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Newbie Qs on stalls and spins



 
 
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  #61  
Old November 21st 04, 02:15 AM
Bill Denton
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My comments in text...




"Peter Duniho" wrote in message
...
"Bill Denton" wrote in message
...
You are both right and wrong on this one.


No. I am entirely right, not wrong at all.

Obviously, different parts of an aircraft stall at different speeds.


This is true, but completely irrelevant to my statement.

[...]
You then take an airplane to 1,000 ft AGL, and trim it so it is flying
perfectly straight and level, but this time you completely close the
throttle. In a short time, the wings will stop producing enough lift to
keep
the airplane in flight, it will pitch down and impact the earth, even
though
some of the airplane's component parts may still be flying.


First, your scenario is completely incorrect as to what would happen if

you
brought the throttle to idle. The airplane would NOT stall. It would
simply pitch down enough to maintain the trimmed airspeed, and glide to
whatever final destination it was aimed at.


Both scenarios are incorrect as originally posted. Please see my second
respone to Bob Moore (just above) for my corrections.



But more importantly, your understanding of a stall is flawed. Even

simply
looking at just the wing, and even ignoring such design features as

washout,
upon reaching the critical angle of attack lift does not go straight from
maximum available lift to 0. There is a very narrow range of angle of
attack where the lift drops off rapidly, and within this range, there is
just as much lift as was available at angles of attack just below the
critical angle of attack.

For a variety of reasons, it's unlikely that a pilot would ever

successfully
negotiate this very narrow range. But it does exist, and a person who
claims that a wing is strictly "not stalled" or "stalled" is simply
demonstrated lack of completely knowledge of what happens during a stall.

A
stall is more like a dimmer light switch (with a very short throw) than it
is like a regular "on/off" light switch.


From my previous post: "Obviously, there is a range between the point where
an element is producing zero lift, where it is producing enough lift to
"fly" the unit itself at a consistent altitude, and where it is produing
enough lift to fly the required load at a consistent altitude."

The inverse would also be true.

Generally, I am using the term "stall" to indicate a state where the object
is producing zero lift, and "flying" to indicate that some lift is being
produced. However, I sometimes use flying to indicate that the object is
generating enough lift to raise itself and it's load above the earth. I will
try to be more consistent and clear in the future.

I don't claim that this is absolutely, or in any way correct, but this is
how I am using the terms.



[...] I think it is also evident that I do understand at least the
basic principles involved in the discussion.


Very basic principles. But you still have quite a ways to go. You might

do
well to stop telling people they are wrong, at least until you've actually
*mastered* the subject.

But please assume an airplane, accept my terminology, and consider the
following:

If a wheel is rolling, you cannot start it rolling.

My statement was: " If the airfoil is flying you cannot take off, and if
it's not flying it's stalled", which would translate as follows: "If the
airplane IS flying it cannot START flying"' the rest reflects the
flying/stalled paradyme, which I readly admit is not absolutely correct.


So you really did mean to write "if the airfoil is flying you cannot take
off". I've got to say, that's got to be one of the most intentionally
obtuse ways of saying something I've seen in a long time.


That is what I mean to write, but again I was not writing from scratch; I
was picking up on the orignal poster.



In any case, you are simply incorrect to say "if it's not flying it's
stalled". That is a patently false proposition. I have an airplane

sitting
in my hangar right now that is not flying (at least, it had better not

be!),
but it is not stalled either.


No argument that I am probably using the terms incorrectly; please see my
previous note.


Actually, it was the original poster who failed to define "flying" and
specify what was flying. As noted above, I am looking at this in the
context
of an entire airplane, which seems to have been the original poster's
intent.


Another red herring. It really doesn't matter whether you are talking

about
the entire airplane or the wing. But for the record, when one refers to a
"stall", they are generally referring to a stall of the main wing (and by
implication, the entire airplane).


Which is the way I am generally using the term, unless I am specifically
referring to a stall affecting only a specific portion of an airplane.


In fact, the airplane doesn't need to move on the runway at all;
given a sufficient releative wind, parts of the airplane would begin to
fly
without the airplane moving forward at all.


I thought your claim was that an airplane that was flying (and thus
presumably parts of an airplane that are flying) cannot take off. Now you
are saying parts of the airplane can fly while still on the ground. Your
statements are inconsistent with each other.


