Crossed Controls Stall?

[Mike Rhodes]

Crossed Controls Stall?

It would be dangerous on an approach to landing.

That was warned about in a reply to my previous thread; by Vaughn, who
only mentioned crossed controls and did not include the word "skid."
But what I'd read in my texts did not seem so concerned about forward
slips to a landing. Forward slips use crossed controls.

But I found a discussion on skids in Kershner's Student Pilot's Flight
Manual. (A good book I've only occasional used as a reference, as it
was aqcuired later than the others.) Specifically his warning was
about skidding the aircraft into a stall (while trying to avoid a
steep bank) while attempting to align the aircraft with the runway
after overshooting the turn to final. Yes, of course, you all know
about that one. Maybe you only think you do.

What he wrote (and this is paraphrased to what I think he wrote) was
that the skidding turn has the wing on the outside of the turn going
faster than the inside wing. This creates more lift outside and less
lift on the inside wing. Using the ailerons to lift the inside wing
increases the airplane's skid, and forces the inside wing into a
higher angle of attack such that it eventually stalls.

Is that your understanding?

Maybe Kershner (and you), know that is not quite right and believe it
is a waste of time to go into other details. I will try anyway.
Maybe I'm wrong. But the details should make sense.

I believe skid/stall danger is not described correctly. The aircraft
does not actually stall into a roll from a skidding turn. It has only
been rolled into a bank (which could be quite steep) in an unusual
manner -- yet it is still flying. That bank would be a surprise and
is not desired close to the ground.

First, as the aircraft is maneuvered into the skid, the outside wing
only _momentarily_ goes faster than the inside, and it does not go so
much faster that the aircraft is uncontrollable.

The increased lift on the outside (forward skid) wing is actually due
to wing dihedral, and it will remain so as long as the aircraft is
skidding. It's angle of attack is increased because the dihedral has
it pointing up into the wind during the skid. There would be fuselage
effects, though the ailerons may be able to counter those.

But the inside wing (behind on the skid) is angled down into the wind
and, by the dihedral, has the airflow pouring over the top of the
wing, losing lift. It's angle of attack is less so there is less lift
-- so it does not stall.

The use of the ailerons to hold up the inside wing only work to lift
it up into a low angle of attack condition. Ailerons are not of
sufficient size to counter the loss of lift over the entire wing. If
the skid is great enough they will be ignored and the aircraft will
roll over. They could, however, pull the nose of the aircraft in a
direction more towards the ground, though not directly towards the
ground. The aircraft is skidding.

The point is that if the aircraft banks over during a skid it is still
flying. Releasing the rudder while pushing the yoke some should
restore the aircraft to a flying condition. Then the ailerons should
be able to level the aircraft, with normal rudder to counter the
troublesome adverse yaw.

However, pulling the nose up after recovery from a skidding rollover
might cause a secondary stall -- an actual stall.

Ultimately a rollover, especially one that is not expected, is still
quite a danger at low altitudes and slow airspeeds. But who really
wants to skid his aircraft that bad? Pilots are certainly not taught
to do so for any purpose. A modest bank, with maybe a little
application of power (or just a drop of the nose) should be sufficient
to align the aircraft with the runway.
--
Michael

[Orval Fairbairn]

In article >,
Mike Rhodes > wrote:

