Mercy! Mercy! That Dang Nabed PERCY!

The Engine Test Stand

Yesterday Linda and I went to Wausau. Linda went to Bath Bed and Beyond and I went to the hobby shop. Actually we went to both places together. While at Popes Hobby-World I noticed on the floor this stainless steel contraption that looked like an engine test stand. Clearly it was more than a test stand and when I asked Warren, the owner, he was rather uncertain how it worked.

The device sat on a heavy rectangular steel base and was beautifully machined. It appears to be some sort of precision scale. Some of its function is self-evident. On top of the base sits a tower for securing a model airplane engine. The legs of the tower are set to tilt forward on cams about a quarter of an inch forward when the thrust of the engine produces the necessary amount of torque, (measured in lbs.) depending on where the weight on the scale is set. In principle it looks to operate like those old scales in the doctors office where the weight bars were slid into the estimated range while the fine adjustment was a small sliding weight that traversed a fulcrum bar that pivoted on top.

Actually it also reminds me of a device used in tractor pulls that ratchets up an incline, increasing the drag until the tractor can go no further. It is like these devices in principle, however it achieves the measurement in a slightly different manner.

I tried to get him to explain its function and he only shrugged. He said it had been sitting in his basement for twenty years and he decided to get rid of it. After some examination we determined how it worked and concluded it was a device used to measure engine thrust with a given propeller. In other words it enables a tester to determine when the engine thrust will tip the cam legs forward in a scientifically measurable way.

It is a beautifully designed precision instrument and I bought it at a ridiculously low price. Knowing engine thrust is one thing but knowing when that thrust is optimized by the propeller is quite another.

What I think the scale shows is the maximum thrust the engine will generate. Since there is always a range of props in the recommended manufacture’s range this device will show the “Most Efficient.” This would be useful as a starting point in deciding, given the weight and volume of the airframe, the most suitable propeller in the range. It should also show if the engine is operating up to its design specifications.

Isn’t life amazing? I was looking for a simple test stand and wound up with one that could perform that function and so much more. Now I need to learn how to apply this knowledge to the airplanes I repair and build.

It would be nice I suppose, if there were such a device that could measure the power a novel was generating. Then, when a student asks, how “Powerful” their manuscript is, I could answer with scientific certainty. While there is some commonality in what it takes to fly a story and an RC model airplane, these analogies are a bit of a stretch.