Coordinated turns without rudder, and autopilots

Ron Natalie wrote in news:465c02e7$0$30412
:

Dan wrote:
\

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

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.

No, it won't, actually. The tendency towards adverse yaw is amelierated
in most modern light airplanes, but it's still there. It's just that
most modern airplanes ahve been dumbed down to allow almost co-ordinated
flight without rudder usage, but there isn't a conventional airplane
flying without CAR that is totally co-rdinated in when roll is
introduced, though many come close.
That includes airliners which we fly with feet on the floor most of the
time. Some, on approach, have some sort of third axis feature, but most
are two axis most of the time (exceptying FBW busses and the 777) The
yaw damper does a lot towards co-ordinating, but if you introduce a high
rate of roll, they'll yaw, at least momentarily, the worng direction.


Bertie

Andrew Sarangan wrote:
On May 28, 11:59 am, Luke Skywalker wrote:
On May 28, 8:11 am, Ron Natalie wrote:





Dan wrote:
On May 27, 5:44 pm, Mxsmanic wrote:
How do autopilots make coordinated turns even when they cannot control the
rudder?
If they don't control the rudder, they do not make coordinated turns!
--Dan
Boy we have the blind leading the blind here.
The whole point of that big vertical slab of metal sticking out of the
ass-end of your airplane is to provide a natural tendency for the
aircraft to fly coordinated. The pedals are just there for the
outlying conditions (low speed, high AOA for example) and fine
adjustment.
Ron...

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

Robert- Hide quoted text -



Ron is correct. The vertical fin makes the airplane weather-vane into
the wind, and that's what co-ordination is all about. The rudder is
there only to help the vertical stab do this job.

A perfect airplane will not need rudder.

Not true. The vertical fin can only provide a weather-vane affect when
a slip or skid has been induced. In coordinated flight there is no slip
or skid and hence the fin provides no lateral force. When you begin a
turn, most airplanes will induce adverse yaw and the rudder can counter
than before a skid occurs. The fixed fin can only act once an
uncoordinated condition has been induced. Sure, it does mitigate the
skid or slip, but it absolutely can't prevent it as it can't provide a
force until uncoordinated flight is already established. The rudder can
do this and is why it is included.

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.


Matt

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.

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

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.

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.

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.

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.

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.

Ron Natalie wrote in
m:

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.

You're wrong, Matt's right.


Bertie

On May 28, 12:26 pm, Andrew Sarangan wrote:
On May 28, 11:59 am, Luke Skywalker wrote:





On May 28, 8:11 am, Ron Natalie wrote:

Dan wrote:
On May 27, 5:44 pm, Mxsmanic wrote:
How do autopilots make coordinated turns even when they cannot control the
rudder?

If they don't control the rudder, they do not make coordinated turns!

--Dan

Boy we have the blind leading the blind here.

The whole point of that big vertical slab of metal sticking out of the
ass-end of your airplane is to provide a natural tendency for the
aircraft to fly coordinated. The pedals are just there for the
outlying conditions (low speed, high AOA for example) and fine
adjustment.

Ron...

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

Robert- Hide quoted text -

Ron is correct. The vertical fin makes the airplane weather-vane into
the wind, and that's what co-ordination is all about. The rudder is
there only to help the vertical stab do this job.

A perfect airplane will not need rudder.- Hide quoted text -

- Show quoted text -

No he is not. Mark W...said the word.

Robert

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.

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.

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.

Matt