A dumb doubt on stalls

Skywise wrote:

Bob Moore wrote in
. 122:


Dylan Smith wrote

Snipola

http://en.wikipedia.org/wiki/Deep_stall

This Wikipedia article leaves a lot to be desired.

Snipola

The beauty of Wikipedia is that YOU can change it.

Brian

Which is why it leaves a lot to be desired.

Matt

"Matt Whiting" wrote in message
...
Jim Macklin wrote:
The tail is more heavily loaded and at a higher angle of attack than the
wing. The tail lift is actually a tail down force. You can look up a
textbook on stability, control and weight and balance to see that with a
conventional tail, the wing lift is located on the center of pressure,
while the CG is located some small distance forward of that point. The
tail provides a downward forced on the tail that creates a moment around
the CG to balance the moment arm between the center of pressure and the
CG.

When the pilot feels a stall buffet, it is caused by air flow separation
that impacts the tail or some other part of the structure. But the stall
break happens when the tail stalls and the CG moment is no longer
countered by the tail down force.

Personally, I don't believe this. If this were the case, then during a
full stall landing, the airplane would rise upward when the tail stalled
as the net force in the vertical direction would be greater upward than
downward. Yes the airplane would rotate about the center of lift and the
nose would fall, but the wing would be rising at the same time. This isn't
the way any airplane I've ever flown behaved.

http://www.faa.gov/library/manuals/a...83-25-1of4.pdf

I did a quick search and find nothing about the tail stalling before the
wing under normal conditions. On which page did you see this?

There's a paragraph on p. 3-21 that makes part (but not most) of the
erroneous claim that Jim attributes to the publication. In particular, the
paragraph does say (in a discussion of a typical GA plane's normal stall)
that the tail loses lift (along with the wings). But it does not attribute
the plane's stall to the tail's supposed loss of lift; on the contrary, it
credits the supposed loss of lift with helping to recover from the stall.
(Additionally, the paragraph claims that the wings' lift *ceases* during a
stall, which is not the case.)

--Gary

Gary Drescher wrote:

"Matt Whiting" wrote in message
...

Jim Macklin wrote:

The tail is more heavily loaded and at a higher angle of attack than the
wing. The tail lift is actually a tail down force. You can look up a
textbook on stability, control and weight and balance to see that with a
conventional tail, the wing lift is located on the center of pressure,
while the CG is located some small distance forward of that point. The
tail provides a downward forced on the tail that creates a moment around
the CG to balance the moment arm between the center of pressure and the
CG.

When the pilot feels a stall buffet, it is caused by air flow separation
that impacts the tail or some other part of the structure. But the stall
break happens when the tail stalls and the CG moment is no longer
countered by the tail down force.

Personally, I don't believe this. If this were the case, then during a
full stall landing, the airplane would rise upward when the tail stalled
as the net force in the vertical direction would be greater upward than
downward. Yes the airplane would rotate about the center of lift and the
nose would fall, but the wing would be rising at the same time. This isn't
the way any airplane I've ever flown behaved.


http://www.faa.gov/library/manuals/a...83-25-1of4.pdf

I did a quick search and find nothing about the tail stalling before the
wing under normal conditions. On which page did you see this?


There's a paragraph on p. 3-21 that makes part (but not most) of the
erroneous claim that Jim attributes to the publication. In particular, the
paragraph does say (in a discussion of a typical GA plane's normal stall)
that the tail loses lift (along with the wings). But it does not attribute
the plane's stall to the tail's supposed loss of lift; on the contrary, it
credits the supposed loss of lift with helping to recover from the stall.
(Additionally, the paragraph claims that the wings' lift *ceases* during a
stall, which is not the case.)

Yes, that was a lot of missinformation in one post!

Matt

I did not reference or even read the FAA Handbook when I
posted my answer. If the wing stalled, the center of
pressure would not be creating a moment arm to drop the
nose, the tail must loose lift (stall) to cause the stall
break which causes the recovery from the approaching stall.

I referenced the "book" only to allow those who asked the
question to find a reference.

BTW, stall behavior changes drastically with the center of
gravity and to a lesser amount with weight.


--
James H. Macklin
ATP,CFI,A&P

"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
|
| No, I said the buffet comes from the wing root, but the
| actual stall is when the tail stalls and looses lift
(down
| force) and then the nose pitches down because the still
| flying wing CP is behind the CG.
|
|
http://www.faa.gov/library/manuals/a...83-25-1of4.pdf
|
| You keep referencing this 111 page document, but you don't
reference
| where in it you found what you mention above. What page?
|
|
| Matt

Matt Whiting wrote in news:Sf_lg.9891$lb.874408
@news1.epix.net:

Skywise wrote:

Bob Moore wrote in
. 122:


Dylan Smith wrote

Snipola

http://en.wikipedia.org/wiki/Deep_stall

This Wikipedia article leaves a lot to be desired.

