A dumb doubt on stalls

Thanks. Now tell them why they use spin chutes.



"Gary Drescher" wrote in message
. ..
| "Matt Whiting" wrote in message
| ...
| Jim Macklin wrote:
|
| If the center of pressure was located at the same
location as the CG,
| there would be no moment or force to cause rotation.
|
| Sure, there is still the force from the tail.
|
| No, Jim is right if he's referring here to the plane's CP
(not just the
| wings' CP).
|
| --Gary
|
|

"Jim Macklin" wrote in message
news:P3mmg.49385$ZW3.25845@dukeread04...
Thanks. Now tell them why they use spin chutes.

Spin chutes are used for reasons that have nothing to do with what's in
dispute here.

If the nose would always go down from a stall, spin chutes
would not be required.

No one has been saying that the nose *always* goes down from a stall. What
we're all saying is that when the nose does go down (in a normally executed
stall on a typical GA plane), it's because the wing stalls, and not
(contrary to your claim) because the tail stalls.

The tail doesn't even come close to stalling; in fact, the decrease in
(downward) tail lift that helps pitch the nose down occurs because the tail
was moved *away* from its (negative) critical angle, not towards it. And
that change occurs because the plane accelerates downward due to the reduced
lift of the stalled wings, thus changing the direction of the relative wind.

--Gary

Jim Macklin wrote:
Feel free to look me up on the FAA web. Certificated
airplanes are designed to not fully stall the wing or the
tail for that matter. But within the limits of what does
happen, and without discussing wash-in, wash-out, twist,
airfoil section changes, control stops, stick shaker and
pullers, gust loading, accelerated stalls, mushing, getting
a useable idea of what happens when the controls are applied
smoothly, violently or the airplane breaks apart in flight.

If the nose would always go down from a stall, spin chutes
would not be required. If the airplane is abused in flight,
it will do some pretty remarkable things. I know a Beech
test pilot who wondered about what would happen in an E90 at
cruise if you put the props into reverse. The airplane did
not break, but they were reported to have changed their
clothes after the flight. Same pilot tried the same thing
in an F90 with the T-tail and nothing really uncontrollable
happened.

It is possible to design a wing that will stall, 100% across
the entire span, but it won't be certified for civil use.

If the tail surface reaches max lift (down-force) and you
try to go slower, it will begin the stall as air flow
reaches the critical angle of attack on the tail
PROGRESSIVELY and the nose will drop because the moment
between the CP and CG will not be countered by the tail
forces. Do it slowly and the nose pitches down slowly.
Pull a few Gs and the reaction is faster and the degree to
which the stall progresses on the tail and wing is much
faster because inertia will carry the aircraft past the
critical angles at a higher kinetic energy level.

I've never seen this discussed in any book on aerodynamics that I've
ever read. Do you have even one credible reference to support your claims?

Matt

No, do I need a credible reference?



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

"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
| Feel free to look me up on the FAA web. Certificated
| airplanes are designed to not fully stall the wing or
the
| tail for that matter. But within the limits of what
does
| happen, and without discussing wash-in, wash-out, twist,
| airfoil section changes, control stops, stick shaker and
| pullers, gust loading, accelerated stalls, mushing,
getting
| a useable idea of what happens when the controls are
applied
| smoothly, violently or the airplane breaks apart in
flight.
|
| If the nose would always go down from a stall, spin
chutes
| would not be required. If the airplane is abused in
flight,
| it will do some pretty remarkable things. I know a
Beech
| test pilot who wondered about what would happen in an
E90 at
| cruise if you put the props into reverse. The airplane
did
| not break, but they were reported to have changed their
| clothes after the flight. Same pilot tried the same
thing
| in an F90 with the T-tail and nothing really
uncontrollable
| happened.
|
| It is possible to design a wing that will stall, 100%
across
| the entire span, but it won't be certified for civil
use.
|
| If the tail surface reaches max lift (down-force) and
you
| try to go slower, it will begin the stall as air flow
| reaches the critical angle of attack on the tail
| PROGRESSIVELY and the nose will drop because the moment
| between the CP and CG will not be countered by the tail
| forces. Do it slowly and the nose pitches down slowly.
| Pull a few Gs and the reaction is faster and the degree
to
| which the stall progresses on the tail and wing is much
| faster because inertia will carry the aircraft past the
| critical angles at a higher kinetic energy level.
|
| I've never seen this discussed in any book on aerodynamics
that I've
| ever read. Do you have even one credible reference to
support your claims?
|
| Matt

Jim Macklin wrote:
No, do I need a credible reference?

