Airplane turns

[Dave]

I'm curious as to how an airplane behaves during turns. It is my
understanding that once you put the plane into a turn and return the
yoke to a level position, the plane will stay in a turn but will
straighten itself out slowly. Does the rate at which the airplane
straightens out vary by model? For instance, a Cessna 152 vs. a
Boeing 747? Does it vary among jetliners, i.e. a 757 vs. a 777?

[Robert Moore]

Dave wrote
> I'm curious as to how an airplane behaves during turns. It is my
> understanding that once you put the plane into a turn and return the
> yoke to a level position, the plane will stay in a turn but will
> straighten itself out slowly. Does the rate at which the airplane
> straightens out vary by model? For instance, a Cessna 152 vs. a
> Boeing 747? Does it vary among jetliners, i.e. a 757 vs. a 777?

From the FAA Flight Training Handbook:

TURNS
A turn is a basic flight maneuver used to change or return to a
desired heading. It involves close coordination of all three flight
controls: aileron, rudder, and elevator. Since turns are a part
of most other flight maneuvers, it is important to thoroughly
understand the factors involved.

For purposes of this discussion, turns are divided into three
classes: shallow turns, medium turns, and steep turns.

• Shallow turns are those in which the bank (less than approximately
20°) is so shallow that the inherent lateral stability of the airplane
is acting to level the wings unless some aileron is applied to maintain
the bank.

• Medium turns are those resulting from a degree of bank (approximately
20° to 45°) at which the airplane remains at a constant bank.

• Steep turns are those resulting from a degree of bank (45° or more)
at which the “overbanking tendency” of an airplane overcomes stability,
and the bank increases unless aileron is applied to prevent it.

Bob Moore
Flight Instructor

[Peter Duniho]

"Dave" > wrote in message
...
> I'm curious as to how an airplane behaves during turns. It is my
> understanding that once you put the plane into a turn and return the
> yoke to a level position, the plane will stay in a turn but will
> straighten itself out slowly.

It depends on the airplane and the bank angle. Most airplanes have a narrow
range of bank angle at which the turn is stable, and the airplane will
continue indefinitely in the turn. At bank angles less than that, the
airplane will eventually return back to level flight. At bank angles
greater than that, the airplane will actually steepen the bank, which left
uncorrected would result in loss of control of the airplane.

The rates at which the bank changes does vary quite a bit from airplane to
airplane, as it depends on a variety of aerodynamic factors in the airplane
design. There are a few airplanes that won't return to level flight at all
without pilot input, as they've been designed as unstable airplanes (some
intentionally, some not).

Pete

[Teacherjh]

To add to this answer (about how an airplane behavs during turns), most
airplanes are designed with dihedral. This means that the wings point up a
little bit. If you looked at a plane from in front of the nose, the wings will
form a slight V shape. This makes the "lift" that each wing produces point a
little bit inward, towards the center of the plane, rather than straight up.
Now, if the plane goes into a shallow bank, the wing that is lowered will
become more level, and the lift will point straight up, while the wing that is
raised will become more tilted, and the lift will point more towards the center
of the plane. More of the lift on this "tilted" wing is "wasted" (in the sense
of not holding the airplane up). So, since the other wing exerts more upwards
force, it causes the plane to return to level flight. This is one of the
things that makes an airplane inherently stable in flight.

Separate from this, when an airplane is banked in coordinated flight and
turning, the outer wing (which is the one that is raised to bank the plane to
make the turn) is actually travelling faster than the inner wing. It has to,
because that wing is further from the center of the turn. (to see this,
imagine the plane turning so sharply that it's just about pivoting on one
wingtip) The faster wing will produce more lift, and cause the airplane to
bank in the direction of the turn. This is called "overbanking tendency".

So, there are two opposite tendencies. Dihedral is more important with shallow
banks (and gentle turns), and the overbanking tendency is more important with
steeper turns and banks. Somewhere in the middle, they cancel out.

Jose

--
(for Email, make the obvious changes in my address)

[William W. Plummer]

