The trials and tribulations of being a third wheel

Here’s a seemingly trivial tidbit that might catch your attention. Two points establishes a line. It takes three points to establish a plane. And by plane, I don’t mean airplane. I mean a flat surface created by a straight line referenced to a fixed point in space. 

And to think, the high school version of yourself never thought geometry or physics would come up in casual conversation.

A bicycle has two wheels. Those wheels touch the ground with the two touch points establishing a line. If you stand a bicycle up on its two wheels and let go of it, it will fall over. If you add a kickstand however, just a small third point of contact with the earth, the bicycle will not fall over.

The third point establishes a plane, a flat surface that exists between the three points. The top-heavy bike stands defiantly in opposition to gravity. 

Airplanes tend to have three wheels, which is what keeps them from falling over when the propeller stops turning and airflow no longer imparts enough pressure to hold the wings level. That has been true for almost as long as airplanes have existed.

The Wright Flyer had no wheels, just wooden skids to land upon. Yet, by the time Orville and Wilbur got around to building the Model B, wheels had become standard equipment. The skid remained, mounted near the tail, although its primary purpose wasn’t to facilitate easy ground handling. Just the opposite, actually. In the early days tail skids were functional as brakes, since actual brakes hadn’t made their debut yet.

To move those early skid-bearing airplanes around on the ground, a device was invented to ease the process. It was essentially a small dolly with wheels, attached to a long pole that would allow the ground crew to steer the lumbering beast wherever they needed it to go. It wasn’t perfect, but it was progress. 

Then one day, someone came up with the idea of getting rid of the dolly and the pole while keeping the wheels. Or at least one of them. And if that wheel was tied in to the rudder, the same inputs that controlled yaw in flight could control yaw on the ground.

I’d like to think there was merriment when that first innovative tailwheel proved successful.

But I suspect it was somewhat short lived. Because — and here we go back to the geometry again — in order to keep the airplane’s tail on the ground it is necessary to place the center of gravity behind the main wheels. 

With the tailwheel in place, Newton’s 1^st Law of Physics guarantees a wild ride now and then. It is absolutely true that an object will persist in a straight line unless it experiences forces that redirect that straight-line movement — cross-winds and errant rudder inputs being the principle culprits. With the center of gravity behind the mains and brakes being of little use on wet grass airstrips, the introduction of the tailwheel begat the discovery of the ground-loop.

To paraphrase an old saying, if you fly tailwheels you’ve either done one or there is one in your future. Prepare for some embarrassment. Especially if friends or family witness your unexpected, uncontrolled excursion from an arrow straight roll-out. 

This potential for emotional disaster and airframe damage got some bright young fellows thinking. If the main gear was just a scoshe further back, the center of gravity would fall in front of them, which would make it possible to put the third wheel at the front of the airplane. That would make the airplane tend to track straight ahead when accelerated for takeoff or decelerated after landing.

Eureka! A new world of safer flight was born. 

There is a cost for every advancement, however. It turns out the price of improved ground handling can be found in the realm of weight and drag. A nosewheel is considerably larger and bulkier than a tailwheel. It’s heavier, too. Both are detrimental to aircraft performance. 

Damn. And we were doing so well. 

The most prodigiously produced aircraft of the taildragger era is the Piper Cub. There are multiple variants, but the J-3 is the one that tugs at my heart. Nearly 20,000 rolled off the assembly line over the years. They’re still a common find at airports all over the world. More than half a dozen of them live on my home field. One of them is mine.

What makes mine different from the run-of-the-mill Cub is not easy to see from just a casual glance. It’s just as yellow as most and every bit as drafty but not quite as underpowered. The addition of a Continental 90-hp engine replacing the anemic 65-hp powerplant my previous Cub had makes all the difference.

No, what makes mine unusual is the steel main gear mounts. They’re weird. Different than the mounts that came from the factory. It takes a trained eye and a curious mind to pick out the difference. A review of the maintenance logs confirms the peculiarity of this bird.

My Cub came out of the factory as a taildragger, somewhere along the line it was converted to a tricycle gear configuration, then in 1997 it returned to its original glory as a taildragger.

Yep, that’s unusual. 

CubCrafters found itself in the news recently as it begins test marketing a tricycle gear airplane known as the NX Cub. It’s weird looking, but it’s practical and holds an undeniable place in the market.

Innovation persists in the aviation industry. 

I don’t know why mine was converted all those years ago. Maybe to lower insurance costs. Perhaps to facilitate easier landings for new students. Or maybe it was just a curious mind trying out a modification to see how well it worked.

No matter. The third wheel moved from the tail to the nose and back again. I believe I’ll keep it where it is, but I sure do enjoy knowing that physics and geometry worked out on that airframe over these 75 years of experimentation.