aileron servo instl vs vibration

[John Ferrell]

RE: "I've always wondered why
> someone didn't make a servo that you couldn't back drive."
Do you mean something like a worm gear drive?

John Ferrell
http://DixieNC.US

----- Original Message ----- 
From: "JOddino" <JOddino at socal.rr.com>
To: <discussion at nsrca.org>
Sent: Saturday, February 21, 2004 1:48 PM
Subject: Re: aileron servo instl vs vibration


> Years ago most servos had the pot wiper driven directly by the servo
output
> shaft.  Pot wear was so bad the famous Giesendanner (Sp?) pot wipers were
an
> after market product all the serious pilots used.  We started using EK
push
> pull linear output servos that used a gear to drive the pot shaft.  It was
> geared so the travel on the pot was about 180 degrees for a normal output
> movement of plus and minus 9/16 inch as I recall.  Pot wear was no longer
a
> problem, which tells me Jerry's theory is correct.  The control surface
back
> driving the servo at the frequencies of vibration and aero buffeting is
the
> culprit.  If the turbines and the electrics don't show the pot wear then
the
> aero buffeting must not be the major contributor.  I've always wondered
why
> someone didn't make a servo that you couldn't back drive.  I guess the
> efficiency would drop but we don't seem too concerned with that anyway.
The
> servo also wouldn't blow back if it lost power but how often to we depend
on
> that.
> Jim
>
>
> ----- Original Message ----- 
> From: "Jerry Budd" <jbudd at QNET.COM>
> To: <discussion at nsrca.org>
> Sent: Saturday, February 21, 2004 9:11 AM
> Subject: Re: aileron servo instl vs vibration
>
>
> > Hi Xavier,
> >
> > A while back Dave von Linsowe tried side mounting the aileron servos
> > to see if the servo pots would be more tolerant of the motor
> > vibration.
> >
> > The theory was that the rotary acceleration forces induced by the
> > motor on the airframe translate into increased vertical acceleration
> > at the aileron servos causing the pot wiper preload to vary
> > cyclically, resulting in increased rate of wear.  It was hoped that
> > the pot wear could be reduced or eliminated by orienting the plane of
> > rotation of the pot wiper in the vertical axis.
> >
> > It didn't help.  Tony Frackowiak also tried it on his Gator G-202 and
> > it didn't work there either.
> >
> > And that makes sense, as the pot wiper preload is not likely to be
> > affected by the inertial forces acting on the very low mass of the
> > pot wiper.
> >
> > The current thought is that the inertial forces acting on the
> > ailerons are back fed into the aileron servo gear train causing the
> > aileron servos to have to work almost constantly to resist the
> > uncommanded movement.  The servo moves slightly (but nearly
> > continuously) around the commanded position to resist causing
> > excessive wear on the pot and gears (similar to servo buzz).  Since
> > the servo spends most of its time around neutral, that's where most
> > of the wear occurs.
> >
> > Interestingly, the ePartner Tony Frackowiak is flying shows no
> > aileron servo pot wear through ~40 flights (go figure!).
> >
> > Jerry
> >
> >
> > >Is there a prefered method to install the aileron servos and protect
them
> > >from the high level of vibration someone was mentioning?
> > >Could the servo be mounted on his side with the arm parralele to the
ribs
> > >wihout risking more wear of the gear ?
> > >I suppose the vibration on the wing servo is mainly up-down
> > >
> > >Thanks
> > >
> > >Xavier
> >
> > -- 
> > ___________
> > Jerry Budd
> > mailto:jbudd at qnet.com
> > =====================================
> > # To be removed from this list, send a message to
> > # discussion-request at nsrca.org
> > # and put leave discussion on the first line of the body.
> > #
> >
>
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