"Teacherjh" > wrote in message
...
> To add to this answer (about how an airplane behavs during turns), most
> airplanes are designed with dihedral. This means that the wings point up
a
> little bit. If you looked at a plane from in front of the nose, the wings
will
> form a slight V shape. This makes the "lift" that each wing produces
point a
> little bit inward, towards the center of the plane, rather than straight
up.
> Now, if the plane goes into a shallow bank, the wing that is lowered will
> become more level, and the lift will point straight up, while the wing
that is
> raised will become more tilted, and the lift will point more towards the
center
> of the plane. More of the lift on this "tilted" wing is "wasted" (in the
sense
> of not holding the airplane up). So, since the other wing exerts more
upwards
> force, it causes the plane to return to level flight. This is one of the
> things that makes an airplane inherently stable in flight.
>
> Separate from this, when an airplane is banked in coordinated flight and
> turning, the outer wing (which is the one that is raised to bank the plane
to
> make the turn) is actually travelling faster than the inner wing. It has
to,
> because that wing is further from the center of the turn. (to see this,
> imagine the plane turning so sharply that it's just about pivoting on one
> wingtip) The faster wing will produce more lift, and cause the airplane
to
> bank in the direction of the turn. This is called "overbanking tendency".
>
> So, there are two opposite tendencies. Dihedral is more important with
shallow
> banks (and gentle turns), and the overbanking tendency is more important
with
> steeper turns and banks. Somewhere in the middle, they cancel out.

Looking at the nose of the plane, we see the V-shape of the wings, the
dihedral angle. Lift is always perpendicular to the wings. So in flight,
the two lift vectors tilt in and "cross" over the plane itself. In level
flight the horizontal components of the two lift vectors are equal and
opposite. Thus, they cancel and the plane flies straight. Now, if you
bank the plane so that one wing is horizontal, that wing will have no
horizonal lift vector component. But, the other wing will have double. The
result is a big, net horizontal force on the plane. This forces the plane
to the center of the turn the way the force in a string swinging a rock
keeps the rock in a circle. That's what makes a plane able to go in a
circle, not the rudder.

[Teacherjh]

>>
Now, if you
bank the plane so that one wing is horizontal, that wing will have no
horizonal lift vector component. But, the other wing will have double. The
result is a big, net horizontal force on the plane. This forces the plane
to the center of the turn the way the force in a string swinging a rock
keeps the rock in a circle. That's what makes a plane able to go in a
circle, not the rudder.
<<

Not quite. This does not change the direction of the nose, which is essential
for turning. By itself, what you post would lead to a slip. The plane would
travel in a straight line, at some angle to the nose.

Jose

--
(for Email, make the obvious changes in my address)

[Greg Esres]

<<Now, if the plane goes into a shallow bank, the wing that is lowered
will become more level, >>


This is NOT how dihedral works.

Dihedral depends on sideslip. No sideslip, no stabilizing force.

[Peter Gottlieb]

"Teacherjh" > wrote in message
...
> >>
> Now, if you
> bank the plane so that one wing is horizontal, that wing will have no
> horizonal lift vector component. But, the other wing will have double.
The
> result is a big, net horizontal force on the plane. This forces the plane
> to the center of the turn the way the force in a string swinging a rock
> keeps the rock in a circle. That's what makes a plane able to go in a
> circle, not the rudder.
> <<
>
> Not quite. This does not change the direction of the nose, which is
essential
> for turning. By itself, what you post would lead to a slip. The plane
would
> travel in a straight line, at some angle to the nose.
>

I guess this confuses me a bit. Maybe I'm tired and my brain confuses
easily.

Isn't it the case, in an earth-centric reference frame, that an object
moving in a straight line, when subjected to a horizontal force
perpendicular to that motion, will move in a circle?

[Roger Halstead]

On Fri, 16 Apr 2004 16:49:38 -0700, "Peter Duniho"
> wrote:

>"Dave" > wrote in message
...
>> I'm curious as to how an airplane behaves during turns. It is my
>> understanding that once you put the plane into a turn and return the
>> yoke to a level position, the plane will stay in a turn but will
>> straighten itself out slowly.
>
>It depends on the airplane and the bank angle. Most airplanes have a narrow
>range of bank angle at which the turn is stable, and the airplane will
>continue indefinitely in the turn. At bank angles less than that, the
>airplane will eventually return back to level flight. At bank angles
>greater than that, the airplane will actually steepen the bank, which left
>uncorrected would result in loss of control of the airplane.
>
>The rates at which the bank changes does vary quite a bit from airplane to
>airplane, as it depends on a variety of aerodynamic factors in the airplane
>design. There are a few airplanes that won't return to level flight at all
>without pilot input, as they've been designed as unstable airplanes (some
>intentionally, some not).

When I was down to Bonanza specific recurrency training (with
characteristics a bit different than the trainers) The one instructor
had me trim (elevator only) in steep turns as an experiment. I put it
right at 60 degrees of bank and gently eased in the trim (and power).
We were holding a tad over 120 MPH, hands off and made two complete
circuits (a 720). In two complete circles the plane had displayed no
tendency to change bank angle or altitude. The altitude varied less
than 20 feet in the check. (better than I can do without lots of
practice)

The Debonair/Bonanzas do have a lot of dihedral

I would say it's probably better behaved in a steep turn like that
than one of only 30 degrees, but OTOH it's been some times since I
took part in that experiment.

I think when I get the Deb back after annual I'm going to take it out
and spend a few hours just practicing. That and I'd like to get it
down to P-ville next month if at all possible.

What with the broken throttle cable and now being out of annual I'm
starting to suffer withdrawal.

I have a couple of guys who really want to buy it, but I keep having
thoughts about keeping it for years to come. It may have been built
in 59 but the airframe only has about 4,000 TT, or a tad less. (time
to go check the logs)

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>
>Pete
>

[Greg Esres]

<<when subjected to a horizontal force perpendicular to that motion,
will move in a circle?>>

In a sideslip, lift is perpendicular to the longitudinal axis of the
aircaft, not the direction of motion.

[Teacherjh]

>>
Isn't it the case, in an earth-centric reference frame, that an object
moving in a straight line, when subjected to a horizontal force
perpendicular to that motion, will move in a circle?
<<

If the force is in fact perpendicular to the MOTION (the course) and not to the
HEADING. In the case of simply banking, the nose does not move (so the heading
remains the same) while the course changes (due to the force you are talking
about). But so long as the nose does not change direction, the force will not
change direction either and the plane will simply continue in a straight line,
in a slip.

(Actually, if you simply bank the plane (with alerons), the nose will tend to
move in the =opposite= direction, because of the drag induced by the alerons.
If your plane uses spoilers, the reverse is true)

Jose

--
(for Email, make the obvious changes in my address)

[Teacherjh]

>>
<<Now, if the plane goes into a shallow bank, the wing that is lowered
will become more level, >>

This is NOT how dihedral works.
Dihedral depends on sideslip. No sideslip, no stabilizing force.
<<

Huh? I don't believe that is true, but explan further.

Jose

--
(for Email, make the obvious changes in my address)

[Greg Esres]

<<Huh? I don't believe that is true, but explan further.>>

First, understand that for an airplane to right itself from a bank,
there must be a moment that rotates the aircraft around the
longitudinal axis. Therefore, the total lift on one wing must be
greater than the other. This extra force, times the moment arm,
creates the necessary moment.

The orientation of the wing lift to gravity is irrelevant.

When the aircraft sideslips in one direction or the other, there is a
component of the relative wind that moves parallel to the lateral axis
of the airplane. Due to dihedral, parallel to the lateral axis is not
parallel to the wing. When you resolve the vectors, you can see that
the sideslip creates a component of the relative wind perpendicular to
the surface of the wing, which increases its angle of attack. The
reverse happens on the other wing.

Most aerodynamics books contain detailed vector diagrams of this. The
FAA's material get this wrong, as does most aviation training
material. The point is, all dihedral effects depend on sideslip. In
theory, an aircraft in a coordinated turn should experience no
righting tendencies.

[Magnus]

Exactly right, dihedral has no effect in a coordinated turn.

On 2004-04-17 10:37:18 -0400, Greg Esres > said:

> <<Huh? I don't believe that is true, but explan further.>>
>
> First, understand that for an airplane to right itself from a bank,
> there must be a moment that rotates the aircraft around the
> longitudinal axis. Therefore, the total lift on one wing must be
> greater than the other. This extra force, times the moment arm,
> creates the necessary moment.
>
> The orientation of the wing lift to gravity is irrelevant.
>
> When the aircraft sideslips in one direction or the other, there is a
> component of the relative wind that moves parallel to the lateral axis
> of the airplane. Due to dihedral, parallel to the lateral axis is not
> parallel to the wing. When you resolve the vectors, you can see that
> the sideslip creates a component of the relative wind perpendicular to
> the surface of the wing, which increases its angle of attack. The
> reverse happens on the other wing.
>
> Most aerodynamics books contain detailed vector diagrams of this. The
> FAA's material get this wrong, as does most aviation training
> material. The point is, all dihedral effects depend on sideslip. In
> theory, an aircraft in a coordinated turn should experience no
> righting tendencies.

[Teacherjh]

>>
First, understand that for an airplane to right itself from a bank,
there must be a moment that rotates the aircraft around the
longitudinal axis. Therefore, the total lift on one wing must be
greater than the other. This extra force, times the moment arm,
creates the necessary moment.
The orientation of the wing lift to gravity is irrelevant.
<<

Gee, now that you mention it, you're right. <gobsmacked>

>>
When the aircraft sideslips in one direction or the other, there is a
component of the relative wind that moves parallel to the lateral axis
of the airplane. Due to dihedral, parallel to the lateral axis is not
parallel to the wing. When you resolve the vectors, you can see that
the sideslip creates a component of the relative wind perpendicular to
the surface of the wing, which increases its angle of attack. The
reverse happens on the other wing.
<<

So the high wing is sort of "blown back down" by the sideways component of the
relative wind. Makes sense to me. (the raised wing has a lower angle of
attack, the lowered wing has a higher angle of attack).

