Backwash Causes Lift?

On Oct 7, 5:54 pm, flightoffancy wrote:
In article ,
says...

The downwash thing is wrong. Yes, there is some dispacemtn of air that
causes lift, but it' only a minor contribution in the bigger scheme of
things.

I admit to being a relative retard on this issue (not as retarded as a
non-pilot probably is, but not as educated as an aeronautical engineer).

I thought I had read in numerous books during training that the primary
component of lift is the air that gets knocked downward by the wing. I
was calling that "downwash". Maybe my concept of downwash is wrong,
maybe it's a separate consideration from the air that gets knocked
downward by the airfoil. Hell I might not be remembering any of that
correctly.

Just wanted to reiterate what I said in my OP and each subsequent post
for you benefit since you just joined the discussion.

If you have an aifoil, and you move it forward, there will be
compression beneath the wing. Newton's law will be at play here, and
there will be downwash. This downwash results from the induced
pressure gradient.

That is not what I was talking about. The books that I have been
reading are talking about downwash that is _on top of_ the wing. The
pictures show air moving at an angle, backward and downward near the
trailing edge of the wing.

Note that these are two "downwashes".

I am saying that downwash on top of the wing does not generate a force
on the wing that causes the wing to move upward.

Anyway you say downwash is minor.

Well okay. But then what are the major contributions that cause lift in
the bigger scheme of things?

-Le Chaud Lapin-

On Oct 7, 6:53 pm, Jim Logajan wrote:
flightoffancy wrote:
I thought I had read in numerous books during training that the primary
component of lift is the air that gets knocked downward by the wing. I
was calling that "downwash". Maybe my concept of downwash is wrong,
maybe it's a separate consideration from the air that gets knocked
downward by the airfoil. Hell I might not be remembering any of that
correctly.

You appear to have the essential concept right. But aerodynamicists call it
"turning" the flow, which is different from what they call "downwash."
Here's NASA's explanations:

http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html

And if you click on "turning" you can see this explanation of the term (and
hopefully why "turning" was chosen):

http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html

And this is what aerodynamicists call "downwash" :

http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

I wanted to thank you again for these NASA links. IThe more I read,
the more it becomes clear that is *not* universal concensus on the
basic mechanisms of flight, not even among experts.

-Le Chaud Lapin-

Le Chaud Lapin wrote:
On Oct 7, 6:53 pm, Jim Logajan wrote:
You appear to have the essential concept right. But aerodynamicists
call it "turning" the flow, which is different from what they call
"downwash." Here's NASA's explanations:

http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html

And if you click on "turning" you can see this explanation of the
term (and hopefully why "turning" was chosen):

http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html

And this is what aerodynamicists call "downwash" :

http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

I wanted to thank you again for these NASA links. IThe more I read,
the more it becomes clear that is *not* universal concensus on the
basic mechanisms of flight, not even among experts.

I'm sorry but IMHO you continue to come to the same untenable conclusion.
There is consensus among the experts. I keep giving the NASA links not
because they are in any way unique, but because it is cheaper than giving
you a list of more books on the subject that you'll never purchase and
read. They seem ideal for this particular discussion and your specific
need.

There are simplified, and therefore inaccurate, statements about
electromagnetics in books aimed at general audiences. Yet would you say
that because of these statements there is no universal consensus about
electromagnetics?

On Oct 7, 7:38 pm, Jim Logajan wrote:
I'm sorry but IMHO you continue to come to the same untenable conclusion.
There is consensus among the experts. I keep giving the NASA links not
because they are in any way unique, but because it is cheaper than giving
you a list of more books on the subject that you'll never purchase and
read. They seem ideal for this particular discussion and your specific
need.

From the NASA link you posted earlier:

"There are many theories of how lift is generated. Unfortunately, many
of the theories found in encyclopedias, on web sites, and even in some
textbooks are incorrect, causing unnecessary confusion for students."

