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Joined: 9/24/2004 From: Annapolis,
MD, USA Status: offline
Hi guys... sorry for this being kinda "outta the blue", but I finally got around to making a video of the geared cox twin that I built last spring and I thought some of ya'll might like to have a look. Here it is, filmed yesterday, spinning a Master Airscrew 8x4 at 10,500 RPM on standard 15% fuel. It has a 1.2:1 gear ratio, so each engine is turning ~12.7K...
Enjoy! -Joe
I had to temporarily remove the video because some eBayer was using it to promote the sale of one of his items without my permission. However, the video is now back up. More info can be found in this thread:
Posts: 464
Joined: 9/24/2004 From: Annapolis,
MD, USA Status: offline
Dukester, nice try.... Yes, it's basically the same version that AJC posted plans in this link.
brocja01; Yep, that's exactly how you start it... and there's no mistaking it when the second engine lights!
KidEpoxy; In theory it could be done, but you loose a lot of power though the gears... as is, this is a +6 oz engine and the power-to-weight ratio is pretty poor. (I have a .10FP which weighs about the same and will probably turn the same prop at 12k+.) I will admit though, I've thought about a triple....
Let's face facts here. For our smaller model sizes no twin is ever going to match the power to weight of a single be it a geared twin like this one or a proper twin with a two throw crank. So it comes down to the appeal of uniqueness. And that a multi cylinder engine has in spades!
I'm not sure about a 3 but didn't Tazanos or some username like that have a 5 cylinder geared engine at one point? And the massively heavy old Gmark 5 cylinder was a geared unit with a light cast bell cover over the gears. On that one I seem to remember that the exhaust was ducted into the bell and outleted from there in order to provide lube oil to the gears.
Another geared project that would be kind of neat would be in inline twin Cox pair with the rear aimed backwards and the two gears coupled to a long fore and aft shaft. The center joiner could be custom made to provide a single carb to feed into an internal T to the two reeds. It would probably need to use either a fairly large diameter shaft or use a center ball bearing in addition to the two end ones. From there it would not take much more to extend the center manifold and backplate option into a double sided affair and bingo-bango-bongo you have a flat 4 running to a common shaft. At that point I'd offset the shaft a little to one side to allow the use of significant gearing down of about 1.7:1 or so and the turning of a 12'ish inch higher pitched prop.
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Joined: 4/1/2005 From: Remington, VA, USA Status: offline
I have said it before and I will say it again, wouldn't it be great if someone would do a production run of the machine parts and sell it as a kit. If someone would just tool off a run of plates and gears (or just provide the part numbers for the gears) to make that 3 cyl we could all go get our 3 pack of surestarts and build away.
< Message edited by subarubrat -- 2/2/2006 4:07:26 AM >
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Joined: 5/27/2003 From: Orangeville,
ON, CANADA Status: offline
I wish the video was longer. It's so soothing. I keep looking at my .010 collection and wondering.. nah, that's silly. But it would sound cool wouldn't it? So would a pair of gnarly combat .049's geared down. Hmm.
Hey ProBroJoe, is that a Pfeffer .036 in your Avatar?
Posts: 464
Joined: 9/24/2004 From: Annapolis,
MD, USA Status: offline
Bruce... thanks... like I needed yet another project!
I'm pretty sure this is what you had in mind, of course missing is the front and rear bearing supports, the manifold, and various other bits... I've retained the stock reed assemblies by cutting down the backplates (thinking that the stubs would "plug" into the manifold with the RC carb attached). The whole assembly could be held together by running long studs front-to-back from the bearing mounts with the manifold sandwiched in between... of course it's still a pipe dream at this point.
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Geared Cox Twin Video - 