Only if you want us to believe you as what you are saying goes against
everything most of us have seen published in the literature.

Matt

"Jim Macklin" wrote in message
news:qcnmg.49388$ZW3.37903@dukeread04...
"Matt Whiting" wrote in message
...
I've never seen this discussed in any book on aerodynamics
that I've ever read. Do you have even one credible reference
to support your claims?

No, do I need a credible reference?

Either that or a credible argument.

You keep insisting that a stalled wing (without a stalled tail) could not
produce a nose-down pitch at the stall onset, even though several of us have
explained how it could do so (by changing the direction of the relative
wind) and even though you haven't pointed out any flaw in that explanation.

And you keep insisting that a normally executed stall on a typical GA plane
can stall the tail before stalling the wing, even though Todd explained that
a stalled tail would produce an outside loop (if you were to keep the yoke
pulled back), and even though you haven't pointed out any flaw in that
explanation. (In fact, what happens in, say, a 172 with the yoke kept back
is just that the stall persists, because the tail sustains the wings' high
angle of attack--which couldn't happen if the tail were stalled as you
claim.)

--Gary

On Tue, 20 Jun 2006 14:00:39 GMT, Larry Dighera wrote:

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.

You're both getting into a more complicated, thoughtful (and accurate)
analysis than I.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

george wrote:
wrote:
Hi Marty,

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

Great short field performance especially the 885

I had an 880, good performance for just 100hp(not talking speed)
Was thinking about buying an 885 but with avgas prices about $11.5/ us
gallon and not much faster than an 880......nah, not a good idea.

-Kees (D-EHNE)

wrote in
oups.com:


george wrote:
wrote:
Hi Marty,

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

Great short field performance especially the 885

I had an 880, good performance for just 100hp(not talking speed)
Was thinking about buying an 885 but with avgas prices about $11.5/ us
gallon and not much faster than an 880......nah, not a good idea.

-Kees (D-EHNE)



What is the speed of the 880? Was your 100hp engine the Rolls-Royce engine
that some of the early Rallye's had? The 885 (aka 235E) has the Lycoming
O540. I get 151 MPH (131 knots) at full throttle, but it burns almost 14
gph at that speed. I like the bigger engine for when I go to places like
Lake Tahoe in the summer as the density altitude at KTVL (6,264 MSL)can
exceed 11,000'. (Just for fun, I pulled a weather briefing for KTVL. The
DA at 12:53 AM PDT (07:53 Z) was 7,706' with an temperature of 11 C. The
forecast for tomorrow shows DA will be 10,000' with a temperature of 30 C.)

Of all the GA planes I've ever been in, either as pilot or passenger, the
Rallye is by far the most fun. My instrument instructor rated it second
best of all the aircraft he had ever piloted from both "fun to fly" and
outside visibility standpoints. Second place isn't too bad when the
aircraft he put in first place for these two factors was the F/A 18 Hornet
he flew when he was in the Navy.

--
Marty Shapiro
Silicon Rallye Inc.

(remove SPAMNOT to email me)

Hi Marty,

I think we are talking different 885s here.
As far as I remember the 885 is the light airframe with the 145 hp
O-300.
The 235 has the heavy airframe, I believe.
Well, does not matter really.

My 880 had the RR O-200, max speed about 90kts.

The only disadvantage of the Rallye I can think of is the difficulty to
get spare parts(never mind the costs, yikkes).

We used the 880 as a two-seater with a lot of luggage room.
The both of us plus full fuel and then we had 100# left for baggage,
and thats a lot if you have to carry it from and to the plane over
several 100 yards.

Having a sore back from hauling baggage is no more, I have a C150 now.

Cheers,
Kees.