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Old 12-04-2012, 01:53 AM   #1
MrBaz
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Default It is a start...

So, as my intro post explains, I have no experience making model engines. I'm working on my BS as a MechE, so I have no problems diving in head first. I'm making all the parts in Inventor first. I'm posting my work/thoughts here for constructive criticism. I will warn you ahead of time, many of my ideas/plans may seem odd or uncomon for what I'm building first. Just give me the pros/cons instead of turning it into a flame war.

The Idea:
I eventually want to work on making a supercharged V12 (similar to the Artus V12 from Germany). For now, I'm going to make a 4-stroke, 2-cylinder opposed engine. The idea is to actually use this on a scale model aircraft (so it has to work). I'll be experimenting on production techniques on this 2-cylinder for experience/ideas on the much bigger V12.

The plan is to run pure methanol with a manual mix of pure nitromethane (not the mixed 'nitro' from hobby shops). Oil control is separate, and pressurized/forced/whatever-have-you. This should allow me to run high compression with slight supercharging.

So first up, the piston design. So far, 1in diameter dished piston. Two rings (will be fine-grained iron - Tremble method). I'm still debating on an oil control ring.




Thoughts?


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Old 12-04-2012, 02:20 AM   #2
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I'm too new at this to be able to offer any thoughts, but I can tell you that we don't do 'flame wars' here. I'm sure you'll get lots of feedback and help though

Good luck with your build!


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Old 12-04-2012, 02:56 AM   #3
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MrBaz, two things, why the dished piston? and is the wrist pin location correct? It seems a little low to me.

I'm no expert mind you, I'm asking for my own knowledge as much as anything else.

Other than that, it's a very nice Inventor model. What version of Inventor are you using? I have 2013 Pro.
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Old 12-04-2012, 02:57 AM   #4
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MrBaz,
Nice rendering. i can use the AutoCAD, but i like to revert back to the paper and pencil i was originally taught with. if you are schooling to become an ME, you are smart to try and balance all that book learning with hands on experience building things, you will find it will help you become a much better engineer over the long run.( has worked for me for over 35 years inthe business) Have always thought my machinist friends have had it over me because they could design and build their designs. Look forward to seeing more of your renderings, and hopefully pix of your model.
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Old 12-04-2012, 03:34 AM   #5
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Nice looking piston, though the ring grooves look rather wide for a 1 inch bore. I'd expect the Trimble method to specify a pretty narrow ring, perhaps 0.040 or so.

Good luck and please keep us up to date on your project.

Chuck
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Old 12-04-2012, 02:09 PM   #6
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Quote:
Originally Posted by trumpy81 View Post
MrBaz, two things, why the dished piston? and is the wrist pin location correct? It seems a little low to me.

I'm no expert mind you, I'm asking for my own knowledge as much as anything else.

Other than that, it's a very nice Inventor model. What version of Inventor are you using? I have 2013 Pro.

It will be a semi-high compression setup that will eventually get supercharged. I'm controlling the compression and piston-to-deck travel with the dish in the piston, just like how they do it on the full-size boosted conterparts.

The wrist pin could possibly use a little more meat on the bottom. Otherwise, I'm not sure what you mean by its location. I've been using JE and Weiso performance pistons as a guide -- they have short piston skirts.
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Old 12-04-2012, 02:14 PM   #7
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Quote:
Originally Posted by kuhncw View Post
Nice looking piston, though the ring grooves look rather wide for a 1 inch bore. I'd expect the Trimble method to specify a pretty narrow ring, perhaps 0.040 or so.

Good luck and please keep us up to date on your project.

Chuck
I was wondering about that. I believe I have the grooves set for a 1/16" (.063in) thick ring. I wasn't sure if I could safely go thinner. Keep in mind that this will be a high compression, supercharged engine.

I forgot to mention a few things:
rings - fine grained cast iron (Durabar 6000 maybe?)
sleeves - cast iron
pistons - 4032 aluminum
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Old 12-04-2012, 09:46 PM   #8
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MrBaz, normal practise is for the wristpin to be located at the midpoint between the piston crown and the bottom of the skirt. It may be parallax error and or the picture, but your wristpin location looks lower than that midpoint.
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Old 12-05-2012, 12:05 AM   #9
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Quote:
Originally Posted by trumpy81 View Post
MrBaz, normal practise is for the wristpin to be located at the midpoint between the piston crown and the bottom of the skirt. It may be parallax error and or the picture, but your wristpin location looks lower than that midpoint.

I see what you mean. Like I said, I was just trying to model off of a typical performance piston from JE, Weisco, etc. If midpoint is preferrable for small scale engines, I'm more than happy to change the design. I do want this to work after all!

Attached is an example of what I'm talking about. You can see how the wrist pin is darn near dead-bottom.
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Old 12-05-2012, 06:37 PM   #10
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MrBaz, wow, they are really nice pistons!! Now if you could just use those it'd be great ... lol

I'm wondering if using such a piston in a model engine, what effects it would have. Would there be too much pressure on the skirts or too much expansion of the crown, given the reduced size for model use?

I have often wondered why modern piston design is not used in model engines. They obviously work in full size engines so why not model engines?

Will your engine be glow or spark ignition?


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