Model Engines vs. "Working Engines"

[BronxFigs]

At what point does a "model engine" become a small working engine?

If you take the plans for a larger, model engine, and scale them up...will the resulting engine be considered a small, working engine? For example, a one cylinder, model steam/gas/compressed air engine:
Bore: 1.00"
Stroke: 2.50"

Scale up the engine to:
Bore: 3.00"
Stroke: 5.00"

Has the "model engine" now become a small, working engine? What is different, generally speaking, about a working engine?

Just asking.

Frank

 

[Tin Falcon]

IMHO it has nothing to do with size. A model engine can be a working engines when used to do work in the form of powering something. it may power a model boat a model airplane, a dynamo etc. A tiny gnat power co2 engine on a tiny airplane still does work.
an engine for the sake of an engine can do work as well.

A model engine may just be built to represent the real thing and run for the sake of running and not power anything.

I do not think folks here really worry about the definitions or semantics. we build engines. some just for fun, some to power things, some for the sake of education like my see though engines. some for the sake of saving and interpretation of history in the case of the guy that built the only known copy of the uss monitor engine and some build engines to learn machining and because they can. no right or wrong reason.

I do and have asked folks if an engine is a working engine . this is because there is more stress on an engines and its components that an engine that just runs at idle. These stresses are more significant at horsepower level than a small mouse power engines. so I like to know use if recommending material.
hope this helps.
What you need to know that is more important than a defintion is the law of scaling.

linear dimensions are directly proportional area are proportional to the square of the change and volumes and power proportionality to the cube.

If you take the plans for a larger, model engine, and scale them up...will the resulting engine be considered a small, working engine? For example, a one cylinder, model steam/gas/compressed air engine:
Bore: 1.00"
Stroke: 2.50"

Scale up the engine to:
Bore: 3.00"
Stroke: 5.00"

Has the "model engine" now become a small, working engine? What is different, generally speaking, about a working engine?

Just asking.

In your example you doubled the size of a model. it is twice as long and twice as high and twice as wide.. the area of the piston is 4 times as big the power increased 8 times and the weight of the engine also increased 8 times. your material cost likely increased 8 times as well.
unless you need a big engine I recommend beginning work with an engine of about 1/2 inch bore (3/8 to 3/4) the engine is small enough for most lathes. the parts are not too tiny . it is not difficult to get running and it will not suck the tank of a compressor empty in minutes.
Tin

 

[GWRdriver]

Hello Frank,
Good question, one I've never ever seen asked before. My take on this is the difference is determined by the purpose of the engine. To me (in a nutshell) the purpose of an operating "model" engine is to reproduce and portray, so far as is practical, the appearance and detail of a prototype. This implies that a "model" engine might have some rather delicate components and while a model engine might be capable of some work it would not hold up to heavy or continuous work. A "working" engine on the other hand is one whose design doesn't pay nearly as much attention to faithfulness to a prototype, or to fine detail, as it does to maximizing trouble-free operation under load over time. I don't think size plays a role in it, both can be large or small.

 

[Brian Rupnow]

All of my model engines are working engines---and I have the videos to prove it. Any engine which runs some device which has no power to run by itself is a working engine. My engines have run various devices, and as I look around my office/shop, I see them running a---Steam Donkey winch---A nodding donkey oilfield pumper---a reciprocating pump----a bubble blowing machine---a slinky machine---a Jacobs ladder moving staircase machine---and a clockwork mechanism. Your question is similar to asking if an elephant carries a log in its trunk, or an ant carries a leaf in its jaws, which one isn't working. As long as an engine powers something else then its a working engine.----Brian

 

[BronxFigs]

I thank you for the well thought answers to a question, in retrospect, should have been a little more specific. Not having a long history in building models, I guess my concept of a model engine vs a working engine was not only referring to size, but also to material selection for various parts, strength, and functions. After reading some of the answers and design considerations, simply scaling-up plans does not necessarily give one a viable, and or, reliable design. Laws of Physics and scaled-up forces, etc. always get in the way and complicate things. I am not an engineer, and I just proved it by starting this thread.

Thanks for the good advice and the caveats re: scaling up plans... it's not that simple in reality, contrary to what I thought. There's many more things to consider.



Frank

 

[aonemarine]

I cant help but to chime in here... To me a model engine runs and can perform work, but not for an extended period of time. A working engine performs work for days on end for years and years. Its a fine line for sure...

 

[Tin Falcon]

Personally I do not see a huge problem with the models we do. scaling is somewhat limited going larger. a 2 or 3 inch bore and a 12" fly whell is going to be the limit for most shops. There may be few guys with a 24 or 36 in swing lath but that is huge buy hobby standards.
and most people have more lilke a (" 7" or less swing lathe.
Tin

 

[RonGinger]

An important writer in MODEL ENGINEER magazine for many years from the late 1930s to I think maybe 1950 used the pen name LBSC. He published dozens of designs that are still very commonly built today. He was quite adamant that he did not design model locomotives, he designed locomotives that just happened to be for small track gauge. He did do things that were not exactly to scale if they caused the engine to be a better performing machine.

 

[Tin Falcon]

Good point Ron. I guess by some standards the engines I build are not realy true models either. they do not represent a larger real artifact that exists. My engines are built for fun and to demonstrate the function of how engines work. Like I said earlier not too worried about definition or semantics. i Build and show models for fun.
Tin

 

[Tin Falcon]

The process of scaling down(or up) is just that a process. going 2 or three times up or down not a real big deal. The challenge come when we take something like a real ships engine that weighs tons and build a 1/16th or smaller table top model.
when scaling down that much off the shelf hardware and bolts may not be the right size or look right or the thread pitch may be way off. the construction methods likely need to change. fasteners may need to be mocked up rather than real. Decisions need to be made . why are you making the model ? how authentic does it need to be? custom tools and hardware may need to be made in order to assemble it.
Modeling in minature can be a challenge.
Tin

 

[Coilmotorworks]

If the engine drives something it would fit the bill as a working engine in my book. Even one of those Ertl models of an antique gas engine with an electric motor in it to make the flywheels spin could be considered able to do work if you hook it up to something and it spins whatever is hooked up.