"Tailwheel"
"Taildragger"
"Little wheel in the back"
These and more are our affectionate terms for landing gear designs common to all aircraft of the past. For some pilots, tailwheel aircraft are all they will ever want to fly. For others, flying a tailwheel aircraft feels like a terrifying carnival ride. Neither are wrong.
If you fly tailwheel aircraft long enough, you eventually find your preference regarding the operation of your tailwheel. Steerable tailwheel? Loose or tight steering chains? Stiff or soft steering springs? At what angle do you like to have the tailwheel "break free" (unlock)? Locking tailwheel? Do you both take off and land with it locked? These options are just the beginning.
Then there are the true black sheep of the tailwheel world: those that like a completely free castering tailwheel. No lock, no steering, just you and your inherently unstable landing gear configuration hanging on for dear life.
(Can you guess my personal preference yet?)
Why would anyone design their own tailwheel assembly?
- Too many assemblies simply do not work (I love you Maule, but your tailwheels are horrible)
- Assemblies that utilize bronze bushings that only last a few hours off airport
- Assemblies that don't even last a few hours off airport
- Durable assemblies but have too many parts
- Durable assemblies but don't offer free castering options
The following diagram is that of a very durable and popular tailwheel assembly:
Does it really take this many parts to make a tailwheel work in the backcountry?
Disclaimer: The following are my design constraints and preferences. I fully suspect your preferences might be different, but this is the best part about Experimental aviation: I can design, build & test exactly what I want for my mission then share the results with you.
After battling various tailwheel assemblies for too many years, I eventually determined I could not do any worse with my own design. I only had two design constraints:
- Simple
- Durable
I don't want 7 specialty washers, 3 expensive oil seals, 2 bronze bushings, or 11 bolts holding the entire thing together. I want to be able to bash it off rocks, dunk it in rivers, and I don't want to constantly fixing the cables with safety wire and duct tape between backcountry strips:
The 3D Model
The first thing I did was source the largest tailwheel rim & tire I could get my grubby hands on. Thankfully, Ted Waltman had me covered:
Armed with the tire, rim, and axle, the 3D model came together quickly.
The entire assembly utilizes only two AN bolts; one to bolt the assembly to the stinger, and one to act as the wheel axle. The tailwheel fork rides on a Delrin (POM) bushing and is retained to the pivot with a single stainless steel retaining clip popular on many large agricultural tractors. The tailwheel fork stem is oversized to easily support my low tail weight of 38 lbs and the whole fork is CNC'd out of a single piece of 6061 T6 billet aluminum.
Remember I said simple and durable. I didn't say inexpensive.
If you guessed I prefer free castering tailwheels, you were correct. No chains, no springs, no pins, pure terror.
Why Free Castering?
While a free castering tailwheel is an acquired taste, it is not nearly the safety hazard some believe it to be. For me, the preference stems from the following:
- Rudder feel in the air is dramatically improved
- This was an unexpected yet most liked result of removing those pesky steering chains. The rudder feel is now lighter and is directly linked to the air across it rather than the feel of the steering chains steering the wheel in the air. This may sound subtle, but I can now judge my airspeed simply by how my rudder feels. This alone is worth the change and was totally unexpected.
- Complexity is drastically reduced
- There is almost nothing to maintain, adjust, or lubricate
- I have drug it across irrigation ditches (oops), ran over a traffic cone with it (don't even ask), and a host of other silly moves. I don't even think about if my steering chains are still attached, or if I just destroyed my lower rudder tube by over-torquing the rudder horn with my antics anymore.
- I can hold any amount of rudder crosswind correction throughout the entire rollout on landing
- Early in my tailwheel training I properly corrected for a crosswind landing, landed flat on the mains, and continued to keep the nose straight down the center line on rollout. Just as the tailwheel touched down the airplane veered hard in the direction of the crosswind correction which then started a cascade of corrections and cursing. All turned out well, but it struck me as odd that I had to let off the rudder correction just when the airplane was at the most precarious position in the rollout. I wanted to add more correction as the rudders lost effectiveness, but doing that would cause the tailwheel to steer me directly into the ditch. Detaching the linkage between the rudder and the tailwheel allows me to use as much rudder as I need any time I need it.
The Prototypes
The best thing about 3D printed prototypes is the ability to quickly and cheaply iterate on a design idea. These plastic parts were strong enough to actually install on the airplane to determine the true angle of pivot to ensure there would not be any tailwheel shimmy in the final version.
CNC'd Eye Candy
The red parts are anodized 6061 T6 aluminum and the black parts are turned Delrin:
Installed
Testing & Impressions
- The assembly now has 128 HOBB hours and is operated off a grass strip in a constant environment of grit and grime (just the way I like it)
- The Delrin bushing nor the tailwheel fork are showing any signs of wear and both are holding their tolerances without issue
- The bushing and pivot are easy to clean and easy to lubricate
- Delrin is considered to be "self lubricating", but in reality its coefficient of friction and ability to withstand compressive loads conveys its magic-like capabilities
- Delrin machines extremely well and is relatively inexpensive. I could replace the bushings yearly for roughly $20 if required.
- The oversized rear clown-wheel raised my tail and lowered my angle of attack on the ground more than I prefer
- That said, the floatation offered by the not-so-tiny wheel in the back on soft sand is fantastic
- Otherwise, the whole assembly performs as expected and so far has been relatively anti-climatic
Questions or comments? Email dave@ColoradoCub.com