A dumb doubt on stalls

Orval Fairbairn wrote:
The Velocity has a very large forward underside that does the same
thing. In fact, the designer rode one all the way into a swamp doing
deep stall tests. He was about to bail out when he noticed that the sink
rate was on the order of 1000 fpm, so he rode it down and emerged unhurt.
In fact, the airplane was repaired and flew again.

Interesting. I can just imagine the thought process in that scenario.
"Oh s**t I've lost it! Oh God!... uh... hey, it's only falling at
1000fpm - this should be survivable!! I'll stay with it then!! G


I heard of a pair of engineers from SRI who took a TC up high and tried
the deep stall. They tried everything to recover and ended up unbuckling
their seatbelts and getting under the panel. The plane finally recovered
into a high speed dive and bent the structure on recovery.

I would like to see two humans fit under the panel in a Twinkie. Were
these guys circus freaks??

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.

On a canard aircraft such as Burt Rutan designs, the forward
wing is heavily loaded and lifts up and the main wing is
more lightly loaded and at a lower angle of attack. When
the plane approaches the stall, the forward wing stalls
first and the nose drops.
see http://www.faa.gov/pilots/training/handbook/
this is the link to the chapters you
need
http://www.faa.gov/library/manuals/a...83-25-1of4.pdf


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

wrote in message
oups.com...
| Jim Macklin wrote:
| The stall buffet comes from disturbance of the air flow
over the wing root, but the
| actual stall comes from the tail.
|
|
| Actual stall comes from the tail?? Meaning?? This is more
arcane than
| I'd bargained for
|
| Ramapriya
|

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



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

"Bob Moore" wrote in message
. 122...
| Jim Macklin wrote:
| The stall buffet comes from disturbance of the air flow
over the wing
| root, but the actual stall comes from the tail.
|
| Ramapriya wrote:
| Actual stall comes from the tail?? Meaning?? This is
more arcane than
| I'd bargained for
|
| I think that Jim got it bassackwards. Approaching the
stall, airflow at
| the wing root separates and strikes the horizontal
stabilizer, shaking
| it and providing the stall warning required by FAR 23.207.
|
| From Wikipedia:
| In aerodynamics, a stall occurs when the critical angle of
attack is
| exceeded, causing loss of lift and a large increase in
drag due to
| disruption of airflow.
|
|
| Section 23.207: Stall warning.
| (a) There must be a clear and distinctive stall warning,
with the
| flaps and landing gear in any normal position, in straight
and turning
| flight.
|
| (b) The stall warning may be furnished either through
the inherent
| aerodynamic qualities of the airplane or by a device that
will give
| clearly distinguishable indications under expected
conditions of flight.
| However, a visual stall warning device that requires the
attention of
| the crew within the cockpit is not acceptable by itself.
|
| (c) During the stall tests required by §23.201(b) and
§23.203(a)(1),
| the stall warning must begin at a speed exceeding the
stalling speed by
| a margin of not less than 5 knots and must continue until
the stall
| occurs.
|
| (e) During the stall tests required by §23.203(a)(2),
the stall
| warning must begin sufficiently in advance of the stall
for the stall to
| be averted by pilot action taken after the stall warning
first occurs.
|
| Bob Moore

"Jim Macklin" wrote in message
news:J4Wlg.49291$ZW3.49195@dukeread04...
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.

If that were true, then it wouldn't be possible to sustain a stall (in, say,
a C172) by maintaining back pressure on the yoke. But in fact, such a stall
can be sustained: the plane is stalled because the wings are past the
critical angle of attack; and the tail, which is *not* stalled and does
*not* lose lift, can hold that angle of attack if up-elevator pressure is
continued.

It is possible to stall the tail if the CG is too far forward. This is
especially likely during a landing flare, resulting in a sudden drop of the
nose. But that's not how a normal stall occurs.

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

Are you referring to the paragraph about stalls on p. 3-21? First, the
information there is partly incorrect--there is no reason to think that the
tail's (downward) lift ceases during a normal stall, and (as I mentioned
above) the sustainability of such a stall (by continued back pressure) shows
that the tail's lift does not cease. Second, the paragraph does not state
that the tail's alleged loss of lift begins the plane's stall, but rather
that it contributes to a stall *recovery*.

--Gary

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.


That applies to canards. Tuft-testing of conventional layouts proves
that the pitch-down comes from the wing's airflow breaking up, and when
that happens the CP moves well aft of the CG and pitches the nose down.
Stalling stabilizers/elevators are dangerous and are not
designed into the conventional airplane. The early Cardinal had that
problem, and would drop the nosewheel hard on the runway during the
flare, sometimes breaking it. Cessna had to put slots in the stabilator
to keep it from stalling. Ice on the stab can also cause stabilizer
stall and control reversal (pull back, nose goes down). Not desireable
at all.
The aircraft service manual will have control surface travels,
as do the Type Certificate Data Sheets. Those travels are intended, in
part, to prevent stalling and control reversal.

Dan

"T o d d P a t t i s t" wrote in message
...
"Gary Drescher" wrote:

"Jim Macklin" 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.

If that were true, then it wouldn't be possible to sustain a stall (in,
say,
a C172) by maintaining back pressure on the yoke.

It depends on what you mean by "sustain a stall." I agree
with you that Jim's explanation of a normal stall is wrong,
but it *is* possible (but bad) to design an aircraft such
that the tail stalls before the wing.

Agreed. My point is just that a typical GA plane (such as the 172 I
mentioned) doesn't stall that way, contrary to Jim's claim. And one
consequence of interest to pilots is that you can remain stalled if you keep
pulling back on the yoke (instead of pushing forward as you're supposed to
when you want to recover from a stall).

--Gary

No. The wing stalls first, usually.

There have been tail stalls due to ice formtion.

karl
ATP CFI ETC


"Jim Macklin" wrote in message
news:I0Wlg.49289$ZW3.19338@dukeread04...
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.

On a canard aircraft such as Burt Rutan designs, the forward
wing is heavily loaded and lifts up and the main wing is
more lightly loaded and at a lower angle of attack. When
the plane approaches the stall, the forward wing stalls
first and the nose drops.
see http://www.faa.gov/pilots/training/handbook/
this is the link to the chapters you
need
http://www.faa.gov/library/manuals/a...83-25-1of4.pdf


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

wrote in message
oups.com...
| Jim Macklin wrote:
| The stall buffet comes from disturbance of the air flow
over the wing root, but the
| actual stall comes from the tail.
|
|
| Actual stall comes from the tail?? Meaning?? This is more
arcane than
| I'd bargained for
|
| Ramapriya
|

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
--
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?

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.

On a canard aircraft such as Burt Rutan designs, the forward
wing is heavily loaded and lifts up and the main wing is
more lightly loaded and at a lower angle of attack. When
the plane approaches the stall, the forward wing stalls
first and the nose drops.
see http://www.faa.gov/pilots/training/handbook/
this is the link to the chapters you
need
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?

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.

Matt

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