Originally Posted by
Meikleour
Wizofoz: I agree with you however I think you will find that I never claimed lift was proportional to groundspeed! For the windshear analogy to apply the momentum must be related to the groundspeed ie. relative to the earth. Why is it therefore that when operating in the "bubble of air" concept then reference to the earth is discounted? Likewise can you help me understand the often observed phenomenon that I cited.
The reference to the Earth is purely one of convenience.
Because we measure wind velocity relative to the Earth!
e.g. if you are heading 270 and you fly through a gradient from 270/10 kts to 270/30 kts then we have a +20 knot effect.
The same as if you went from 090/5 to 270/15.
It really doesn't matter what the absolute values are relative to the Earth, only what the change is.
But, if you wanted to calculate it based on reported wind values,we measure wind relative to a stationary point on the ground. This might give the impression that the relationship to the ground is fundamentally important rather than being a book keeping convenience.