Coordinated turns without rudder, and autopilots

"Mxsmanic" wrote in message
...
...
Except I do see adverse yaw in turns in my (simulated) Baron, so either
the
simulation is in error, or the AP knows something about making coordinated
turns without rudder input that I do not.

Yup, that pretty much sums it up. Either your simulation is in error, or you
havn't mastered the basics yet.

Mystery solved.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On May 29, 8:36 pm, Matt Whiting wrote:
Andrew Sarangan wrote:
On May 29, 7:16 am, Matt Whiting wrote:
Ron Natalie wrote:
Matt Whiting wrote:
Not true. The vertical fin can only provide a weather-vane affect
when a slip or skid has been induced.
You have no clue what you are talking about. The skid and slip are the
result of the airplane NOT weather vaning into the wind. There are
a number of reasons for this. The primary one in turns is the "adverse
yaw" due to the differing drag caused by the displaced ailerons. Many
designs do a lot of things to mitigate this. Still it takes a lot of
aileron displacement to overcome the natural desire for the airplane
to track into the wind (due to the vertical stab).
In coordinated flight there is no slip or skid and hence the fin
provides no lateral force.
This is the definition of coordinated flight, not cause and affect.
The rudder isn't there to help the vertical stab do its job, it is
there to do a job that the vertical stab can't do.
Sorry. The incorrect. You need the vertical stab to even fly
coordinated when you are not turning. If it is two small the
airplane will tend to yaw on it's own (the more bulbous your
fuselage, the more this is a probelm...there was a design Piper
tried that used an almost helicopter like bubble on the front...
without the slab sides to help the vertical stab, the plane
just would as well fly slipping as nromal).
The vertical stab is nearly always set up to get the aircraft
to fly coordinated in normal cruise level flight. It is frequently
slightly offset to correct for other aerodynamic unbalances.
The rudder is just at trim to handle other flight regimes.
It's mostly there for the high AOA regimes of Take-off and
landing.
I don't know where you got your engineering degree, but you better
demand a refund. A vertical stabilizer does not provide any lateral
force unless there is some degree of slip or skid. In coordinated
flight, it is just along for the ride. Many airplanes will oscillate
slight in the yaw axis for this reason. It takes a very large vertical
stab to keep the excursions small enough to not be detectable,
especially in a longer fuselage airplane. The rudder can provide a side
force in anticipation of a slip or skid and thus maintain coordinated
flight and never allow the slip or skid to develop in the first place.

Matt- Hide quoted text -

You are assuming that the primary role of the rudder is to fly co-
ordinated. I would argue the opposite. The primary role of the rudder
is to fly un-coordinated, such as in a cross-wind landing, forward
slip, spin etc.. An airplane that always flies perfectly co-ordinated
(with or without rudder) would be of little use.

I'm not assuming that at all nor did I ever say that. The rudder has
many roles. Coordinating turns is just one of the roles. My point was
simply that the vertical stabilizer alone will not provide a coordinated
turn with an airplane whose ailerons generate any adverse yaw at all.

Nevertheless, I don't believe your analysis is correct, even from an
engineering control system point of view. The vertical stab and yaw
can be thought of as a closed loop system. Yaw is the error signal.
The vertical stab creates a lateral force that minimizes the error
signal by providing a negative feedback. One could argue that a
vertical stab serves no purpose if there is no yaw. But no airplane
flies perfectly co-ordinated. They continuously slip and skid as they
fly, and it is the vertical stab that kicks in the feedback to
stabilize the system. Since the effect of the vertical stab is highly
dependent on the airspeed, at lower airspeed one would need a bigger
vertical stab. In other words, you would need an adaptive feedback.
Since it is clearly not practical to enlarge the vertical stab during
flight, the next best thing you can do is to rotate it, and this what
the rudder does. Simply put, a rudder provides the means to enhance
the effect of the vertical stab during flight.