That was what I stated, if the ENTIRE airplane is flying, i.e. with no parts
in contact with the earth, it cannot take off.

But with a tail dragger, doesn't the horizontal stabilizer begin to produce
enough lift to raise the tail, and raise the tailwheel above the earth,
before the wing produces enough lift to raise the entire airplane abouve the
earth?



And given a relative wind even
slightly higher than the stall speed of the aircraft, it could
theoretically
take off and continue to ascend with no forward movement.


No, it could not. With a strong enough wind, the airplane might lift off
the ground, but it would immediately begin to slow within the airmass
(accelerating backwards relative to the ground) and descend back to the
ground. There would be no "continue to ascend" about it.


"accelerating backwards relative to the ground" is not the same as "no
forward movement".

I was incorrect with "continue to ascend".


I agree with your definition, but it has to be consiered in light of
whether
we are discussing a single element or an entire airplane.


We are discussing the wing, which is the only thing of interest in this
case. If you want to call that "the entire airplane", that's fine too,

but
make no mistake: it's still just the wing.


But just a wing in a wind tunnel behaves differently than the same wing when
attached to an airplane. And parts of an airplane other than the wing can
generate lift.



If an airplane is only moving at 1
kt. down a runway, it is probably not flying.

Again, you'll have to define "flying". But the wing certainly is

developing
lift, and certainly is NOT stalled.


I should have added "in a condition of zero wind". Given that, there are
probably wings out there that would not generate appreciable lift at 1 kt.



How 'bout if I throw in a 10 kt tailwind? g


If you want to change the discussion in an attempt to make your comments
make sense, feel free. I probably won't have the patience to bother

though,
and will simply feel justified in assuming that you aren't really

interested
in learning what the facts are.

I recommend you stick with the original ideas, and where you've clearly
meant "1 knot of relative wind" by saying "if an airplane is only moving

at
1 knot down a runway", you should avoid complicating things by trying to
reinterpret what you've written.


As I noted above, I failed to address relative wind and referred only to the
aircraft's speed.



Simply untrue. Virtually all of my landings involve touching down and
coming to a stop without ever exceeding the wing's critical AOA. I

hesitate
to claim that I've *never* stalled the wing during a landing, but I

sure
don't do it intentionally.


And this comes back to the flying/stalled paradym.


Sometimes I rely too much on spell chekers.



The word is "paradigm". And frankly, I have no idea what you mean by

"this
comes back to". This thread *should* have stayed with the question of a
stall all along. Only your digressions have prevented that.

The bottom line here is that your statements that "you can't take off
without a stall" and that "an aircraft will not land until it has reached

a
stalled state" are both patently false. You can very much both take off

and
land without ever stalling the airplane.


Again, that comes down to terminology; and I again state that I may well be
using it incorrectly.



Pete




  #62  
Old November 21st 04, 05:26 AM
Hilton
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Hi,

Hint to everyone involved in this thread: Don't use the word "flying" wrt
stalls etc - it is completely ambiguous. Use "exceeding the critical AOA",
"stalled", "producing lift", etc. It's hard enough discussing aerodynamics
on the NGs, why waste bandwidth trying to define ambiguous words?

Just my 5c.

Hilton


  #63  
Old November 21st 04, 06:17 AM
G.R. Patterson III
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Bill Denton wrote:

You then take an airplane to 1,000 ft AGL, and trim it so it is flying
perfectly straight and level, but this time you completely close the
throttle WHILE ATTEMPTING TO MAINTAIN THE ORIGINAL PITCH. In a short time,
the wings will stop producing enough lift to keep the airplane in flight, it
will pitch down and impact the earth, even though some of the airplane's
component parts may still be flying.


Well, perhaps some might. If you maintain a level pitch attitude in my aircraft
with the throttle closed, the plane will simply descend. The airspeed will be
between 60 to 70 mph with 0 degrees of flaps (stall is about 55 in that
configuration). If you want mine to stall, you'll have to get the nose pretty
high.

Now, if I were to close the throttle and attempt to maintain *altitude* by
raising the nose, she'd stall. When that happens, the nose repeatedly drops a
bit and then goes back up, and the plane descends at a moderate rate of speed in
a nose high attitude.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.
  #64  
Old November 21st 04, 06:21 AM
Peter Duniho
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"Bill Denton" wrote in message
...

