REFLECTOR: Aileron Rigging

[John Dibble]

Thanks, Doug.  That's the help I was hoping for!

John

Douglas Holub wrote:

> In a closed loop control system, if there is too much gain in the feedback
> loop the output will oscillate. With a gain of 15k the output (airplane
> rolling) was changing faster than the autopilot could control. The wings
> were probably constantly doing a little dance. It looks like the first thing
> he did was reduce the electronic gain from 15k to 9.2k, and when that wasn't
> enough he moved the aileron control cable closer to the axis of the bell
> crank so that the same amount of bell crank turning commanded by the
> autopilot would result in less aileron movement.
>
> I would guess that lowering your ailerons so that they are 1/16" up in level
> flight has reduced the gain in your autopilot's feedback loop since the air
> is moving slower closer to the wing so that the same amount of aileron
> movement would have less effect on roll. This would explain why the
> autopilot isn't tracking as well as it was.
>
> So I guess you could increase the gain again either electronically or
> mechanically and observe the results. But I don't know how dangerous that
> roll dance is or how linear the effect of increased gain will be on the
> magnitude of the oscillations. Too bad there's not a way to adjust it on the
> ground. If it was me, I would call the autopilot company and chat with a
> knowledgeable person before I started making changes.
>
> Doug Holub
> 2009 Standard FG
>
> ----- Original Message -----
> From: "John Dibble" <aminetech at bluefrog.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Friday, December 30, 2011 10:37 AM
> Subject: REFLECTOR: Aileron Rigging
>
> > After the discussion a few weeks back I decided to try a different
> > aileron position.  Mine are 1/4" up with 1/8" total play.  To have them
> > in line with the wing TE during straight and level flight, I would need
> > to have them 1/16" down.  I decided to try an intermediate position of
> > 1/16" up.  Now I have to use more stick force to enter a roll.  It feels
> > like I'm flying a bus.  On the plus side, the roll is more stable
> > meaning when I let go while flying straight, it tracks better.  I like
> > this better for IFR flying.  I had 5 kn more airspeed on a recent flight
> > from MS to NY, but this may be due to the colder temperatures.  I plan
> > to keep it this way for a while and see if I can get used to the "bus"
> > feel.  One other thing, the A/P doesn't track as well.  Before it would
> > maintain the heading to within a degree or so.  Now it's more like 5-10
> > degrees.  I set my gps CDI scaling to the smallest (0.3 mi) range to see
> > if that helps when tracking the gps.  Of course that won't help when
> > flying the heading bug.
> > The builder modified the roll gain.  Here's the entries he made in the
> > logbook.
> >
> > "Change A/P roll gain from 15k to 9.2k & test
> > Change A/P roll gain mechanically & test
> > A/P wing rock problem gone"
> >
> > Does this mean the A/P was too responsive before?  If so, can I un-do
> > this modification to get more response with the A/P?
> >
> > Wondering if I have universal joints......
> >
> > John
> >
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