A very basic question

Andrew Sarangan wrote:

Sure, but that still does not explain why the airplane turns. A horizontal
component of lift will make the airplane side-slip, not turn. It is the
stability (weathervane effect) that makes the airplane turn.

By definition, the 'weathervane effect' occurs because air exerts more
pressure on one side of the object (aircraft) than the other - same
definition as slipping. Therefore, are you are asserting that an aircraft
turns because it is slipping? More over, it will only turn if it is
slipping?

Hilton

On Sun, 07 Nov 2004 06:13:43 -0500, Cub Driver
wrote:

He wants to know why his pilot can't simply do rolls around the
plane's longitudinal axis.

Perhaps it would help to know what inputs are necessary to make such a
roll? If you are rolling to your left, do you apply right rudder?

It depends on the aircraft you're flying. I imagine jets
require very little "top rudder" to do an axial roll. Some
of the hot aerobatic planes scarcely allow time for
rudder input, I imagine.

Here's the sequence I learned for a slow, axial roll:

Input aileron. Hold it through the maneuver for a
steady roll rate.

Input "top rudder" as the plane reaches knife-edge.
If rolling to the left, right rudder will be on top first.

Back to neutral on rudder as the plane goes
inverted. Push on the stick to maintain level
flight upside-down.

Release the pressure on the elevator.

Input top rudder as the plane reaches knife-edge.
In the example of rolling to the left, this will now
be left rudder.

Release the pressure on the rudder as the
plane rolls upright.

Apply any necessary backpressure to maintain
level flight.

This is so much easier to do than it is to explain
in writing.

To do a rolling circle, add in appropriate inputs
toward the center of the circle as needed. To
do the rolls in a straight line, be careful to get
the inputs in at the right time.

Marty

We are on the same page. The analogy with describing lift is spot on.

Never flown a 195 but I bet it rolls a bit with rudder too. I'd bet it has
a little to do with fuselage blanking the trailing wing lift a bit while
the leading wing works a little better. But all of that is a wild ass
guess. I'll have to ask our resident 195 guy how it responds to rudder.

Thanks.
"Dudley Henriques" wrote in message
ink.net...

"Maule Driver" wrote in message
om...
I was always under the impression that in most light a/c, the dominate
rolling effect from 'inside' rudder is the result of dihedral (or
alternatively, sweep back). RC modelers are pretty adept at setting
up
aircraft for 'pure' yaw from rudder input - no dihedral, symmetrical
layout,
etc. Or setting up aircraft to bank and turn without ailerons - lots
of
didedral.

Though I'd agree that the "forward motion of the outside wing"
explanation
accurately predicts the rolling effect from rudder input that occurs
on most
a/c - which is ok for training purposes.

I would agree with this completely. Dihedral contributes heavily to the
lateral stability of the aircraft if sideslip is present to be sure. The
prime contribution of dihedral is in the development of a stable rolling
moment with sideslip, which is consistent with what most of us are
saying.
The problem with answering many questions in aerodynamics is that there
isn't one single example or answer that will suffice.
(Lift is a PRIME example of this. ) Anyone trying to explain lift in a
simple sentence will find a slew of missing data soon to follow :-) The
problem in aerodynamics is that in much of what is happening, several
explanations are in force physically together at one instant in time.
The way we look at dihedral in the flight test community is primarily as
it's effect on the lateral stability scenario which relates with
sideslip present to relative wind, differential in angle of attack,
changes in lift raising a windward wing producing stability.
I think we're both on the same page, and dealing with the same effect
since all of what we're discussing is present in complimentary yaw IF
dihedral is present.
Now, if we inject an airplane into this equation like a Cessna 195 for
example.......... :-))))
Dudley Henriques
International Fighter Pilots Fellowship
for email; take out the trash

"Hilton" wrote in
ink.net:

Andrew Sarangan wrote:

Sure, but that still does not explain why the airplane turns. A
horizontal component of lift will make the airplane side-slip, not
turn. It is the stability (weathervane effect) that makes the
airplane turn.

By definition, the 'weathervane effect' occurs because air exerts more
pressure on one side of the object (aircraft) than the other - same
definition as slipping. Therefore, are you are asserting that an
aircraft turns because it is slipping? More over, it will only turn
if it is slipping?

Hilton




Think of the space shuttle. If you fire rockets horizontal to the flight
path, the shuttle will slide sideways. It will not turn the nose towards
the direction of travel. An airplane turns because it wants to point the
nose into the relative wind.

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"Cub Driver" wrote in message
...
On Sun, 07 Nov 2004 05:09:36 GMT, "Dudley Henriques"
wrote:

"why does the banking of wings by
the use of ailerons not just roll an aircraft but also produces a turn

He wants to know why his pilot can't simply do rolls around the
plane's longitudinal axis.

