A letter I sent to the Wings Channel

"Steve House"
wrote:

According to my textbooks that's not true. Maximum lift is just before the
stall. Once in the stalled condition itself, at or beyond the separation
point of the flow of air over the airfoil, lift is lost and "the airplane
ceases to fly." (From The Ground Up, Aviation Publishers, Ottawa, page 35
and Flight Training Manual, Transport Canada, page 75)

You completely misunderstand stall and your misunderstanding
is perpetuated by the complained-about programming. Maximum
lift is just before stall and just after stall the lift is
just about equal to that maximum. Understanding that lift
is produced during stall is essential to a proper
understanding of spins and aerobatic flight.

Of course not all
lift is gone - if you want to get picky about it, even a dropped brick has
SOME lift -

The lift remaining just after stall is almost the same as
the lift just prior to stall, and is still supporting almost
all of the aircraft's weight.

but what does remain is insufficient to support the weight of
the airplane

The one difference is that as AOA increases, lift decreases,
and since the aircraft is designed to increase AOA when the
wings are not producing enough lift, after stall, the plane
automatically produces less and less lift if the pilot
allows the pla ne to "do its thing" and increase AOA
further.

It is actually possible in some fully aerobatic high-powered
aircraft to supplement the small amount of missing lift from
a stalled wing with engine thrust. The plane can then be
flown with the wings fully stalled. I saw it demonstrated
last year. Similarly, some spin modes have both wings fully
stalled, and the descent rate is constant. Thus, the wings
are fully supporting the weight of the aircraft with the
lift produced when stalled.

and as you said in another message, the airplane is indeed
falling rather than flying. Thus "at the stall" would be the point at which
the wing stops producing (adequate) lift, just as he said.

Saying it produces less lift after stall is correct. Saying
it stops producing lift is not correct and is highly
misleading.


Todd Pattist
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"Todd Pattist" wrote in message
...
....snip...
According to my textbooks that's not true. Maximum lift is just before
the
stall. Once in the stalled condition itself, at or beyond the separation
point of the flow of air over the airfoil, lift is lost and "the airplane
ceases to fly." (From The Ground Up, Aviation Publishers, Ottawa, page 35
and Flight Training Manual, Transport Canada, page 75)

You completely misunderstand stall and your misunderstanding
is perpetuated by the complained-about programming. Maximum
lift is just before stall and just after stall the lift is
just about equal to that maximum.

Not relating my understanding but giving close to a direct quote from the
two training manuals I've been told to use for my ground school and flight
training, plus my online ground school materials itself. The phrase "the
airplane ceases to fly" IS an exact quote, that's why the quotation marks.
Those training materials are consistent with the statements that you have
taken exception to that were presented in the TV program in question. You
may be correct and they wrong, but the burden is on you.

....snip...

and as you said in another message, the airplane is indeed
falling rather than flying. Thus "at the stall" would be the point at
which
the wing stops producing (adequate) lift, just as he said.

Saying it produces less lift after stall is correct. Saying
it stops producing lift is not correct and is highly
misleading.


So the whole debate is about whether the instructor in question should have
used the words "adequate lift" instead of just "lift." So how many angels
was it you said could dance on that pinhead?

Steve House wrote:

So the whole debate is about whether the instructor in question should have
used the words "adequate lift" instead of just "lift." So how many angels
was it you said could dance on that pinhead?

Beyond the stall, the airplane will begin losing altitude; that much
everyone agrees on. If it were truly "falling", as if the wings were
not there, it would accelerate until it reached terminal velocity (I
believe a speed over 10000 ft/min). That doesn't happen. Instead, the
vertical speed (in a bugsmasher) goes to some considerably smaller value
and sits there. Since the airplane is travelling in a straight line at
constant speed, the wing must not only be producing lift, it must be
producing exactly as much lift as it ever did--namely, the weight of the
plane. (I'm neglecting additional lift from the fuselage, prop, etc. I
think as a first approximation this is legal.)

If lift truly went away at the stall, pilots would *beg* to enter spins,
just to slow the plane down.

Tim

Tim Bengtson wrote:

Beyond the stall, the airplane will begin losing altitude; that much
everyone agrees on. If it were truly "falling", as if the wings were
not there, it would accelerate until it reached terminal velocity (I
believe a speed over 10000 ft/min). That doesn't happen. Instead, the
vertical speed (in a bugsmasher) goes to some considerably smaller value
and sits there. Since the airplane is travelling in a straight line at
constant speed, the wing must not only be producing lift, it must be
producing exactly as much lift as it ever did--namely, the weight of the
plane. (I'm neglecting additional lift from the fuselage, prop, etc. I
think as a first approximation this is legal.)

