BMatthews

The crankcases to the manifold block would be a bit odd. I'm sort of thinking that the the crankcases would have 2-56 studs in the holes that match with locating holes in the manifold plate. From there long 4-40 rods are then used in the holes of the front and rear plates to pull the whole mess together. Not much else that would work since the holes are all in alignment so there's no way to put the screws into the last one. The other option that may work is that if the center manifold plate may be thick enough that notches could be cut into the edges to allow the threaded studs to protrude into the center line cutouts to allow 2-56 nuts to slip in there and go onto the ends of the studs. It would be a tricky bit of assembly but it could be done with only a bit more room than what is needed for the double nuts alone.

Patrick, granted that this would not be super powerful but with care in the building it would easily produce as much power as a typical low power loop scavenged .20 at only about twice the weight... But pure performance is not what this sort of thing is all about anyway. But mounted in a lightly built scale homebuilt design it would be TOTALLY KEWL!

ptulmer

My Feedback: (5)

You know Bruce, in the past some people have said the twins are nice to look at, but not really usable in an airplane. I think your right. Not only would it fly something, it would be excessively cool doing it.[sm=cool.gif] Thus the "flyable power" rating. If there was so much power loss that it woulldn't fly anything, it wouldn't be worth doing.

build light

I think the "Cool Factor" alone would fly it!!!
Seriously though, I think it would be powerful enough to fly something cool. Not a rocket, not a prop hanging 3D thing, but a plane which would take off in a normal fashion, do some circuits around the field, not to mention some low, slow flybys (it would be throttled wouldn't it?) and a touchNgo for good measure then land like an airplane lands with a few exceptions.

Exception #1
I am sure that most if not all heads would turn following every move and manuver.

Exception #2
Most if not all would enjoy the sound emitted by such a creation especially when each cylinder note was add to the choir.
Exception#3
Most if not all would jump at the chance to help restart the wonderful creation the next time around.
Exception #4
Most if not all would wish their engines would sound so cool!

Robert

BMatthews

There was a fellow at our field a few years back that had one of the rare Gmark 5 cylinder radials. He set it up to run and I was right there in anticipation of the music to follow. However I was actually somewhat dissapointed. The gnashing of the gears combined with the sound of 5 exhaust pulses per rev conspired to make it sound nasty by anyone's definition. However I've also heard a geared twin before PBJ's movie and it sounded nice, Mostly due to the matched firings I suspect.

indoorff

My Feedback: (2)

Love the twin! I have seen plans for these on ebay, and figured it would be a fun project.

Here's another idea - How 'bout making a Sure-Start version of this: http://raysrocketry.websanon.com/index.php?itemid=32 Cant see why it wouldnt work, apart from it being hard to start (rear prop first i guess) !!

build light

Indeed Bruce I was basing my anticipation on the sounds I heard on the twin-bager video. I could be wrong. I bet a belt drive would make some difference. Though I haven't seen very much done with belts. I know there are some but I don't know anyone who personally has used such a system. Never have I seen one used for something like a multiple Cox set-up. Not saying it hasn't been done, just that I haven't seen one.

All I can say for sure is that I just loved the sound of PBJs creation and wish one day to have one myself!!

Robert

ProBroJoe

Wow... I really didn't expect to stir up this much interest in the twin, (or a flat four for that matter). Thanks for all the feedback!

PT, the attached rendering should give you a better idea of what I had in mind. Alternatively, I suppose I could omit the full length studs, have threaded "ears" or "bumps" on the manifold and run screws from the outer bearing blocks into the mainifold, effectively sandwiching the engines together...

Bruce, 2-56 studs, notches in the mainifold and (16) little #2 nuts? Yikes! No thanks!

I'd have to look closer, but if a person would drill the backplate mounting holes all the way through to the front of the crankcase, would that create a leak? That may be another way to go....

indoorff, plans for the twin on e-bay? Don't bother, Andrew Coholic posted free plans here on RCU a coupla years ago (and that's where I got the information to builld mine). If you're interested, [link=http://www.rcuniverse.com/forum/m_1199286/mpage_1/tm.htm]here's link to the original thread.[/link] I meant to include that information in my first post...


Well, here's where this impromptu "project" stands... (D*mn you Bruce! )

-Joe

KidEpoxy

Instead of timing them 90deg apart, time them 80deg with a 40 degree flywheel coast, just to seriously mess with peoples minds & ears

ProBroJoe

One more pic, to give a better feel for the general asembly (the manifold is designed to hold shaft bearings if need be).


-Joe

BMatthews

WOW! These 3D shots are looking real fine. It looks like I should be able to reach in through the screen and fondle them....

Joe, the last pic is the perfect place to show the location studs I reffered to in a previous post. The threads in the case are 2-56 of course so what "we" need is some short threaded studs of 2-56 thread to a straight sized pin to extend about 1/8 inch from the case. The plastic manifold would have matching holes to recieve the studs. This would prevent the engines from rotating within the mount until the front and rear clamps are tightened. You wouldn't need all four studs by any means. Perhaps just one or two. They are only there to key the Sure Starts into place until it's all snugged down.

