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AOPA Stall/Spin Study -- Stowell's Review (8,000 words)



 
 
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  #11  
Old September 1st 03, 09:33 PM
David Megginson
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"Wayne" writes:

Since the airspeed indicator (pitot tube) is pointed the same as the
wing, then "indicated airspeed" does mean something. For instance,
if you were to put the wing at a 90 degree AOA to the relative wind,
then the airspeed would also read nothing or almost nothing correct?

So I agree that airspeed doesn't matter, but indicated airspeed
does.


His point was that the stall speeds marked on the ASI (Vs and Vso) are
applicable only at 1 G, maximum gross weight, and the appropriate
flap/gear configuration. That's why an angle-of-attack indicator
would be nice.

If you're doing anything that increases the G-load on the plane, like
turning or pulling up from a dive (i.e. anything that presses your
behind into the seat), the stall speeds will be higher; if the plane
is loaded below maximum gross weight, the stall speeds will be lower;
and so on.

It's a bit of an overstatement to say that stall speeds don't matter,
but you do have to take them with a big grain of salt. Let's say that
you have just recovered from a stall or spin and are now in a dive
heading quickly towards the ground. If you pull up hard, you might
stall the plane at close to double the Vs marked on the ASI.


All the best,


David
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  #12  
Old September 1st 03, 09:38 PM
Greg Esres
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I don't dispute that there's more to stalls than airspeed. I just
think you're all putting too fine a point on this.

I agree with you.

For every constant g-loading, there is an airspeed which is safe to
fly.



  #13  
Old September 1st 03, 09:40 PM
Chris Hoffmann
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"David Megginson" wrote in message
...
His point was that the stall speeds marked on the ASI (Vs and Vso) are
applicable only at 1 G, maximum gross weight, and the appropriate
flap/gear configuration. That's why an angle-of-attack indicator
would be nice.


Well, in a way, the airspeed indicator IS an angle-of-attack indicator.

--
Chris Hoffmann
Student Pilot @ UES
30 hours




  #14  
Old September 1st 03, 10:04 PM
David Megginson
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"Chris Hoffmann" writes:

His point was that the stall speeds marked on the ASI (Vs and Vso) are
applicable only at 1 G, maximum gross weight, and the appropriate
flap/gear configuration. That's why an angle-of-attack indicator
would be nice.


Well, in a way, the airspeed indicator IS an angle-of-attack indicator.


It's related to angle-of-attack, but note all the cautions in the rest
of this thread. It's definitely not the same thing (that's why you
see AOA indicators in some military and aerobatic aircraft).


All the best,


David

  #15  
Old September 2nd 03, 10:37 AM
Happy Dog
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"ShawnD2112" wrote in message

You can stall the airplane at Vne if you pull hard enough. There are

enough
warbird accidents where the pilot stalled at the bottom of the loop and
flopped flat into the ground to prove the theory.


But not likely at Vne. That is likely to massively overstress the airframe.
moo


  #16  
Old September 2nd 03, 06:31 PM
Jim
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On Mon, 01 Sep 2003 20:40:51 GMT, "Chris Hoffmann"
wrote:

"David Megginson" wrote in message
...
His point was that the stall speeds marked on the ASI (Vs and Vso) are
applicable only at 1 G, maximum gross weight, and the appropriate
flap/gear configuration. That's why an angle-of-attack indicator
would be nice.


Well, in a way, the airspeed indicator IS an angle-of-attack indicator.


I've seen this
The airspeed indicator is an airspeed indicator ONLY. It is not, and
should not be thought of as, ANY sort of AOA indicator. If you fly
long enough, this will kill you.

Stall AOA, for example, is a constant. The airspeed occuring at the
stall AOA can and will vary, depending on wing loading resulting
primarily from the weight loaded into the aircraft or loads imposed by
maneuvering the aircraft.
  #17  
Old September 2nd 03, 10:49 PM
Jim
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On Mon, 01 Sep 2003 20:18:34 GMT, "Chris Hoffmann"
wrote:

Airspeed alone means nothing with regard to when or whether the
airplane will stall. We need to think in terms of airspeed AND G-load
-- these are the two parameters that will give us a clue as to our
margin to the stall, or whether or not we are moving closer to, or
farther from, critical angle of attack.


.....But won't airspeed alone change the "cushion" that you have to maneuver
with? A steep turn at 90 kts isn't usually a problem. Doing something like
that near Vso on final will almost certainly be one. As you point out, at
lower airspeeds the aircraft will stall with less of a load.

I don't dispute that there's more to stalls than airspeed. I just think
you're all putting too fine a point on this. If the hypothetical instructor
said, "Watch your airspeed, or you'll reduce the amount of G-load that the
airplane can handle and may invoke a stall if you decide to maneuver
drastically", then you probably wouldn't have a problem with it, but in the
time it took to say all that, the instructor and student would be hitting
the ground! Proper instruction of what causes a stall is one thing. Not
letting your student get out of control on an approach is another.

