Autopilot fighting for control

Mxsmanic wrote:
Robert M. Gary writes:

The autopilots that have "pitch control" (terminology used to denote
that it does more than hold altitude, it holds VS) usually have trim
control as well. The familiar "Trim, in motion" annunciator that seems
to go off everytime I click the mic to call tower in the G1000
aircraft.

Doesn't trim make its own noise? I've read notes in voice recorder
transcripts that mention "trim wheel moving at autopilot speed,"
although that is in large aircraft. I assume it must make quite a
noise if this gets recorded.

Its an annunciator just like any other. There is one annunciator that
has multiple preprogrammed channels. I believe mine has 40 different
things it can say, although few are hooked up. A signal goes down the
wire to the annunciator and the voice speaks. Its not part of the
autopilot or trim system itself.
Mine often says "Check landing gear" just as I call up tower when on
approach. Its a bit annoying.

-Robert

Mxsmanic wrote:
Do you feel more pressure in the controls as the A/P tries to trim
away your pitch change?

God yes. It only says "trim in motion" for extream changes. This is
usually when moving flaps or if you pull back power but forget to
reduce the VS. I've gotten it into situations where it gets on the back
side of the pitch control (more pitch up results in less VS) and it
starts to fight, I push down, it moves the trim forward and the
pressure becomes MUCH higher. The best solution at that point is to
disengage the altitude of course the real solution is to reduce the VS
before reducing power and not let the AP get behind the pitch curve.

-Robert

Robert M. Gary writes:

Mine often says "Check landing gear" just as I call up tower when on
approach. Its a bit annoying.

The simulated Baron I have says "Check gear!" constantly below certain
throttle settings (I'm not exactly sure what sets it off, though).
It's very irritating, but if it's in the sim, it must be doing that in
real life as well.

--
Transpose mxsmanic and gmail to reach me by e-mail.

If the autopilot is over=powered the auto-trim will run to
try to get control forces back in the acceptable range.
This will place the airplane seriously out of trim. A pilot
can over-power the autopilot, but if this is done it should
be either as a demonstration during checkout or in response
to an autopilot actuator run-away. The pilot should
maintain attitude control, over-powering the autopilot while
they
1 push the disconnect button
2 pull the circuit breaker
3 manually retrim
4 land ASAP



--
James H. Macklin
ATP,CFI,A&P

"Robert M. Gary" wrote in message
oups.com...
|
| Mxsmanic wrote:
| In simulation, if I set the autopilot to maintain the
altitude, and
| then try to change pitch with the controls, the control
surfaces
| barely move, and I can hardly have any effect on pitch.
|
| I think this is a limitation of the simulator. My guess
is that, in
| real life, the autopilot continuously adjusts trim, and
so, if you try
| to change pitch with the yoke, the A/P retrims to cancel
out your
| efforts, and the net effect is that you can change
pitch, but you must
| exert very high control pressures to do it (in order to
overcome the
| trim that the A/P is applying to neutralize your
efforts).
|
| Is this correct? I can see why this is difficult to
simulate with
| controls that don't provide feedback, but I want to make
sure that I
| understand the difference between the sim's way of doing
it and the
| real thing.
|
| It takes pretty minimual control to over power the
autopilot. However,
| if you disrupt it a great deal (make a big pitch change
for instance)
| the autopilot may overcorrect a few times before settling
back to the
| correct pitch. The ability to return to the correct pitch
with minimal
| over correcting is a function of the quality of the
autopilot.
| Sometimes when you make changes such as lowering flaps you
need to
| "help" the autopilot but holding the yoke in the right
place for a bit
| until the autopilot figures out what is going on. This
even with the
| more expensive autopilots (like the new KAP140).
|
| However, it is very easy to hand fly the plane while the
autopilot is
| on. The Cessna training instructors told us that they
routinely hand
| fly procedure holds on approach w/o changing the mode on
the autopilot,
| just over powering it.
| In my plane I'll hand fly through turb but I'll leave the
autopilot on
| because it gives me a nudge back to course (i.e. I can
feel it trying
| to pull me back on course). If I take my hands off during
turb though
| it will make the turb worse.
|
|
| -Robert
|

If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

Autopilots have a supplement in the POH, it should be read
and understood.