> Crossed Controls Stall?
>
> It would be dangerous on an approach to landing.
>
> That was warned about in a reply to my previous thread; by Vaughn, who
> only mentioned crossed controls and did not include the word "skid."
> But what I'd read in my texts did not seem so concerned about forward
> slips to a landing. Forward slips use crossed controls.
>
> But I found a discussion on skids in Kershner's Student Pilot's Flight
> Manual. (A good book I've only occasional used as a reference, as it
> was aqcuired later than the others.) Specifically his warning was
> about skidding the aircraft into a stall (while trying to avoid a
> steep bank) while attempting to align the aircraft with the runway
> after overshooting the turn to final. Yes, of course, you all know
> about that one. Maybe you only think you do.
>
> What he wrote (and this is paraphrased to what I think he wrote) was
> that the skidding turn has the wing on the outside of the turn going
> faster than the inside wing. This creates more lift outside and less
> lift on the inside wing. Using the ailerons to lift the inside wing
> increases the airplane's skid, and forces the inside wing into a
> higher angle of attack such that it eventually stalls.
>
> Is that your understanding?
>
> Maybe Kershner (and you), know that is not quite right and believe it
> is a waste of time to go into other details. I will try anyway.
> Maybe I'm wrong. But the details should make sense.
>
> I believe skid/stall danger is not described correctly. The aircraft
> does not actually stall into a roll from a skidding turn. It has only
> been rolled into a bank (which could be quite steep) in an unusual
> manner -- yet it is still flying. That bank would be a surprise and
> is not desired close to the ground.
>
> First, as the aircraft is maneuvered into the skid, the outside wing
> only _momentarily_ goes faster than the inside, and it does not go so
> much faster that the aircraft is uncontrollable.
>
> The increased lift on the outside (forward skid) wing is actually due
> to wing dihedral, and it will remain so as long as the aircraft is
> skidding. It's angle of attack is increased because the dihedral has
> it pointing up into the wind during the skid. There would be fuselage
> effects, though the ailerons may be able to counter those.
>
> But the inside wing (behind on the skid) is angled down into the wind
> and, by the dihedral, has the airflow pouring over the top of the
> wing, losing lift. It's angle of attack is less so there is less lift
> -- so it does not stall.
>
> The use of the ailerons to hold up the inside wing only work to lift
> it up into a low angle of attack condition. Ailerons are not of
> sufficient size to counter the loss of lift over the entire wing. If
> the skid is great enough they will be ignored and the aircraft will
> roll over. They could, however, pull the nose of the aircraft in a
> direction more towards the ground, though not directly towards the
> ground. The aircraft is skidding.
>
> The point is that if the aircraft banks over during a skid it is still
> flying. Releasing the rudder while pushing the yoke some should
> restore the aircraft to a flying condition. Then the ailerons should
> be able to level the aircraft, with normal rudder to counter the
> troublesome adverse yaw.
>
> However, pulling the nose up after recovery from a skidding rollover
> might cause a secondary stall -- an actual stall.
>
> Ultimately a rollover, especially one that is not expected, is still
> quite a danger at low altitudes and slow airspeeds. But who really
> wants to skid his aircraft that bad? Pilots are certainly not taught
> to do so for any purpose. A modest bank, with maybe a little
> application of power (or just a drop of the nose) should be sufficient
> to align the aircraft with the runway.
> --
> Michael

My first flight instructor demonstrated a cross-control stall on one of
my first flights. It spun RIGHT NOW!

[Mike Rhodes]

On Wed, 20 Jul 2011 01:03:35 -0500, Mike Rhodes
> wrote:

>The aircraft
>does not actually stall into a roll from a skidding turn. It has only
>been rolled into a bank (which could be quite steep) in an unusual
>manner -- yet it is still flying. That bank would be a surprise and
>is not desired close to the ground.

Radio controlled hobby aircraft, (the simple type without ailerons),
take advantage of a steep dihedral for stability, but also to ensure
that the aircraft banks readily when told to turn thru the rudder.

By simple geometry the forward wing of a dihedraled pair in a skid
will have the steepest angle of attack, and the greatest amount of
lift, and therefore the one most likely to stall. (Not the wing
inside inside of the skid.) Aileron use will not change that --
except they force the aircraft to remain in a skid when operated
"crossed controlled."

So what's the problem?
--
Michael

[vaughn[_3_]]

"Mike Rhodes" > wrote in message
...
> By simple geometry the forward wing of a dihedraled pair in a skid
> will have the steepest angle of attack, and the greatest amount of
> lift, and therefore the one most likely to stall. (Not the wing
> inside inside of the skid.) Aileron use will not change that --
> except they force the aircraft to remain in a skid when operated
> "crossed controlled."

