HUD h'zon pitching on airspeed change, why?

Hi,

I have tried to search, but as has been discussed the forum search is broke..

In ArduPlane 2.74 and possibly also with older versions: When I blow into my pitot tube, I see the horizon showing a pitch down. I do remember having read about this before, but I cannot remember what the reason is for this? The attitude of anything has not changed after all.

Regards

Soren

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Replies

  • I have found out why (at least I believe I have...).

    The IMU output attitude doesn't change when there is a forward airspeed. It does change when there is a change in airspeed, also known as forward acceleration or deceleration.

    The accelerometers are used in the attitude estimation, ideally measuring the gravity vector. More precisely they measure the plane's acceleration in its inertial frame. When the plane sits on the table or flies level with constant velocity, it is "g" upward. When the plane flies level and accelerates, it is "g" upward plus some acceleration forward. So changing the speed will affect the attitude estimation to "think" the nose is pointing up above horizontal. What we see when blowing into the airspeed meter is the effect of something made to compensate for that - it bends the attitude nose-down when the plane appears to accelerate by airspeed.

    So all is OK but it does look like a strange bug...

    Regards

    Soren

  • I think the reason might be that the HUD does not display the attitude of the aircraft, but rather the attitude of the velocity vector. By blowing the pitot tube the APM think it is traveling straight forward and corrects the attitude solution.. 

  • I'm use 2.75beta have this problem too. 

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