Autopilots... failure modes

"Michael" wrote in message
om...

http://avionicswest.com/articles/kno..._autopilot.htm

That's not a bad article. I do have some issues with it.

First off, it ignores the most important difference between rate-based
and attitude-based autopilot - performance in turbulence in a slick
airplane. Attitude-based autopilots (those that use pickoffs on the
horizon gyro) work all the time. Rate-based autopilots (those that
use pickoffs on the turn coordinator) work in smooth air or with
light, draggy airplanes. In a heavier slicker airplane, especially a
twin, turbulence makes for a very uncomfortable ride because all the
corrections are too much too late. There are NO rate-based autopilots
in the transport category - they just wouldn't work.

You might want to take a gander at this article. I'm not sure what you mean
by slow corrections, but evidently S-TEC (taken with a grain of salt) has
optimized the corrections, as well as smoothed them to avoid overstressing
the aircraft in turbulence.

See Pages 6 & 7.

http://www.s-tec.com/pdf/autopilotbook.pdf


Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

Matt,

You might want to take a gander at this article. I'm not sure what you
mean
by slow corrections, but evidently S-TEC (taken with a grain of salt) has
optimized the corrections, as well as smoothed them to avoid overstressing
the aircraft in turbulence.

See Pages 6 & 7.

http://www.s-tec.com/pdf/autopilotbook.pdf

....but the S-Tec related Meggit line of products just offerd an autopilot
aimed at the multi/turboprop market, and it's attitude(position) based.

Seems the realized that a rate-based auto is not on par with the airplane
when installed in, e.g, a fast single-engine turboprop, just as Michael
said.

Regards

Kai

Basically, autopilot failure modes can be summarized as these:
Turns right instead of turning left
Turns left instead of turning right
Goes up instead of going down
Goes down instead of going up
An airplane is ALWAYS turning and going up or down, it's never really
in steady state. These pertubations can be small or large. (like a
steep turn descending spiral or a gentle turn).

john smith wrote in message ...
I am interested in learning from everyone...
a. What autopilot your aircraft is equipped with?
b. What aircraft your autopilot is installed in?
c. What does your autopilot use for heading/altitude/attitude reference?
d. What does your autopilot use for loc/gs reference?
e. If your heading/altitude/attitude reference fails, what functions
does you autopilot still provide?
f. With failed heading/altitude/attitude reference, does the loc/gs
still function?

"Matt Barrow" wrote in message news:...

You might want to take a gander at this article. I'm not sure what you
mean
by slow corrections, but evidently S-TEC (taken with a grain of salt) has
optimized the corrections, as well as smoothed them to avoid overstressing
the aircraft in turbulence.

See Pages 6 & 7.

http://www.s-tec.com/pdf/autopilotbook.pdf


Addendum to lost (by my ISP) post.

Meggitt 1500 & 2100 AP's use a hybrid of attitude and rate information
through the ADAHRS system. Sorta of "best of both worlds"?

(Doug) wrote in message . com...
Autopilot failure modes are a bit of a mystery, but I can tell you
from first hand experience, some failure modes would be very bad
indeed. One absolutely needs to keep an eye on the gyros the autopilot
DOES NOT use and turn the autopilot off if there is disagreement.

Mine once turned the yoke full right to the stops and rolled us into a
steep turn until I was able to grab it and right the craft. I was
following a VOR and the VOR went out of range. However, that isn't
what the autopilot is suppose to do in that situation.

-Robert