The Showcase > Engines
4 cylinder opposed layout
petertha:
I'm contemplating an opposed 4 cylinder for a future build. Screen grabs show some layouts from drawings I have of various displacements. Not that I'm attempting to model as a semi-scale at this point, but looking at the the FS Continental reference, it has what I would loosely call 'slightly' staggered cylinders. Maybe its more of a visual thing but I prefer this over the wider offset cylinder stagger.
The Jung (largest engine) has 2 connecting rods sharing the same CS throw. Whereas the Ohrndorf, Peewit & OS layouts all have dedicated CS throws. The Peewit has a bit of L on the small end of connecting rod because the rod is offset relative to piston axis.
I'm kind of favoring the shared throw layout. Naively, seems like 2 less journals to machine & get right LOL. From a model standpoint, are there any other factors to consider? Balance maybe? Would bottom end journal sizing be any different between shared or dedicated? Are there any other model engines you have come across I should look at?
steamer:
Well Horses for courses. Either layout will make a running engine obviously. What do you intend to do with the engine?
Dave
RReid:
Another option you might consider is shared journals with a "knife & fork" conrod arrangement. This would allow the opposing cylinders to be directly inline, no stagger.
petertha:
--- Quote from: steamer on December 11, 2022, 12:57:41 AM ---Either layout will make a running engine obviously. What do you intend to do with the engine?
Dave
--- End quote ---
Well I'm a longtime RC guy but strangely I don't have as much affection to building & flying scale models vs other RC facets. Never say never, but I suspect it will power a test stand for fun & enjoyment, maybe the occasional show. At least that's the plan for my radial. So I do want it to run well with a reasonable prop, idle, transition & not have mechanical issues. This might be my crack at integrating spark ignition vs glow but probably unrelated to rod layout issue. I guess I was more wondering out loud why a particular model designer chose an arguably more complex 4 throw CS with wider cylinder offset vs a 2 throw with narrower stance, when they are all somewhat mimicking FS aircraft engines from the exterior look. Maybe because the FS did have a 4-throw CS & managed to squeeze the cylinders together whereas the smaller scales just don't shrink to scale the same way without other tradeoffs?
Hmm.. I just thought of something, optimal firing order vs throw position maybe?
Now that I think of it, I may have some drawings of Satra engine which looks pretty close to FS layout. I'll check out hw he went about it.
crueby:
The offset ends on the Peewit are very interesting, I have never seen that before. No advice to offer, but I will be watching along, looks like it will be a fun journey.
:popcorn:
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