The Technology of X-Plane

[28sweep]

So I'm reading a lot about this sim. Seem's to be getting a lot of attention these days.  So I am an Engineer but it's been a while since I took Fluid Mechanics so forgive the following: so as I understand  the flight models in X-plane work opposite to AH and other sims.  In X-plane u define the shape of the air foil-for example- mass etc. and X-plane does the integral calculus necessary in real time to dynamically "react" to the air plane as it is flying-just like the real thing.  I guess in AH u program the airplane to move for example: at x speed for y altitude w/ z roll rate.  I have heard that the sim. is ground breaking and in fact the USAF has bought licenses for training purposes.  It seems like a sim. engine like that would be way more accurate and subject to less subjectivity.  No expert here but any comments would be appreciated......I guess the reason for this post is the differences in flight models that I have encountered from sim to sim has been astonishing.  Roll rates...stall's etc. are all different and subject to a lot of interpretation...The X-plane engine would solve all of that......

[Wotan]

deezcamp I knew it........

[Toad]

Wotan, you have been charged with deliberately and with malice aforthought  inducing BBS readers to spray "nostrilized coffee" on their monitors.

How do you plead?

[straffo]

Guilty I guess ...



I'm cleaning my desk currently ....

[Hristo]

"define the geometry and x-plane will figure how it flies"

Hmmmm, without any hidden agenda, this little thingie is very tempting to a physics freak. Still, obtaining accurate geometry data to an ordinary flightsim enthusiast is practically impossible. What, do I have to close measure my 1/48 models ?

You mean atmospheric/power curves are modeled too ? All those things characteristic for one model but not for another ?

With everyday work with CAD/FEM programs I know a lot is possible, but there is that GIGO approach too (Garbage In Garbage Out). In the end you end up with curves again. The difference is you went a hard to way to get them, while the usual way is to gather them from flight test data.

Think again what would it take to figure out roll rate at 13,500 ft while flying at 300 IAS. The usual way would be to interpolate, I guess. With X-plane approach, you'd have to know the exact linkage between control column and ailerons, friction etc etc - only to end up with curve that may or may not be close to an interoplated one.

A brave and noble effort, but applicable to our flightsim market ?

[Zigrat]

if you think anything can calculate the flowfleld around a configuration in real time you need to stop smoking the crack pipe.

[28sweep]

apparently it uses some method of picking 8 points on the gemotry of the airplane to aprrox. these calculations......

[Pongo]

8 points out of the infinite number that there are..
not very high fidelity.

[Chairboy]

It's of higher fidelity then the lookup tables AH  uses.

X-Plane DOES model the airflow around a set number of points in realtime.  Each plane has the airfoil specified as a mathematical formula (it has a library of NACA airfoils as well as a number of custom ones) and it performs a laminar flow simulation along X points on each control surface.  

The wings, stabs, fuselage, even gear doors are modelled.

In response to a snarky comment above, yes, it  does have what it takes to figure out the roll rate at 13,500 ft while flying at 300IAS.  Air density is integrally modelled.

The FAA has approved the use of X-Plane time to count as hours towards commercial airline transport certification.

As for hardware support, it outputs data to everything from full motion-control simulators to aircraft instrumentation you can use to build your own cockpit.  It's easy to write drivers for because it outputs everything via a documented UDP interface, so you can even set up multiple computers to interface w/ and run hardware for your simulation (as well as drive extra monitors).

I find it quite humorous how easilly people crap on the simulator without even bothering to visit the website or try it out for themselves.  It's a free flight-time-limited download, for goodness sake.

x-plane.com

[sling322]

Heh...first word that flashed thru my mind when I saw this was "DeeZcamp"  

But then I read Chairboy's post and decided that 28sweep aint DeeZCamp....Chairboy is.  

[Upchuck]

It's using more than 8 points for the whole plane.  The 8 points is per flight surface, and if I'm not mistaken it also allows more than 8, up to around 10 or 12 separate points per flight surface.  The flight surfaces that are included in these calculations are the wings (more than 2 are allowed), stabilizers, propellor blades (more than 4 are allowed) and the fuselage.  There might even be more surfaces included now.  It's been a while since I've played around with X-plane.

It's based on the concept that the difference between calculating the overall effect of the entire flowfield for essentially an infinite # of points and calculating the lift moments for roughly 10 separate points is negligible.  When you consider that calculating the whole flowfield across an infinite # of points is, as has been pointed out,  impractical, as well as the fact that the value obtained from calculating it across roughly 10 points is essentially 90-95% as accurate, which are you going to use?

Atmospheric data is used.  In fact, X-plane not only allows you to fly on Earth, but you can also design and test fly aircraft for flight on Mars, using data for gravity and atmospheric pressures (at various altitudes) etc. as measured by NASA probes on Mars.

X-plane doesn't include stick forces and mechanical friction etc. in it's simulation.  If you ask me that's not all that necessary.  If, however, you want it I'd double check with Austin Meyer, the maker of X-plane, to be sure it couldn't be added.  He's very responsive to user input and requests.

X-plane has been used by more than one company, currently and in the past, as the primary preliminary test bed for design concepts and test flying an idea before you put up the $ to actually build one.  How many folks have done that with Aces High, Warbirds, WWIIOL, CFS, AirWarrior combined?  Answer = none.

Don't knock X-plane until you've tried it.  At least go check out the website and download it.  You can fly for free, for 5 minutes.  After 5 minutes flight control input is ignored, but you can still have some control with the trim etc.

[sling322]

I take that back.....Upchuck is DeeZCamp.

[GRUNHERZ]

"if you think anything can calculate the flowfleld around a configuration in real time you need to stop smoking the crack pipe."

Did you lift that out of some Star Trek episode Zigrat?

edit:

Deezcamp I never gave you a hard time about your x-plane enthusiasm but this is getting a bit desperate and alltogether wierd. Sorry...

[Toad]

Does it have X-Guns on the X-planes yet?

Is it MMOG?

Can I dance the skies on flowfield modeled wings while engaging and killing others that are attempting the same feat?

[hitech]

Did Xplane change any in the last year in the way it calcs things?

If it hasn't it is not doing any thing magic, it's just calculating AOA at a given number of sample points. It's basic input is not shape but normal NACA airfoil numbers, These out put lift, drag ,Cm ,CP tables, which it then uses for it's real time calcs.

Now look for detailed engine modeling in it.

There hype is much overstated to how there plane setup works.