Snipola

The beauty of Wikipedia is that YOU can change it.

Brian

Which is why it leaves a lot to be desired.

Matt

I have heard more than once that a collection of average
people is smarter than a few experts. If no one corrects
the data then it will continue to be wrong. I've been
seriously thinking of getting an account so I can make
changes as I see the need. Mostly minuscule stuff, but
every bit would help. The only concern I have is time.

I find it fascinating, the human capacity to bitch about
something, yet not have the willingness to actually DO
soemthing to fix the problem. I'll admit up front I've
done that myself, and it's something I should change.

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html
Sed quis custodiet ipsos Custodes?

Hi Marty,

Rallyes are really fun, I miss mine from time to time. :-(

-Kees (D-EHNE)

"Skywise" wrote in message
...
The beauty of Wikipedia is that YOU can change it.


Which is why it leaves a lot to be desired.

I have heard more than once that a collection of average
people is smarter than a few experts.

Nice saying, but I'm not willing to believe it. I've seen plenty of
evidence that a handful of experts can have very good, detailed, accurate
information even as the general population fails to have even a marginal
understanding of the same issue. This happens even in run-of-the-mill
educational situations, but is even worse when dealing with an issue that
has a political side, and thus numerous people who wish the science wasn't
correct making false statements about the science. It is *much* easier to
fool a collection of average people than a few experts.

There are probably situations in which the collective arrives at better
conclusions than a few experts, but I would be surprised if that's the usual
outcome.

That said, most articles in Wikipedia are not authored by a collection of
average people. The information within is generally being provided by a
small number of experts in each narrow field to which the article applies.

Nature did a comparison between Wikipedia and Encyclopedia Britannica, and
the two came about basically the same. Out of 50 randomly selected science
articles, each had only 4 serious errors, but both also had over a hundred
"minor" errors (with Wikipedia having slightly more than Britannica):
http://www.nature.com/news/2005/0512...l/438900a.html
http://news.bbc.co.uk/1/hi/technology/4530930.stm
http://news.com.com/2100-1038_3-5997332.html

Britannica, of course, questions the validity of the comparison:
http://news.bbc.co.uk/2/hi/technology/4840340.stm

There is every reason to trust Wikipedia as a reasonable resource, at least
as reasonable as any other single repository of information. Beyond that,
anyone who trusts only a single source of information to answer a question
deserves whatever faulty information they get. No single source of
information, not even the Encyclopedia Britannica or similar
well-established reference, can be considered reliable enough to stake any
serious debate on it.

The real problem comes when a person blindly trusts any source of
information, as if they can just throw out their own responsibility to know
and understand the basis for that source of information and the
characteristics that affect its reliability.

Pete

Jim Macklin wrote:

I did not reference or even read the FAA Handbook when I
posted my answer. If the wing stalled, the center of
pressure would not be creating a moment arm to drop the
nose, the tail must loose lift (stall) to cause the stall
break which causes the recovery from the approaching stall.

What?? The weight of the airplane is what creates the rotation once the
lift from the wing is greatly reduced after the wing stalls.


I referenced the "book" only to allow those who asked the
question to find a reference.

To find a reference that is wrong.


BTW, stall behavior changes drastically with the center of
gravity and to a lesser amount with weight.

Sure does.

Matt

Skywise wrote:

Matt Whiting wrote in news:Sf_lg.9891$lb.874408
@news1.epix.net:


Skywise wrote:


Bob Moore wrote in
.5.122:



Dylan Smith wrote

Snipola

http://en.wikipedia.org/wiki/Deep_stall

This Wikipedia article leaves a lot to be desired.

Snipola

The beauty of Wikipedia is that YOU can change it.

Brian

Which is why it leaves a lot to be desired.

Matt


I have heard more than once that a collection of average
people is smarter than a few experts. If no one corrects
the data then it will continue to be wrong. I've been
seriously thinking of getting an account so I can make
changes as I see the need. Mostly minuscule stuff, but
every bit would help. The only concern I have is time.

If I was average, I'd say this also.

Matt

Skywise wrote:

I've been seriously thinking of getting an account [on Wikipedia] so I
can make changes as I see the need.

In about the same amount of time it took you to write that sentence, you
could have made your account. Just got to http://tinyurl.com/6fvtg, type
in a user name and a password, and you're done.

Wikipedia and usenet are similar in many ways. On both, there are experts
and idiots and everything in between. The difference is that on Wikipedia,
articles have a decent chance of evolving towards containing better and
more correct information. On usenet, the same crap just gets recycled.