AUTOPILOT PROS & CONS

"Judah" wrote in message
. ..
"Al" wrote in
:

Some autopilot failures are very subtle. I was shooting a coupled ILS
to minimums with a King autopilot in a Mooney. After capturing the
glideslope, I noticed the rate was about 75'/min more than I was used
to. As we got closer to DH, the DME was still showing about 2 miles to
the airport. I leveled at DH, and while motoring along 200' above the
houses, I tapped the Vor/loc. The GS needle snapped to the top of the
case. It was "stuck" centered, and the autopilot
was literally flying the needle. Iron Mike, indeed.

Technically speaking, that wasn't an autopilot failure, it was a GS needle
failure.

Correct.

The results would have been nearly identical if you were hand-
flying. Although you might have noticed inconcistencies in airplane
response more quickly and fixed it earlier.

Naw, If I'd set the plane up for the descent, and got it exactly right the
first time, with no additional trim, I'd be real suspicious...Never happened
before.

Then again, you might have been
so busy keeping the needle centered that it would have gone unnoticed
until
you flew your plane right through someone's living room.

Hard to say.

It's really a matter of cross checking and a cynical attitude.

Al

On the Century-2000 equipped Bonanzas I fly, there's an interesting
trim problem with the AP, which is basicly that it doesn't trim.

Engage the AP while you're being vectored for the ILS and let it
fly the approach, as you keep reducing power to slow down and then
track the GS. As you slow down, you should be dialing in nose-up trim
(and, indeed, the AP prompts you to do this, but if you're not paying
attention, you can miss the flashing light).

Now, at DH, click off the AP to hand-fly the landing. All of a
sudden, you've got a fistfull of yoke trying to pull your arms out of
their sockets until you get the trim fixed. Even worse if you didn't
see the runway and clicked off the AP to execute the missed.

Of course, the AP is performing as designed, and it's the pilot who's
unairworthy, but it's a common enough mistake that I've got to believe
it's a design flaw in the system. If nothing else, it should have a
more obvious alert than a small blinking light outside of your main
visual scan. Like maybe a mechanical arm that smacks you upside your
head with a rolled-up sectional while a synthesized voice says, "Trim
up, trim up".

The auto-pilot should be running the trim, the annunciation
is intended to be advisory. Using the electric trim will
disengage the auto-pilot. I'm guessing that you have a bad
relay.
It is not airworthy as it is, you might be able to placard
it in-op until you can get it in the shop. Read the POH FM
supplement for a description of the required pre-flight
tests, you may not be doing them properly and thus the A/P
won't engage.

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



"Roy Smith" wrote in message
...
| On the Century-2000 equipped Bonanzas I fly, there's an
interesting
| trim problem with the AP, which is basicly that it doesn't
trim.
|
| Engage the AP while you're being vectored for the ILS and
let it
| fly the approach, as you keep reducing power to slow down
and then
| track the GS. As you slow down, you should be dialing in
nose-up trim
| (and, indeed, the AP prompts you to do this, but if you're
not paying
| attention, you can miss the flashing light).
|
| Now, at DH, click off the AP to hand-fly the landing. All
of a
| sudden, you've got a fistfull of yoke trying to pull your
arms out of
| their sockets until you get the trim fixed. Even worse if
you didn't
| see the runway and clicked off the AP to execute the
missed.
|
| Of course, the AP is performing as designed, and it's the
pilot who's
| unairworthy, but it's a common enough mistake that I've
got to believe
| it's a design flaw in the system. If nothing else, it
should have a
| more obvious alert than a small blinking light outside of
your main
| visual scan. Like maybe a mechanical arm that smacks you
upside your
| head with a rolled-up sectional while a synthesized voice
says, "Trim
| up, trim up".

In article 5u4ag.20816$ZW3.8687@dukeread04,
Jim Macklin wrote:
The auto-pilot should be running the trim, the annunciation
is intended to be advisory. Using the electric trim will
disengage the auto-pilot. I'm guessing that you have a bad
relay.

There is no electric trim. I believe it's an option, but our boxes
don't have it.

I've never seen a Bonanza without electric trim and an
autopilot installed. What you have seems to be just a wing
leveler with heading and [maybe] tracking.


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

"Roy Smith" wrote in message
...
| In article 5u4ag.20816$ZW3.8687@dukeread04,
| Jim Macklin wrote:
| The auto-pilot should be running the trim, the
annunciation
| is intended to be advisory. Using the electric trim will
| disengage the auto-pilot. I'm guessing that you have a
bad
| relay.
|
| There is no electric trim. I believe it's an option, but
our boxes
| don't have it.

In article PG5ag.20818$ZW3.19044@dukeread04,
Jim Macklin wrote:
I've never seen a Bonanza without electric trim and an
autopilot installed.

Apparently not :-)

What you have seems to be just a wing leveler with heading and
[maybe] tracking.

Nope. It does heading, tracks nav, altitude hold, course intercepts,
and coupled ILS approaches. Once we get the kinks worked out of the
new add-on box, it'll be doing GPS roll steering too. We've got one
driven from a CDI, another with an HSI. It just doesn't have electric
trim. It's an option, and we don't have that option. Wish we did,
but we don't.

I would skip the fancy nav steering and coupling, you can
always use the heading bug to track the needle and get the
pitch trim ASAP. But, it isn't my airplane. A wing leveler
like Mooney installed is a big aid, but real altitude hold
and trim is just as important.

If you want to get spoiled, fly a $500,000 Sperry autopilot
in a King Air. I've flown a few hundred different Bonanzas,
from late 1940 models to the B36TC, if they had an
autopilot, [all the ones built after about 1965 that I flew
did] they had electric trim.

We did a Category II certification on the Beechjet and
encountered a problem caused by a poorly written flight test
schedule. The DER that was hired wrote a schedule that
called for the coupled approaches to be flown at a
stabilized speed of 1.3 Vso from the OM to landing or missed
approach. We could hand fly within the tolerances, but the
autopilot could not. We had to do extreme fore and aft CG
and the autopilot would get wild on the ILS. Came to find
out several things... FAR 25 requires that the airplane trim
function to 1.4 Vso, so 1.3 Vso might not be a trimable
speed, depending on CG. Also the autopilot was certified at
1.3 Vso +10, as far as those who did the original
certification could remember.
So we re-wrote the flight test schedule and the autopilot
flew well within the 95% 1 dot on all the approaches because
it was in trim at 1.3 Vso+10.


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

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Roy Smith" wrote in message
...
| In article PG5ag.20818$ZW3.19044@dukeread04,
| Jim Macklin wrote:
| I've never seen a Bonanza without electric trim and an
| autopilot installed.
|
| Apparently not :-)
|
| What you have seems to be just a wing leveler with
heading and
| [maybe] tracking.
|
| Nope. It does heading, tracks nav, altitude hold, course
intercepts,
| and coupled ILS approaches. Once we get the kinks worked
out of the
| new add-on box, it'll be doing GPS roll steering too.
We've got one
| driven from a CDI, another with an HSI. It just doesn't
have electric
| trim. It's an option, and we don't have that option.
Wish we did,
| but we don't.