Re: S-Tec 50 Autopilot

["Brian K. Michalk" <michalk@awpi.com>]

> I have been reading off & on about problems with the S-Tec 50 two-axis
> autopilot and opinions from different guys on how to fix such problems.
> My personal experience was that both, the aileron and the elevator servos,
> were over controlling and producing oscillating movement which could go from a

I've got a beef with using only altitude as an input for an autopilot.
As most of you may know, I'm rolling my own integrated computer
into the "Goose".  One of it's functions will be autopilot.
Actually the autopilot will be handled by an embedded PC from Zworld,
and it will be instructed from the main computer via RS485 for the altitude
to hold.

We know that when one is sufficiently "in front of the power curve"
(I hate that saying) that attitude will at least temporarily 
affect altitude.  So a pitch up results in an increase in altitude.
The AP should take altitude as an input and change attitude
by a prescribed amount.

Correct me if I'm wrong, but if we have a perfect non-precessing
gyro, and we know that we are X amount of feet away from our 
altitude and we are currently straight and level, then a Y degree
change in pitch would be called for.

In turbulence this would be great.  If you are at altitude, and the aircraft
is upset, the AP would instantly correct for pitch rather than altitude.

In reality, I think a cheap piezo electric gyro would
work.  Damp out the really long wavelengths on the order of more than 5 minutes
to fix precession.  Also one of the sensitive ADXL01 chips

that measure acceleration might work.  Mount it with it's sensitive
axis longitudinal to the aircraft.

Oh well, just my two cents.  This is one of the reasons I'm
building my own airplane.
I think it's gonna be a hoot to try out
all these ideas I have knocking around
inside my head.

-- 
Brian Michalk  <http://www.awpi.com/michalk>
Life is what you make of it ... never wish you had done something.
Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
musician, home-brewer, entrepenuer and SINGLE!