Doubling Plan Sizes

[davidyat]

I want to build another Rudy Kouhoupt's 5 Cylinder Radial, only bigger. If I doubled the dimensions on everything, do you think I will run into unexpected problems? I'm an amateur machinist. I did build the smaller version of the 5 cylinder, but now want to build a bigger one.
Grasshopper

 

[Lloyd-ss]

One thing to think about is that if you double all the linear dimensions of the engine, that the engine displacement will go up by the cube of 2, in other words, the displacement will be 8 times the original.

If you only want to double the displacement, then the linear dimensions only need to go up by a factor of 1.26 times the original. (the cube root of 2)

 

[davidyat]

LLoyd,
I run my steam engines on compressed air. I have 125 psi available. My smaller version, I built, ran great. The original displacement calculated out to 0.1103 cubic inch. The new displacement, as you predicted, is 0.8824 cubic inch. I did make a twin V compressed air engine with both cylinders at 1.2272 cubic inch and it ran great on 125 psi. So, I think the doubling shouldn't be a problem for me. AND, thanks for your input.
Grasshopper

 

[stevehuckss396]

I would think you will be fine. I have 3 air radials of the same design. The original has a 1 inch bore. I made 2 copies, the first being 1/3 scale and the second being 1.75X scale. Couldn't double it because i didn't have a big enough piece for the crankcase. All 3 run equally fine and spin at the shows for the entire day.