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.
No, you do not need to calculate groundspeed to understand winds hear- because the aircraft is not interacting with the ground, so it's momentum relative to it is irrelevant. Windshear happens when the aircraft's momentum relative to the AIR changes.
Say you are turning on a still air day- but on the ground there is a passing truck- you could calculate your momentum relative to IT- it is as relevant a momentum figure as that of the earth, but it doesn't change the dynamics of the situation does it?
As to the increased rate of descent you cite, did it come with an increase in airspeed also? I have often observed older FMCs get caught out but changes in wind and do some radical stuff to maintain programed path.