If lift truly went away at the stall, pilots would *beg* to enter spins,
just to slow the plane down.

When I owned my Pitts Special, one of the exercises that my aerobatic coach had
me do frequently was precision turns to ground reference headings using nothing
but rudder. What made them interesting was the requirement that the airplane had
to be kept in a fully stalled condition while making those turns, which of course
meant that they were all done during a descent. Clearly there is a significant
amount of lift produced by an airfoil which has exceeded the critical angle of
attack. Whether an aircraft can maintain a certain altitude or attitude beyond
the critical angle of attack is a function of the thrust it can create from its
powerplant.

Going back to the remark made by the instructor (which I didn't catch, although
I've seen a few episodes of the show), I'm not inclined to denounce his
technically inaccurate remark. When you take a five hour student pilot up and
introduce stalls, you must make very basic explanations, sometimes filling in the
blanks later down the line (or later in the lesson.) I doubt that 'Kyle' would
have been ready to listen to a dissertation on aerodynamics at that moment in the
flight.

-Ryan
CFII-A/MEI/CFI-H

On Wed, 30 Jul 2003 03:13:06 GMT, Ryan Ferguson
wrote:

Tim Bengtson wrote:

Beyond the stall, the airplane will begin losing altitude; that much
everyone agrees on. If it were truly "falling", as if the wings were
not there, it would accelerate until it reached terminal velocity (I
believe a speed over 10000 ft/min). That doesn't happen. Instead, the

With the nose down many would well exceed the 10,000 fpm (120 mph)
which is for the human body in free fall.

You could throw out a sheet of plywood and if you could keep it
positioned perpendicular to the direction of travel it would fall
quite slowly. There might be some lift, but it is mainly drag. The
same thing is true for terminal velocity of a human...bout 120 mph.
Again it's mainly drag that keeps terminal velocity low.

vertical speed (in a bugsmasher) goes to some considerably smaller value
and sits there. Since the airplane is travelling in a straight line at
constant speed, the wing must not only be producing lift, it must be
producing exactly as much lift as it ever did--namely, the weight of the
plane. (I'm neglecting additional lift from the fuselage, prop, etc. I
think as a first approximation this is legal.)

As the plane is not maintaining level flight there would not be quite
that much lift. It may not be accelerating, but it's not holding
altitude. I's hazard a guess and say a good portion of the lift in
the stalled state is actually drag. Maybe not as much as the lift
produced by the wind...but who knows?

I base this on an article on deep stalls . The author stalled either
a Cozy or long eze I believe and actually climbed out on the wing
trying to get it un stalled. He rode it all the way to the water.
He remarked in the article that there was almost no airflow over the
wing and he felt only a slight breeze. The travel was almost vertical
with the plane in a horizontal position. As I recall he wasn't even
hurt.


If lift truly went away at the stall, pilots would *beg* to enter spins,
just to slow the plane down.

At extremely high angles of attack such as 90 degrees as in the above
example the drag is so high the speed never builds up to the point
where the wing is capable of flying. To me the deep stall is much
like an unrecoverable spin, but with a very slow rate of descent. Not
something I'd want to try in anything other than a plane with very
light wing loading.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)


When I owned my Pitts Special, one of the exercises that my aerobatic coach had
me do frequently was precision turns to ground reference headings using nothing
but rudder. What made them interesting was the requirement that the airplane had

I've flown a number of planes where I kept them in a stalled
conditions. The cherokee was one where it was easy to make turns in
the stalled state. The 172 was not bad, but the Deb takes all the
rudder work to just stay upright.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

to be kept in a fully stalled condition while making those turns, which of course
meant that they were all done during a descent. Clearly there is a significant
amount of lift produced by an airfoil which has exceeded the critical angle of
attack. Whether an aircraft can maintain a certain altitude or attitude beyond
the critical angle of attack is a function of the thrust it can create from its
powerplant.

Going back to the remark made by the instructor (which I didn't catch, although
I've seen a few episodes of the show), I'm not inclined to denounce his
technically inaccurate remark. When you take a five hour student pilot up and
introduce stalls, you must make very basic explanations, sometimes filling in the
blanks later down the line (or later in the lesson.) I doubt that 'Kyle' would
have been ready to listen to a dissertation on aerodynamics at that moment in the
flight.

-Ryan
CFII-A/MEI/CFI-H

Todd Pattist wrote:

a lot of good stuff

Oh good; the cavalry. I was getting worried.

Tim

Tim Bengtson wrote:
Oh good; the cavalry. I was getting worried.

Sorry we were late, there was trouble in the Indian Country.

(this has intentional double meaning - one aviation related,
one cavalry related)

If you've got a sound card, go he
http://www.rangerhorse.org/gowen.mid


Todd Pattist
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