Steam Engine build in double scale?

[Upnorth]

I'm looking at building a model steam engine. I have run across the Elmer's engine plans. There are certainly lot's of them. They are a bit smaller than what I want to build though.

So here is the question. Can I just build everything in double scale? I am wondering if there will be issues where doubling diameters changes things like airflow too much for it to work correctly.

 

[DavidR8]

I would think some things would scale up just fine but others may not. Piping may not scale well as a doubling of diameter is approximately 4 times larger cross sectional area.

 

[Upnorth]

I would think some things would scale up just fine but others may not. Piping may not scale well as a doubling of diameter is approximately 4 times larger cross sectional area.

Yeah that was my thought also. I might be better off just looking for a different plan that is already built and tested in a bigger scale.

 

[phaxtris]

i dont think it matters with the doubling of diameters in the piping, after all a steam engine is an external combustion engine, all the airflow that matters is happening outside of the steam engine itself. The engine is not drawing air in like a conventional internal combustion engine

you may not be able to double up some of the sizes anyhow, you will be somewhat limited to what size of tubing you can get for the steam lines

 

[Upnorth]

I should have pointed out it will never run on steam just compressed air. It's really just a demo project to show some things that can be done in my shop.

 

[Proxule]

I am in on what ever project this is, lol

 

[phaxtris]

steam, compressed air, it will still work fine if you double everything

it is just a model, so long as it goes chuga chuga chuga youve won

if it were an ice engine you would need to be concerned about flows, but not so much with a steam engine, and especially not a model

 

[VicHobbyGuy]

I've built a couple of Elmer's engines at 150% and they work just fine. His models are just too small for my abilities. So I think 200% would work OK, too.
I think the increased cost and inconvenience of making larger parts (e.g. flywheels not from castings) kept me from building at double size.

 

[Tom O]

It shouldn’t matter with steam due to the rate of expansion, air is just a constant pressure.

 

[trevj]

Agree with the rest, esp. for a project that does not have any 'performance' goals, like say, a flash steam speed boat motor, you are in wide open territory, if all you need it to do is run well.

Most engines will run well on far smaller passages than those provided in the plans. I figure a LOT of the design choices are made based upon durability of the tooling, rather than any 'flow' calculations!

 

[CWelkie]

I've built engines both larger and smaller than the original design. All have worked out fine. One consideration not mentioned so far (likely because it is os obvious) relates to fasteners. You may not be able to find "exact doubles" of the originals - just use what's close watching for margins and clearance.

 

[Upnorth]

I've built engines both larger and smaller than the original design. All have worked out fine. One consideration not mentioned so far (likely because it is os obvious) relates to fasteners. You may not be able to find "exact doubles" of the originals - just use what's close watching for margins and clearance.

I'm not worried at all about the fasteners. I have a large collection of aircraft hardware that I can design around. Strength will never be an issue but it may not look scale. Maybe to get a balanced look I can just add in a few more fasteners.