#102 FGAccelerometer does not take into account G ?

closed
nobody
None
5
2012-10-31
2011-08-21
Brice André
No

After reading the code of FGAccelerometer and after having used it in my application, my feeling is that this component does not take into account the gravitation in its computation.

If my guess is correct, then the output of this component does not correspond to the output of a real accelerometer sensor. Is there something I did not understood or is there a problem with this component ?

Discussion

  • Jon S. Berndt
    Jon S. Berndt
    2011-08-21

    Brice - you may very well be right. The Accelerometer has not been extensively checked. The initial implementation was quickly done (by me). Any help in looking into that firther would be appreciated - otherwise, someone will get to it sooner or later. :-)

    Thanks for the report!

     
  • Brice André
    Brice André
    2011-08-21

    I can help you, but I am not an expert in flight dynamics. I use JSBSim to correct my equations, but if I implement myself the corresponding JSBSim equations, I cannot guarantee this is correct :-)

    I joined a patch of what I would do in order to take into account the gravity in the accelerometer code. But I am sincerely not sure this is correct.

    I think my code is not accurate because, I think that the gravitation vector is not oriented to (0,0,1) in NED frame. As the earth is not spheric, I think we should take into account the divergence between geodetic and geocentric latitude for this computation. But, OK, I don't think this has a big influence on the final result.

    So, if you think this patch is OK, feel free to use it. But, as stated before, I cannot guarantee I did not make a mistake.

    Regards,
    Brice

     
  • Brice André
    Brice André
    2011-08-21

     
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  • Bertrand
    Bertrand
    2012-01-15

    Also in JSBSim, the vertical axis of NED frame is not oriented along the local vertical but is pointing toward the Earth center. Therefore the gravity is correctly oriented.