Aileron use affects the effective angle of attack of a wing. One way to turn
mere wing drop (caused by a stall or near-stall) into a real spin is to use
aileron to try to raise the stalled wing. This is one of thse disturbing cases
where a pilot's instinctive reaction can kill!

If you don't believe me, listen to Wolfgang:
(Stick & Rudder by Wolfgang Langewiesche, Page 166. "Under some conditions, an
aileron that is set to lift a drooping wing may actually stall that wing and
drop it viciously.")

Vaughn

[Mike Rhodes]

On Thu, 21 Jul 2011 10:31:18 -0400, "vaughn"
> wrote:

>"Mike Rhodes" > wrote in message
...
>> By simple geometry the forward wing of a dihedraled pair in a skid
>> will have the steepest angle of attack, and the greatest amount of
>> lift, and therefore the one most likely to stall. (Not the wing
>> inside inside of the skid.) Aileron use will not change that --
>> except they force the aircraft to remain in a skid when operated
>> "crossed controlled."
>
>Aileron use affects the effective angle of attack of a wing. One way to turn
>mere wing drop (caused by a stall or near-stall) into a real spin is to use
>aileron to try to raise the stalled wing. This is one of thse disturbing cases
>where a pilot's instinctive reaction can kill!

So the adverse yaw on a wing on the verge of a stall will pull the
aircraft into a dangerous spin, when it would have been just a stall.

The slow, draggy aileron will yaw the aircraft like a rudder. Wing
dihedral will cause the opposite wing to rise into the yaw. Still,
full ailerons may be applied to counter the roll.

But the aircraft rolls over surprisingly in the direction opposite of
the applied aileron. This is because of wing dihedral (and inherent
aircraft stability); not because of wing stall, or because the aileron
changes the angle of attack of that wing to cause it to stall. The
aileron is acting like a rudder to yaw the aircraft. Dihedral
stability then rolls the aircraft -- oppositely.

But since the aircraft has rolled then the elevator no longer has
gravity (or the inertia of a bank) to push against, so angle of attack
rises rapidly. Then the wings stall. The aircraft is in an aerobatic
attitude. The tail feathers will ensure the nose will then point
down.


The problem with uncoordinated controls and the stall is that, in a
coordinated bank, the elevator pushes 'up' against the COG properly.
But when the turn is not coordinated (when the aircraft just rolls
over) then the elevator lift is no longer restrained by the load of
the COG, and can raise the nose of the aircraft rapidly such that the
wings then stall.
Slips and skids, however, do not generally cause the plane to roll.
In those conditions elevator control of the COG is not usually in
doubt.

When an aircraft is slow then a lot of elevator is applied to hold the
nose up. Other than the flare, this condition is most likely to occur
when doing stalls.
It is could also occur during the turn when a pilot has overshot
final from base. That is the danger point on final. And the roll
into a spin probably came while using coordinated controls. The
aircraft just stalled in the turn.
It does not typically happen during a level approach while using
crossed controls to skid the aircraft to align with the runway.
(Which students may instinctively do to fine-tune their approach,
which instructors may instinctively hate. It seems a matter of
prejudice.)
--
Michael

[a[_3_]]