That is precisely what I said. As a controls engineer, I'm quite
familiar with the operation of control systems. My point was that you
must have an error (yaw) in order for the fin to provide any stabilizing
force. This means that you have to enter uncoordinated flight before it
does anything. The rudder can be used similar to feed-forward control
or model predictive control. When a turn is planned, the rudder can be
applied in coordination with the ailerons to exactly offset the adverse
yaw force and maintain coordination throughout the turn entry. With a
fin alone, the airplane will be uncoordinated during the turn entry and
will only enter coordinated flight again once the transient has been
damped. That is the entire point and is in contrast with Ron's earlier
comment about a rudder not being needed to provide coordinated flight
and only being needed for "outlying" conditions. I guess if you
consider turning the airplane to be an outlying condition, then Ron is
correct.

The original statement that the rudder simply assists the vertical
stab at the outlying regions is correct. If a vertical stab could be
designed such that its effectiveness is independent of airspeed, then
a rudder won't be necessary to fly co-ordinated. But for reasons I
stated earlier, such an airplane would still not be very useful.

No, that statement is not correct. The rudder doesn't just assist the
vertical stab, it does things it can't do. The stab can't prevent
unbalanced forces from the ailerons from causing adverse yaw. It will
provide a restoring force once the adverse yaw exists, but it won't
return the airplane to coordinated flight until the unbalanced aileron
forces cease. The rudder CAN prevent adverse yaw by countering the
unbalanced aileron forces BEFORE coordinated flight has departed.

This is a simple concept. Is it really that hard to understand?

It is like the difference between controlling your speed manually in
hilly country vs. using cruise control. If I want to invest the
concentration, I can hold speed much more precisely on hills than can my
car's cruise control. The reason is that I can anticipate the hill and
start feeding in throttle before the car slows down. The cruise
control, OTOH, is like the vertical stab and can't do diddly until after
the car has already begun to slow down as it needs an error signal to
work with. I don't need an error signal and can thus control the speed
more tightly. Same when going over the crest of the hill. I can
anticipate this and back off the throttle before the car beings to gain
speed. Most cruise controls will overshoot at least 2-3 MPH going over
a hill as they need an error in order to start responding and the
natural lag in the system will cause overshoot.

Matt- Hide quoted text -

- Show quoted text -

Your analogy with driving tells me a little about your line of
thinking. In that case, why does the car to slow down when it hits a
steep hill? It is due to the inability of the engine to respond fast
enough for the sudden demand in power. Obviously, the cruise control
does a pretty good job over small hills otherwise we would not be
using them at all. If the engine were powerful enough and had a quick
response, it should be able to maintain a constant speed over a steep
hill. When you manually apply some extra throttle in anticipation of
the approaching the hill, you are in fact 'helping' the cruise control
do its job better. You are not doing something the cruise control is
inherently incapable of doing. You are simply reducing the transient
period. If left to its own device, the cruise control should
eventually reach the set cruise speed over the hill, unless the engine
is too small for the hill.

Consider an imaginary airplane with an infinitely large vertical fin.
Would it need rudder to fly co-ordinated? I hope you would agree that
the answer is no. The infinitely sized fin will generate an infinite
restoring force, which really means the airplane will never deviate
from co-ordinated flight. Now reduce the fin size to something smaller
and practical. The restoring force will also scale down. In this case,
the force may not be large enough to restore co-ordinated flight in
all possible scenarios, such as slow flight and steep turns. In some
cases it may experience a longer transient, and in some cases it may
not reach co-ordinated flight at all. It all depends on how large the
fin is, and how much air is flowing around it. In such cases where the
fin can't do its job satisfactorily, the rudder is used to help it
along.

So I still do not see your line of thinking.

P.S. I am continuing this discussion only because you seem to be
capable of carrying on a civil discussion even though we disagree.
Please do not be influenced by "Bertie the Bunyip", "Maxwell" and
"Erik" etc.. who have never had anything useful to say.

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com writes:

What in the world makes you think that an autopilot can make a "coordinated"
turn without using the rudder if a pilot can't?

Presumably a pilot can; I want to know how. And nobody has been able to tell
me thus far.

