> On Thu, 2005-04-07 at 17:36, Erik Hofman wrote:
> >
> > Yes, the C172p. At least and the F-104, F-15 and F-16 are based on
> > windtunnel data. The T-37 is partially based on flight test data.
> > And Both the Fokker 70/100 and Fokker 50 use available data where possible.
> >
> > None of them are extensively validated though (although I do trust the
> > windtunnel and test-flight data).
> >
>
> Now, maybe I was trolling a bit when I started this, but replies like
> this (and Curt Olson's) make it seem quite worthwhile!
>
> I'd never been able to find any claims on accuracy of FlightGear's FDMs;
> not from the FG website, the FAQs nor trawling the devel-list archives.
> And yet, here it is!
>
> Surely someone ought at least to mention this level of FDM fidelity on
> the FAQ? It could only help increase FG's street-cred.

Hi, Steve:

Building an acceptable flight model is not too terribly hard if you stick to 
it. Building
a really good, high fidelity model is also not too hard if you have the right 
data on hand
or know how to derive it.

The sim I work on in my day job takes fidelity to pretty extreme lengths:

- modeling landing and rollout on a runway where the edges of the runway are 
modeled,
various runway conditions are modeled, etc.
- the aero tables are printed in two volumes, each about four inches thick.
- the engineering sim I work on was used by others to "re-enact" the shuttle 
Columbia's
last entry, and the results used to determine when the aero coefficients began 
to diverge
from nominal.
- etc.

It's a very high fidelity space vehicle simulator.

Andy is right about using aero coefficients from flight test data to model 
flight
dynamics - you often can't get it (at least easily) and you have to know what 
you are
doing, and what the test conditions were. Nevertheless, all military and space 
real-time
simulators that I am aware of use the coefficient build-up technique to do 
flight modeling
because it affords the best way to match actual flight dynamics.

Now, with that said, I have tried for a couple of years to put together enough 
information
to model a B-17G. I have not found any good aero data on that aircraft, 
although I am SURE
it must exist somewhere (probably in Boeing's archives!). There are other ways 
to derive
that information, and tools are being built to make that task MUCH easier and 
more
accurate. Stay tuned. Check out the JSBSim newsletters on the JSBSim web site 
for more
information on our approach (www.jsbsim.org).

Jon
--
Project Coordinator
JSBSim Flight Dynamics Model
http://www.jsbsim.org


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