Thread: simulators
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Old August 2nd 03, 02:30 AM
Jon Berndt
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Default simulators

"Peterson, David" wrote in message

I haven't tried it yet, but there is a program called X-plane that
allows you to fly the shuttle. There is an article about it in Popular
Science this month. This simulator attempts to calculate aerodynamic
forces in real time and you can enter your own designs.


Well, pretty much all game-type consumer flight simulators I know calculate
aerodynamic forces (and moments, too!) in real time. The thing with X-plane
is that the total aero forces and moments are not calculated by classical
techniques of using coefficients and stability derivatives to build up those
forces and moments, but instead using something I think he has called "blade
element theory" - which I have always heard as relating to propeller theory.
In any case, the approach splits up the aircraft into parts - the wing into
parts spanwise, the rudder and elevator into parts, the fuselage, etc.
Then, the local condition at each part is used to calculate the forces and
moments on the whole. There's a LOT more to it than that, but that's the
general idea. I think that approach (if done well) can lend itself to
providing decent results in normal flight regimes, and plausible results in
off-nominal conditions. But, I have a hard time believing it can do better
than using actual flight test data and using the classical approach. But, in
the case where you have no flight test data, it's a bit of work to come up
with good estimates for aero - and very difficult or impossible to come up
with plausible results for the off-nominal conditions. So, the X-plane
approach whereby aero is calculated based on geometry has an advantage in
that it is much easier to enter geometry data than to go off and calculate
aero coefficients for a given aircraft.

I have been a developer in the FlightGear (www.flightgear.org) project for
several years, providing what is currently the default flight dynamics
model, JSBSim (www.jsbsim.org). We use the classical approach. There is
another flight model you can select when running FlightGear called YASim
(don't ask where these names come from ... long story). YASim uses an
approach very similar to X-Plane. However, our sim runs on Linux, IRIX,
Mac, and Wintel machines.

The amazing thing is one guy in South Carolina wrote the whole program.


Austin has done some good work, but from what I understand his hype exceeds
even the good work he has done in producing X-Plane (notice how many
exclamation points he uses). When he posted his shuttle FAQ I had to laugh
a little. I sent him some corrections. I think he implemented most of
them. IIRC, someone else wrote the FAQ for him.

Anyone have experience with this program? Any good?


I haven't used it, but from all accounts it's pretty good. I wish someone
would pay me to write simulation code all day.

Oh, wait. They do.

Jon