that axis. JSBSim > >seems more complicated only because it lets you define new > >coefficients are runtime, rather than hardcoding them in the C++. For > >example, where UIUC has simply > > > > CL CL_adot 1.7 # [/rad] FG c172_aero.c > > > >JSBSim has > > > > <COEFFICIENT NAME="CLadot" TYPE="VALUE"> > > Lift_due_to_alpha_rate > > FG_QBAR|FG_WINGAREA|FG_ALPHADOT|FG_CI2VEL > > 1.7 > > </COEFFICIENT> > > > >The JSBSim C++ code doesn't actually know anything about CLadot (we > >could have called it "CLfoobar" if we had wanted), but the effect is > >the same -- both examples contain exactly the same aerodynamic > >information. > > > > > >All the best, > > > > > >David > > > Ahhhhh ... thank you ... I see it now. The fact that "CLadot" gets > included on the fly is pretty neat. As our list of hard-coded coefficient > capabilities grows longer and longer w/ the uiuc_ code, we've been seeing a > need for something like this.
I should have also pointed out that you can view the loaded coefficients via the property browser, look under /fdm/jsbsim/aero/buildup and you can also apply a gain or bias to each coefficient, also via the property picker. e.g. if you think the c172 has too much longitudinal stability you might use the property picker to set the gain on Cmalpha to 0.8 or whatever. > > I now see the need to include the foobar string > "FG_QBAR|FG_WINGAREA|FG_ALPHADOT|FG_CI2VEL" together w/ XYZfoobar? It > includes all the things multiplying the foobar coef. > > For the Pioneer nonlinear model, we have 1605 lines of lookup data: > [297] > m-selig@qtee:/home/m-seligSim/work/fgfsbase-0.7.9/Aircraft/UIUC/pioneerUAV-v2-nl> > wc -l *.dat > 210 aircraft.dat > 28 CDfa.dat > 244 CDfade.dat > 155 Clfada.dat > 28 CLfa.dat > 244 CLfade.dat > 28 Cmfa.dat > 201 Cmfade.dat > 197 Cnfada.dat > 254 Cnfbetadr.dat > 16 CYfbetadr.dat > 1605 total > > For our Twin Otter we have 14,000 lines of nonlinear aero data: > [331] > m-selig@qtee:/home/m-seligSim/work/uiuc-aircraft/011112-TwinOtterNonlinWithFlaps> > wc -l *.dat > 236 aircraft.dat > 298 Clfabetaf0.dat > 298 Clfabetaf20.dat > 298 Clfabetaf40.dat > 326 Clfadaf0.dat > 326 Clfadaf20.dat > 326 Clfadaf40.dat > 126 Clfadrf0.dat > 226 Clfapf0.dat > 226 Clfapf20.dat > 226 Clfapf40.dat > 154 Clfarf0.dat > 154 Clfarf40.dat > 276 Cmfabetaf0.dat > 276 Cmfabetaf20.dat > 276 Cmfabetaf40.dat > 151 Cmfadef0.dat > 151 Cmfadef20.dat > 151 Cmfadef40.dat > 155 Cmfaqf0.dat > 155 Cmfaqf20.dat > 155 Cmfaqf40.dat > 276 Cnfabetaf0.dat > 276 Cnfabetaf20.dat > 276 Cnfabetaf40.dat > 326 Cnfadaf0.dat > 326 Cnfadaf20.dat > 326 Cnfadaf40.dat > 126 Cnfadrf0.dat > 226 Cnfapf0.dat > 226 Cnfapf20.dat > 226 Cnfapf40.dat > 154 Cnfarf0.dat > 154 Cnfarf40.dat > 276 CXfabetaf0.dat > 275 CXfabetaf20.dat > 276 CXfabetaf40.dat > 201 CXfadef0.dat > 201 CXfadef20.dat > 201 CXfadef40.dat > 155 CXfaqf0.dat > 155 CXfaqf20.dat > 155 CXfaqf40.dat > 276 CYfabetaf0.dat > 276 CYfabetaf20.dat > 276 CYfabetaf40.dat > 326 CYfadaf0.dat > 326 CYfadaf20.dat > 326 CYfadaf40.dat > 126 CYfadrf0.dat > 226 CYfapf0.dat > 226 CYfapf20.dat > 226 CYfapf40.dat > 154 CYfarf0.dat > 154 CYfarf40.dat > 276 CZfabetaf0.dat > 276 CZfabetaf20.dat > 276 CZfabetaf40.dat > 151 CZfadef0.dat > 151 CZfadef20.dat > 151 CZfadef40.dat > 155 CZfaqf0.dat > 155 CZfaqf20.dat > 155 CZfaqf40.dat > 14443 total > > The point - are plans underway to have JSBSim include nonlinear aero data > via path/filename, rather than including all that nonlinear data in the > single xml file? > > Also, does JSBSim accept aero data in the body axes as well as the > stability axes? > > Can JSBSim do 3D interpolation for, say, data as a function of angle of > attack, sideslip and flaps? We have this in our Twin Otter setup, for example > 276 CYfabetaf0.dat > 276 CYfabetaf20.dat > 276 CYfabetaf40.dat > decodes to > CY as a function of alfa, beta & 0, 20, and 40 deg flap (fabeta + f0/20/40) > > Thanks, > Michael > > >-- > >David Megginson > >[EMAIL PROTECTED] > > > > > >_______________________________________________ > >Flightgear-devel mailing list > >[EMAIL PROTECTED] > >http://mail.flightgear.org/mailman/listinfo/flightgear-devel > > > > ************************************************** > Prof. Michael S. Selig > Dept. of Aero/Astro Engineering > University of Illinois at Urbana-Champaign > 306 Talbot Laboratory > 104 South Wright Street > Urbana, IL 61801-2935 > (217) 244-5757 (o), (509) 691-1373 (fax) > mailto:[EMAIL PROTECTED] > http://www.uiuc.edu/ph/www/m-selig > http://www.uiuc.edu/ph/www/m-selig/faq.html (FAQ) > ************************************************** > > > _______________________________________________ > Flightgear-devel mailing list > [EMAIL PROTECTED] > http://mail.flightgear.org/mailman/listinfo/flightgear-devel -- Tony Peden [EMAIL PROTECTED] We all know Linux is great ... it does infinite loops in 5 seconds. -- attributed to Linus Torvalds _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
