Coordinated turns without rudder, and autopilots

So in theory I should be able to turn myself with ailerons only in the same
way, without the need to use the rudder to stay coordinated. What's the
secret? Each time I try to turn at the same rate that the AP manages, I have
to use the rudder to stay coordinated.


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.

Mxsmanic wrote:
Dan writes:


So where is this perfect airplane? I don't know about you, but I need
the rudder pedals to fly the aircraft.


But autopilots apparently do not, and that's what puzzles me.

Autopilots in simulators do not. Actual (that's opposite of virtual)
light aircraft need a rudder. If you turn the yoke, the plane will
bank, turn and eventually become coordinated, but for a while in
the interim, you'll be flying uncoordinated.

Some of these differences are why I disregard anything you may say,
correct or not, because you don't understand the basics of actual
flight regardless of how much of a master h4xor you are in the
simulator.

Mxsmanic wrote:

Dan writes:


So where is this perfect airplane? I don't know about you, but I need
the rudder pedals to fly the aircraft.


But autopilots apparently do not, and that's what puzzles me.

Where the hell is Bertie.

Sorry about the troll thing, you were totally right.

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.

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.

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.

Erik writes:

Autopilots in simulators do not. Actual (that's opposite of virtual)
light aircraft need a rudder.

Autopilots on light aircraft do not, and I'd like to know why.

Ron Natalie writes:

Get in most any aircraft. Take it to a normal cruise airspeed.
Put your feet flat on the floor and roll her into a standard rate
turn. I can almost guarantee the ball will be centered. It
would be a highly inefficient and impractical design if it
doesn't fly coordinated without rudder impact in that
regime.

Then why would you ever need the rudder in a turn?

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?

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)?

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.

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?

Mxsmanic opined

Bob Moore writes:

An unwanted side-effect of aileron operation is adverse yaw — a yawing
moment in the opposite direction to the turn generated by the ailerons. In
other words, using the ailerons to roll an aircraft to the right would
produce a yawing motion to the left. It is caused by an increase in induced
drag due to the greater effective camber of the wing with a downward-
deflected aileron, and the opposite effect on the other wing. Modern
aileron systems have minimal adverse yaw, such that it is barely noticeable
in most turns. This may be accomplished by the use of differential
ailerons, which have been rigged such that the downgoing aileron deflects
less than the upward-moving one. Frise ailerons achieve the same effect by
protruding beneath the wing of an upward deflected aileron, increasing drag
on that side. Ailerons may also use a combination of these methods.

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.

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.

-ash
Cthulhu in 2007!
Why wait for nature?

Mxsmanic wrote in
:

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


They don't fjukkktard.



Just like you can't.


Bertie