Alan Baker wrote:
Jim Logajan wrote:
Alan Baker wrote:
Net force down on air: net momentum down.
Transmitted at the speed of sound, not at the speed of the downwash.
Find me a single reference that agrees with you...

Since we have made differing claims that are actually testable by simple
experiments, why not use them to determine the real truth? Nothing else
would be as definitive at resolving the claims than an experiment simple
enough that anyone could run independently, so anyone having any doubts is
not slaved to trust the claims of others. The methodology would also be
open to independent analysis and critique. I.E. we use good old scientific
method.

I can think of a possible experiment that uses a large box (cardboard may
suffice) hanging from a ceiling from four vertical strings (or wires or
ropes) so that it can swing back and forth with two opposite ends that can
be opened and closed.

A small fan can be taped in place inside the center of the box and some
tests run - first with the ends opened (to measure the thrust of the fan
using some simple trig on displacement and known weight of the fan+box, and
thence compute the average wind speed of the fan) and then with the ends
closed. Based on how much the closed box swings when the fan is turned on,
one should be able to determine which of our theories is correct.

If your claim is correct, the box will swing more than what my claim
predicts (because the wind from the fan travels slower than the speed of
sound, so if you are correct the fan would push the box farther along in
its swing before the force of that wind hits the interior wall of the box.)
The approximate amount of swing (which could be recorded several simple
ways) should be predictable for both our theories based on several factors
that should be measurable using common equipment like a ruler and weight
scale (though a bathroom scale might not be precise enough to measure the
box+fan weight, though such scales are fairly common.)

So if you think the above is reasonable, or you need more insight into what
I am proposing before you commit, I am willing to flesh out the proposed
experiment in more detail.