[...]
Generally, I am using the term "stall" to indicate a state where the
object
is producing zero lift,


As has been pointed out numerous times, this is not the correct definition
of "stall".

If you want to participate in discussions in this newsgroup on the topic of
a stall, you need to use the same definition the rest of us are using. It
is pointless to make up your own definition and then go around telling US
that WE are wrong, just because we're not using the same screwed up
definition of a word you're using.

and "flying" to indicate that some lift is being
produced.


No, that's not how you're using the term "flying". If it were, then you
would not claim that "If the airfoil is flying you cannot take off", because
by your NEW definition of "flying" (given above) the airfoil is indeed
flying long before takeoff.

It's bad enough you're making up your own non-standard definitions for words
that have reasonably well-accepted definitions in aviation (and in the case
of "stall", that has a very specific and well-understood definition). But
if you can't even be consistent about your OWN use of the made-up
definitions, it's basically impossible to carry on any sort of discussion.

However, I sometimes use flying to indicate that the object is
generating enough lift to raise itself and it's load above the earth. I
will
try to be more consistent and clear in the future.


Yes, please do. As I said, you simply compound your basic error (using the
wrong definition in the first place) with your error of inconsistency.

I don't claim that this is absolutely, or in any way correct, but this is
how I am using the terms.


It's good you don't claim the uses are correct, because they are not.

[...]
I thought your claim was that an airplane that was flying (and thus
presumably parts of an airplane that are flying) cannot take off. Now
you
are saying parts of the airplane can fly while still on the ground. Your
statements are inconsistent with each other.


That was what I stated, if the ENTIRE airplane is flying, i.e. with no
parts
in contact with the earth, it cannot take off.


Again, the main problem here appears to be your lack of any semblance of
consistency. By at least one definition of "flying" that you are using, it
would be impossible for just some of the components of the airplane to be
"flying". As I said, your statements are inconsistent with each other.

But with a tail dragger, doesn't the horizontal stabilizer begin to
produce
enough lift to raise the tail, and raise the tailwheel above the earth,
before the wing produces enough lift to raise the entire airplane abouve
the
earth?


Yes, generally. But so what?

And given a relative wind even
slightly higher than the stall speed of the aircraft, it could
theoretically
take off and continue to ascend with no forward movement.


No, it could not. With a strong enough wind, the airplane might lift off
the ground, but it would immediately begin to slow within the airmass
(accelerating backwards relative to the ground) and descend back to the
ground. There would be no "continue to ascend" about it.


"accelerating backwards relative to the ground" is not the same as "no
forward movement".


No, it's not. So what?

I was incorrect with "continue to ascend".


Yes, you were. That was the entire point of that part of my reply.

But just a wing in a wind tunnel behaves differently than the same wing
when
attached to an airplane. And parts of an airplane other than the wing can
generate lift.


So what? They don't contribute much, and in any case, they don't stall the
way the wing does. We are still only talking about the main wing stalling.
No matter how many times you try to redirect the conversation to some
mythical component-based analysis of the airplane, we are still just talking
about the wing, its angle of attack, and what happens if and when that angle
of attack exceeds the critical angle of attack for a stall.

If an airplane is only moving at 1
kt. down a runway, it is probably not flying.

Again, you'll have to define "flying". But the wing certainly is
developing
lift, and certainly is NOT stalled.


I should have added "in a condition of zero wind". Given that, there are
probably wings out there that would not generate appreciable lift at 1 kt.


Most wings would not generate very much lift at all at 1 knot of relative
wind. But they do generate lift (ALL of them), and they are NOT stalled.

[...]
Again, that comes down to terminology; and I again state that I may well
be
using it incorrectly.


Yes, you are. Utterly. This entire subthread is a direct result of that
incorrect use of the terminology, and your insistence on *correcting* those
of us who are using the CORRECT terminology.

Pete


  #65  
Old November 21st 04, 06:34 AM
G.R. Patterson III
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Bill Denton wrote:

Generally, I am using the term "stall" to indicate a state where the object
is producing zero lift, and "flying" to indicate that some lift is being
produced. However, I sometimes use flying to indicate that the object is
generating enough lift to raise itself and it's load above the earth. I will
try to be more consistent and clear in the future.

