Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Check out my Prony Brake . While I don't think there is any way to really measure horsepower , you can compare engines to see how they rate against each other .


D.E.Jones

Very creative and very well done !

   I should explain how I use this thing. After the boiler reaches full pressure, and the engine is belted to the brake, I run the engine at full power while tightening the friction nuts . I tighten the nuts until the engine stalls , and record the maximum scale reading in ounces. Since the distance from the pivot point to the scale is three inches, I multiply the scale reading X 3 . I think that should yield torque in inch-ounces. I use the same size pulleys on my engines as well as the brake to get a fair comparison between engines . There are some problems with this procedure . The first problem is the fact that these small boilers cannot maintain full boiler pressure under full throttle settings . As it takes some time to perform one of these tests , steam pressure is constantly falling . The second problem is belt slippage . When you provide enough belt tension , the resistance builds , and affects the test reading . But hey , it is only a toy and is fun to build and use , but also a way to do some interesting testing as well.

D. E. Jones

That seems a very reasonable and well thought out approach!

It will be very interesting to see your results with different engines and perhaps different boiler pressures as well.

I could see plotting and graphing different readings against different boiler pressures at stall, to come up with extrapolated value ranges between and beyond actual data points.

Hummmmmm ...... this sounds like fun!!!

Beautiful job you could possibly try using dual belts to minimize slipage it wouldn't take much to check rpm using one of those digital tachometers.