Piper single axis autocontrol question.

[Mike Noel]

My '74 archer developed an intermittent problem where the aileron would have
a 'soft stop' at one end of the control throw. I thought a mechanic might
have left a rag or some such under the floor that moved around and sometimes
prevented full control deflection, so I removed the floorboard under the
back seats. I found instead that the aileron servo pulley had several wraps
of cable and what appears to be a pin stake to keep the cable against the
pulley, presumably to prevent the cable from sliding on the pulley. At one
end of throw the pin stops the cable from unwrapping from the pulley and the
cable bends down, giving the feel of a soft stop.

Anyone familiar with the mechanics of this arrangement? My best guess is
that the cable is actually sliding around the pulley slightly when I help
the autopilot in rough air and sometimes the pin is in a position to allow a
natural hard stop and at other times it stops the aileron short of full
throw.

--
Best Regards,
Mike

http://photoshow.comcast.net/mikenoel

[[email protected]]

I don't know the pipers well enough to comment specifically,
but this surely shouldn't be happening. it's a safety of flight
issue.

The cable should be constrained so it can't slip on the capstain.
Sometimes this is done with a bead staked on the cable in the
middle of the capstain... it drops down into a small hole in the
capstain. There might be other mechanisms to do this, but there
will be some way to do this.

If the travel isn't well centered, something may collide near the
end in one direction or the other. There usually isn't a lot of
excess travel available; that is they only use enough wraps to
get the job done in the first place.

You may want to loosen the bridle cable clamps and reposition
them slightly so that travel to each end is the same.

The cables should have some tension in them; if they are loose,
the autopilot may oscillate.

bh



On Apr 19, 5:50*pm, "Mike Noel" > wrote:
> My '74 archer developed an intermittent problem where the aileron would have
> a 'soft stop' at one end of the control throw. *I thought a mechanic might
> have left a rag or some such under the floor that moved around and sometimes
> prevented full control deflection, so I removed the floorboard under the
> back seats. *I found instead that the aileron servo pulley had several wraps
> of cable and what appears to be a pin stake to keep the cable against the
> pulley, presumably to prevent the cable from sliding on the pulley. *At one
> end of throw the pin stops the cable from unwrapping from the pulley and the
> cable bends down, giving the feel of a soft stop.
>
> Anyone familiar with the mechanics of this arrangement? *My best guess is
> that the cable is actually sliding around the pulley slightly when I help
> the autopilot in rough air and sometimes the pin is in a position to allow a
> natural hard stop and at other times it stops the aileron short of full
> throw.
>
> --
> Best Regards,
> Mike
>
> http://photoshow.comcast.net/mikenoel

[John Kunkel]

"Mike Noel" > wrote in message
...
> My '74 archer developed an intermittent problem where the aileron would
> have a 'soft stop' at one end of the control throw.
> Anyone familiar with the mechanics of this arrangement? My best guess is
> that the cable is actually sliding around the pulley slightly when I help
> the autopilot in rough air and sometimes the pin is in a position to allow
> a natural hard stop and at other times it stops the aileron short of full
> throw.

The cables don't stop the aileron travel, there are adjustable hard stops
near the bellcrank in each wing.

[Mike Noel]

I pulled the rear floorboard again and tried turning the servo capstan with
a wrench on the center shaft nut. I was able to turn the capstan while the
aileron was at the end of its travel, confirming that the cable is able to
slip through the cable stake. Will the fix be inserting a new stake tightly
enough to keep the cable fixed on the capstan, or perhaps replacing the
capstan/cable assembly? Looks like the main trick for the mechanic will be
getting the tension correct on the bridle cable.

--
Best Regards,
Mike

http://photoshow.comcast.net/mikenoel


" > wrote in message
...
I don't know the pipers well enough to comment specifically,
but this surely shouldn't be happening. it's a safety of flight
issue.

The cable should be constrained so it can't slip on the capstain.
Sometimes this is done with a bead staked on the cable in the
middle of the capstain... it drops down into a small hole in the
capstain. There might be other mechanisms to do this, but there
will be some way to do this.

If the travel isn't well centered, something may collide near the
end in one direction or the other. There usually isn't a lot of
excess travel available; that is they only use enough wraps to
get the job done in the first place.

You may want to loosen the bridle cable clamps and reposition
them slightly so that travel to each end is the same.

The cables should have some tension in them; if they are loose,
the autopilot may oscillate.

bh



On Apr 19, 5:50 pm, "Mike Noel" > wrote:
> My '74 archer developed an intermittent problem where the aileron would
> have
> a 'soft stop' at one end of the control throw. I thought a mechanic might
> have left a rag or some such under the floor that moved around and
> sometimes
> prevented full control deflection, so I removed the floorboard under the
> back seats. I found instead that the aileron servo pulley had several
> wraps
> of cable and what appears to be a pin stake to keep the cable against the
> pulley, presumably to prevent the cable from sliding on the pulley. At one
> end of throw the pin stops the cable from unwrapping from the pulley and
> the
> cable bends down, giving the feel of a soft stop.
>
> Anyone familiar with the mechanics of this arrangement? My best guess is
> that the cable is actually sliding around the pulley slightly when I help
> the autopilot in rough air and sometimes the pin is in a position to allow
> a
> natural hard stop and at other times it stops the aileron short of full
> throw.
>
> --
> Best Regards,
> Mike
>
> http://photoshow.comcast.net/mikenoel

[[email protected]]

On Apr 21, 7:31*pm, "Mike Noel" > wrote:
> I pulled the rear floorboard again and tried turning the servo capstan with
> a wrench on the center shaft nut. *I was able to turn the capstan while the
> aileron was at the end of its travel, confirming that the cable is able to
> slip through the cable stake. *Will the fix be inserting a new stake tightly
> enough to keep the cable fixed on the capstan, or perhaps replacing the
> capstan/cable assembly? *Looks like the main trick for the mechanic will be
> getting the tension correct on the bridle cable.

Buy turning with a wrench, you might not be getting the answer you
think.
Generally there will be a safety clutch between the shaft of the motor
and the
capstan. So if you turn the shaft and the ailerons have hit their
stop, you will
be slipping the clutch.

So you need to see if the cables move relative to the capstan.

Bill Hle

[Mike Noel]

Bill, in this case I could see the capstan slipping under the cable.
Evidently the cable could slip on the capstan easier than the capstan could
slip on the clutch.

--
Best Regards,
Mike

http://photoshow.comcast.net/mikenoel


" > wrote in message
...
On Apr 21, 7:31 pm, "Mike Noel" > wrote:
> I pulled the rear floorboard again and tried turning the servo capstan
> with
> a wrench on the center shaft nut. I was able to turn the capstan while the
> aileron was at the end of its travel, confirming that the cable is able to
> slip through the cable stake. Will the fix be inserting a new stake
> tightly
> enough to keep the cable fixed on the capstan, or perhaps replacing the
> capstan/cable assembly? Looks like the main trick for the mechanic will be
> getting the tension correct on the bridle cable.

Buy turning with a wrench, you might not be getting the answer you
think.
Generally there will be a safety clutch between the shaft of the motor
and the
capstan. So if you turn the shaft and the ailerons have hit their
stop, you will
be slipping the clutch.

So you need to see if the cables move relative to the capstan.

Bill Hle