David Culp said:

> > > I would suggest to use airspeed as input to a PID controller, your
> > > desired airspeed as reference and the elevator control surface as output.
> > > I haven't tried this, so good luck!
> >
> > Works like a charm :-) I got it stable with: Kp=0.0125, Ti=30.0, Td=0.0
> > with the Piper. You can start from there, and I'm sure that fine tuning
> > will get better performance.
> 
> Thanks Roy, it works better now, but still not enough to prevent crashing.  It 
> looks like I'll still need an external monitor to clamp the pitch angle.  For 
> instance, if I'm doing an idle descent at 250 kts and reset the speed to 300, 
> I need to keep the airplane from going straight down.
> 

You might also want to look at the lookahead feature, similar to one used in
the 747 autothrottle configuration, especially for larger aircraft.  While
overshot can be tuned for with PID, this seems to help a bit by directly
incorporating the rate at which you are approaching the goal.

Best,

Jim


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