If your airplane has an Aviation Products (API) tailwheel already installed and you’d like to change the assembly out, there are a number of extra considerations to take into account before you begin.
The API tailwheels use different standards for the diameter and height of the tailwheel pivot shaft, as well as different axle bolt sizes from the Van’s standard equipment. As such, virtually none of the tailwheel parts are interchangeable between parts built on Van’s standards (which are used by all Flyboy Accessories tailwheel items) and the API units.
If your API tailwheel assembly is worn and you’d like to replace it with more standard parts, replacing the whole assembly (tailwheel fork, tire, mounting kit, and possibly tail spring) is generally your best bet, and we will cover how to do this later in this document.
Identifying the API Tailwheel Assembly
Start by determining whether you have the API tailwheel assembly. Consult the visual reference below. API tailwheels do look somewhat similar to our Doug Bell and Condor2 tailwheel forks, but the API units are easily identified by their machined aluminum mounting socket (where Van’s parts are welded steel).
If you have any doubt, drop the tailwheel fork out of the mounting socket and measure the diameter of the pivot shaft. API tailwheels use a 3/4″ diameter shaft where Van’s parts use a 7/8″ diameter shaft.
A note on hole orientation
It’s fairly common for the API tailwheels to be mounted on the spring with one or more bolts mounted vertically through the spring. Since vertically applied loads on the tail spring will stress the top and bottom surfaces of the spring primarily, introducing a vertical hole may weaken the spring at that point, especially if the hole has enough clearance to allow movement.
You must be very careful with this hole when changing the socket, as any slop in this hole will likely lead to catastrophic failure of the tail spring. If possible, replace the spring and drill any new mounting holes horizontally through the spring (Van’s recommends two AN3 bolts installed horizontally for their 0.635″ diameter tail spring). DO NOT leave a vertically-drilled hole in the tail spring un-filled.
A note on hole position
Note that the portion of the API mounting socket that sleeves over the tail spring is longer than the analogous part on the Van’s assembly by about an inch. It’s common for a mounting hole to be drilled near the front of the API socket.
If you have a mounting hole drilled near the forward end of the API socket, you cannot leave these holes unfilled when you change to new parts. We would recommend either ordering one of our special API replacement mounting sockets, which are made with a longer sleeve portion, or replacing the tail spring altogether.
Replacing the tailwheel assembly
You have two options to replace the tailwheel assembly. Your circumstances may determine which option you choose.
Option 1: Replace only the mounting socket and tailwheel assembly
If your tail spring is still in good shape, replacing fewer parts may be the simpler option. To get an idea of what’s involved, take a look at our document “Replacing A Mounting Socket“
You will need to carefully measure the aft diameter of your tail spring before ordering. Typically, the tail springs are tapered, but the aft 2-3 inches are held to a constant diameter. Van’s parts use an odd size, 0.635″ as their standard. You may also have a spring that’s 0.625″. If you have an older RV-3, you may have a smaller diameter… contact us for directions if that’s your situation.
List of necessary parts
- Tailwheel Mounting Kit (specify mounting diameter and control arm style)
Note that if you have a bent tail spring or a vertically-drilled mounting hole, it may be worth replacing the whole tail spring.
Option 2: Replace the tail spring and tailwheel assembly
Replacing the tail spring itself can be a bit challenging, as you have to match-drill the front hole of the tail spring to match your existing tail spring. This hole was likely drilled by hand, so you’ll need a competent machinist and a bespoke fixture to get the new hole in the right spot. See our document “Drilling the Tail Spring” for more information and direction on this process.