Perhaps it would help to know what inputs are necessary to make such a
roll? If you are rolling to your left, do you apply right rudder?

A slow roll is extremely difficult to visualize with verbal
interpretation only.
The best way to describe what you are asking..say a slow roll to the
left is to first understand that a slow roll isn't exactly a roll dead
on the longitudinal axis as the axis relates to a "level" roll. The
visualization of a slow roll to the left can be made by envisioning a
reverse capital letter D, which naturally isn't in my little bag of
computer symbols, so a roll to the right is much easier to visualize. So
to the right, you can envision a capital letter D.
The reason for the D shape is because to do the roll properly, you will
have to pass through exact inverted at the airplane's level flight
inverted attitude to keep altitude in check during the roll. The
tightness of the D shape will depend on the wing design of the airplane
you're flying. A symmetrical wing on a Pitts, or an Extra for example
will be a much tighter D than say a Citabria with a high lift cambered
wing.
Anyway, the vertical line of the D represents the raising of the nose
during the first half of the roll until right past the full inverted
position. At that point, the nose must again be lowered to a normal
level flight attitude, and this is represented by the curve on the D
returning the airplane back to upright level flight attitude.
The roll can be done with inside rudder at roll initiation or without
insider rudder. When flying airshow demonstrations, I seldom used inside
rudder with inside aileron when initiating a slow roll. Reason for this
is that adverse yaw will pull the nose outside, which if caught exactly
right, will result in your going straight to the required top rudder you
need to carry you through knife edge at the right spot on the roll axis,
and if it's a point roll, you don't have to change feet at the first
point, but to do this requires a fairly fast roll rate, so it's aircraft
specific. In the P51 for example, the roll rate isn't fast enough to use
the adverse yaw generated so that it negates the normal inside rudder
you need to counter that adverse yaw, which in turn means you enter with
aileron and insider rudder, and immediately go to top rudder as soon as
a positive coordinated roll entry has been accomplished.
Back to the Pitts, entering into the first knife edge, you have steady
inside aileron and have blended in enough positive pitch with elevator
to climb the vertical D line nose high for the inverted level
transition.You hold top rudder through knife edge and then start
blending in whatever forward stick you need to pint the nose at level
inverted. You're also blending off the top rudder at this point at a
rate that will neutralize it passing through inverted. Stick at this
point is forward and in the corner for aileron and elevator blending.
Passing through inverted, you switch to opposite side top rudder and
reverse the procedure, blending in past the second knife edge, as you
come back down the backside of the D curve whatever back pressure you
need to return the nose to normal level flight attitude.
What I've just described is much better learned in actual flight, where
a slow roll can be done by rote, then understood
afterwards...........and in far less words to boot :-)
Dudley Henriques
International Fighter Pilots Fellowship
for email; take out the trash

"Dudley Henriques" wrote in message
ink.net...

"Cub Driver" wrote in message
...
On Sun, 07 Nov 2004 05:09:36 GMT, "Dudley Henriques"
wrote:

"why does the banking of wings by
the use of ailerons not just roll an aircraft but also produces a
turn

He wants to know why his pilot can't simply do rolls around the
plane's longitudinal axis.

Perhaps it would help to know what inputs are necessary to make such
a
roll? If you are rolling to your left, do you apply right rudder?

A slow roll is extremely difficult to visualize with verbal
interpretation only.
The best way to describe what you are asking..say a slow roll to the
left is to first understand that a slow roll isn't exactly a roll dead
on the longitudinal axis as the axis relates to a "level" roll. The
visualization of a slow roll to the left can be made by envisioning a
reverse capital letter D, which naturally isn't in my little bag of
computer symbols, so a roll to the right is much easier to visualize.
So to the right, you can envision a capital letter D.
The reason for the D shape is because to do the roll properly, you
will have to pass through exact inverted at the airplane's level
flight inverted attitude to keep altitude in check during the roll.
The tightness of the D shape will depend on the wing design of the
airplane you're flying. A symmetrical wing on a Pitts, or an Extra for
example will be a much tighter D than say a Citabria with a high lift
cambered wing.
Anyway, the vertical line of the D represents the raising of the nose
during the first half of the roll until right past the full inverted
position. At that point, the nose must again be lowered to a normal
level flight attitude, and this is represented by the curve on the D
returning the airplane back to upright level flight attitude.
The roll can be done with inside rudder at roll initiation or without
inside rudder. When flying airshow demonstrations, I seldom used
inside rudder with inside aileron when initiating a slow roll. Reason
for this is that adverse yaw will pull the nose outside, which if
caught exactly right, will result in your going straight to the
required top rudder you need to carry you through knife edge at the
right spot on the roll axis, and if it's a point roll, you don't have
to change feet at the first point, but to do this requires a fairly
fast roll rate, so it's aircraft specific. In the P51 for example, the
roll rate isn't fast enough to use the adverse yaw generated so that
it negates the normal inside rudder you need to counter that adverse
yaw, which in turn means you enter with aileron and inside rudder, and
immediately go to top rudder as soon as a positive coordinated roll
entry has been accomplished.
Back to the Pitts, entering into the first knife edge, you have steady
inside aileron and have blended in enough positive pitch with elevator
to climb the vertical D line nose high for the inverted level
transition.You hold top rudder through knife edge and then start
blending in whatever forward stick you need to pin the nose at level
inverted. You're also blending off the top rudder at this point at a
rate that will neutralize it passing through inverted. Stick at this
point is forward and in the corner for aileron and elevator blending.
Passing through inverted, you switch to opposite side top rudder and
reverse the procedure, blending in past the second knife edge, as you
come back down the backside of the D curve whatever back pressure you
need to return the nose to normal level flight attitude.
What I've just described is much better learned in actual flight,
where a slow roll can be done by rote, then understood
afterwards...........and in far less words to boot :-)
Dudley Henriques
International Fighter Pilots Fellowship
for email; take out the trash

