How does FSX actually create flight models?

[Guest azflyboy]

I've been fairly involved in MSFS for the last eight years or so, but I realized that I have never seen anything that explains exactly how FS uses the aircraft.cfg and airfile to create a flight model.From what I understand, the .cfg is where FS gets the basic parameters (wing area, engine data etc...) for the flight model, but I don't understand exactly what the airfile does, or how FS applies physics (since FS doesn't use fluid dynamics like X-Plane) to create the flight models.Is there something available that explains, in some level of detail, how flight models in FS work?

[Guest ExtraPilot]

You can read the paper, "AIRCRAFT SIMULATION TECHNIQUES USED IN LOW-COST, COMMERCIAL SOFTWARE," by one of the aeronautical engineers on the team; it is available on the Microsoft Web site:http://www.microsoft.com/games/flightsimul...4_zyskowski.asp

[Murmur 3,941]

>From what I understand, the .cfg is where FS gets the basic>parameters (wing area, engine data etc...) for the flight>model, but I don't understand exactly what the airfile does,>or how FS applies physics (since FS doesn't use fluid dynamics>like X-Plane) to create the flight models.The pdf linked by ExtraPilot explains it very well (see pages 5-6-7).Just a note: X-Plane actually does not use fluid dynamics (CFD), as a lot of people believe. PC's are not powerful enough to model real time fluid dynamics, and will not be for decades to say the least. Also, using CFD on a PC flight simulator would be probably overkill.Basically, the only difference between MSFS and X-Plane is that MSFS considers the aircraft "as a whole", in other words the coefficients entered in its airfiles describe the end result of the action of all the aerodynamic surfaces of the aircraft (wings, stabilizers, fuselage, etc.).On the other hand, X-Plane flight model breaks down the aircraft (wings, etc.) in many little pieces, calculates the forces and moments on each of them, then sums them up. Basically, the only coefficients it uses are the 2D Cd, Cl, Cm for the various airfoils the wings and stabilizers are made of, plus some other coefficient as fuselage drag, etc.For this reason, it is much easier to nail exactly known performance figures using MSFS than X-Plane.On the other hand X-Plane flight model is inherently a bit more versatile (can better model a wider range of aerodynamic configurations), and in some cases may have some advantages in modeling secondary aerodynamic behaviours. Marco

[Guest azflyboy]

Thanks for the replies, that link helped a lot, but it didn't really explain what the relationship is between the airfile and aircraft.cfg.The way I understand the relationship is that the .cfg contains the generic information for the aircraft, whereas the airfile contains parameters that dictate how information in the .cfg is interpreted by the simulator.Am I at all close to what the relationship actually is?

[FlyingsCool 3]

There have been lots of discussions on this subject here at avsim and elsewhere. Search for Ron Freimuth and Douglas K. for the most recent ones.Thomas[a href=http://www.flyingscool.com] http://www.flyingscool.com/images/Signature.jpg [/a]I like using VC's :-)N15802 KASH '73 Piper Cherokee Challenger 180

[Guest Ron Freimuth]

>Thanks for the replies, that link helped a lot, but it didn't>really explain what the relationship is between the airfile>and aircraft.cfg. I got your email and will explain more. For now, I'll explain aircraft.cfg vs the AIR file. MSFS used to have all the aerodynamic and powerplant parameters in the AIR file. But, wouldn't tell anything about what was in it. Figuring out the AIR file took a few years work by a dozen or so individuals. "Aired" and "Aircraft Airfile Manager" are two apps which can read and edit the AIR file parameters. Many parameters are in graphical form, some go to three dimensions. Some years ago MS started moving things in the AIR file to aircraft.cfg. Also, adding things such as electrical, that were never in the AIR file, to aircraft.cfg. One now sets some basic AC parameters in the AIR file. That includes Wing Area, Weight, Powerplant(s), fuel tanks, etc. The AIR file is still used for all the more subtle details of the flight and powerplant models. MS assumes one can use the AIR file from a similar AC and get a new AC out of it. Rarely is that satisfactory, so flight dynamics guys always set the basics in aircraft.cfg, then modify the AIR file for the specific AC modeled. Ron