Disclaimer

This blog is for entertainment purposes only, and is not meant to teach you how to build anything. The author is not responsible for any accident, injury, or loss that occurs as a result of reading this blog. Read this blog at your own risk.

Wednesday, October 14, 2020

Ch 20 - Winglet and rudder - Part 2

Another plans error


Enough of JT, let’s get back to my long term project (aka #2) for today. 


You might remember I elected to spare the stress to my marriage, and buy foam cores already precut by Eureka CNC’s hot wire foam cutting machine. 


Cutting foam by hand is simple, but it does require good coordination between two individuals. Any misstep could wreck the very reason to DIY this (aka cost saving), forcing one to purchase another load of fairly expensive foam. If that wasn't enough, depending on the level of frustration reached in the process, one could even earn himself a night in the doghouse


In any successful marriage one develops a sixth sense about how far he can push things, and my spider senses tell me this would have been way out of bounds.


With that out of the way, the plans’ directions on how to cut the foam becomes a moot point, except to note that the winglet’s rear edge is cut 48” long (along the foam)


This will become important shortly.



Foam cutting directions. Red lines represent the hot wire cut lines.



Eureka’s winglets foam cores come in three pieces each. The two tall ones make up the top winglet and need to be joined together, however they are left long for the builder to cut as needed.



Eureka CNC's breakdown of the winglet (I added the 48" dimension for clarity)


Left and right winglet cores as they came from Eureka CNC


Taping the seams in preparation for joining LUW1 and LUW2

Microslurry spread on the joint


After slurrying both sides, I prepared wet-micro to add to the middle of the joint.

I slide the cores back and forth, until the wet-micro works its way to the surface, then secure the foam in place with nails.


With tape and nails removed the next day, we are ready to continue this journey.



Now, let's take a look at some other key winglet dimensions from the original plans...



Original winglet plans with the small rudder. I cleaned this drawing up and added the red references.



Note on the picture above that if one subtracts Water Line 18.4 from Water Line 65.4, one gets 47” which is the same vertical distance from the previous Eureka CNC’s drawing.


So far so good.


The small rudders were upgraded a long time ago with a supplemental optional set of High Performance Rudder plans (LEZHPR) to improve crosswind takeoff and landing handling, and shorten the crosswind takeoff distance required due to the reduced amount of brake-steering necessary. 


The problems start when referring to these newer plans.



High Performance Rudder plans. I added all red markings.


I have modified the above picture to reestablish some reference points from the original rudder plans, but did not otherwise change anything else. 


The interesting thing in this image is that the distance along the winglet trailing edge (39” + 9”), and the vertical distance between waterlines (WL 66.4 - WL 18.4) both equal 48”, which is physically impossible.


Needless to say, this generated about a week's worth of back and forth between myself and a few other builders, stopping all progress on the winglets, and was never really resolved to anyone's satisfaction. Eventually most everyone agreed that either the Water Lines are wrong, or the dimensions of the rudder are incorrect. 


Because nothing else references these Water Lines (that I am aware of), we all somewhat blamed them for being off. However, the more I thought about this discrepancy, the less I concurred with this decision.

 

You see, the High Performance Rudder plans were designed with a dual purpose, one can use them to make a major modification to an existing winglet, or build anew, and in the first case the winglets dimensions with their Water Lines would have been established a long time before, and with no sign of any errors. The confusion only surfaces after the introduction of the LEZHPR plans. So, if I were to pick a villain in this story, my money would be on the 9" dimension to the top of the winglet.


Now, the much more important question becomes how all of this affects one's build, and in my case I'd say not at all, since I plan on cutting the rudders very similarly to the way Terry cut them on JT.



JT's rudders are not cut perpendicularly to the hinge line, but parallel to the longerons, making the cuts look horizontal in flight.


I am cutting my rudders 0.5" wider than JT's at the bottom to approximate the LEZHPR surface area


Because some other builder will eventually run into this discrepancy in the future, I wanted to address it here so that new builders can quickly put this issue behind them, and press on with their projects without wasting any more time on it.



Thursday, October 08, 2020

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