[Jsbsim-users] Stevens & Lewis F-16

[Kunz, D. L C. U. A. AFIT/E. <Don...@af...>]

I'm trying to build a model of the F-16 identical to the one in
"Aircraft Control and Simulation" by Stevens & Lewis.  Our stability and
control research will be using other aircraft, but my inclination is to
first make sure that I understand how the simulation works on a known
model.  It's also a good way to learn how to use JSBSim.  I have 3
questions.

 

1. The S&L model includes the engine angular momentum, which appears in
the EOM in the roll and yaw equations.  What I have done is include the
moment due to the angular momentum (q*Hx) in the aero yaw moments.  Does
that make sense, or is there a better way?

 

2. The S&L engine model has a state which appears in the EOM to model
engine lag.  Does JSBSim include something similar?  I'm not an engine
guy, and would rather not get too deep into JSBSim's engine model; but I
will if I have to.

 

3. Currently, my model trim solutions compare quite well with Table
3.6-2 between 200 and 700 fps (sea level, cg at 0.35*cbar).  The trim
failed at the other airspeeds, but that's probably because I only used
the default ICs.   The trim solution also matched the first column of
Table 3.6-3.  However, when I move the cg to 0.3*cbar and 0.38*cbar, the
trim solutions are way off.  The only way that I can match the trim
conditions is to multiply the cg offsets by a factor of approximately
2.66.  JSBSim should perform that transformation automatically,
shouldn't it?  Has anyone else run into a similar problem?

 

Don

 

// SIGNED //

Donald L. Kunz, Ph.D., P.E.
Associate Professor of Aerospace Engineering, AD-23
Department of Aeronautics & Astronautics
Air Force Institute of Technology
2950 Hobson Way, AFIT/ENY
Wright-Patterson AFB, OH  45458-7765
Phone: 937-255-3636 x4548 (DSN 785)
Fax: 937-656-7053 (DSN 986)