Backwash Causes Lift?

Of course, but the specific statement I wanted made clear had to do
with getting conservation of momentum from Newton's relationship
between force, mass, and acceleration. The OP claimed to be an
engineer, he was suggesting something I thought was unlikely and you
demonstrated that nicely.

Tina wrote:
Of course, but the specific statement I wanted made clear had to do
with getting conservation of momentum from Newton's relationship
between force, mass, and acceleration. The OP claimed to be an
engineer, he was suggesting something I thought was unlikely and you
demonstrated that nicely.

Didn't he say he was an electronics engineer? Unless he's doing work on
electromechanical devices I can see how one can get rusty on dynamics.

I'm not sure questions regarding lift belong in a piloting group anyway.
Fluid dynamics is a particularly difficult subject because it is easy to
overlook things, such as: if a wing accelerates air downward, then
according to conservation of momentum some other mass must be accelerated
upward.

Jim, I guess it depends on the institution and the intellegence of the
student. My husband graduated even longer ago than I did with degrees
in electronics, but he was well trained in mechanics as well. It may
be the newer schools don't offer as broad a base in classical
mechanics and physics.

What is especially interesting is that theories are offered that do
not predict observations very well. I skydived a few times, and my
sensation was that my arched body (the negative of a classic airfoil)
was being supported by a pillow of air, not being drawn up into a
partial vacuum. In fact if memory serves I don't remember the jump
suits of others bellowing in the back either.

And if one holds one's hand out of a car window, the psudo lift
provided by air deflecting from the surface facing the wind does not
seem to come from something at the trailing edge -- in fact one can
put one's wrist in the trailing position and still feel the same
impact -- delta momentum - forces.

For a theory to be accepted it has to predict observations. Trailing
edge downwash and some other things written here don't seem to do
that. But it is fun. Shall we talk about flying a kind of roll with
having the pilot experience exactly 1 G into the seat during the
sequence? That is about as much fun as talking about an airplane take
off from a belt sander, or taking off into a 70 KT headwind, turning
downwind and not falling out of the sky.




On Oct 4, 7:48 pm, Jim Logajan wrote:
Tina wrote:
Of course, but the specific statement I wanted made clear had to do
with getting conservation of momentum from Newton's relationship
between force, mass, and acceleration. The OP claimed to be an
engineer, he was suggesting something I thought was unlikely and you
demonstrated that nicely.

Didn't he say he was an electronics engineer? Unless he's doing work on
electromechanical devices I can see how one can get rusty on dynamics.

I'm not sure questions regarding lift belong in a piloting group anyway.
Fluid dynamics is a particularly difficult subject because it is easy to
overlook things, such as: if a wing accelerates air downward, then
according to conservation of momentum some other mass must be accelerated
upward.

Tony writes:

For a theory to be accepted it has to predict observations. Trailing
edge downwash and some other things written here don't seem to do
that.

Actually, downwash can be directly observed in appropriate atmospheric
conditions. There are pictures on the Web that illustrate this.

Remember, in order to accelerate something upward, something else must be
accelerated downward.

When you hold your hand out the window of a car at an angle, and you feel it
being raised, where does the energy to raise your hand come from?

"Jim Logajan" wrote

Didn't he say he was an electronics engineer? Unless he's doing work on
electromechanical devices I can see how one can get rusty on dynamics.

Jim, this is MX reborn. Give it up.
--
Jim in NC