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Thread: altimeter out

  1. #11
    Captain MadamBreakneck's Avatar
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    Quote Originally Posted by Asgard View Post
    ... Acceptable to who?
    Honestly I don’t know, are GPS approaches allowed in this country yet? ...
    There seems to be a procedure to apply for one, but beyond that I don't know. I don't fly at North Weald any more but this thread on the Flyer forum discusses an application by neighbouring Stapleford and gives further pointers if you are interested.



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  2. #12
    Co-Pilot Arielarts's Avatar
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    GPS height estimations are much less reliable than horizontal position info because of the very tiny angular change with height, as 'viewed' from the low earth satellites.


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    Captain Randombloke's Avatar
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    Quote Originally Posted by Arielarts View Post
    GPS height estimations are much less reliable than horizontal position info because of the very tiny angular change with height, as 'viewed' from the low earth satellites.
    The last few instruments I have reviewed have had the designers disagree with this, and especially where uncertified instruments are concerned which can use 3 or 4 different GNSS.

    One manufacturer is now confident enough to have both QNH and take off height automated on switch on, and fed to a barometric transducer purely for rate of climb, when GNSS lags behind. One other manufacturer has a choice between auto and manual QNH. So far, I've not seen an accuracy issue.

    GPS heights might still be inaccurate, but unless locked into GPS by certification you could be looking at GLONASS, Galileo or Beidou, or a combination of them.
    Steve U.
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  4. #14
    Captain MadamBreakneck's Avatar
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    Quote Originally Posted by Randombloke View Post
    ...

    One manufacturer is now confident enough to have both QNH and take off height automated on switch on, and fed to a barometric transducer purely for rate of climb, when GNSS lags behind...
    That's interesting. Any link to look at on the subject? How do the prices of these units compare with a conventional mechanical altimeter?



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  5. #15
    Captain Randombloke's Avatar
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    Quote Originally Posted by MadamBreakneck View Post
    That's interesting. Any link to look at on the subject? How do the prices of these units compare with a conventional mechanical altimeter?
    It's a complete flight computer:

    https://www.syride.com/en/instruments

    Click on SYS'Evo.

    Paragliding is now using GPS altitude for competitions as it's less easy to cheat by setting too low a take off height.
    Steve U.
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  7. #16
    Captain MadamBreakneck's Avatar
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    Quote Originally Posted by Randombloke View Post
    It's a complete flight computer:
    Isn't it just!

    Edit: looking further today, I found this interesting review of GPS alt versus pressure alt. It seems to come down in favour of pressure alt.
    https://www.naviter.com/2015/02/gps-...sure-altitude/
    Last edited by MadamBreakneck; 18-11-19 at 10:49 AM.



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