I don't claim that this is absolutely, or in any way correct, but this is
how I am using the terms.


That's certainly not the correct definition of a stall. See any good textbook (I
suggest Jeppesen-Sanderson's "Private Pilot Manual"). I agree with Hilton that
the term "flying" is ambiguous in the literature.

But with a tail dragger, doesn't the horizontal stabilizer begin to produce
enough lift to raise the tail, and raise the tailwheel above the earth,
before the wing produces enough lift to raise the entire airplane abouve the
earth?


Not really. The stabilizer on a conventional aircraft pushes down on the tail;
it produces reverse lift, if you like. The tail is usually raised on a
taildragger by forward elevator. There *is* a certain amount of lifting force
caused by the impact of air against the lower surface of the stabilizer, and
this *may* be sufficient to get the tail off the ground before the mains lift
off. If I'm trimmed for takeoff, however, and I simply neutralize the controls,
my taildragger will bring all three wheels off at about the same time. At an
uncomfortably low airspeed, I might add.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.
  #66  
Old November 21st 04, 04:34 PM
Bill Denton
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I think it's time that I wake up on this beautiful Chicago day and realize
that I have once again spent more time talking than listening, with the
consequence that I have managed to talk my head completely up my ass. Which
generally leaves one talking out there ass! Unfortunately, I do that
sometimes.

I'm reasonably intelligent, logical, and creative, and often that allows me
to come up with some really good conclusions and solutions. But I sometimes
fail to remember that others may have gotten there and gotten it right long
before I even start down the road.

For those of you who have spent your time and energy trying to help me "get
right with God" on this subject, I truly appreciate your patience and help.
I will try to do more listening than talking in the future.

For those of you who long since gave up on me, I admit to sometimes being
the donkey in the parable about the donkey and the brick, and it sometimes
takes a few licks with a few bricks for me to get the picture.

For all of you who simply put up with my lack of knowledge; thank you.

For those of you who tried to help me and teach me something; thank you. I
will try to be more receptive in the future.

And to all of you, my sincerest apologies for being such a pain in the ass.




"Todd Pattist" wrote in message
...
Peter's comments on this are right on.

I'll add a bit to the difference between a landing and a
"level" stall in flight. As you may recall, the total drag
on an aircraft is the sum of induced drag and parasitic
drag. The induced drag is high at low speeds and parasitic
is high at high speeds.

Anyway, as you slow in your attempt to produce a level
stall, induced drag rises very quickly (by a factor
proportional to one over the airspeed squared.) This rapid
drag rise causes a descent that quickly increases the angle
of attack of the wing to above the critical angle and thus
you quickly get to the stall and beyond it., producing a
loss of lift and the continuation of the descent.

During landing, the increased induced drag tries to cause
the same descent you experienced aloft, but fortunately your
wheels are there to catch you, and you never get the rapid
AOA increase that you got aloft, so you never get a true
stall.

"Andrew Sarangan" wrote in message
. com...
You guys are challenging my understanding of landings :-)


Challenge is good for the soul.

The landing technique, as taught by many before us, is to
progressively increase elevator deflection to maintain zero vertical
speed.


That's the ideal. In practice, it's nearly impossible to obtain exactly
zero vertical speed, and it's bad form for your vertical speed to go
positive (i.e. start to climb). In a properly executed landing, vertical
speed is always negative (i.e. a descent), and one typically reaches the
runway before reaching the critical AOA.

I suppose it is possible that you can reach max elevator
without reaching critical AOA.


Certainly once the main gear is on the ground, it is. I commonly

continue
to increase elevator back pressure after touchdown, so as to allow the
nosewheel to touchdown gently, and may well reach max elevator travel

before
allowing the nosewheel to touch. But this is a red herring in any case,

as
there is no requirement nor even a recommendation to reach max elevator
travel during a landing.

But I think that is unlikely, because
that would mean you will never be able to perform power-off stalls in
level unaccelerated flight.


At least one plane does have this characteristic (Ercoupe). Landings in
that airplane, one in which it is impossible to stall (in level
unaccelerated flight, anyway, such as one would experience during a
landing), are pretty much just like landings in any other airplane.

