Re: [Flightgear-devel] JSBSIm, aeromatic, crosswind taxiiing, et cetera

[Jon S. B. <jon...@co...>]

> From: John Denker [mailto:js...@av...]
> 
> On 06/19/2011 06:46 AM, Jon S. Berndt wrote:
> 
> > Maybe I've gone wrong somewhere here, but something similar might
> work.
> > Also, in situations like a flat spin or tail slide this probably
> falls
> > apart!
> 
> Let's postpone discussion of exotic flight conditions such as flat
> spins and tail slides.

John,

I agree, but the comment I made was more of a disclaimer than anything.

> The value of these features can hardly be exaggerated.  For example,
> according to page 4-3 of the POH the "maximum demonstrated crosswind"
> for a C-172 is 15 knots.  It is important for pilots to know what
> happens if they use soft-field takeoff procedure with a 15-knot
> crosswind.  We do not want them to discover this the hard way, in a
> real airplane.  It would be extremely valuable to have a simulator
> that faithfully models the real behavior.
> 
> Et cetera.  For more perspective and motivation, see appendix below.
> 
> Returning to the technical issues:  AFAICT the most fundamental issues
> are not "JSBSim" issues strictly speaking, but rather aeromatic issues.

I agree, again. One problem with having a tool such as Aeromatic is that
some people use it to generate the template and then don't modify it.
Ideally, Aeromatic would be modified to produce better output in these
circumstances. I might look into that at some point, but I'll need to find a
26 hour day lying around somewhere... ;-)

> Another constructive suggestion:  While we are reorganizing the
> aircraft.xml file, we should get rid of the notion of "lift due to
> alpha" et cetera.  I suggest a more faithful model would work with
> things like "force due to wing" and "force due to elevator".  As a
> first step, compatible with the existing approach, we can treat the
> wing as a whole.  Then, later, as a second step we can model the
> wing in four parts:  port outboard (with aileron), port inboard (with
> flap), starboard inboard (with flap), and starboard outboard (with
> aileron).  This is AFAICT the only reasonable way to model the effect
> of flaps near the stall, the effect of flaps in inverted flight, the
> loss of aileron authority near the stall, et cetera.  It is also the
> only reasonable way AFAICT to model swept wings.

There is soon going to be a donation of JSBSim code mods that *may* be
useful in implementing this approach. Stay tuned.

> I would be happy to discuss the details with anybody who wants to
> contribute in this area.

If you do a writeup for this, it would be helpful.

Jon