Originally Posted by
Wizofoz
but the sign of the wind speed has changed with the reference velocity direction.
They are talking velocity, not speed.
Try it this way- if you drive your car in reverse at -30KPH for an hour, how far are you from your origin?
That figure is a MAGNITITUDE (which is what scalar quantities like speed reference)- they do not have positive or negative signs. if you are 30K from where you were an hour ago, your average SPEED has been 30K/PH.
If you want to reference an origin and call a direction from it negative, you can, but this is velocity, not speed.
NASA are very clear in their example '
the wind speed is -20 mph' in reference to the plane. A high enough positive sign wind can produce a negative sign GS in reference to a plane. There is no absolute value rule in the calculation for GS.