Let's "approach" this another way: You're the instructor in this case. Do
you want your student to maintain a certain airspeed on approach? If so,
why? And if they allow the plane to get below that speed, what are you going
to say to them?


If the instructor only says to the student "Ensure your airspeed on
approach is above the stall speed", then the instructor is not
fulfilling his/her responsibility to the student.

If the instructor says to the student "Since we are flying at just
about a constant 1G throughout the approach, the Vso stall speed
marked on the airspeed indicator is the speed at which the aircraft
will stall. Therefore, keep a margin of whatever the instructor
determines is appropriate knots above that Vso airspeed as some
protection against a stall." then the instructor is working a a
proper foundation of understanding for the student.

By the way, "Stick and Rudder" is probably my favorate book on
flying too, but it must be read carefully and critically.
  #18  
Old September 2nd 03, 11:43 PM
Dan Thomas
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"Roger Long" om wrote in message . ..
I think the whole answer would be:

Keep your airspeed up (1.3 Vso) , bank angle below 30 degrees, and do
everything deliberately and gracefully.

Most trainers will tolerate a lot of off center ball if you do this but it's
still important to stay coordinated due to wind gusts and other unexpected
factors.



1.3 Vso is plenty. Many folks "add a bit just to be safe," and end
up with a high approach speed that can end up taking them off the end
of the runway, where they get hurt. Wasn't getting hurt what a higher
approach speed was supposed to avoid? Or they leave lots of rubber and
smoke behind. Or they bounce the nosegear and bust the airplane. Or
wheelbarrow off into the rhubarb.
Adding airspeed will often cause more damage and injury than it
prevents. Nail that airspeed and hold it, using power to adjust
glidepath, remembering to raise the nose as power is added and
vice-versa, or airspeed will fluctuate.
We spend considerable time with students exploring aircraft
behavior in slow flight, stalls and spins. They need to understand
that the airplane will do exactly as they ask, and that they need to
pay attention in the circuit, not start adding airspeed to make up for
inattention or incompetence.
Some of my instructors were former bush/jungle pilots who were
proficient at 1.1 Vso approaches, using plenty of power, to get into
really short strips. With power on, the stall drops markedly and safe
approaches can be made in experienced hands. Flare was made with power
instead of attitude.
Note the "experienced hands." Don't try this at home.

Dan
  #19  
Old September 3rd 03, 12:25 AM
Roger Long
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Turns are where the problems usually arise. I was taught 1.3 through the
turn to final then aiming for 1.1 to 1.2, depending on wind conditions, as
you come across the threshold.

I've had good luck doing the power thing with 40 degree flaps, arresting the
descent more with a burp of power than flare. Of course, if you got to that
point and discovered that your engine was just windmilling on you, you'd
probably make a spectacular bounce. I always check at runup that the
engine keeps running at idle with the carb heat on.

--
Roger Long


  #20  
Old September 3rd 03, 01:03 AM
Robert M. Gary
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"Chris Hoffmann" wrote in message ...
John - Just to be clear, I'm only referring to approaches. I thought that's
what that part of the original post was about - a student learning to land.

Sean-
How can you say that stalls are unrelated to airspeed, when airspeed is
related to your angle of attack? (and John, at the top of a loop at zero
airspeed, where is the relative wind coming from, or at least about to come
from? Good thing a cliff doesn't magically appear under you at that point.)

You aren't (hopefully) coming in to land at Vne. Yes, you can stall an
airplane at any speed, but the point is you don't want to let your airspeed
drop too low on approach. Period.

Maybe I'm seeing this as two seperate training issues, whereas others are
seeing it as one and the same?


Chris, you have a good point. Yes, the stall speed of your plane
changes with a variety of factors but we're talking about a known
situation, landing. Not a 3 G turn or floating a loop over the top at
..5 Gs. While a J-3 cub is easily landed without reference to airspeed,
as you go up in aircraft watching *SPEED* on final becomes more
important, unless you are likey enough to own an AOA gauge. In fact,
in heavy iron flying this *SPEED* is computed for that exact flight,
so each approach may have a different approach speed. For a 172,
things like weight variations aren't as critical as in a 747 so we
provide students with a target number for appoach. Of course, if you
choose to pull a 3 G turn or over gross the plane, that number will
not work. I think people are just poking you here to see how you will
react. As a Mooney owner I can tell you speed is critical. The Mooney
Aircraft & Pilots Association recommends no more than 1.2 Vso for
normal landing since being 10 knots fast sucks up about 1500 feet
extra runway. Yes, weight or G loading will effect this (density
altitude and humidity will effect the TAS of the stall too, but we're
just interested in IAS here). Bush pilots often stall there planes
before coming down to know what indicated *SPEED* their plane will
stall at with the current weight. This allows them to land very, very
short.

-Robert, CFI
 




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