That sounds to me like there are a lot of sources that are incorrect.
My Jeppesen book, for example, says the exact opposite of what NASA is
saying. Let's see...whom should I believe, the NASA version or one of
the leaders in flight education?

There are simplified, and therefore inaccurate, statements about
electromagnetics in books aimed at general audiences. Yet would you say
that because of these statements there is no universal consensus about
electromagnetics?-

Simplification does not necessarily make something in accurate. I
have studied electronics most of my life to some degree. With the
exception of maybe 5-10 incidents on esoteric, I do not recall
reading anything that is inaccurate, and in one of the cases, it was
simply a gross error made by author of book, not fundamental
difference of opinion of the underlying physics.

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

NASA is not simplifying, digesting, or even offering an alternate
model that is mathematically and functionally equivalent from abstract
point of view. They are saying that the other theories are simply
wrong. That they think that the theories are wrong should be evident
from the last word in the URL above.

-Le Chaud Lapin-

On Oct 7, 9:26 pm, flightoffancy wrote:
He has barely begun flight training, claims his instructors are wrong
about what makes airplanes fly, claims that because instructional
materials at the beginner's level are incosistent therefore there is no
agreement about aerodynamic theory at all, and then essentially
dismisses NASA's explanations as "just another theory of many" and so he
has no reason to believe them either.

I did not dismiss NASA's explanations.

For the Nth time...

....I said that I agree with NASA's explanation that the other
explantions are wrong.

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

-Le Chaud Lapin-

Le Chaud Lapin writes:

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

NASA is not simplifying, digesting, or even offering an alternate
model that is mathematically and functionally equivalent from abstract
point of view. They are saying that the other theories are simply
wrong. That they think that the theories are wrong should be evident
from the last word in the URL above.

Look also at the "K-12" in the URL.

flightoffancy wrote:
Jim, let me say about LCL (in cliche fashion) that you can lead a
horse to water but cannot make it drink.

He has barely begun flight training, claims his instructors are wrong
about what makes airplanes fly, claims that because instructional
materials at the beginner's level are incosistent therefore there is
no agreement about aerodynamic theory at all, and then essentially
dismisses NASA's explanations as "just another theory of many" and so
he has no reason to believe them either.

Hmmm. This puts me in a quandry because I actually understand the source of
LCL's frustration and don't fault him for that feeling - just some of his
approach. On one hand he is correct that many sources give incomplete or
inaccurate explanations for lift. So he's attempting to work out why lift
works on his own - which IMHO is a fantastic learning exercise. From my own
experience tackling a complex problem clarifies in a person's mind many of
the fine points of the problem (but for complex problems not normally the
correct solution). Once that is done, one has (IMHO) a better appreciation
for the sources and explanations that are more comprehensive and exact.
He'll understand at a base level the statement "It's a complex
subject." :-)

A complete neophyte stands up and claims he has no reason to believe
that what NASA publishes about flight is correct.

I think he's already addressed that in another post.

What can one say about someone who is willing to make such big claims
with so little knowledge?

A typical Usenet poster? ;-)

"Don't feed the trolls."

Not everything under the bridge is a troll. Some of them are pillars
holding it up. :-)

flightoffancy writes:

But airfoils aren't planar, they are curved. Why do varying curvatures
of airfoils significantly affect wing lift / stall speed?

They don't affect lift, they just affect drag and stall speed. I don't know
the theory well enough to comment on why this is so. From a piloting
perspective, it is only necessary to know that AOA determines lift, and the
shape of the airfoil is irrelevant.

Bertie the Bunyip writes:

Actually, yes it is.

Show me an aircraft that does this.

Le Chaud Lapin writes:

If that is the case, what is pushing the air?

You may be able to get past this by considering that the airfoil actually
turns the flow, rather than push or pull it. It turns the flow downwards, and
this acceleration of the air mass engenders an upward force that is lift.