Thread: Discussion A non-aerodynamic proof that a lifting wing pushes down on the earth View Single Post
Mar 09, 2012, 04:45 PM
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The Willamette Valley, Oregon
Joined Dec 2008
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(Edit May 2012-- my thoughts on this matter have now changed significantly-- I'm still convinced that the earth "feels" a downward push from the wing of an aircraft in flight, equal in magnitude to the weight of the aircraft, which is also equal to the upward gravitational attraction that the aircraft exerts on the earth, but I no longer believe that this downward force need involve any specific amount of downward momentum of the air (downwash). For more, see posts 58, 61, and 72. End edit.)

Quote:
 Originally Posted by aeronaut999 2) But looking in more detail, if there is a downwash at distance Y below the wing (ignoring horizontal distances, just looking at the vertical distances), with downward momentum Z, then at distance Y+1 below the wing, can the downward momentum of the downwash be less than Z? If so, where has the momentum gone? Is this loss of momentum (say through inelastic collisions) still consistent with the basic Newtonian laws?
My understanding may be fuzzy but my understanding is that momentum in any particular direction must be conserved even if the collisions are inelastic. Am I wrong?

I just googled "downwash momentum weight" and found the following-- do you feel that this is in error? Please follow this link and see what you think. (The link should open to a heading "Section 1.8 Incompressible Flow over Finite Wings", which is at the top of page 79. ) The author is arguing that the downward momentum of the downwash is in fact conserved all the way to the ground. Source: the textbook "Mechanics of Flight" by Warren F. Phillips. Actually, the author's argument is so similar to mine one might think that I am stealing it from him-- and I believe I actually own this book, haven't read it all the way through-- but if you've followed my posts over the lasts several weeks I think you can see I originated these ideas clumsily and independently, anyway nothing here is fundamentally new to science, it's all familiar ground in one form or another....

Steve