A dumb doubt on stalls

"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

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.

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??

"Kingfish" wrote

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

I would say that if you thought you were about to die, but could be saved by
crawling into my back pocket, you would probably find a way to fit! g
--
Jim in NC

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?

I'm assuming you mean *either* power on or off in which case:
Yes and without going into a deep stall and staying within the CG
limits.

Or does aircraft design inherently
preclude that?

Typically the design makes it either easy to get out of such an
attitude ,or makes it difficult to achieve.


If you try, you can stall a Bonanza, a 150, 172, or a Cherokee 180
and keep the nose up. The nose will not necessiaril fall through
until you release or at least ease off on the back pressure.

I can put the Deb into a stall, nose high and end up with a rather
high sink rate (phenomenal compared to a 150). The hard part is not
keeping the nose high, tail low, but keeping it right side up.


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Thanks in advance,

Ramapriya