Backwash Causes Lift?

On Oct 7, 2:14 pm, flightoffancy wrote:
In article . com,
says...

An airplane can stay aloft if rarefication is somehow created above
the wing. This is what's happening with the blow-over-paper trick.

What you are saying is: if less pressure exists above the wing than
below, then airpressure will force the wing higher, just like a round
weight sealed in a round tube will be forced higher if the pressure
under the weight exceeds the pressure above the weight.

Right, that's what I'm saying.

No one questions that.

But I don't think the blowing on paper "experiment" demonstrates the
principle.


There are too many uncontrolled variables for you to draw such a
conclusion. For instance, it could simply be the case that some airflow
gets under the sheet of paper and pushes it up -- just like air

Certainly you don't believe that the air is actually running around
the paper so it can get under the wing?

impacting any plane at an angle will impart some vector force in an
"up" direction. Also the paper does not remain stiff -- it undulates.
That introduces a tremendous amount of complexity which casts your
interpretation in doubt.

Also: the airspeed of your paper is not 0 -- it's groundspeed is zero.

The leading edge of the airfoil, the paper in this case, will have an
airspeed of 0. You can do this by making sure that, when you blow
over the paper, your mouth is a good 3 or 4 centimeters beyond the
leading edge, on top of the paper in fact.

-Le Chaud Lapin-