A dumb doubt on stalls

Kingfish wrote:

I just started flying p/t as SIC in a Pilatus PC12.

Neat plane!

I saw one a few weeks back @ MMK. I was amazed at the landing and
takeoff performance.

Kingfish wrote:
We're based at OXC (Oxford CT)



Going to the Rinker Buck thing tonight?

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

Kingfish wrote:
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.

I've never flown anything with a real AOA sensor, but it seems obvious
that on any aircraft equipped with one, anything having anything to do
with stall detection would be driven by it. What else would be the
point of having the sensor in the first place?

B A R R Y wrote:
Kingfish wrote:
We're based at OXC (Oxford CT)


Going to the Rinker Buck thing tonight?

Don't know anything about it. I'll be there for training though. Is he
making an appearance?

Kingfish wrote:
B A R R Y wrote:
Kingfish wrote:
We're based at OXC (Oxford CT)


Going to the Rinker Buck thing tonight?

Don't know anything about it. I'll be there for training though. Is he
making an appearance?


Check your hotmail.

wrote in
oups.com:


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.



In the Rallye 235E, power off, as you reach full back on the yoke, you will
encounter mild buffet and descend in a level flight attitude at slightly
over 1,000 fpm with an IAS of about 40 MPH. Aerilons are still effective
and you can easily turn in this configuration without using your rudder.
(You will get a very nice adverse yaw demonstration doing this). Just relax
slightly from full back on the yoke and the nose drops immediately. For
more fun, keep the yoke back and slowly add power and watch your VSI jump
past +500 fpm while you are still encountering mild buffet.

--
Marty Shapiro
Silicon Rallye Inc.

(remove SPAMNOT to email me)

In article .com,
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

The short answer is, "yes, it is possible, under unusual conditions."

Airplane certification requires nose-down pitch upon stall; however,
stalling with aft CG (usually well beyond the approved envelope) or deep
stall may result in an unrecoverable, nose-high sink.

Some examples:

Twin Comanche in deep stall

Beech Baron in deep stall

Velocity in deep stall.

The baron and TC have nacelles that have flat undersides that cause
major pitch-up moment in a deep stall.

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.

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.

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

Roy Smith wrote:
I've never flown anything with a real AOA sensor, but it seems obvious
that on any aircraft equipped with one, anything having anything to do
with stall detection would be driven by it. What else would be the
point of having the sensor in the first place?

Obvious to you, maybe. The Pilatypus was a big step up from a Lance for
me, with exposure to systems I've never flown with before.