If you have "observed" this then, either A) Your simulation falls a bit
short in terms of simulating how the simulated autopilot works - I assume
it's easier to program a simulated autopilot without adding the "make it
appear un-coordinated" feature. Or, B) You only think that the autopilot
does a much better job than a pilot does - perhaps you are a bit ham-fisted
with your simulation - without ever being in in airplane, it would be easy
to not realize what you are doing given the lack of feedback and the fact
that no one has ever "flown" with you - I find that I "overcontrol" when
flying a sim...

Or (C) nobody here has a clue and nobody wants to admit it, even though their
argument among themselves makes it obvious.

Do you know how it's done, or don't you?

Ash Wyllie writes:

Looks like you found a simulator error.

Load a 172, and try very slow flight without using the rudder. Use power, hold
altitude and keep slowing until you stall.

You should emd up in a spin.

Why would I do that? It has nothing to do with my question: How can
autopilots make coordinated turns without control of the rudder?

Paul kgyy writes:

They also start the turn rather gradually, which minimizes the adverse
yaw.

They turn quickly considering that they are not touching the rudder. I want
to know how they do it.

Maxwell writes:

Nothing, the turns are not perfectly coordinated, they don't have to be.

The ball hardly moves. It moves a lot more if I attempt to roll into a turn
myself without using the rudder. Why?

Is Mxsmanic a Terrorost or a wannabe writes:

People often fear what they don't understand.

People often fear things that they should fear, too.

"Andrew Sarangan" wrote in message
ups.com...

P.S. I am continuing this discussion only because you seem to be
capable of carrying on a civil discussion even though we disagree.
Please do not be influenced by "Bertie the Bunyip", "Maxwell" and
"Erik" etc.. who have never had anything useful to say.

Perhaps you should read a little more and type a little less yourself.

MX posts a stupid and useless question, in a single sentence no less, like:

"How do autopilots make coordinated turns even when they cannot control the
rudder?

And you morons struggle for days, wasting hours of your time, nit picking
every possible aspect of the issue literally to DEATH - while he sits back
enjoying the party and contemplates his next one liner. And just because
some of us don't chime in and join the useless "nit pick", you want to
openly accuse us of having nothing useful to add.

Wake up and smell the coffee chump, you are being played like a grand piano
by simple social outcast with minimal trolling skills.

Viperdoc writes:

Hey Anthony you butthead- your basic premise is incorrect: the autopilot in
small planes (like the Baron I've flown for around 500 hours) does not do
coordinated turns. Just because there might be some anomalous behavior in
your game does not make is so in real life.

There is no anomaly in the game. The only anomaly I see is that nobody here
knows the answer. Lots of people strutting about and claiming to be experts,
and calling each other stupid, but nobody really knows, and that is pretty
glaringly obvious to the observer.

However, so little rudder is needed at speed, it makes no difference if the
ball is halfway out, in terms of comfort.

Then my attempts to keep it centered with the rudder are not necessary,
either.

Also, a standard rate turn is not
necessarily a coordinated turn, although some of your statements suggested
that you do not know the difference.

I know the difference.

As good as you might think it is, do not mistake the flying model of a $50
computer game with real flying. Your presumed knowledge and the basis of
your questions are obviously limited by the shortcomings of MSFS.

Do not assume that every anomaly is a simulator defect. The simulator is a
lot better than you think. Indeed, it predicts the behavior of an aircraft a
lot better than anyone here does.

"Mxsmanic" wrote in message
...
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com writes:

What in the world makes you think that an autopilot can make a
"coordinated"
turn without using the rudder if a pilot can't?

Presumably a pilot can; I want to know how. And nobody has been able to
tell
me thus far.

If you have "observed" this then, either A) Your simulation falls a bit
short in terms of simulating how the simulated autopilot works - I assume
it's easier to program a simulated autopilot without adding the "make it
appear un-coordinated" feature. Or, B) You only think that the autopilot
does a much better job than a pilot does - perhaps you are a bit
ham-fisted
with your simulation - without ever being in in airplane, it would be
easy
to not realize what you are doing given the lack of feedback and the fact
that no one has ever "flown" with you - I find that I "overcontrol" when
flying a sim...

Or (C) nobody here has a clue and nobody wants to admit it, even though
their
argument among themselves makes it obvious.

Do you know how it's done, or don't you?

BS, you're just trying to fuel the nit fest.