By Martin Bech - 6/29/2016 12:58:25 PM
Would it be possible to readout(voice) actuel airspeed when in the landingroll? Then I do not need to look at the instrument but can concentrate on looking out.
Regards
Martin
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By geohawk - 7/15/2016 12:08:49 AM
GNSS velocity error doesn't quite work like that.
What is specified when positioning accuracy is listed is a singe point solution with respect to the earth. This can be up to about 10m off horizontally and 30m vertically in most situations.
These values are typically better than that and are usually within about 3-5m horizontal and 5-8m vertical.
However, GNSS is far more precise than it is accurate when obtaining an autonomous solution. The point to point repeatability between any two epochs is typically less than 1 meter horizontal and less than 3 meters vertical. That is to say that even though the absolute error of each is, say 5m, it is likely that they share the same error and therefore the relative difference between them (precision) is far less than the accuracy.
Since positioning accuracy isn't relevant for velocity calculations, (only precision is) this translates into some very accurate velocity values. To make it even better, some systems use signal Doppler shift, smoothing and /or Kalman algorithms to improve this precision. So in reality, some GNSS receivers achieve horizontal velocity precision at around 0.1..0.5 m/s
http://www.insidegnss.com/node/4433
https://www.fig.net/resources/proceedings/fig_proceedings/fig2016/papers/ts06b/TS06B_wieser_boffi_et_al_8443.pdf
No matter the case, GNSS doesn't provide any wind correction (as others have already clearly stated) so it isn't advisable to use GNSS for anything other than navigation.
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