Never thought of it all the way through that way. Thanks.

Jose

--
(for Email, make the obvious changes in my address)

[Peter Gottlieb]

"Teacherjh" > wrote in message
...
> >>
> Isn't it the case, in an earth-centric reference frame, that an object
> moving in a straight line, when subjected to a horizontal force
> perpendicular to that motion, will move in a circle?
> <<
>
> If the force is in fact perpendicular to the MOTION (the course) and not
to the
> HEADING. In the case of simply banking, the nose does not move (so the
heading
> remains the same) while the course changes (due to the force you are
talking
> about). But so long as the nose does not change direction, the force will
not
> change direction either and the plane will simply continue in a straight
line,
> in a slip.


I'm having a hard time wrapping my brain around this. Maybe the different
reference frames are confusing me.

Let's say I put the plane into a 30 degree bank with ailerons yet maintain
neutral rudder. To simplify things let's say I do this instantaneously.
Right at that moment, the nose is pointing in the original heading. But
what happens as this fairly large (earth referenced) horizontal lift force
acts on the plane; clearly it moves it sideways. But what happens to the
heading, that is messing me up. If the force continues, either it results
in an acceleration which causes increasing velocity or it reaches a terminal
velocity where the force is balanced by drag. Does the slip result in such
large drag so quickly that the net result is similar to a crosswind, or does
the plane act in the medium it is flying in (of course ignoring the earth
below) and have the nose indeed change heading because the plane is now
"climbing" sideways? I know from experience I need a lot of *opposite*
rudder to counteract a 30 degree bank and keep the nose on the same heading
(as in crosswind landings).

[Teacherjh]

>>
Let's say I put the plane into a 30 degree bank with ailerons yet maintain
neutral rudder. To simplify things let's say I do this instantaneously.
Right at that moment, the nose is pointing in the original heading. But
what happens as this fairly large (earth referenced) horizontal lift force
acts on the plane; clearly it moves it sideways. But what happens to the
heading, that is messing me up.
<<

The heading does not change. The force is pushing the aircraft sideways.

Well, ok, the vertical tail will encounter some (sideways) resistance, causing
the plane to weathervane a bit into the wind and changing the heading too, but
that effect is small for small banks.

>>
If the force continues, either it results
in an acceleration which causes increasing
velocity or it reaches a terminal
velocity where the force is balanced by drag.
<<

The latter, ultimately. And yes, the plane is then "climbing" sideways. Part
of the reason for the heading change you would fight is the tail, which
produces down lift, keeping the nose up against gravity. When banked, this
results in a turn. But then less is available to keep the nose up, which is
why you apply back pressure on the elevators.

So all these things are interdependent, and become more so as the amount of
bank is increased.

Taken to the extreme (an aerobatics pilot might chime in here), if the wings
are vertical (a knife edge) the only thing keeping the airplane up is the
(once) vertical stabilizer and the fuselage. The (once) horizontal tail will
want to keep the nose "up", which is sideways, and the plane will want to turn
(do a loop horizontally). Ignoring other effects, of course. :)

Jose

--
(for Email, make the obvious changes in my address)

[G.R. Patterson III]

Peter Gottlieb wrote:
>
> Let's say I put the plane into a 30 degree bank with ailerons yet maintain
> neutral rudder. To simplify things let's say I do this instantaneously.
> Right at that moment, the nose is pointing in the original heading.

In my aircraft, the nose would swing in the opposite direction to the bank. The plane
would continue to fly the original heading. Sideways.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".

[David CL Francis]

On Sat, 17 Apr 2004 at 14:53:33 in message
>, Teacherjh
> wrote:
>So the high wing is sort of "blown back down" by the sideways component of the
>relative wind. Makes sense to me. (the raised wing has a lower angle of
>attack, the lowered wing has a higher angle of attack).

Don't think too much in terms of raising and lowering as it is a
sideslip effect and can occur at any attitude. The sideslip can be
generated by the rudder. This is why it is surprisingly easy to fly an
RC model with rudder and elevators only. Plenty of dihedral and a
powerful rudder and the slip generated by the rudder will create a roll
and you fly around almost forgetting you have no ailerons. There are
some things you cannot do tidily though. Not easy to do an axial role
for example.
--
David CL Francis