Coordinated turns without rudder, and autopilots

"Denny" wrote in message
ups.com...
.
On the other hand however, in a T38, you can fly a complete aerobatic
sequence including point rolls with both feet planted firmly on the floor
of
the rudder tunnels.
Dudley Henriques- Hide quoted text -

- Show quoted text -

I've always wanted to fly a 38 but never had the opportunity...
My Super Viking was one of those few GA machines with adequate tail
volume that you could fly instrument approaches with your feet on the
floor... Conversely, you could fly the plane nicely without ailerons
just using that powerful rudder...

One of the little tricks I do when 'unbrain washing' the pilots I have
helped over the years, is to say to them that: "you have just snapped
the cables to the ailerons and the elevator... now fly me back to the
airport without touching the yoke!"... Some have been totally
helpless... A few have almost instantly figured it out.. And most need
only be shown how for a few seconds... The majority have been amazed
after they successfully herded the plane a dozen miles back to the
airport and it is gratifying to see the light bulb in their head
suddenly light up as they begin to understand how the controls
actually work...

denny


I agree with this technique completely and have used it myself when teaching
all through my career.
Dudley Henriques

"Mxsmanic" wrote in message
...
Maxwell writes:

It's honestly just one of those things that do not hold true to form on
PC
simulators.

Real autopilots on real aircraft do not necessarily have control over the
real
rudders, and yet they execute real coordinated turns without those
rudders.
How do they do it?

They don't.


But turns do not always have to be perfectly coordinated.

Why are they more coordinated when performed by the autopilot than when
performed by the pilot (without rudder)?

They are not.


Especially shallow ones initiated by wing levelers or low end autopilots.

Autopilots often put the aircraft into a standard-rate turn, which isn't
exactly shallow, even if it isn't terribly steep.

No, it's not.

"Mxsmanic" wrote in message
...
Paul kgyy writes:

As Maxwell observes, this may just be a simulator limitation. In
actuality, a small amount of rudder should be applied when initiating
and recovering from a turn, but once in a constant bank turn, the
aircraft will normally be in coordinated flight without rudder
application.

But the autopilot has no control over the rudder, and yet the turn is
coordinated. What is it doing to make this possible?

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

Ron Natalie wrote:
Matt Whiting wrote:

A vertical stabilizer does not provide any lateral force unless there
is some degree of slip or skid.

Precisely! Now you are beginning to understand. As soon
as uncoordinated flight occurs (skid or slip) the vertical stab
deflects the aircraft back into the coordinated flight.

It does sounds like you are beginning to understand! With use of the
rudder, you can enter and exit a turn and maintain coordination at all
times. Without rudder and depending on the fin alone, you will be in
and out of coordinated flight as you enter and exit the turn. The
degree of departure from coordinated flight maybe be large or small
depending on the specific airplane and the rate at which you enter and
halt the turn, but without using the rudder, you will NOT be coordinated
at all times.



That's it's job! It is the primary job to provide the primary
aerodynamic forces to keep the airplane coordinated.

In coordinated flight, it is just along for the ride.

Yep, and as soon as something deflects the aircraft from coordinate
flight, it generates a force to correct it.

Yes, which is precisely what I said at the start. You have to enter
uncoordinated flight for the fin to work. With proper rudder use, you
can remain coordinated at all times (if you are good enough).


Many airplanes will oscillate slight in the yaw axis for this reason.

And they oscillate in pitch, and they oscillate in roll. This is
one of the fundamental modes of stability.

Yes, and that is one reason you have control surfaces, to stop these
oscillations or prevent them.


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.

Are you trying to tell me that you sit there and tweak the rudders
during flight continually to damp yaw oscillations? Don't think
anybody finds that fun. The few airplanes where it is a persistant
problem have autopilots that do that, but for most it's unnecessary
in normal flight regimes.

No, that is what yaw dampers are for. But, yes, I use the rudder and
ailerons and elevator to damp oscillations caused by turbulence when
they exceed a certain threshold. No sense in waiting through several
oscillations when you have the controls to stop it now.

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

Ron Natalie wrote:
Matt Whiting wrote:


Then you should know that the vertical stab can't prevent yaw, it can
only help eliminate yaw once it occurs as it can't provide any
restoring force until some degree of yaw occurs. A rudder an prevent
yaw from occurring in the first place. Fundamental difference here.


Nope. In most flight regimes if you displace the rudder you are
generating yaw not preventing it. What you are trying to wrap
your brain around is that you can use the rudder to accellerate
the responsiveness of the vertical stabs natural tendencies,
but by your own admission, in coordinated flight the stab is
streamlined.

No, I'm trying to get you to wrap you brain around the fact that the
rudder can act preemptively to prevent a departure from coordinated
flight. The vertical stab can not act preemptively. Fundamental
difference.


Matt

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.

However, so little rudder is needed at speed, it makes no difference if the
ball is halfway out, in terms of comfort. Also, a standard rate turn is not
necessarily a coordinated turn, although some of your statements suggested
that you do not 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.

On May 29, 5:40 am, Ron Natalie wrote:
Luke Skywalker wrote:

\

Ron...

oh my goodness...get some time with a good book on the subject and
then a CFI.

Robert

I have plenty of good books and practice on the subject.
You should find an aeronautical engineer and find out how
planes are designed to work.

..Well...you build them, I will fly them and we need the rudder to
coordinate turns particularly but not exclusivly with ailerons.

Robert

On May 29, 1:37 pm, Mxsmanic wrote:


Why are they more coordinated when performed by the autopilot than when
performed by the pilot (without rudder)?

Especially shallow ones initiated by wing levelers or low end autopilots.

Autopilots often put the aircraft into a standard-rate turn, which isn't
exactly shallow, even if it isn't terribly steep.

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

If I hand-fly a standard rate turn, the rudder application only lasts
for maybe 3 seconds at the beginning and end of the turn.

"Mxsmanic" wrote in message
...
Dudley Henriques writes:

Rudder use to acheive the objective of keeping the tail lined up with the
nose can accurately be said to be relative to aircraft type and airspeed.
You need a fair amount of rudder to handle yawfor example in a typical
light
general aviation type airplane to execute a coordinated turn entry and
exit.

So how does the autopilot do it? As far as I understand, autopilots in
small
aircraft don't generally have control over the rudder, and yet they can
execute coordinated turns.

What in the world makes you think that an autopilot can make a "coordinated"
turn without using the rudder if a pilot can't? That's complete and utter
nonsense.

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...

--
Geoff
The Sea Hawk at Wow Way d0t Com
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