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

GPS has no knowledge of an aircraft's airspeed.  The only speed directly available from a GPS based system such as SkyDemon is the ground speed.




George E A Reid

Ipad Mini 5,  IOS 14.4,  SD 3.15.0.288
PC(Win 10, Version 19041.804)  SD 3.15.0.0

As George mentioned, this would be rather unsafe as GPS only knows your groundspeed and even this is sometimes subject to a little lag. It really isn't suitable for real-time tactical readouts of speed, which presumably need to be airspeed.

I quite agree but in theory could SD not calculate airspeed using GS and weather data from nearest winddata - wind, windspeed, windangle, qnh and heading? If so, how about testing that? I use Garmin GLO that updates GPS-position 10-times often than build in Ipad GPS.

Are there any instrument that could feed airspeed data to SD? I just want SD to be in the very front :-)

The most efficient airspeed indicator is already in front of you
And even if it becomes unreliable for any reason, you should absolutely refrain from using a GPS based speed during take-off or landing.

The speed that the wing is interested in is AIRspeed, GPS can only show GROUNDspeed; Groundspeed is only useful for navigation, not for taking-off, landing or other flying related activities. 

Thanks all - Good discussion.

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.