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26th Nov 2012, 08:56
Microburst2002

Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,342
Gennlemen

One thing that amazes me about physics is that we don't even know what a force actually is... For us it jIs ust whatever makes a mass to accelerate or decelerate, whatever the hell it might be. There is something that makes that happen, and they called it Force.

But we don't really know what is the nature of forces, or their origin. Again our fate is to recur to the empirical method.

I think I demonstrated to you what is the effect of weight in drag for normal flight AoAs: less than proportional than the mass increase. It coincides with the intuitive notion of higher momentum or higher KE will leas to longer stopping distance. However, at high AoAs drag force will increase more than proportionally to mass, and the heavy airplane will actually slow down faster than the light one, which is against anyones' instinctive answer.

So Newtons second law is the right choice, after the above analisis.

a=F/m.

Sometimes F increases more than mass, sometimes it does increase less than mass. sometimes acceleration is slower, sometimes it is faster.

It all depends on the AoA.

Owain said above the two airplanes can fly at the same speed, 226 kt, with the same L/D, which is amazing to me, but since I tend to believe him, I thought a bit about it and I deem that the heavy at 226kt is above max L/D AoA while the lighter one, at that speed is below it, and they happen to be the same L/D. Is that right?

Last edited by Microburst2002; 26th Nov 2012 at 08:56.