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Ricardo2696

Xplane flight model limitations

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Yesterday i read a comment of a developer complaining about xplane´s flight model. He said, i quote " XP flight model is not "excelent", actually, it's bad and have alot of errors and bugs. It's not possible to properly model an aircraft aerodynamics in transonic region, only using a huge hacks. It's uncontrollable (not enought parameters to fit actual aircraft) and nonisolatable (to use it in engeneering software). (....)  A huge fake pitching momentum proportional to CG shift and aircraft weight is added continiously all the time. Instead of computing total reaction forces from gears on ground, he simply add's this fake momentum to produce different gears loading with different CG shift. "

Do you guys from the IXEG team think the same? whats your opinion in this topic? 

I posted this same thing in the xplane 11 forum to get answers from the devs and try having a healthy conversation but it got deleted because it was seen as "trolling" by a moderator for some reason. Hope you guys can give me an answer :) 

Thanks

Ricardo

Edited by Ricardo2696
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The short answer... nonsense.  If he is taking X-Plane/Planemaker "out of the box, as is" - which it might seem he is - there are limitations, simplifications and bugs, this is true. But it is in no way "bad".  However, serious design teams  "bend" the flight model in some areas to fit their aircraft using plugins, so in theory you can do almost anything by reverse engineering and programming like we do on the 737.  So it is in no way impossible, but you off course need to know what you are doing.  About "fake pitching" moment and CG, I'm not sure I understand what he is talking about, but X-Plane uses Radii of Gyration for momentum calculations.  He might have missed that.  It is just not practical or realistic for any normal XP aircraft designer to know how much each aircraft part weighs, it's distribution/density etc.  Only the manufacturer of the aircraft will know that, and all aircraft are different.

Should he have documentation for what he believes is off, the great thing about XP is that we can always discuss this with Austin (we do it often) and have it corrected fairly soon if we can prove it.  X-Plane' flight model has been in development for some 20+ years, during this time hundreds of engineers have been working on improving it, and we will continue to do so :)

 

 

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The ixeg 737 is clearly one of the best aircraft ever made for any flight sim so i really value your opinion, thank you so much for answering!

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The dev in question is assert of FlightFactor. He said that as the reason/justification for making an external flight model for their a320. As he believes that they cant accurately make an a320 flight model with the built in tools, I believe same with the 737. 

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6 hours ago, snapshot21 said:

The dev in question is assert of FlightFactor. He said that as the reason/justification for making an external flight model for their a320. As he believes that they cant accurately make an a320 flight model with the built in tools, I believe same with the 737. 

Well, I guess we have proven it IS possible (we can document it off course), although parts of ours is also "external" like the engine model and some other parts that are "modified".  We spent about 6 years on our flight model, so it has not been a trivial task - but worth it. They choosing a different route is off course up to them, but just because they did not succeed does not mean that others can't!  Not sure what they did, but I suspect it is highly table based since from what I understand it is ported from some other sim, and table based flight models have their share of weaknesses. In a way you could say we (IXEG) takes the best from both worlds. Also, on an A320 - that uses FBW (artificial stability and augmentation) - that you hardly ever fly in direct law, the dynamics are not as important from pilot or engineering perspective anyway as it is on a classic Boeing without FBW where you fly hands-on in "direct law" a lot of the time.

But I wish them good luck, a great A320 finally would benefit XP a lot and attract more users from the other sim's :)

M

Edited by Morten
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