Coordinated turns without rudder, and autopilots

Paul kgyy writes:

As others have posted, most lightplane autopilots don't adjust the
rudder for adverse yaw when turning, so you do get a few seconds of
slightly uncoordinated flight. However at normal cruise speeds this
creates no hazard or discomfort.

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.

If flying close to stall, the autopilot should be turned off even for
straight and level flight. If the airplane is on the verge of
stalling and starts to turn because of engine p-factor or any other
reason, the autopilot will attempt to correct with aileron. This may
actually induce stall on one wing, producing sudden wing drop and a
potential spin.

I have an aversion to stalls and I usually stay well away from them. The AP
will put the aircraft into a stall if airspeed is too low to maintain altitude
easily (I don't know if this is an artifact of simulation or just like the
real thing--I know my simulated autopilot doesn't have all the modes of the
real one).

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

As others have posted, most lightplane autopilots don't adjust the
rudder for adverse yaw when turning, so you do get a few seconds of
slightly uncoordinated flight. However at normal cruise speeds this
creates no hazard or discomfort.

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.

If flying close to stall, the autopilot should be turned off even for
straight and level flight. If the airplane is on the verge of
stalling and starts to turn because of engine p-factor or any other
reason, the autopilot will attempt to correct with aileron. This may
actually induce stall on one wing, producing sudden wing drop and a
potential spin.

I have an aversion to stalls and I usually stay well away from them. The
AP
will put the aircraft into a stall if airspeed is too low to maintain
altitude
easily (I don't know if this is an artifact of simulation or just like the
real thing--I know my simulated autopilot doesn't have all the modes of
the
real one).

It's honestly just one of those things that do not hold true to form on PC
simulators. But turns do not always have to be perfectly coordinated.
Especially shallow ones initiated by wing levelers or low end autopilots.

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.

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. It
would be a highly inefficient and impractical design if it
doesn't fly coordinated without rudder impact in that
regime.

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

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

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.

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.

..
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