We’ve all heard the expression “Grease the squeaky wheel,” but I’m guessing most of us have never thought much about its origin. Last summer, I came across the farm cart in the photograph (below right) near Helsinki, Finland, and couldn’t help but wonder what kind of story it could tell. It was a form of transportation, as is the Beechcraft King Air, but from an earlier age – maybe 1900?
Our main business at Marsh Brothers Aviation is designing and making non-metallic polymer bearings and seals. While the wheel bearings on this cart were likely no more than a wooden hub on a wooden axle, if one started squeaking the fix was to jack up the wheel, knock out the retaining pin, pull the wheel and smear the bore with grease. Reassemble and it’s good to go.
We will likely be developing wheel bearings for vertical takeoff and landing (VTOL) electric aircraft some day because they don’t see high speeds. Right now, tapered roller bearings are as good as they get. However, many other bearings or bushings on an aircraft such as the King Air are made of bronze and are greased.
Several decades ago, I decided to make torque link bearings for my first airplane – a 1957 vintage Beechcraft Bonanza – out of a self-lubricating polymer our company produced. That might have been around 1970. It was a test. The Thordon bearings were tiny but they worked, and I was able to replace the grease zerks with plastic plugs.
Fast-forward to 2012. I had sold the Hawker Sea Fury I’d been using for business transportation. Hey, don’t laugh! This airplane was pulled through the air with an 18-cylinder radial engine cranking out just about 3,000 horsepower. It was equipped with a glass panel and autopilot, and I flew IFR from Northern Canada to Mexico. Those were the days!
Anyway, I acquired my second Bonanza, a V-35 V-tail I used as my transportation ship while I was rebuilding my third Aerostar from the ground up, more or less. That Aerostar was in the shop for two years where it was completely upgraded with everything new I could get my hands on. This was to be the platform where I would go all out with the objective of replacing every bronze bearing with our polymer AeroTough GF. Most installations were STCed and while we’ve had to make a few adjustments, the point has been absolutely proven. There is no necessity for a grease gun to come anywhere close to an airplane anymore.
We could do the same thing for the King Air, but the costs involved in making such wholesale changes would likely never be recovered.
Think about cars. In my younger days, dad would take his car into the garage for an oil and filter change and a grease job. Today that grease job is just a memory.
So why would anyone bother eliminating greased bronze?
Well, one benefit is weight savings. Bronze weighs seven times more than our AeroTough GF. On the Aerostar we were able to cut empty weight by 12 pounds. That’s not a huge amount, but on airplanes every pound saved counts.
The next area of improvement comes with replacing dynamic O-rings with Thorseals, another self-lubricating polymer. While studying mechanical engineering at Northrop University, our fluid dynamics professor told the class: “If you’re designing a cylinder, do not use O-ring seals for dynamic positions; specify V-seals.” I’ve always remembered that and it’s the reason most of the Aerostar dynamic seals were replaced by our Thorseals.
It’s why we changed the piston rod seals in our brake master cylinder rebuild kits from O-rings to Thorseals. They’re just better. They won’t take a compression set, and in landing gears they can tolerate more radial movement of the piston rod or piston inside a cylinder or gland.
Flap rollers are an interesting study in upgrade opportunity. On the Aerostar, the OEM roller comprises a steel sleeve, a steel roller and two steel thrust washers bearing against each side of the steel flap track. It requires oiling the rollers and greasing the tracks. The MBA upgrade eliminates all lubrication because the stainless steel rollers are bushed with AeroTough GF. Thrust surfaces are machined AeroTough washers. No lubrication needed, period.
The King Air flap tracks are aluminum and the rollers are stainless steel needle bearings with a Teflon washer against a single flange. That washer is supposed to prevent wear on the softer aluminum track. It does that if it stays in place. The rollers will roll as long as the grease is not so viscous (due to super cold air) that they slide instead of rolling.
Our mission in developing the STCed King Air flap roller replacement was to reduce or eliminate flap track wear. Only time will tell if this objective has been met.
The development process involved building two test rigs where flap operation was simulated and loads and speeds duplicated. We were successful in running three times longer than the OEM average replacement cycle.
What we thought would take less than two years in development took us four years before finally being awarded STC approval.
We knew we would need to design a test rig capable of duplicating as accurately as possible the dynamic conditions the roller is exposed to through a typical flight cycle. However, the test rig we designed and built exhibited too much flexibility when side loads were imposed and it was necessary to totally redesign the rig and stiffen the structure, which took close to a year.
Then, we needed to allow Transport Canada to view the rig’s operation in real time any time they wished and that required a remote video link. After finally receiving Transport Canada’s approval, we applied for FAA approval. That process took longer than it typically does.
It’s good to see the rollers that have now been supplied to customers and installed on aircraft are all performing as expected. However, verifying the reduction or elimination of flap track wear will take years of service. As I mentioned earlier, we could eliminate every grease fitting on every King Air if conditions support it. We know it’s possible due to our Aerostar experience but the time and money to get there makes the business case difficult to justify.
It is easier for us to get 10-foot diameter main shaft bearings approved for a hydro-turbine than a project to replace the relatively tiny bronze bushings in King Air torque links!
Aircraft seals and bearings development has been driven more by a personal desire to do something good for aviation than by the promise of a financial return. It shouldn’t be this way but it is because of the need to deal with regulatory bureaucracies with little motive for expediency.
In a world I know is technically achievable, I can imagine every King Air operating with no bronze or steel bearings in the landing gear, grease-free flap rollers and no O-rings sealing pistons or rods. It’s possible, but unlikely.
Electric airplanes are different. Here, we have the chance to start from scratch. If the squeaky wheel is the designer or owner who says, “Let’s get rid of these archaic engineering designs and look ahead to reliability and much-reduced maintenance cost,” then maybe it will happen. The design will be from a clean sheet.
King Airs usually fly a lot more than many smaller general aviation aircraft and cutting operating costs and empty weight is important to owners. Initiative may come from fleet owners who want to cut operating costs; maybe there is hope.
George A. (Sandy) Thomson has been flying since he was just 18 years old, beginning with a 1950s vintage Beech Bonanza. He later went on to study mechanical engineering at Northrop University in Inglewood, California, and is now an ATP licensed pilot with more than 6,000 flying hours. Sandy is the founder of Marsh Brothers Aviation (MBA), a manufacturer of grease-free polymer bearings and seals for applications such as landing gears, actuators and other positions where a low friction, self-lubricating alternative to bronze could prove beneficial. MBA’s new King Air Flap Roller Bearing kit has been approved by the Federal Aviation Administration for commercial use on USA-registered King Air aircraft. FAA approval, which follows Transport Canada approval in 2024, paves the way for U.S.-based operators and maintenance organizations to replace seizure-prone greased needle flap rollers with a more robust, self-lubricating, grease-free bearing solution.