On Jul 22, 12:47*am, Mike Rhodes > wrote:
> On Thu, 21 Jul 2011 10:31:18 -0400, "vaughn"
>
> > wrote:
> >"Mike Rhodes" > wrote in message
> ...
> >> By simple geometry the forward wing of a dihedraled pair in a skid
> >> will have the steepest angle of attack, and the greatest amount of
> >> lift, and therefore the one most likely to stall. *(Not the wing
> >> inside inside of the skid.) *Aileron use will not change that --
> >> except they force the aircraft to remain in a skid when operated
> >> "crossed controlled."
>
> >Aileron use affects the effective angle of attack of a wing. *One way to turn
> >mere wing drop (caused by a stall or near-stall) into a real spin is to use
> >aileron to try to raise the stalled wing. *This is one of thse disturbing cases
> >where a pilot's instinctive reaction can kill!
>
> So the adverse yaw on a wing on the verge of a stall will pull the
> aircraft into a dangerous spin, when it would have been just a stall.
>
> The slow, draggy aileron will yaw the aircraft like a rudder. *Wing
> dihedral will cause the opposite wing to rise into the yaw. *Still,
> full ailerons may be applied to counter the roll.
>
> But the aircraft rolls over surprisingly in the direction opposite of
> the applied aileron. *This is because of wing dihedral (and inherent
> aircraft stability); not because of wing stall, or because the aileron
> changes the angle of attack of that wing to cause it to stall. *The
> aileron is acting like a rudder to yaw the aircraft. *Dihedral
> stability then rolls the aircraft -- oppositely.
>
> But since the aircraft has rolled then the elevator no longer has
> gravity (or the inertia of a bank) to push against, so angle of attack
> rises rapidly. *Then the wings stall. *The aircraft is in an aerobatic
> attitude. *The tail feathers will ensure the nose will then point
> down.
>
> The problem with uncoordinated controls and the stall is that, in a
> coordinated bank, the elevator pushes 'up' against the COG properly.
> * *But when the turn is not coordinated (when the aircraft just rolls
> over) then the elevator lift is no longer restrained by the load of
> the COG, and can raise the nose of the aircraft rapidly such that the
> wings then stall.
> * *Slips and skids, however, do not generally cause the plane to roll..
> In those conditions elevator control of the COG is not usually in
> doubt.
>
> When an aircraft is slow then a lot of elevator is applied to hold the
> nose up. *Other than the flare, this condition is most likely to occur
> when doing stalls.
> * *It is could also occur during the turn when a pilot has overshot
> final from base. *That is the danger point on final. *And the roll
> into a spin probably came while using coordinated controls. *The
> aircraft just stalled in the turn.
> * *It does not typically happen during a level approach while using
> crossed controls to skid the aircraft to align with the runway.
> (Which students may instinctively do to fine-tune their approach,
> which instructors may instinctively hate. *It seems a matter of
> pree patjudice.)
> --
>
You're over-thinking this. The only times in a the pattern I'd even
consider uncoordinated flight is a slip -- not a skid -- to lose
altitude, or when landing in a cross wind. If you find yourself
cross controlling, add throttle, get coordinated, tell the tower
you're going around and try again.

If I have to slip to lose altitude it means my planning has been bad
unless the slip was part of the landing plan (that does not often
happen unless the approach end has something intruding on the flight
path, or it's a failed engine landing and I carried some altitude as
insurance on short final.

A competent pilot, from the time he or she is on downwind, until on
the taxiway, will only have to reduce throttle -- he or she should not
have to increase it unless there's an unusual circumstance.

Further, the competent pilot, speaking of ground reference, will not
be aiming for the numbers, but for perhaps a thousand feet from his
(or her) turn off. If you only have to retard the throttle from
downwind to turn off, plan your exit from the active correctly, you're
my kind of pilot.

I have too often seen a 152 touch down on the numbers and taxi 1500
feet to exit the active.

You may be a student pilot, perhaps a 'sophomore'. The literal of that
word means 'wise fool'. There's lots to learn about being a safe
pilot, and it's not all in books.

For example: when this was an active newsgroup a discussion led me to
accept that I should use oxygen above 11,000 feet, especially at
night. It keeps vision better. Something I learned after 2k house of
PIC. Ditto, clearing turns when on the 45 degree entry to downwind.
I have a low winged airplane, an M20J, and there might be a Cessna
below me. As such I tend to fly at pattern altitude from a mile out on
entry leg so I can see who might be descending from above me. If I had
a high wing airplane I would come in higher.

And I fly en route altitudes at nominal less 50 or 75 feet, especially
if VFR, and I consider it bad form to pass directly over a VOR because
too many guys have their auto pilot on and will pass dead center, a
possible meeting grounds.

