The Design, Construction, and Use of a SMALL PRONY BRAKE


| July/August 2000



Sweet's Pattern

11155 Stout Road, Amanda, Ohio 43102

In 1998, when I displayed an engine at an engine show for the first time, I decided that when I took an engine to a show I wanted to exhibit the engine not only running, but running something. At my first show this was easy, I chose to show a Novo engine that was directly connected to a small antique air compressor and mounted on its own cart. Then I looked ahead to 1999 for something that I could power with any of my other engines that would show the engines running, and ideally, running under a substantial load. The idea that came to mind was to construct a small Prony brake capable of absorbing about 10 horsepower. As 1 thought about this, I realized that this would allow me to run an engine under any load that I wanted. (I don't believe that I had ever seen a hit and miss engine running under a full load.) Another advantage that I saw with the Prony brake was that it would be possible for others to belt up their engines and see them perform under load and also get some idea of how much power the engine was producing at the same time. Yet another anticipated benefit of having a small Prony brake would be that it would demonstrate to the spectators at a show just how horsepower used to be measured and it would clearly illustrate what is meant when someone refers to 'Brake Horsepower.' And last but not least, a Prony brake could be small enough that it could be mounted on wheels so that I could load and unload it myself.

When I decided to investigate the possibility of constructing a Prony brake I don't believe that 1 had ever seen one. And I know that I had never see one in use. My only knowledge of them came from textbooks. I approached the project by reading every old text that I could find that had any reference to the Prony brake or dynamometer. I needed to find the answers to such questions as:

How big should the brake drum be to measure 10 horsepower?

How big will the scale need to be to measure that horsepower?

What is the best material to use for the brake lining?