A typical "normal" landing involves flying a slightly fast approach speed
(1.2 to 1.3 Vs0), and then flaring and touching down while still above

Vs0.
One hopes that during the flare, airspeed is reduced to as close to Vs0

as
possible so as to minimize touchdown speed. In optimal conditions, a
well-executed landing will even be done with the stall warning going off.
But touchdown itself should still occur prior to the stall occurring

(which,
of course, prevents the stall from occurring at all).

Bottom line: just as George said, "no normal landing involves a stall".

Pete


"It is possible to fly without motors, but not without knowledge and

skill."
Wilbur Wright



  #67  
Old November 21st 04, 05:00 PM
external usenet poster
 
Posts: n/a
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Bill,

You are so cool! Each of us should reflect upon our own participation
in rec.aviation.*, and once again become so humble as to thank your
mentors (and adversaries), and once again attempt to absorb the
incredible knowledge (often) portrayed here!

I, for one, am thankful for what I have learned here, and the little
that I am privileged to say about mountain flying.

Jer/ Eberhard

Bill Denton wrote:
For all of you who simply put up with my lack of knowledge; thank you.


For those of you who tried to help me and teach me something; thank you. I
will try to be more receptive in the future.


And to all of you, my sincerest apologies for being such a pain in the ass.


Best regards,

Jer/ "Flight instruction and mountain flying are my vocation!" Eberhard

--
Jer/ (Slash) Eberhard, Mountain Flying Aviation, LTD, Ft Collins, CO
CELL 970 231-6325 EMAIL jer'at'frii.com WEB http://users.frii.com/jer/
C-206 N9513G, CFII Airplane&Glider, FAA-DEN Aviation Safety Counselor
CAP-CO Mission&Aircraft CheckPilot, BM218 HAM N0FZD, 221 Young Eagles!
  #68  
Old November 21st 04, 09:45 PM
Rick Macklem
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Stefan wrote in message ...
Ramapriya wrote:

Oh, so the ones that become transport aircraft pilots don't ever get
to practice stall and spin recoveries, then? That'd make me more
jittery before going on a plane the next time...


I think most of them train stalls in the simulator on a regular basis.
Spins however... I might be wrong, but to my knowledge, most transport
category airplanes would break on spin recovery.

Stefan


There are now companies (www.fcitraining.com, www.stallion51.com to
name two
examples) that are trying
to market specialty training in unusual attitude recovery, using
aircraft capable of aerobatics. I don't know if any of the major
airlines have bought into this,
but I understand that some of the corporate flight departments have.

I will also note that just about any airline pilot has practiced stall
recovery
in light planes during their training and some have done spin training
in light
aircraft, as well.

Whether or not this is revelant to large aircraft operations
or not seems to be a "hot topic" these days and I, personally, have no
idea
what the answer is?

rick, who loves to loop and roll light aircraft but has no idea if
this
would be useful training for airline pilots
  #69  
Old November 21st 04, 11:16 PM
mhquay
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Bill Denton wrote:

Generally, I am using the term "stall" to indicate a state where the

object
is producing zero lift, and "flying" to indicate that some lift is

being
produced. However, I sometimes use flying to indicate that the object

is
generating enough lift to raise itself and it's load above the earth.

I will
try to be more consistent and clear in the future.

I don't claim that this is absolutely, or in any way correct, but

this is
how I am using the terms


Bill

Without getting too technical.

An aircraft is "flying" regardless of whether it is climbing, decending
or "flying" level.
By using the throttle and the attitude of the nose of the aircraft the
pilot controls the relative airflow over the wing and thus determines
the mode of flight he wants.

Climbing - Lift is Greater than weight
Level - Lift = weight
Descending (including landing) - Lift if less than weight

All the above are controlled "flying"

The stall is uncontrolled "flying" and the only time this should happen
whilst "flying" is in stall recovery practice, aerobatics and sometimes
a second prior to touchdown.

Phil


--
mhquay
------------------------------------------------------------------------
Posted via OziPilots Online [ http://www.OziPilotsOnline.com.au ]
- A website for Australian Pilots regardless of when, why, or what they fly -

  #70  
Old November 22nd 04, 12:04 AM
Peter Duniho
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"Bill Denton" wrote in message
...
And to all of you, my sincerest apologies for being such a pain in the
ass.


Apology accepted. At least you didn't call anyone any names...which,
around here, is a shining compliment indeed.


 




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