Upgrading to a Full Swivel Tailwheel: A Sonex Owner’s Guide

Benefits of upgrading

If you’re flying a Sonex now or have a Sonex kit, you’re probably familiar with the tailwheel assembly. Whether it’s the new machined tailwheel assembly or the stock welded caster setup, the Sonex tailwheel assembly, like many small aircraft tailwheels, does not full swivel. This allows the kit manufacturer to cut costs, but comes at the price of several on-the-ground performance drawbacks.

If you’ve flown on one of these tailwheels or handled an aircraft on the ground, you already know what these drawbacks are: wide turning radius on taxi, difficult ground handling when pushing into your hangar, not to mention the jealousy you experience when you watch one of your RV-flying buddies whip their machine into a zero-radius turn for runup.

With the Sonex tailwheel mounting kit and one of our tailwheels, the ability of the fork to unlock and swivel allows you to make zero-radius turns from the pilot seat, and makes the aircraft a breeze to handle on the ground in and out of the cockpit. What’s more, all of our tailwheels will increase obstacle clearance of the tailwheel so you don’t have to worry as much about catching the tailwheel on bumps, clumps, and expansion joints.

The mechanism that our tailwheels use is based on the same locking pin mechanism flying on thousands of RV’s and other aircraft. It’s simple, reliable, and effective.

Necessary changes

Upgrading to one of our tailwheels will give you the full benefits of a high-performance full-swivel tailwheel, but there are a few necessary modifications you will need to make to the airplane in order to fly safely.

Differential Brakes

Since the new tailwheel will have the ability to unlock, it is unlikely but possible for a strong crosswind gust or other circumstance to cause the tailwheel to unlock into its free-swiveling condition. You MUST have a set of reliable differential brakes as an alternative means to steer the plane on the ground.

Raising the tail

The upgraded tailwheel assembly will lift the tail of the airplane a few inches (the actual change will vary depending on which tailwheel setup you choose to use). For most pilots, this won’t be any issue, but if you like to do three-point landings you may consider what a few extra inches of tailwheel height does to your AOA on landing. You may consider upgrading to larger-diameter main wheels to balance things out. From the reports we’ve had in the field, the four-inch tire and Racer fork is a good option that doesn’t change the tailwheel geometry too much. There are a handful of Sonex drivers that have used our six-inch tires with the Screaming Eagle or Bell fork with good results as well, but a small minority of those found that the tail height was an issue for their landing style.

Adjusting the link control

The tailwheel parts that we have are originally made for the Van’s RV tailwheel, which has a bit wider rudder throw than the typical Sonex. Until we can get some Sonex-specific parts made, you may need to make a few small adjustments.

The big thing to pay attention to is the interplay between the steering linkage and the control arm which steers the tailwheel. The tailwheel needs to be able to reach its unlocking point on both sides before the rudder hits the stop and jams it up. Getting this adjusted properly usually is as simple as drilling another hole in the control arm inboard of where the existing hole is (do a little trial-and-error on the plane to get it set to the right spot).

Another way to approach the same problem would be to fabricate a spring-incorporated steering linkage with the ability to expand or contract to accommodate the extra travel or to opt for a double-sided rudder horn and tailwheel control. Contact us if you have any questions with these three options.

Parts list

So what will you need to do this job?

Which tailwheel is right for me?

Many Sonex owners have upgraded from the stock 4″ tire to a larger 6″ tire and are understandably resistant to returning to a smaller tire. There are two things to consider when covering the topic of tailwheel size: obstacle clearance and tail height. One major reason to size up the tire is simple obstacle clearance. A small tailwheel in a low-angle fork is easy to clip on clumps of grass, expansion joints, and other obstacles, and a bigger tire is an easy way to address the issue, within limits. The limit comes in terms of tail height… raising the tail is nice for visibility reasons, but at some point, it begins to interfere with the three-point landing or the takeoff characteristics of your plane.

Because our tailwheels are designed to full-swivel, their geometry is inherently taller than the stock tailwheel units on the Sonex line; the tail spring has to attach above the level of the wheel so that the wheel doesn’t hit it as it swivels around. So, even with our four-inch tailwheel fork and tire, the tail will sit as much as a few inches higher than it would with the stock Sonex tailwheel assembly or even the upgraded 6-inch assembly.

The Sonex Mounting Kit on our website can be used with any of our tailwheel forks, but in general our recommendation for Sonex owners will be to go with our Racer Mini Tailwheel Fork with the 4-inch DJM Lightweight Tire. This will provide the best of all worlds: improved obstacle clearance and handling, conservative tail height change, and all the benefits of a full-swiveling system.

If you’re dead-set on a larger tailwheel, you can also use our Screaming Eagle or Doug Bell tailwheel forks, which are designed for a 6-inch wheel. These larger tires have benefits but some customers have noted that they are hitting the tailwheel earlier when performing a 3-point landing. For this reason, I would not recommend using our Condor2 fork with its nearly 8-inch tire on the Sonex line of aircraft.

How does the full-swivel mechanism work?

For an in-depth look on the function of this tailwheel assembly, take a look at our teardown video here: