More Titanium components for the 750SDXtreme! This article is definitely about the controls, but it might be better suited with the title “Losing Control”. While waiting on several major pieces of this puzzle from various companies and machine shops, I have really fallen down the rabbit hole with titanium. It all started a few months ago with my first self-inflicted experience with the precious metal, when I decided to make the steering rods out of titanium. These were a simple and straight-forward design with two pieces: just a rod that is threaded on one end and has a trimmed and drilled piece of plate welded to the other end. They didn’t require any special tools to fabricate and even the Tig welding went very smoothly.
Fast forward from then, to my previous article in the Kitplanes August ‘25 issue and you will remember that I took this a step further with adding a simple argon purge setup to my welding equipment, bought a better tubing vise to jig these pieces up, and expanded my titanium fabrication into building the rudder pedals from titanium tubing. I’m still not ready to fully reveal my whole new pedal/steering/suspension system design, but I do have several more parts ordered to complete that new setup so stay tuned. While I am anxiously waiting on those parts, I have been looking at the rest of the control system for this 750SDXtreme. I had really planned to stop falling into the world of titanium with this build at the rudder pedals, but as I was sitting in my shop chair inspecting the main control torque tube, I found an imperfection that I just could not overlook. It was a crack at the end of the tube where a cromoly plate is bent and welded onto the tube and the aileron control rods attach to it. I have looked at this piece over and over, and while I really don’t believe it would ever cause a problem because this factory component is plenty robust and structurally sound enough to withstand any normal flying abuse, it is still a crack and I would always know there was an imperfection in this build and that would haunt me forever. I have no doubts that Zenith would ship me a new torque tube quickly if I had told them about the issue, but there were also a couple of other things leading me into more titanium work with this component. The connection point of the control stick to the torque tube is designed/manufactured in a way that is almost impossible to remove all the slack. After inspecting this same joint in my 700+hr Super701, I noticed it has developed more slack than it had when it was built, and there is just not a good way, or easy way, to fix it.
So here we go, head first, into the next titanium project: a new torque tube and control stick. My main objective with building these from scratch is to eliminate the minuscule slop in the control system. Zenith uses a cromoly bushing material and welds it into the torque tube. This is robust and simple, but the bushing material does not perfectly fit the supplied AN3 attachment bolt, which is used to join the control tube to the torque tube. Once this bushing is welded into the tube, the weld overlap is drilled back out to the correct size for the AN3 bolt and cleaned up on the outside of the tube. At first, this allows a reasonably tight-fitting joint, however, as the weld wears back to the bushing material size, there becomes a slightly increased slack in this joint. Let me emphasize that there is nothing wrong with the Zenith design and even your great-grandkids will never wear out this joint enough for it to become a real control issue. I am simply chasing perfection and this is one spot that I am focusing on while waiting on other modified/prototype pieces to arrive. I am also indulging my newly acquired skill of working with titanium, and even shedding a fair amount weight in the process, which is never a bad thing.
Moving forward, the only way I could see to improve this setup is to incorporate replaceable and tighter fitting bushings into the torque tube. Since all the control tube pressure is transferred to the outside edge of the torque tube, I decided to weld a small plate to each side of the torque tube where the control tube plates will overlap. This will add a little more material and contact area for the bushing. To make all this work, I went with a slightly smaller diameter, but thicker torque tube. Each end of the tube has a piece of the standard size tube fitted over and welded onto it, so I can utilize the Zenith bearings and keep the extra bearing surface area for the front and rear of the torque tube. After a lot of careful measuring, fitting, and welding, I finally have a usable titanium torque tube that is significantly lighter than the original.
Next up is the control tube. Since the area on the torque tube was expanded slightly in width because of the added plates for the bushings, now the standard control tube attachment point won’t work because it is slightly too narrow. To help compensate for the additional width, I went with a 1.25” control tube instead of the standard 1.125”. This width comes out almost perfect to allow nylon bushings with 1/16” flanges in between the torque tube and the control tube. Now it is time for a lot more careful measuring and mocking things up. After sitting in my Super701 and also talking to several other Zenith flyers, I’ve been thinking about shortening the control stick by ~15mm. This is not much and will most likely not even be noticed, but could allow for a slightly sharper control feel and possibly a little more comfort for me personally. I am most definitely going to stay with the Zenith Y stick design. Many people have asked me about this setup in the Zenith airplanes through the years and quite a few builders do change it to an available dual stick control system. I have to admit that I was seriously considering changing the Y stick when I built the Super701, but I had mixed feelings and decided I would give the Y stick a try because this wouldn’t be a hard modification to do after the plane was flying. I am very glad I tried the Y stick and have since fallen in love with it. It is a very simple design and does not require all the extra joints and complexity that are required if you do decide to change it. The Y stick also just fits me extremely well ergonomically. While on trips, I find myself using it for an armrest just as much as I use it for actually needing to control the easy flying Zenith airplanes. It also makes the accessibility of getting into and out of the side-by-side seating arrangement in these Zeniths much easier than having to deal with control sticks in between your legs.
