Re: [Jsbsim-devel] IC vcas

[Bill G. <bi...@be...>]

 

> -----Original Message-----
> From: David Culp [mailto:dav...@co...] 
> Sent: Thursday, May 12, 2011 2:27 PM
> To: jsb...@li...
> Subject: Re: [Jsbsim-devel] IC vcas
> 
> On Sat, 7 May 2011 16:50:38 -1000
> dpculp <dp...@gm...> wrote:
> 
> > I'll run more tests when I get back from vacation.
> 
> 
> Test 1:  Starting FlightGear with --altitude=3000 --vc=300
> result:  Aircraft starts flying backwards, sideways, and tumbling
> 
> 
> Test 2:  Starting with --prop:/sim/presets/altitude-ft=3000 and
>          --prop:/sim/presets/airspeed-kt=300
> result:  Aircraft starts flying forward/sideways
> FGIC: vcas: 300 , Mach: 0.477795 , vt_fps: 527.818
>       alt_ASL: 3000 , SAT: 507.972 , Sos: 1104.69
> FGAux: vcas: 236.417 , MachU: 0.223568 , vt_fps: 527.818
>        alt_ASL: 3000 , SAT: 507.972 , Sos: 1104.69
>        VAeroUVW: 246.975, 466.467, 1.8277
>        Mach: 0.477795 , mUW: 60999.9 , pt: 1963.95
>   Sorry, udot doesn't appear to be trimmable
>   Trim Results: 
>        Angle of Attack:    3.1  wdot:  2.46e-05 Tolerance: 
> 1e-03  Passed
>               Throttle:    0.5  udot:  1.23e+02 Tolerance: 
> 1e-03  Failed
>             Pitch Trim:  -0.19  qdot: -8.73e-12 Tolerance: 
> 1e-04  Passed
> 
>   Trim Statistics: 
>     Total Iterations: 4
>     Sub-iterations:
>     wdot: 11 average: 2.75  successful:  1  stability: 8.2222
>     udot: 0 average: 0  successful:  0  stability: 29.375
>     qdot: 8 average: 2  successful:  4  stability: 2.9333
>     Run Count: 662
> 
> *********************************************
> 
> This may be a FlightGear/JSBSim interface issue only, so 
> unless someone gets similar results with JSBSim stand-alone 
> I'll drop the issue for now.
> 
> 
> Dave


I set up a test with the C172x model. All it does is start the engine
in-air, trims, and runs for 1 second to verify that it is trimmed. It claims
to trim, but it doesn't really trim. When released from trim, it pitches up
3 degs in the first second. Engine looks to be fairly steady, as well as
other parameters. Have used the same test with my Citation jet-powered model
and it worked fine. I'll have to think on this some more later on why it
fails, but thought I'd offer up my findings and my test technique.

Unzip the attached file under the JSBSim/aircraft/c172x, and execute the
following command:

	JSBSim --scripts=aircraft/c172x/scripts/trim-cruise.xml

Bill