I wrote:

If you're doing a non-derivative
design and want some hope at all of being close...

smjmitchell ...

I agree there is no way that you can accurately
simulate the behaviour of an airplane without
the use of derivatives.

If your statement above was in respose to my
"non-derivative" statement, I wasn't referring
to stability derivatives, I was referring to a design
that's derived from a prior design, i.e. evolutionary.
Accurate simulation without the use of stability derivatives
is easy if you have estimated aero data. Dynamic derivatives
make it easier, but often times damping derivative estimates
are so inaccurate you might as well not use them anyway.

But having said all this, a simulation of a lightplane-envelope-type
airplane is not required before building one. Personally
I'd spend the time trying to get good aero estimates
or hard data (truck testing, R/C, etc) than in tweaking a
sim...and you need the hard data to do real tweaking anyway.

For home-design type stuff I use a CAD package(*) - designCAD right
now, but I've been know to use AutoCAD. Aero analysis is back-of-the
envelope. Structures so far is TLAR, but before I cut metal I
will have a professional FEA done by a non-advocate. I haven't
gotten to the engines yet :-)

The stuff I use at work is a little more detailed and somewhat
more accurate (and far more specialized), but the results are
usually pretty close to the home-done level stuff, which is
where we start anyway.

(*) and I barely scratch the surface of its capability.

Dave 'engineer, professional and amateur' Hyde