World Axes accelerations vs. Body Axes accelerations

[dfournie]

Pete,

I'm currently using the world frame axes offsets to successfully determine all my positional information, velocities, and accelerations. When I am at a steady state, no accel/decel, no wind, on the ground, the world frame axes show no relative movement as would be expected. However the body frame reference variables from their associated offsets appear to be sensing positional movements and accelerations. The values appear to be very small, but are there nonethless. Is the body frame reference actually seeing engine vibration from the aircraft standing still? I would think these extremely small velocities would be present in a very high resolution flight model, but not in FS2004.

[Pete Dowson]

Is the body frame reference actually seeing engine vibration from the aircraft standing still? I would think these extremely small velocities would be present in a very high resolution flight model, but not in FS2004.

Sorry, I don't know. I really don't know anything about any of that stuff -- the values themselves were located in earlier FS versions by other folks, I just documented them. I have cross-checked some of them against the values saved in the Flight files, so that I can re-identify them from FS version to FS version, but that's all.

Maybe someone else reading this will have sufficient knowledge of the FS modelling to be able to comment.

Regards,

Pete

[alandyer]

Commonly, when dealing with flight models on rotating spherical bodies the body axes are rotated as the craft translates relative to the body.

This is to keep the "down" body axes pointed at body center.

What are referred to as LHLV coordinates.

(Local Horizonal, Local Vertical).

Even when there is no movement relative to body,

there is movement relative to the intertial frame i.e. body is slowly rotating. (Sunsets are marvellous things).

This might be what you are oberserving.

(body rotation, not sunset :)

Could also be calculation residues (rounding errors, etc).

Best bet is FS team at Microsoft.

However, they do not give out email, for obvious reasons.