Important “WARNING” about the Visual Model Origin (VMO) location

[MSFS 2020] Questions & Community Discussions SDK: Tools/Samples/Documentation
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There is an important statement in the SDK concerning your aircraft’s VMO. This statement includes a warning and may be located in a section of the SDK unexplored by some as not all developers are aeronautical engineers.

The guidance is located in:
SAMPLES, SCHEMAS, TUTORIALS AND PRIMERS/PRIMERS/FLIGHT MODEL PHYSICS/ Referential Frames And Conventions/ Aircraft Body Frame

It reads:
This frame is attached to the aircraft body. According to historical FSX conventions inherited by Microsoft Flight Simulator it is centered on the centerline chord aft of the leading edge.

The point in the model is the visual center when loaded into Microsoft Flight Simulator. The term “centerline chord” is the ¼ root chord. This is usually the exact same point in the model. By default Microsoft Flight Simulator defines the center of lift as the model’s center, which means the center of lift is (by default) defined at the ¼ root chord position.

Be careful, this is only true if the modeler did in fact set the model’s mesh origin to the ¼ root chord position! If the modeler chose for some reason to set the model’s origin at the tip of the aircraft nose, then all bets are off on the model ever being able to be properly configured…

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I would highly recommend that the above guidance is included in “How to Create an Aircraft” section of the SDK. Every developer will surely read “How to Create an Aircraft.” However, it is probably safe to say that not every developer is going to dive into the underlying physics and calculus of MSFS. Guidance on VMO location is located under “File Setup”.

It reads as follows:

  • The plane must be positioned so that top view displays the nose pointing downward.

  • The plane should be positioned in the file so that the center is approximately 1/3 of the way down the wing from the front as in the image. In the Z axis the center should be approximately where the water level would be.Approximate position of aircraft in file

  • All objects must have their xforms and transforms reset (100, 100, 100 scale - 0, 0, 0 rotation).

This appears detailed enough on the surface but the “Flight Model Physics” guidance is quite specific and mentions the consequences of not placing your VMO at 1/4 chord!

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Thanks for posting this. We also found this recently and have been considering the implications.

We’d like know from Asobo how to properly set up a helicopter aircraft, as we don’t have a 1/4 wing chord reference.

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Hadn’t considered the 1/4 chord requirement as it pertains to helicopters. That would be a challenge for sure. Don’t know how those devs that have brought helicopters to the sim have dealt with that.
Best of luck!