Trim motor

[Jim]

I have a series 5 with the electric trim on the stabilizer. I adjust it as per the manual. It always goes up full stroke. I can not get it to stop at the required clearance. Any thoughts? Jim
jezim@pro-ns.net

[SWeidemann]

Jim,

I will be watching your replies, as I have a Model 5 Vixen and a new trim motor/jack screw in hand to install with not much documentation.

Skot

[jiott]

I have a series 7 but I think they are the same. The ballscrew always goes full stroke, but by adjusting the stem per the manual it will stop on the upper end where you want it to. You set the upper limit and the lower limit is not separately adjustable.

[Jim]

My problem is with the up travel. I set it per the manual, run it down & when I run it up it goes full stroke. I can't adjust it the stop short. It always goes until it hits the tubing. Thanks for your input. Jim

[jiott]

Do you have the stabilizer installed and all the little links?

[kitfox2009]

Hi Jim
Have you checked your wiring or possibly the switch? It should stop immediately when you release the rocker switch to neutral.
A few years ago the switch stuck at full down (I believe we had something jammed on the switch when flying- Two guys winter gear)
Anyway it ran to full stop and then burned out the motor. Still flyable but heavy controls.
Take care
Don

[kitfox2009]

Hi Jim
This was a Vixen.
Don

[Jim]

Do you have the stabilizer installed and all the little links?

Every thing is as the plans show.

[Jim]

Hi Jim
Have you checked your wiring or possibly the switch? It should stop immediately when you release the rocker switch to neutral.
A few years ago the switch stuck at full down (I believe we had something jammed on the switch when flying- Two guys winter gear)
Anyway it ran to full stop and then burned out the motor. Still flyable but heavy controls.
Take care
Don

It stops immediately anywhere when I release the switch. The up travel is supposed to stop 7/16 of an inch from full travel. Mine will go to full travel if the switch is held.

[jiott]

The black rod that moves up and down when you activate the motor is adjustable by screwing it in or out by hand when the links are disconnected. At full stroke up you screw it in or out until you have the 7/16 clearance, then reconnect the links so it can't turn. If you do this there is no way it can go beyond where you set it.

[Jim]

The black rod that moves up and down when you activate the motor is adjustable...

This morning I disconnected the scissors link & the rod end and ran it to full up. I turned the inner shaft clockwise until the scissors link tab was down against the outer tube. I did this a dozen times. I attached the heim joint and adjusted to get my 7/16 inch clearance. I ran the stabilized full down, ran it up and it goes to no clearance.
Full up stabilizer is nose down. I can't imagine ever needing that much up travel. You thoughts.

[jiott]

This is incredible, I can't believe it! After you have made the adjustment and reconnected and locked the scissor links and rod end, there is no way the unit can extend farther. If it does, I give up; maybe there is something drastically wrong with the trim motor unit.

[jiott]

By the way what is a "heim" joint?

[Dave S]

Heim Joint is street rodder speak for rod end;)

DS

[Jim]

Also the name of the company that makes them.

[jtpitkin06]

I read this post a few times and tried to figure out what was so difficult. Then I went back and read the manual instructions. Yeah… clear as mud.

OK, here’s the deal. In the final assembly instructions you are directed to check that the rod end is threaded all the way into the end of the actuator. If it is not, then you adjust it inward by disconnecting the scissor links (do not disconnect the rod end) and rotate the actuator rod counter clockwise.

You are screwing the actuator upward onto the rod end. Why do it this way? Because it is much easier to take off the scissor link and rotate the actuator rod than it is to pull the rod end out of the stabilizer. This method keeps the stabilizer attached to the fuselage at all times.

Then you are instructed to adjust the rod end by rotating the actuator clockwise. When you rotate the rod clockwise the ball screw turns inward and the assembly gets shorter. At the same time the rod end unscrews and the assembly gets longer. This is why the instructions say to reapply power to extend the actuator and recheck your measurement.

Just to make the instructions simple let’s rewrite them here:


Adjust the rod end to obtain 7/16 clearance between the top of the horizontal stabilizer leading edge and the fuselage directly above it with the trim actuator fully extended.

Step 1. Make sure the rod end is screwed into the actuator all the way.
Step 2. apply power to the actuator to fully extend the rod. You may use a 9 volt transistor radio battery as a power source.
Step 3. Measure the vertical clearance at the leading edge of the stabilizer.
Step 4. To make adjustments, disconnect the scissor link and rotate the actuator rod.
Step 5. Apply power again to the actuator to fully extend the rod. Recheck the clearance. Repeat step 4 if needed.
Step 6. reconnect the scissor links and install cotter pins.

Step 7. Tighten the rod end lock nut and secure with Loc-tite

You’re done!!!

First, let’s make it clear that turning the actuator rod does not adjust any internal end points inside the ball screw actuator. If you screw it in manually it will still travel to full extension or retraction when operated electrically. The actuator will extend to the end of the stroke and then it simply recirculates the balls. You can manually run the screw full in and full out and the length of the electrical stroke does not change.Likewise you can fully retract the actuator electrically and it will reach the minimum extension where the balls recirculate.


You can only change the total length of the mechanism by adjusting the rod end.

If you adjust the rod end by rotating the actuator rod you temporarily change the ball screw total extension. No problem. Just run it electrically out to full extension and recheck your stabilizer clearance for the 7/16 measurement.

Now if you have attempted to do the adjustment and your stabilizer is hitting the fuselage, it indicates you do not have your rod end screwed all the way in. It is also possible you are using a lock nut that is too thick preventing the rod end from screwing in the necessary amount.


That’s all there is to it!!!
John Pitkin
Greenville, TX

[jiott]

John's got it dialed. A much better explanation than I was trying to give.

[SWeidemann]

John,

Looks like a well done set of instructions. I've prtinted them to take back to the hangar shop.

Thanks much, Skot

[jrevens]

Thanks for that explanation, John... excellent!

[Jim]

I read this post a few times and tried to figure out what was so difficult...

John,
Thanks for the reply. Many of your replies over the years have been a learning experience.
My problem still exists. As a test I disconnected the rod end from the stabilizer but left the scissors link connected so the rod would not spin. I extended the rod full length.5 1/4 inches. I disconnected the scissors and turned the rod clockwise until it stopped. 1 1/4 inches now sticking out.
Re installed the scissors link and extended the rod. It went right back to 5/14 inches. The same thing happens when I do the adjustment. Jim

[jiott]

It is doing exactly what it is supposed to do! The extension and retraction range of the rod never change no matter how you turn it. The adjustment is done by screwing the rod end in or out with the actuator rod at full extension. The total range of motion of the stabilizer never changes; By adjusting the rod end you just set the point at which it stops at the upper end. The lower end stop will continue to be the same total distance from the upper end stop.

As an FYI, on my SS7 after flying it for a while I decided that the 7/16 factory recommended adjustment was not to my liking. I wanted more nose up trim (for use with full flaps). So I adjusted the rod end so my total range was moved down (nose up) to where the bottom end point was at the bottom of the slots in the tail access covers.