Proper control stick friction

My Dream Flyer is due for an annual inspection 3/27/2015.

My local A & P (who has built an RV-4) says there should be no stick force when the plane is at rest. "the stick should flop over on it's own".

It flies PERFECTLY and feels PERFECT now. I am VERY reluctant to "fix" something that is not broken.

My question: does it need to be adjusted (the torque tube friction) to be loose?

Thanks for your input.

Daddyman

One question. Do you have a spring bias aileron trim in the airplane?

I have a -4 that I built, and I'm also an AP/IA. The stick in mine wont "flop" but will, and should stay almost any place you move it based on the controls being "balanced". The elevator is balanced to be neutral, and the ailerons offset each other. There is no "friction" generation anywhere other than the rod end bearings (not much), or if you have Stick boots,aileron seal boots at the root, autopilot, ect. When I have done checks on other R/V's that I have inspected or helped ready for the first flight, I usually feel and listen for any interference through full range of travel and that's it. All the hinge and attach points are easy enough to see and get a little shot of LPS..but I have yet to see one just "flop" to the side.

daddyman said:

My local A & P (who has built an RV-4) says there should be no stick force when the plane is at rest. "the stick should flop over on it's own".

Click to expand...

Maybe his does that. But that is not the "standard". I would not mess with it. There could be many configuration differences between the 2 planes (ie auto pilots, control boots, aileron trim spring, control surfaces balancing, etc.)

If his is flopping over I would be interested to know if it always flops over to the same side.

Randy,
No. I do have electric trim for both elevator and ailerons.

Daddyman

Ailerons are not generally a problem, the surfaces and stick should move freely with almost no effort.

Elevators are a different story.. I find many of them incorrectly setup and binding. I also find the hinge bolts loose in an attempt to compensate for the center bearing being incorrectly shimmed.

ALL attach/hinge bolts should be tight in the control system and there should be no binding.

You should be able to move any of the control surfaces with VERY light pressure with one finger.

Walt said:

Ailerons are not generally a problem, the surfaces and stick should move freely with almost no effort.

Elevators are a different story.. I find many of them incorrectly setup and binding. I also find the hinge bolts loose in an attempt to compensate for the center bearing being incorrectly shimmed.

ALL attach/hinge bolts should be tight in the control system and there should be no binding.

You should be able to move any of the control surfaces with VERY light pressure with one finger.

Click to expand...

Walt is spot on. Diligent shimming of the center bearing followed by shimming of every hinge as required will dramatically reduce elevator hinge friction by reducing bearing side loads. Reduction of friction will greatly help the aircraft maintain pitch trim. The goal here is perfection, not 'good enough'.

Note that on the elevator system, the weight of the push-pull tube in the fuselage will cause the elevator to return to a neutral position. That is, on an airplane without an autopilot servo. On my -6, the elevator sits above neutral. Pushing it all the way down and releasing, it freely comes back to that position.

daddyman said:

Randy,
No. I do have electric trim for both elevator and ailerons.

Daddyman

Click to expand...

Ailerons -

If it's connected up from a servo to springs like a servo version of the manual trim, then that will probably keep the stick centered.

If it's connected with a servo inside the aileron driving a trim tab, then it would probably flop down under gravity with the servo aileron down.

Elevator and hinge friction

Randy Hooper said:

One question. Do you have a spring bias aileron trim in the airplane?

Click to expand...

Walt said:

Ailerons are not generally a problem, the surfaces and stick should move freely with almost no effort.

Elevators are a different story.. I find many of them incorrectly setup and binding. I also find the hinge bolts loose in an attempt to compensate for the center bearing being incorrectly shimmed.

ALL attach/hinge bolts should be tight in the control system and there should be no binding.

You should be able to move any of the control surfaces with VERY light pressure with one finger.

Click to expand...

Thanks to all for you expertise and reply.
My hinges are just right.
The elevator moves with no effort at all, in fact, it will occasionally settle aft with no input.
The ailerons require very gentle input (side-to-side).
When trimmed in flight it actually does fly "hands off".

Daddyman

Hey Vern,
It currently holds trim perfectly.
I can move the stick with a single finger easily.
I will try to measure the non-flying pull force with a trigger measuring device.
Daddyman

Flopping over

My -4 has no aileron trim and the ailerons are balanced. There is no detectable friction in the control stick movement at rest in any axis. In pitch you feel the weight of raising the elevator, but in roll there is nothing. The stick will stay vertical but if you push it slightly to one side the WEIGHT OF THE CONTROL STICK AND GRIP are enough to cause it to "fall" over to that side. It will not stay in any position other than neutral aileron/stick straight up because once it is off center the weight of the stick brings it to full deflection.

I think this is what you'd call "normal".

FWIW: I added a tru-trak servo and the friction of the servo changes all this. It is enough to overcome the weight of the stick and now it will rest in any position.