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

"Chris Hoffmann" wrote in message ...
The first thing that jumped out at me from your report is this:

Another myth cited in the AOPA study is "watch your airspeed, or
you're going to stall this airplane!"

Pardon me, but if your airspeed gets below stall speed, you ARE going to
stall. Further, if your airspeed is below the usual 1.3 Vso safety cushion,
you are getting to the point where all it takes is a turn too steep, or a
bit of tailwind, or a yank back on the yoke, and you are LIKELY to stall.
This is not "myth".


Ah, but therein lies the rub! Within the ability of the structure to
withstand G-load without deforming/breaking, the airplane can be
stalled at ANY airspeed. In that context, every airspeed is a
potential "stall speed" provided the G's applied are sufficient to
exceed critical angle of attack. "Getting below stall speed" is only
meaningful if the instantaneous G-load is specified.

For example, if I pull 3.8 G's while at Maneuvering speed, Va, the
airlane will stall (Va = 1.95Vso). If I am in wings-level flight (1
G), then the stall speed is Vso. An infinite number of G and speed
combinations exists in between Va and Vso that will result in a stall,
even 1.3Vso is a stall speed at the appropriate G-load (G can also be
interpreted as bank angle).

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.

To reduce the likelihood of stalling: If airspeed is decreasing,
G-load MUST also decrease; if airspeed is increasing, then the
airplane can tolerate an increase in G's. We need to develop a sense
of changes in both speed and G to have any reasonable chance of
sensing our proximity to stall.

Also, even the AOPA study correctly identifies the "watch your
airspeed" statement as a myth. I was just expanding on it...



On the other hand, this:

"Just don't let airspeed get below a safe value and
stalls are not a problem."

is not an axiom to fly by. Students *should* know/be taught that a stall can
occur at any speed, any attitude, of course. But I see nothing wrong with
training students to keep their airspeed where it's supposed to be in the
pattern and on approach, which, I believe, is the context from which those
two quoted remarks were taken.

Sensing airspeed AND G-load trends are critical, not airspeed alone.
The V-G diagram is the best illustration of the interaction of speed,
G, stall, and structural damage.

Be Safe,

Rich
http://www.richstowell.com

(Rich Stowell) writes:

For example, if I pull 3.8 G's while at Maneuvering speed, Va, the
airlane will stall (Va = 1.95Vso). If I am in wings-level flight (1
G), then the stall speed is Vso. An infinite number of G and speed
combinations exists in between Va and Vso that will result in a stall,
even 1.3Vso is a stall speed at the appropriate G-load (G can also be
interpreted as bank angle).

Don't forget to add in the case of pulling out of a dive.


All the best,


David

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.

Wayne



Remove "bra" and "panties" to reply

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

"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

"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

"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

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?

--
Chris Hoffmann
Student Pilot @ UES
30 hours

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.