"Robert M. Gary" wrote in message
ups.com...
|
| Ron Natalie wrote:
| Robert M. Gary wrote:
| However, it is very easy to hand fly the plane while
the autopilot is
| on. The Cessna training instructors told us that they
routinely hand
| fly procedure holds on approach w/o changing the mode
on the autopilot,
| just over powering it.
|
| Ick. What's the point? Which mode where they in to
start with?
|
| The autopilot is in nav/approach mode. This is coupled
with a G1000 so
| it doesn't do holds on its own (its based on the 430
software, not the
| 480 software). So, rather than switch the autopilot into
heading mode,
| and then back into approach capture mode, they leave it in
approach
| mode. That way, as soon as you turn in bound you can just
let go and it
| flys the approach (KAP140 has pitch control and can fly a
GS). It just
| saves you from leaving nav mode and havnig to go back into
capture
| mode. I think part of their point is that it doesn't do
any harm to out
| mussle the autopilot.
|
| -Robert
|

The Cessna instructors are probably showing that the servos
can be over-powered with pilot muscle, no reason to lose
control. But I'm sure they also teach the location of CWS,
the trim switch, the red disconnect button and the A/P CB
and avionics master.


wrote in message
ups.com...
|
| Robert M. Gary wrote:
|
|
| However, it is very easy to hand fly the plane while the
autopilot is
| on.
| -Robert
|
| Ouch.
|
| My old Skylane has a KAP-150.
|
| "Easily" over power the yoke/trim with the AP on? No.
|
| I have a nice big red circuit breaker handle on the trim
breaker just
| for this reason.
|
| Pre-start includes saying out-loud: "Run-away trim, pull
red breaker."
|
| Fly an approach while overpowering the AP?
|
| Who are these Cessna instructors?
|
| They might want to RTFM, that's what CWS is for.
|
| Adam K.
|

Jim Macklin wrote:
If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

I'm simply quoted chapter and verse what the Cessna factory instructors
are saying. If you have a disagreement with the technique you are free
to discuss it with them.

Mxsmanic wrote:
Robert M. Gary writes:

Mine often says "Check landing gear" just as I call up tower when on
approach. Its a bit annoying.

The simulated Baron I have says "Check gear!" constantly below certain
throttle settings (I'm not exactly sure what sets it off, though).
It's very irritating, but if it's in the sim, it must be doing that in
real life as well.

Its the poor man's gear check. On my plane its anything below 12" MP.
However, most of the time I can't run more than 10" MP when being
vectored on the approach to a lower altitude without gaining speed, so
I have to listen to it. However, I have a 2 phase cancel button. If I
press it once, it overrides the "check gear" annunciator for something
like 30 seconds. If I press it twice quickly it overrides it for 5
minutes.

-Robert

I will at the next pilot meeting that Cessna hosts in their
meeting room just south of the Wallace plant on K42. These
are regular CFI meetings jointly with the FAA and Cessna and
other groups.

BTW, the factory instructors can be wrong. Or the person
who reported to you could be wrong. Part of a good
autopilot checkout should include showing that the servos
are not so strong that a pilot can't maintain control. But
that is a demo, the correct procedure is the hand fly, with
or without the FD or use the A/P console to command the
airplane.

Of course if the object is to have a student get an airplane
with the trim 100% wrong...


--
James H. Macklin
ATP,CFI,A&P

"Robert M. Gary" wrote in message
ups.com...
|
| Jim Macklin wrote:
| If the autopilot is flying, use the autopilot console to
fly
| the airplane. Over-powering the autopilot is always BAD
| technique. Many autopilots will disconnect if they
sense a
| problem which can include input on the control wheel.
|
| I'm simply quoted chapter and verse what the Cessna
factory instructors
| are saying. If you have a disagreement with the technique
you are free
| to discuss it with them.
|

Robert M. Gary wrote:
Ron Natalie wrote:
Robert M. Gary wrote:
However, it is very easy to hand fly the plane while the autopilot is
on. The Cessna training instructors told us that they routinely hand
fly procedure holds on approach w/o changing the mode on the autopilot,
just over powering it.
Ick. What's the point? Which mode where they in to start with?

The autopilot is in nav/approach mode. This is coupled with a G1000 so
it doesn't do holds on its own (its based on the 430 software, not the
480 software). So, rather than switch the autopilot into heading mode,
and then back into approach capture mode, they leave it in approach
mode. That way, as soon as you turn in bound you can just let go and it
flys the approach (KAP140 has pitch control and can fly a GS). It just
saves you from leaving nav mode and havnig to go back into capture
mode. I think part of their point is that it doesn't do any harm to out
mussle the autopilot.

Still Ick. I don't know about the KAP150, but switching autopilot
modes is just a button push (well, two, but you can mash NAV and
APR at the same time, I even can do HDG+NAV+APR together without
strain). Switching the autopilot modes is a lot easier than
fighting the thing trying to drive you back to the final course.