Side port or reed, it doesn't matter. You still need some way to pressurize the crankcase and the usual radial master rod setup does not result in a volume change inside the common case. So that won't work.
There was a two stroke radial done a few years back but it used a crank driven vane style pump to provide a positive crankcase pressure.
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Joined: 2/12/2004 From: , MA, USA Status: offline
well, I guess that doesn't help me much then. I really thought I was on to something with the side-port engine. Like they say, there really isn't anything that hasn't been tried before. any idea how much pressure you would need in a fan? would a centrifugal setup work at this size or would you need something in the roots style? neither one would be a simple task to implement.
At these revs a simple fan won't work. You need a positive displacement style of pumping action. Roots would work but it's a fussy bit of machining at that size. The vane style is far, far easier.
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Joined: 9/24/2004 From: Annapolis,
MD, USA Status: offline
Bruce, you've had a lot of good ideas and I think I've incorporated them all!
I was able to fit in a split collet to hold the front prop shaft gear - the rear gear is now soldered. The forward portion of the prop shaft has been reduced to 5mm in diameter and a split collet will bear against this shoulder on the shaft. The front gear has a tapered bore like a lot of the current engines' prop drivers. The "prop driver" in this case will be keyed to the shaft with a set screw - to be tightened after snugging up the prop - this should be a one time thing as subsequent removal and attachment of the prop shouldn't effect the assembly.
The reed block(s) and manifold - I never felt comfortable with turning the backplates down and trying to sandwich them into the manifold and getting them to all to seal. At first I thought it was a good idea, then the more I thought about it the more it looked like there wasn't going to be a lot of "meat" left to be of any use. I have since changed to two double-ended reed holders that will be pressed into the manifold (or held with a set screw / Loctite) and then crossed drilled to form the intake passages. A small plug will partially back-fill the hole. I had thought about angled passages to clear the prop shaft, but because I wanted to keep the manifold small & light, there just isn't enough room to do this - sealed bearings and a snug-fitting prop shaft should aleviate any concerns.
Simple exhaust collectors have been designed and affixed to the engines. The outlets are 1/4" O.D.... someone else can design the muffler! Come to think of it, a coulpe of "trial size" mousse cans would probably work nicely... (As a side note, the twin is LOUD - the video does it no justice.)
Gears and bearings are readily available RC car parts in an effort to keep costs down.
Reeds and retainer springs are standard Cox parts.
AUW, with exhaust collectors, is just under 12 oz.
I think at this point it's safe to say that this is a viable design. The front prop gear attachment may not be ideal because it was designed around OTC gears. Buying gears from Berg, Stock Drive, etc... would be pricey, but other ratios and more secure mounting methods could be used.
All that exists at this time are the 3D CAD models of the parts, and unless there's an overwelming demand for plans, that's about as far as it's going to go at this time. Bruce - check with your CAD software to see if you can open any 3D file types and let's see if we can work something out. (In order for me to create a .DXF/DWG file, I first have to detail a full 2D drawing of the parts and then export this as a .DXF. I love to design in 3D, but detailing takes the fun out of it!)
Now that Bruce and I designed this thing, one of you guys gotta build it!
-Joe
< Message edited by ProBroJoe -- 2/14/2006 6:08:27 AM >
This is getting to be as fine looking a Widget as any I have ever seen. Someone has GOT to build one of these. Joe, you've outdone yourself. For a guy that just ran with an idea this is above and beyond the call of duty. I doff my cap to you.
The new option for getting the reed holders in there suggests a way to easily angle drill the passages up to the hole where the carb fits. But then there's nothing to hold the stub of the carb. But if the carb was flange mounted to the top of the block with 4 small screws then it would work. I just can't help but think that it would be better than using sealled bearings or real seals to prevent air leaks around the shaft passage. That need to seal at the mid point will put a high need for accuracy there and may prove a source of drag if it's not just right.
