Ch 19 - Wings and ailerons

Aileron woes

I really didn’t see this coming, but I could no longer ignore reality… the right aileron wasn't moving anymore, except in very rough jerks. Had I not been on the ground, examining the wing on a stand, I would have crapped the proverbial brick. 

This discovery came about while removing the right aileron control pushrod (CS126) for an upgrade. This pushrod moves parallel to the firewall, and connects the control stick to the left wing’s bellcrank, and eventually the left aileron.

Left aileron control pushrod before removing the wings

You can see both aileron control pushrods in this picture

 

Right wing root pocket seen from above

 

Right wing on a rack with the CS126 pushrod removed, looking at the bellcrank in the wing root.

With the wings on a stand in the hangar, and the fuselage at home in my garage, I was getting ready to wrap up a four month upgrade program that included splitting the ailerons control rods, and installing quick disconnects per plans (plans' page 16-3). 

Left aileron CS126 pushrod after being split in the middle to comply with the quick disconnect plans

Left aileron CS126 pushrod and quick disconnect hardware

That’s when I discovered that moving the right aileron had become very difficult. Increasing amounts of force applied to the control rod generated no movement until such time when something gave and the aileron jumped to a new position with a loud creaking noise. Manipulating the aileron directly yielded the same result, making even Gina cringe at the noise. Needless to say, solving this issue had become the new priority.

Disconnecting all pushrods isolated the problem to the spherical bearing interface

Thinking back in time, I don’t remember ever feeling any resistance in the control stick while flying, but I did notice that it would sometimes hang momentarily when pushed to the far right during preflight. Because it always returned back to center when touched, I never thought much about it, except to secretly blame some phantom friction in the newly installed GRT aileron servo for this sticky conduct.

Roll servo arm connecting to the right CS126 aileron pushrod

You can see a video of this behavior here...

Digging deeper into the flight control system, I learned that the torque tube connecting to the aileron via a universal joint, is actually made up of two parts, a long ¾” OD aluminum torque tube (CS151), and a much shorter ⅝” OD 4130 steel tube (CS152) inserted and bolted directly to it (see image below). The latter emerges at the wing root, where it connects via a separate control rod to the aforementioned bellcrank. 

Section view of the right wing root pocket at the aileron torque tube station (seen from the rear)

Left wing root pocket

Due to the slight built-in misalignment present between the aileron and the aluminum torque tube (CS151), the 4130 steel tube (CS152) doesn’t just rotate, but it also translates back and forth ever so slightly.

Now, as the steel tube (CS152) rotates and slides in and out of the wing root, it rides on a phenolic block (CS150), which in my case was substituted by an Infinity Aerospace wing root spherical bearing in order to reduce friction in the control system.

Infinity Aerospace spherical bearings

Due to the metal on metal sliding motion, it is imperative that this location be lubricated and inspected regularly if the aileron is to swing unimpeded.

As you might have guessed by now, JT must have been missing out on this treatment, probably ever since it was sold the first time over a decade ago. As years of neglect added up, CS152 developed a rust coating that eventually prevented the smooth movement within the tight tolerance spherical bearing. 

17 years old spherical bearing on right wing 

 You can start to see some of the problem (rust)

Removing the bearing required a puller to get it past the rust ring, after which it easily came off by hand.

 My friend Nick let me borrow this puller. Dunno what it costs but it's definitely worth every penny. 

No way in hell this bearing would have ever come out without Nick's puller. "Thanks again Nick!"

Finally getting eyes on the problem

Aileron and torque tube removed from the wing

"Yeah, that's gotta go!"

Aileron, universal joint, torque tube, and spherical bering.

A better look at the aileron, universal joint, and torque tube assembly.

Universal joint (brown) allows the slight offset between the aileron and the torque tube (CS151)

Torque tube and associated hardware

Some light rust on the stainless surface as well

Inspecting the left wing revealed a similar pattern in the works.

Left wing root

Harder to see the issue on the left wing

Rust much easier to see with the bearing removed

Aileron and torque tube removed from wing

Left wing missing the aileron

Here's what the left CS152 looked like

Left wing hardware

Both CS152s

The parts were a bit too far gone for my liking, so I decided to remake them from scratch. 

I did flirt with the idea of using stainless, doubling the wall thickness to make up for the lesser strength, but with the right size 4130 steel tube already on hand, I was able to complete this job in just a day, save a few bucks, and spare JT the indignity of the extra weight.

The job was easy, basically cut the new tube to length, match drill the holes, then reinstall in the wings. 

Setting CS152 length on the bandsaw with a stop

Cutting a new 4130 steel CS152

Cleaning the inner bearing by hand this way did not work

Spinning the ScotchBrite at 1500rpm while holding the bearing by hand worked great 😁

I'm calling this clean enough

Outer surface still looked good

Match-drilling CS152 to CS151 (torque tube)

Looking to avoid a repeat of this issue, I used Birchwood Super Blue gun blueing compound on both CS152 as an extra layer of protection against corrosion. It was quite amazing seeing them promptly turn blue/black right before my eyes. I then soaked them in Birchwood Barricade for twelve hours to complete the treatment.

Gun Blue turns metal black right in front of your eyes. Barricade finishes the treatment.

After brushing on Gun Blue

After spraying with Barricade

Left overnight

Finished CS151s

The long aluminum torque tubes needed to be lightly scuffed back to shiny metal as they were showing some early signs of corrosion. I did this by chucking them up in my lathe, and sanding them gently. Later, I primed them twice (inside and out) before putting them back into service.

Cleaning up some superficial corrosion

Nick highly praised this etching primer

You are going to want to use a respirator with this primer (even outdoors)

Dries up very quickly.

Finally putting everything back

CS152s are unfortunately buried quite deep in the plane, and unless your A&P knows to look for them come Condition Inspection time, they can easily escape any lubrication efforts. 

From now on I will make it a point to dig deep enough to uncover them at least once a year, and make sure they remain well lubricated and rust free.

Mike Bush swears by this stuff