Other real pilots, add your favorite bits of wisdom, we may learn from
one other.
Or, a 'wise fool' might learn something that could be life saving.

[vaughn[_3_]]

"Mike Rhodes" > wrote in message
...
> On Thu, 21 Jul 2011 10:31:18 -0400, "vaughn"
> > wrote:
>
>>Aileron use affects the effective angle of attack of a wing. One way to turn
>>mere wing drop (caused by a stall or near-stall) into a real spin is to use
>>aileron to try to raise the stalled wing. This is one of thse disturbing
>>cases
>>where a pilot's instinctive reaction can kill!
>
> So the adverse yaw on a wing on the verge of a stall will pull the
> aircraft into a dangerous spin,

Did I say anything above about adverse yaw? I actually said that aileron use
affects the AOA. A stall happens...when? I even gave you a reference, which
you apparently snipped.

The rest of your crazy stuff is snipped unread. Frankly, many of your ideas are
downright dangerous. Perhaps you are terribly uninformed, or perhaps you are
trolling, but please read up on this subject before posting any further. I
highly suggest the classic text in that field, "Stick and Rudder" by Wolfgang
Langewiesche, but there are thousands of others. Visit your local public
library.

For anyone else reading this thread, please don't take piloting advice from
Internet "experts". (Even from me.) Go to trusted sources for your
information. You are far more likely to live longer and die in bed that way.

Vaughn CFI

[Alpha Propellerhead]

" The aircraft
does not actually stall into a roll from a skidding turn. It has only
been rolled into a bank (which could be quite steep) in an unusual
manner -- yet it is still flying."


And at 200' AGL, the pilot's physical reaction is typically to pull
up. The only visualization you need to know is very simple: In a
skid--especially in a low-wing--much of the root of the inside wing is
in the shadow of the fuselage, and is not providing lift. IF

This would be a fascinating academic exercise, perhaps, if so many
people hadn't witnessed these types of crashes happen. But what you
really need to know is that if the inside wing drops in a skid, you
will very likely strike the ground before you have time to flip
through all of your Kershner books and internet theories. Odds are,
you're four or five seconds from your own fireball.

[Alpha Propellerhead]

....fat-fingered and hit Send by accident. To clarify:

In a skidding, cross-controlled turn, particularly in a low-wing, the
root of the inside wing is in the shadow of the fuselage and is not
generating lift. The inboard wing is thus closer to a stall.

IF the plane stalls in that condition, the low wing stalls and drops
first, and you've already got 30 degrees of bank in, you'll be at 50,
60 or 90 degrees before you even have time to react, and you're losing
altitude.

If the high wing stalls and drops, on the other hand, it's going to
drop through wings-level before that wing becomes low, giving you more
of your precious remaining seconds to recover.

That's all you need to know. If you're inside, low wings stalls
turning final, you could very easily die before you recognize the
problem.

The rest is just hangar talk, and it's particularly dangerous because
you don't want to spend the last five seconds of your life reviewing
all the physics theories you've heard.

Chris G
Commercial Pilot, CFI

[Dan Thomas]

On Aug 1, 1:17 pm, Alpha Propellerhead > wrote:
> ...fat-fingered and hit Send by accident. To clarify:
>
> In a skidding, cross-controlled turn, particularly in a low-wing, the
> root of the inside wing is in the shadow of the fuselage and is not
> generating lift. The inboard wing is thus closer to a stall.
>
> IF the plane stalls in that condition, the low wing stalls and drops
> first, and you've already got 30 degrees of bank in, you'll be at 50,
> 60 or 90 degrees before you even have time to react, and you're losing
> altitude.
>

Nope. Not even close. In a descending turn the inside wing is at a
higher angle of attack than the outside wing. If we skid the airplane
the difference becomes greater. If we slip it, it becomes less. I
built a machine for my students so they could see it easily. Go to
Pilots of America and see it:
http://www.pilotsofamerica.com/forum/showthread.php?p=672873#post672873

Dan