Backwash Causes Lift?

TheSmokingGnu writes:

Then why do wings generate lift at negative AOA?

They don't. That's a very common misconception, even among pilots.

The effective AOA is always positive when the wing is generating lift.

On Oct 4, 6:27 am, Mxsmanic wrote:
TheSmokingGnu writes:
Then why do wings generate lift at negative AOA?

They don't. That's a very common misconception, even among pilots.

The effective AOA is always positive when the wing is generating lift.

Once again, thou knowest not of what thou speakest. I
just told you, in apost not long ago, that some airfoils will generate
lift at up to -4° AOA. Here's a graph that shows lift being generated
on some anonymous airfoil at -5°:
http://en.wikipedia.org/wiki/Lift_coefficient
Bernoulli at work. Newton, too, because there's downwash being
generated.

Dan

writes:

Once again, thou knowest not of what thou speakest.

Several others from the treehouse club here have told you the same thing.

No positive AOA, no lift. Learning this is extremely useful to pilots.

I just told you, in apost not long ago, that some airfoils will generate
lift at up to -4° AOA.

No airfoil generates lift at a negative angle of attack.

Here's a graph that shows lift being generated
on some anonymous airfoil at -5°:
http://en.wikipedia.org/wiki/Lift_coefficient

Would you like me to draw a graph that shows something different and upload it
in place of that one?

wrote:
On Oct 4, 6:27 am, Mxsmanic wrote:
TheSmokingGnu writes:
Then why do wings generate lift at negative AOA?
They don't. That's a very common misconception, even among pilots.

The effective AOA is always positive when the wing is generating lift.

Once again, thou knowest not of what thou speakest. I
just told you, in apost not long ago, that some airfoils will generate
lift at up to -4° AOA. Here's a graph that shows lift being generated
on some anonymous airfoil at -5°:
http://en.wikipedia.org/wiki/Lift_coefficient
Bernoulli at work. Newton, too, because there's downwash being
generated.

Dan


Don't bother. Believe me it's not worth it. You can talk this guy to
death and all he will do is count you as another response.

Angle of attack as we all know (with one exception it seems :-) can be
both positive or negative.
In fact, in high performance jets with a fuselage loaded IYMP, entering
a coupled spin after a departure, it's extremely disorienting if the
aircraft goes through PSG and stabilizes in an inverted spin mode where
yaw is opposite to roll. g is a bad indicator as with a fuselage loaded
IYMP you can get negative g either erect or inverted.
The way we deal with this is through instrument interpretation rather
than trying to eyeball what's happening, which can be next to impossible.
The AOA indicator in the aircraft has a positive and negative side. If
the AOA is stabilized at some value on the negative side, and the
airspeed is stabilized at some mean low value, the spin is inverted. The
turn needle will show spin direction either way.

Again, don't waste your time.

--
Dudley Henriques

Mr Dudley, once again you are confused. Most define angle of attack as
the chord line of a wing, and of course with that definition it can be
negative and still generate lift. Mr Mx chooses a different way of
defining it. It is some angle such that when it goes negative the
airfoil can generate no lift. Do you remember the disbarred former
president Clinton saying something about "It depends on what 'is'
means"?

In Mx's case, words change meaning so that he is NEVER wrong. It must
be an interesting version of English he teaches.

But he does offer amusement for some of us on otherwise humorless
days, doesn't he?

Tina wrote:
Mr Dudley, once again you are confused. Most define angle of attack as
the chord line of a wing, and of course with that definition it can be
negative and still generate lift. Mr Mx chooses a different way of
defining it. It is some angle such that when it goes negative the
airfoil can generate no lift. Do you remember the disbarred former
president Clinton saying something about "It depends on what 'is'
means"?

In Mx's case, words change meaning so that he is NEVER wrong. It must
be an interesting version of English he teaches.

But he does offer amusement for some of us on otherwise humorless
days, doesn't he?



AOA actually can be defined relative to any given reference datum, but
normally it's considered in the industry as being the angle formed
between the chord line of the wing and the relative wind as you have
correctly stated.

Quite frankly, I read what Mxemanic writes on occasion and can't figure
out how he can be so close to getting it right and still manage to get
it wrong. He's amazing, and an interesting study if nothing else.
It's too bad he's taken this path on these groups. I've always felt he
has a genuine interest in things aviation and would like to contribute,
but he seems to be such a jerk that he gets in his own way.

--
Dudley Henriques

Dudley Henriques writes:

AOA actually can be defined relative to any given reference datum, but
normally it's considered in the industry as being the angle formed
between the chord line of the wing and the relative wind as you have
correctly stated.

The angle of attack is the angle between the forward stagnation point and the
trailing stagnation point. The points of intersection of the chord line with
the airfoil surface are static, but the stagnation points can change, altering
the angle of attack.

If the angle of attack is not positive, there is no lift. You cannot have
lift at negative angles of attack because that is not symmetric. If a
negative angle of attack can produce positive lift, what happens when you turn
the airfoil upside down? Logically that would mean that even a positive angle
of attack would force the wing down, which makes no sense.

Mxsmanic wrote in
:

Dudley Henriques writes:

AOA actually can be defined relative to any given reference datum,
but normally it's considered in the industry as being the angle
formed between the chord line of the wing and the relative wind as
you have correctly stated.

The angle of attack is the angle between the forward stagnation point
and the trailing stagnation point. The points of intersection of the
chord line with the airfoil surface are static, but the stagnation
points can change, altering the angle of attack.

If the angle of attack is not positive, there is no lift. You cannot
have lift at negative angles of attack because that is not symmetric.
If a negative angle of attack can produce positive lift, what happens
when you turn the airfoil upside down? Logically that would mean that
even a positive angle of attack would force the wing down, which makes
no sense.


Nope


Bertie

On Oct 5, 6:27 pm, Mxsmanic wrote:

The angle of attack is the angle between the forward stagnation point and the
trailing stagnation point. The points of intersection of the chord line with
the airfoil surface are static, but the stagnation points can change, altering
the angle of attack.

This has never been an accepted definition of angle of attack and
your creation of it has no credibility. You just create even more
confusion in your mind and in the minds of innocent truth-seekers
here.

If the angle of attack is not positive, there is no lift. You cannot have
lift at negative angles of attack because that is not symmetric.

So you don't believe NASA or NACA or anyone else that finds
lift at negative AOAs on some airfoils?

Dan