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Joined: 9/24/2004 From: Annapolis,
MD, USA Status: offline
Thanks Bruce.
If someone really wants to build one, I have no problem collaborating with them to get it done. (i.e. I'll provide detailed drawings or solid models & you build it.) I don't have the time nor the finances right now to take on yet another project. Of course if someone were to donate to the cause....
A flange style carbie, like the old Foxes, eh? (Two screws would do it.) Hey, why not? I'll see what I can come up with for the sake of making this a complete and certainly viable project.
The bad thing about CAD is that you can create all sorts of projects for yourself in no time at all. I betcha I have over a dozen "Widgets" like this one that I may get around to building one day (including other engine projects).
Now, who out there has access to CNC / EDM equipment and can run off a bunch of these parts for us?
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Joined: 9/24/2004 From: Annapolis,
MD, USA Status: offline
Emachineshop.com... yea, I've seen it and even wondered the same thing, but knowing it would be cost prohibitive for anything under 100 pieces, I didn't bother to persue it.
(Already working on changing the carb mounting option - stay tuned...)
That's an interesting product but I wonder at how truly effective it would be.
In particular for a larger displacement you'd need an equivalently larger vane pump. The one on the radial I saw in the article was about twice to 2.5 the diameter of the one in the pic and was used on a 60 size displacement if I recall correctly. In this case size does matter as the volume flow per second of the pump must be enough more than the volume flow through the engine that the proper crankcase pressure is maintained. Remember that for a pumped radial engine this means probably 3 to 4 psi more than atmospheric. Whereas the pumped single like in your pic will still have it's charge pumped by the descending piston. The fact that they share the use of a charging pump is only coincidence.
But the whole point is that a two stroke radial with a common crankcase IS doable. You just need to do the math to ensure the case pressure is sufficient to charge the cylinders in a manner equivalent to a regular single cylinder engine.
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Joined: 2/12/2004 From: , MA, USA Status: offline
after doing some reading on the RB innovations web site I found that they make this setup to work with for up to a .7 cubic in motor. they spin it up to 50% over engine RPM. engine RPM of a 40-70 size engine is about the same as what I'm guessing the radial would run. say, 13-15k rpm, this should be plenty of air for a .441 cu in radial.
the other thing about the radial is it will only be firing one cylinder at a time. granted for one revolution it will fire all 9 cylinders.
< Message edited by revkev6 -- 2/14/2006 8:02:02 PM >
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Joined: 4/28/2003 From: Brunswick,
GA, USA Status: offline
Joe, just wondering about emachineshop. I'd be willing to take this project on, IF Bruce let's me have a thread that you guys can walk me through the tough spots. I'm not new to a micrometer, but I ain't NEVER done anything like this. Heck, I'm still waiting on Uncle Sam to send my money back. Now would be a good time to tell me if there's anything special I might need. I'm going with the Grizzly 9x19. Lotsa accessories and cheap shipping. Enco has the milling attachment that works with it.
after doing some reading on the RB innovations web site I found that they make this setup to work with for up to a .7 cubic in motor. they spin it up to 50% over engine RPM. engine RPM of a 40-70 size engine is about the same as what I'm guessing the radial would run. say, 13-15k rpm, this should be plenty of air for a .441 cu in radial.
the other thing about the radial is it will only be firing one cylinder at a time. granted for one revolution it will fire all 9 cylinders.
And that is where the problem lies. You need enough volume to feel all 9 per rev and to feel them at a pressure above normal atmospheric. However if it will operate a .7 cu inch with a power boost then it should be able to charge the crankcase of a 9 cylinder radial at .44 ci. I think you may just have a solution there if it works as advertised.
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All Forums >> RC Airplanes >> "1/2 A" & "1/8 A" airplanes >> RE: Geared Cox Twin Video 
RE: Geared Cox Twin Video - 
Come to think of it, a coulpe of "trial size" mousse cans would probably work nicely... (As a side note, the twin is LOUD - the video does it no justice.) 