Now that I have a plan, it is time to cut more titanium tubing and meticulously cope the ends to get everything fitted up tightly and ready to weld. Once the pieces of tubing for the basic Y are laid out and ready, it is time to focus on the attachment point at the bottom of the stick. This requires two pieces of 1/8” plate to be cut and formed. I say “formed” because titanium does not like to be bend, at all. Titanium is too hard and brittle to handle the same “S” bend that the factory puts into their cromoly pieces. I also don’t see a good reason to make the lower end of the plate be parallel with the control tube, because this is the attachment point for the elevator cable and that cable doesn’t care which way it is turned as long as it is in the center of the tube, like the original control stick. So I decided to form that plate with a gentle curve, to ensure there is no degradation of its strength. These lower plates are also the pivot and attachment point of the control stick where it articulates with the torque tube.
I kept the basic shape of the larger plate by making a template out of plywood and then plasma cutting the titanium plate to match. A little extra time with the belt sander and I have a couple of nice pieces of titanuim plate cut to match the standard profile. To form the curve, I simply used a bench vise with pieces of rounded wood as a form and tightened the titanium plate down in the vise to achieve the offset it needed. Unfortunately, this was one of those nights where I came to the shop after eating supper to work on the airplane “for a little bit” and several hours later I stepped back outside the shop to find out it was getting daylight. So the jigging and welding of all these pieces would have to wait until the longer-than-normal workday was over, and possibly a little rest.
We are still way behind on the farm with our cropping season because of record-breaking rainfall for the month of May. So every chance we get, we are trying to catch back up on that. In between the farming, consulting, and all my other responsibilities, I am working on this 750SDXtreme as much as possible.
So…..Back to it! After a few hours of jigging up and Tig welding all these pieces, I finally have a nearly complete control system ready to install into the 750SDXtreme! It was exciting to see these newly made titanium components come together as I mocked them up into this custom Super Duty.
What’s next? Well, as I look at the titanium control system, there are only a couple of pieces of cromoly left that haven’t been replaced with titanium. I already plan to make most of the push/pull rods out of titanium and that leaves one last piece, the flaperon control mixer. This is a fairly large component that I have already modified to work with my custom manual flap control setup. It is also already fully installed into the airplane with the bearings fitted, greased, and finished, so I am trying to talk myself out of taking it back apart and redoing this component, yet again, in titanium. This mixer sits pretty far back into the W&B envelope of the plane, so for now I will wait until later on to decide if I will pursue another titanium project. One of the most common questions I get regarding the titanium is, how much weight does it save? The new titanium control stick and torque tube saves just over 1.5 pounds, comparing them to the cromoly parts they are replacing. With all the pieces being replaced by titanium in the 750SDXtreme, I am expecting over 10 pounds saved overall.
In my last article, I gave my dad credit for my engineering mindset and for my inspiration in chasing perfection. Now it is time to give a shoutout to the incredible young lady whom I give full credit for igniting my passion for aviation, my mom. As far back as I can remember, it was my mom and I who would run outside together to look up at what was flying over every time we heard an aircraft. Luckily, when I was little, our farm was in a direct path for local military training runs, so it was very common for mom and I to watch C-130’s and many various helicopters fly over. We would run outside to watch whatever was flying overhead, both day and night! Our farm is also located in the “southeast training area” for a few local airports and it is very common for us to see plenty of GA aircraft training and even doing some aerobatics above the farm. Mom and I still look up at the skies together every chance we get! Mom was also my passenger/copilot on the very first day I was able to allow passengers in my newly built Super701 back in 2018 (a memory I will never forget). So Happy Birthday to my mom, my copilot, and my absolute biggest fan/supporter, and thanks for igniting and fueling this aviation passion that I will carry and share for the rest of my life!
