@CONF iture
Ground speed is affected, but not airspeed.
Once airborne, the glider is in the air mass that is moving at the speed of the wind, but for the glider itself regarding that air mass, there is no notion of tail or head wind.
Sure, but the remark is, the airspeed should change when the inertial speed stays the same, whereas the airspeed is perceived to be constant (which in effect isn't, but this is masked by other factors).