Two different airspeeds, gauge and GTN750

[MartinRex007 390]

Flying at 8,000ft no wind and the airspeed gauge indicates168knts, and the Ground Speed on the GTN 750 indicates 188knts, shouldn't those two be the same given there was no wind? Anybody else see this?

 

Also I bumped up the power_scalar from 1.0 to 1.3 but I don't think that should make a difference in the two readings?

 

Thanks

Martin

[skelsey 765]

Airspeed Indicator = Indicated Airspeed

GPS = Ground Speed (i.e. True Airspeed + wind component, in this case 0)

 

TAS is approx 2% higher than IAS for each 1000ft of altitude, so at 8000ft an indicated airspeed of 168KIAS is approximately 194KTAS (168 + ((168 x 0.02) x 8)) -- this is only an approximation though.

[MartinRex007 390]

Simon, thanks that seems to explain it :smile:

 

Cheers

Martin

[scottb613 1,186]

Hi Martin,

 

Also be aware - the GTN has the "Tools" page - under that there should be something that says TAS something or other... It will automatically compute the current TAS for you... You have to enable it to "Use Sensor Data" for automatic computation - it's a button on the screen...

 

Regards,

Scott

[MartinRex007 390]

Thanks Scott, I'll look into that!

 

Cheers

Martin