Has anyone done something like this where you take a few of the same size engine and mount them in a radial configuration to spin a large prop?

http://www.rcuniverse.com/forum/m_11229618/tm.htm

Edit: not a radial, but the same principle could be applied to more than 2 engines to make a radial.

There have been a number of folks who made geared glow engines ganged together to make a radial engine.

The little G-Mark radial engine is widely known, as they made a fair number of them.
















The biggest geared engine radial setup is this one using five OS four stroke engines:

OMG

That last one was what I had in mind. Would love to see it in action.   Some day I hope to get a mill and lathe so I can start tinkering around with these.  The real trick is timing them so they fire off in a way that is smooth.

Odd number of cylinders W/odd # cylinders firing on 1 revolution, even # cylinders on the 2nd revolution.



1-3-2-1, 1-3-5-2-4-1, 1-3-5-7-2-4-6-1, 1-3-5-7-9-2-4-6-8-1, etc.

Unless it's a 2-stroke.

Some day I would like to put 4 units together, 9 cylinders each, for a B-17.  The trick is getting the size just right for scale appearance.  The sound though, would be the icing on the cake, imagine a flyby of a scale B-17 that SOUNDED like a B-17.   We have a few 9 and 18 cylinder radials in the shop, would be cool to take one apart and miniaturize it.   I know it can be done as I have seen a couple 9 and 18 cylinder engines that run, but they were too large to be practical.

There are many choices for RC 4-stroke radial engines, why not just use something already on the market? 9cyl, 7cyl, I doubt you will hear any difference.

No challenge if someone already built it. [&:]    Besides if I can pick up 9 engines from swap meets of the same displacement for cheap, then make the mount and gear set, it would be a lot less expensive that way.

That a full scale radial engine will operate in the low 3000 RPM range.

A small R/C radial will opreate @ @ least 2X that, 3 x in really small engine.

A 5 cylinder radial opproximates the sound of a full scale 18 cylinder radial quite well.

[youtube]http://www.youtube.com/watch?v=_vfdhFYmmlo[/youtube]

Even better than an actual 18 cylinder R/C engine IMO.
[youtube]http://www.youtube.com/watch?v=PWlB_s_hkQc&feature=player_embedded[/youtube]

The secret is getting a low idle speed/operating RPM range. An "oversquare" engine geometry W/spark ignition is one of the best ways to acheive that.

Um , , More like 36 engines of the same displacement ..... Best be buyin that lathe and milling machine

( That is , if we're still thinkin bout that B-17 )

Yeah, I was thinking for the proto type, but your right, 36 engines. Hell if I were to get the Lathe and mill, thenhttp://www.agelessengines.com/9cyl.htm
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The Moki 215cc and 250cc engines sound incredible. It would have to be a very big B-17 for four of those engines.

Yeah, but not as big as the one currently in our work shop.

Well it looks like the links to the video of the geared OS engines radial running are no more.
But here is the original thread about it.
http://www.rcuniverse.com/forum/m_57...anchor/tm.htm#

The ones in the video I posted are 400s! [X(]

So simple its stupid!  That was pretty much how I envisioned doing it, but the prop would be backwards without spur gears, turning the engines around solves that. 

The real trick now would be a central single carb.

The model radial engines all suffer from uneven air/fuel distribution to all of the cylinders. With a single carb you are cursed with a compromise for the adjustments. There have been various methods used to help aleviate the problem though. But those solutions can be quite complicated too. When the one guy did the separate OS engines, he left the carbs on each engine so each engine could be tweaked as needed. He simply bench ran each engine and adjusted it. Then bolted them all together. Then when he ran it, each engine was closely set already, so it wasn't difficult to dial them in then.

If you route the intake manifold plumbing for all of the cylinders to a single carb, now you have problems with the fuel falling out of the air in the tube and wind up with more problems such that the engine won't run at low speed well at all. You see similar problems with large car racing engines using long intake tubes like that too.

The downside of separate carbs though is timing them so they all move at the same rate so the engines run at the same speed.

Oh heck, Fuel inject them!

Wanna see them flying?

http://www.rcuniverse.com/forum/fb.asp?m=11259768

The problem with small radials is the sound. The smaller they are the less 'radial like' they sound. It has something to do with the piston size and exhaust tone. A 5 cylinder OS or Saito sounds too much like a high winding race car engine vs. that of an aircraft radial. A Saito 450 sounds better, but even at high RPM they lose that deep rumble. The Mokis are probably the best sounding RC radials, and they can sound 'off' if the exhaust isn't configured right. Somebody said that they sound best if the exhaust pipe size is ever expanding from the port to the exit, ie. each pipe gets bigger. The collector ring is bigger than the port pipe, and the final exit pipe is bigger than the collector ring. Of course this doesn't work too good with unpumped glow radials since they need the back pressure.

I had built two Royal B-17 model in the past and had started a third that never got done (it got destroyed in moving a long time ago).
But they all sounded awesome with four .20 size two stroke engines on them.

I agree as the engine gets smaller the RPMs go up and the less realistic they sound. So a 5 cylinder radial would tend to sound more like a double row or triple row radial does.  Anyway four 5 cylinder model radial engines would sound prettry awesome in a model B-17 too.