A dumb doubt on stalls

Is it possible for an aircraft to stall and sink nose-up tail-down
instead of pitching nose-down? Or does aircraft design inherently
preclude that?

Thanks in advance,

Ramapriya

On 2006-06-20, wrote:
Is it possible for an aircraft to stall and sink nose-up tail-down
instead of pitching nose-down? Or does aircraft design inherently
preclude that?

Conventional light planes should not do that (i.e. certified, non-canard
designs). However, some rear engined T-tailed airliner designs WILL do
that. It is called a deep stall, and is irrecoverable.

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

has a diagram. Note that in a rear engined T tailed plane, the wash from
the wing will prevent appreciable thrust being made by the engines, so
you can't just 'power' out of it either.

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On 20 Jun 2006 03:30:46 -0700, wrote:

Is it possible for an aircraft to stall and sink nose-up tail-down
instead of pitching nose-down? Or does aircraft design inherently
preclude that?

Thanks in advance,

Ramapriya

Thinking about it simply, if the airplane is not generating lift, it should
fall with the heaviest end down. For most light GA a/c, the engine is up
front, so that end goes down first.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Dylan Smith wrote

On 2006-06-20, wrote:
Is it possible for an aircraft to stall and sink nose-up tail-down
instead of pitching nose-down? Or does aircraft design inherently
preclude that?

YES

Conventional light planes should not do that (i.e. certified, non-canard
designs). However, some rear engined T-tailed airliner designs WILL do
that. It is called a deep stall, and is irrecoverable.
http://en.wikipedia.org/wiki/Deep_stall

This Wikipedia article leaves a lot to be desired. Stick Shakers are not
related to the deep stall. Stall Warning devices which include stick
shakers are required because of a lack of sufficient natural stall warning
buffet in any airplane. The cure for the Deep Stall was the "Stick Pusher"
which prevented the aircraft from reaching the stalling AOA in the first
place.

has a diagram. Note that in a rear engined T tailed plane, the wash from
the wing will prevent appreciable thrust being made by the engines, so
you can't just 'power' out of it either.

Wing wash had nothing to do with engine power available, the extreamly high
AOA for the deep stall also put the engine cowls at an extream angle from
the relative wind resulting in compressor stalls.

Bob Moore

Dylan Smith wrote:
Conventional light planes should not do that (i.e. certified, non-canard
designs).

A Morane Saulnier Rallye is a conventional certified light plane and it
just drops with its nose up and tail down when stalled.
But I suppose it is an exception to the rule.

-Kees.

Ron Rosenfeld wrote:
Thinking about it simply, if the airplane is not generating lift, it should
fall with the heaviest end down. For most light GA a/c, the engine is up
front, so that end goes down first.


The wing's center of pressure moves forward as the stall is
approached, as the laminar flow over the top of the wing breaks up
toward the trailing edge and lift is lost over the aft area of the
wing. At the stall, the center of pressure moves aft as the whole
laminar flow goes turbulent, and the CP shift lifts the tail.
The loss of effective downforce on the stabilizer as speed
decreases contributes to the nose drop. That's the "heavy end down"
effect you speak of.

Dan

This Wikipedia article leaves a lot to be desired.

Why not edit it? That's how a wiki works.

Jose
--
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for Email, make the obvious change in the address.

The location of the center of gravity directly relates to an
aircraft's dynamic and static stability. Stall behavior
with a CG aft of the center of pressure on a wing will cause
the stalled aircraft to pitch deeper into the stall. The
stall buffet comes from disturbance of the air flow over the
wing root, but the actual stall comes from the tail.


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

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wrote in message
oups.com...
| Is it possible for an aircraft to stall and sink nose-up
tail-down
| instead of pitching nose-down? Or does aircraft design
inherently
| preclude that?
|
| Thanks in advance,
|
| Ramapriya
|

On Tue, 20 Jun 2006 07:36:13 -0400, Ron Rosenfeld
wrote in
::

On 20 Jun 2006 03:30:46 -0700, wrote:

Is it possible for an aircraft to stall and sink nose-up tail-down
instead of pitching nose-down? Or does aircraft design inherently
preclude that?

Thanks in advance,

Ramapriya

Thinking about it simply, if the airplane is not generating lift, it should
fall with the heaviest end down. For most light GA a/c, the engine is up
front, so that end goes down first.

You may recall, that Galileo Galilei (1564-1642) performed experiments
to verify that heavier bodies do not fall faster than lighter ones,
rather that they fall at the same rate, therefore your analysis is
incorrect.

While it is true, that an airplane in a vacuum will fall in any
orientation, in the atmosphere, it is practically impossible to
prevent the falling airplane's wings from providing some lift. Given
an airplane correctly loaded within its weight and balance envelope,
when the wing is generating lift, the center of lift is located behind
the aircraft's center of gravity. The center of gravity acts as a
fulcrum, and the lifting force aft of the CG is acting in the
direction roughly upward, while the gradational force acts uniformly
on the entire airplane in a downward direction resulting in the nose
dropping as the aircraft was designed.

Bob Moore wrote:

Stick Shakers are not related to the deep stall. Stall Warning devices which include stick shakers are required because of a lack of sufficient natural stall warning
buffet in any airplane. The cure for the Deep Stall was the "Stick Pusher"
which prevented the aircraft from reaching the stalling AOA in the first place

I just started flying p/t as SIC in a Pilatus PC12. Never had any
exposure to a stick shaker or pusher, but the PC12 has both. Stall
training in that plane was *interesting* although I did't realize those
systems were driven by the AOA sensor and not airspeed.