"Maule Driver" wrote in message
om...
We are on the same page. The analogy with describing lift is spot on.

Never flown a 195 but I bet it rolls a bit with rudder too. I'd bet
it has
a little to do with fuselage blanking the trailing wing lift a bit
while
the leading wing works a little better. But all of that is a wild ass
guess. I'll have to ask our resident 195 guy how it responds to
rudder.

I flew one years ago. Strong airplane...reminded me of something made
out of solid aluminum :-)) It flew wonderfully...extremely stable. Sort
of like a Beaver really.
As for a turn resulting from pure rudder input on these airplanes....you
still have that outside wing going faster than the inside wing
irregardless of the existence or non existence of dihedral, so it will
turn anyway eventually :-)
Dudley

I don't think anyone has hit on what is really going on here. The
explanations about the sideways force created by lift when the AC is banked
cause it to move ( accelerate ) to the side, but not rotate. The dihedral
wing explanation doesn't work either, because the raised wing's horizontal
force is applied aft of the CG, thus causing rotation in the opposite
direction of the turn. The major reason that a plane rotates about the
vertical axis during a turn is wind vaning.

You bank the plane, the lift is broken into horizontal and vertical
components. The horizontal force causes the plane to accelerate to the
side, but not rotate as others have stated. Now with the plane picking up
speed in the lateral direction, the relative wind is now coming from one
side of the plane, a forward quartering headwind! As anyone who has taxied
on a windy day knows, planes have a natural tendency to face into the wind.
This is caused by the big wind vane we call a tail. This rotates the plane
into the wind. The relative wind is thus always leading the plane by a few
degrees, causing a continued rotation. And as a side benefit, the
horizontal acceleration is countered by the centripetal force of the turn,
so we don't continue to accelerate to faster and faster horizontal speeds.

Andrew,

Andrew Sarangan wrote:
Hilton wrote:

Andrew Sarangan wrote:

Sure, but that still does not explain why the airplane turns. A
horizontal component of lift will make the airplane side-slip, not
turn. It is the stability (weathervane effect) that makes the
airplane turn.

By definition, the 'weathervane effect' occurs because air exerts more
pressure on one side of the object (aircraft) than the other - same
definition as slipping. Therefore, are you are asserting that an
aircraft turns because it is slipping? More over, it will only turn
if it is slipping?

Hilton


Think of the space shuttle. If you fire rockets horizontal to the flight
path, the shuttle will slide sideways. It will not turn the nose towards
the direction of travel. An airplane turns because it wants to point the
nose into the relative wind.

I understand that, but you never answered my question: "Are you asserting
that an aircraft turns because it is slipping (weathervaning)?"

Hilton

On 6 Nov 2004 07:37:15 -0800, (Ramapriya) wrote:

Hi guys,

Unlike the elevators and rudder that change an aircraft's pitch and
yaw with no other secondary effect, why does the banking of wings by
the use of ailerons not just roll an aircraft but also produces a turn
(yaw)?

Very basically, because the wings are producing lift. They continue
to produce lift no matter what angle the airplane banks to. When the
wings are banked, the lift pushes sideways now, not straight down
anymore. So the airplane now lifts around in a curve.

Logically, one would expect an aircraft to keep going straight
ahead even if the pilot banked the aircraft left or right. Where does
the turning effect come from?

Lift. Bank the airplane sideways and the lifts around in the
direction of the bank.

Is there a website you know of that can teach me such basics, without
having to bug you?

Corky Scott