When you combine machining skills, raw materials, and a bit of ingenuity, you can do almost anything. The possibilities are endless. That’s what home shop machining is all about!
Two metric-size tires: a ribbed-tread 200×50 next to the 200×80. Note the bumps molded into the bead of the 200×80 tire.
This month’s project is a shop-made wheel for an Aero Classic 200×80 balloon-style tire, one of a couple of metric tires in Desser’s Aero Classic line, the other being a 200×50. If you’re building a taildragger and want something plusher than a skinny inflatable or solid rubber tailwheel, the 200×80 tire might be a good option, albeit with one minor drawback: nobody makes a compatible aftermarket wheel. Fear not! With these plans and a few hours of shop time, you can make your own.
When using angular contact bearings, consideration must be paid to the correct facing. For the 200×80 wheel design, the inside cone must be toward the outside. To help future maintainers, the race was electro-etched with an arrow and the word “Out.”
According to the Desser website, the 200×80 is a replacement tailwheel tire for Sukhoi SU-26 aerobatic planes (1754 pounds max) and at least one Yakovlev (probably the Yak-18 trainer at 2200 pounds max). Unless you’re familiar with those birds, you’d never know the tire existed. I stumbled across it by accident when I was looking for some heavy-duty 200mm tires for a Crazy Cart (If you don’t know what a Crazy Cart is, google it). Tires that are 200×80 have a 200-millemeter diameter (about 8 inches) and an 80-millimeter width (a tad over 3 inches). The bead diameter is 66 millimeters (about 25/8 inches), and the bead width is around 54 millimeters (about 21/8 inches). Armed with those basic dimensions, it’s relatively simple to sketch out a basic wheel configuration.
The wheel consists of six basic aluminum parts: two nearly identical flanges, an axle spacer, a center tube, and two identical outside axle spacers. A set of two Delrin “bead spacers” (center top of drawing) take up the small gap between the tire and wheel center tube. You can download a larger view of this drawing, as well as additional views, at kitplanes.com/hadley-tailwheel.
An interesting feature that seems to be particular to the 200×80 tire is a pattern of wide radial lines molded into the bead. As near as I could tell, when installed on a rim with a matching pattern, they’re to keep the tire from slipping and tearing out the valve stem, something akin to a rim-lock on a dirt bike. This complicates the rim design, but only slightly, as the 5C spin indexer made the job easy.
With the wheel diameter, width, and bead detail worked out, I came up with a design that consisted of two flanges with a tubular center section. After looking at similar size wheels by Beringer, Grove, and Matco, I settled on three 1/4-28 cap screws to fix the assembly. Most aircraft wheels use tapered roller bearings, but the smallest, reasonably priced, tapered roller bearing was too big, and considering the maximum load of the tire is 400 pounds at 50 psi (as stated on the sidewall), a bearing rated for 4000 pounds was overkill. So the choice was between cartridge-style radial bearings or cartridge-style angular contact bearings.
Using the spigot to hold the flange while completing the preliminary facing operations, which include boring the 1-inch through-hole for the axle and rounding the outside edges. Turning the (optional) scalloped relief (shown here) was done last, after the valve stem hole, bolt holes, and bearing seats were added. The scalloped relief removes some weight, but is primarily aesthetic. It makes it look like a “real” wheel.
An arbor was turned and press-fit into the 1-inch through-hole to provide a temporary collet hold in the 5C spin indexer. The notch detail was milled using a 3/16-inch two-flute end mill by plunging down to the quill stop, on center, and then traversing the Y-axis to minus (-) 0.163, then to plus (+) 0.163 (shown), and then back to zero. Next, the quill was raised and the part indexed 36 degrees. This was repeated until all 10 notches were milled, then holes were drilled for the three bolts.
Although radial bearings are used on many small tailwheels, I decided to go with angular contact bearings (size 7002-RS, 32mm x 15mm x 9mm) because they are built for, and better withstand, side (thrust) loads. You might have noticed (and even wondered) about using metric bearings on a project with English Imperial dimensions. It turns out that angular contact bearings aren’t made in Imperial sizes. Normally, I consider it bad form to mix metric and Imperial in the same design, but since the tire is metric and the raw materials Imperial, that ship—as they say—had sailed.
A paper pattern was centered on the one-inch through-hole (aided by a piece of scrap tubing), and the bolt holes were marked for drilling with a Starrett automatic center punch.
To assure the notches in the rim flanges lined up with the bands molded in the bead of the tire, both flanges were carefully indexed to the tire (with the center tube in place) and then marked using a transfer punch.
The final pieces to the puzzle were where to put the valve stem, and then mount the tire and balance by adding 1/4-ounce adhesive-backed weights (for motorcycle wheels), as needed, to the inside of the center tube.
(Left) A 1/4-28 bottoming tap was used in the blind holes. (Right) A planer gauge was used to set the counterbore depth on the drill press.
The project is mostly lathe work. A vertical mill and indexer is required to make the notches. The rest is simple drilling, counterboring, and thread tapping. The photos show the basic machining sequence and provide the essential details of the various setups and operations.
(Left) The axle and outside spacers were basic lathe work: turning, drilling, and boring. The axle center length was left slightly long to allow fine-tuning during assembly. (Right) Note the black Delrin bead spacers. They were added to assure the tire is centered by taking up the slight difference in diameter between the tire bead and the 2-inch-diameter wheel center tube. The small holes in the outside spacers are for a cotter to keep the spacers in place during assembly. The bearings are fitted so that when the axle is tight, the wheel spins freely.
Bob Hadley is the R&D manager for a California-based consumer products company. He holds a Sport Pilot certificate and a Light-Sport Repairman certificate with inspection authorization for his Jabiru J250-SP.