scaling Steam path dimensions

[dazz]

Hello
I am planning on building a 4" scale compound steam engine. Changing the linear scale by 1/3 affects area by a factor of 1/9 and volume scale by 1/27. Physics doesn't scale so I am concerned that changing the linear scale may require modifications to the steam path dimensions, especially on a compound engine.

Does the scaling require any non-scale modifications to the steam path?
eg. steam pipe bore dimensions, piston/cylinder dimensions, stroke etc.

 

[Charles Lamont]

Scale passages will be fine, but models are arguably at an advantage here because of the lower Reynolds Numbers involved. This is why small engines can get away with a drilled passage instead of a big rectangular section one. At 4", the bore and stroke can be scale or pretty close.

 

[dazz]

Hi
I have copies of the original factory drawings for the 1925 Yorkshire Patent Steam Wagon that I plan to model. I have figured out that the easiest way to build a model is to simply scale and follow the factory drawings. The manufacture was highly optimised based on contemporary methods and technology. If I make a non-scale change from the factory drawings, it is likely to have a domino effect that will take more time and effort to model than just following the drawings. Avoiding changes to the steam path is an important goal.

Dazz