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23rd Nov 2012, 20:15
Owain Glyndwr

Join Date: Jun 2011
Location: West of Offa's dyke
Age: 83
Posts: 474
Read it properly before jumping in.

I did NOT say they have the same drag coefficient did i ????
No you didn't - I did as part of an explanation.

in fact i seem to think i said that plane A had 1.5 times the drag of plane B which is NOT saying the drag is the same is it ???
That is what you said, but it is just as wrong. Aircraft A will NOT have 1.5 times the drag of Aircraft B if the only difference is weight.

i said they DID have the same lift / drag ratio, purely for the maths, as a theoretical calculation.
And that is where you went wrong because you postulate a non-valid equivalence

Why can't they have the same lift/drag ratio. ?????
If I really have to explain that I'm wasting my time. If you understood the basics of how drag varies with lift coefficient and how lift coefficient varies with speed and weight you wouldn't need to ask that question.

As to force vs momentum

Momentum = mass * velocity
Force = mass * acceleration
Acceleration = rate of change of velocity
Force = rate of change of momentum.

Last edited by Owain Glyndwr; 23rd Nov 2012 at 20:21.