Ken:
I was fascinated by your explanation below. I presumed there
were "suitable" circuits which conducted such activities, but had not the
slightest idea how. Your Proportional-Integral-Derivative trio twigged my
imagination.
Perhaps for tyhose of us less educated, you could "animate" the internal
circuitry of the NavAid device...? I used to instruct aviators, from
ab-initio to advanced and always found that if they understood how any
device "thinks" they could better operate it. I can see how the Derivative
portion might mitigate the Proportional segment, but the overall effect
escapes me (and perhaps others).
Happy Landings
Ferg A064
P.S: 'scuse the double message to you.....
----- Original Message -----
From: Kenneth Whiteley <kenwhit@kenwhit.demon.co.uk>
Subject: Re: altitude oscillations
> In message <005901c126e9$5cf85aa0$6e820b18@plstn1.sfba.home.com>, Dave
> DeFord <davedeford@home.com> writes
> >Hi Folks,
> >
> >N135TD tends to oscillate slowly in altitude when the stick is left free.
> >This is most noticeable when the Navaid autopilot is on, since there is a
>
> I wouldn't touch anything on the aircraft until you are certain that any
> control parameters accessible in the Navaid have been optimised. Any
> feedback control system tends to oscillate unless the control parameters
> have been matched to the system being controlled. In industrial
> controllers it is usual to have three control parameters:
>
> Proportional which generates a signal proportional to the difference
> between the desired value and the actual value (the error signal). In an
> aircraft control system there would also be limits to the commanded
> pitch changes.
>
> Integral which feeds in a signal continuously as long as the system is
> out of balance. Without an integral term a new controlled state could
> not be achieved accurately because the proportional signal would be
> needed to generate a changed control signal.
>
> Derivative outputs a signal proportional to the rate of change of the
> error signal. Although it is sometimes possible to avoid using
> derivative action, this parameter can overcome oscillation.
> Kenneth Whiteley
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