As for drilling through to the front I'm not sure that will work with the upper ones. Certainly the lower two are safe but I believe the threads would be exposed a little through the cylinder area on the upper ones. Whether or not this would foul the piston or rod in their travels I don't know. But if it didn't then a simple fiber washer gasket on the "upper" bolts would seal things just fine.

This is really shaping up to be a viable project from the looks of it...... As if you need any more encouragment...

ptulmer

My Feedback: (5)

That double clamp is ingenious.

ProBroJoe

OK, here's where the project stands:

1.) I've incorporated mounting holes in the bottom of the front and rear bearing/engine mounts (for beam style mounting).

2.) Added locating holes in the manifold and pins on the engines per Bruce's suggestion.

3.) Ditched the screw-in carb w/ locknut in favor of the more common setscrew fastening method. (Hey, I already had that carb in CAD)

4.) Went ahead and added bearings in the manifold block. These will be of the sealed variety because when I redesigned the manifold block in an effort to make things more compact, the prop shaft now passes through the intake passages. Will have to weight the pros and cons of this later...

5.) The front and rear mounting plates are now thicker to provide a better grip on the engines with a marginal weight increase.

6. Model now shows the proper propshaft gear with a 1.5:1 gear ratio. This ratio was chosen because this was the largest "over the counter" RC car pinion gear available. A smaller gear on the engine would allow higher ratios, so some experimentation may be in order...

Now, some concerns...

1.) Need to come up with a convenient way to mount the rear propshaft gear so engine can be disassembled. (The front gear is silver soldered to the shaft.) Not a biggie, just isn't done yet.

2.) It would probably be just as easy to machine new reed holders as it's kind of a PITA to hold the new style backplates (SureStarts) in the lathe for turning. Again, no big deal, and it actually allows a bit of customizing and design freedom - it just adds another level of complexity to the project.

3.) A radial mounting option may be nice.

4.) Gear covers?

5.) Exhausts? Even if it meant collectors around the cylinders and four exhaust stubs...

6.) As it stands, the engine weighs (according to CAD) about 10 ounces... [X(]

Thanks for all the encouragement guys, but don't expect to see one running soon.

Now with that being said, if anyone is interested is tinkering with the design, I have no problem sharing the 3D models (no plans are available at this time). All that I ask is that you don't claim it as "your own" and try to profit from my generosity. A lot to ask in today's society I know, but I think for the most part we're all in the same boat here and just want to see one of these "come to life".

-Joe

ptulmer

My Feedback: (5)

10oz ain't too bad! A .25la weighs 9.5oz and has all the power of four good reedies. Shoot, if I had any clue how to use 3d software... Now, forget the exhaust and gear covers and get back to work![>:][sm=lol.gif]

BMatthews

Simple. Instead of the front gear solder on the rear gear instead. Then fix the prop driver using a set screw or collet style retention. The rear gear will then take the thrust loads. And go for a snug but not press fit push fit on the shaft to bearing inner race fits.

Can you make up a collet fixture to hold the backplates from the round reed portion so you can turn down the backplates? For the shapes you show that's what I'd do. But it wouldn't be much trouble to turn the reed mounts since the modified ones you show are just round turnings. So 6 of one and 1/2 a dozen of the other ...

This thing is long enough that I'd stick with the beam mounts. The loads it would cause would be horrendous and a lot of vibration would be the likey result.

Some cute little carbon fiber molded shield covers would be slick but I wouldn't loose any sleep over them. On the other hand I'd like to see a couple of collector manifolds for the exhaust to allow ducting to a muffler or two. And from that a side tube to provide a small amount of oily exhaust to squirt on the gear teeth would be a cinch and probably a wise thing to do.

I think something like this needs an exhaust system. The Gmark radial even with the exhaust collectors but no muffler was terribly loud. And the noise from this thing would be far too much with no mufflers. Besides the throttle action with mufflers or even a manifold with restrictor would be far better than with open exhausts.

As for the center manifold. Can't the passages from the carb be angled down in a ^ shape to pass by the bearing mount area?

.... I'd like a set in dxf or dwg please. And don't worry, if it ever sees the light of day it'll have a little plaque on it with you listed as designer for sure...... I know my build record around here isn't the best but my keeness for my other hobbies is running down to more of a normal setting and the ol' model bug is coming back. Perhaps next winter.....

build light

Imagine if you would a Fly Quiet Tuned System On this bad boy! C'mon! close your eyes and try it!

Robert

KidEpoxy

Great start, could use some more cylinder pairs in the 12 & 6 positions, if you can remote carb it....on your way to a 049 Double Wasp 18

Bipe Flyer

I love it! Not great power to weight, but it sure would be nice on an old timer or a WWI biplane.

revkev6

hey guys, this really is a wierd coincedince, I've been dreaming up a radial based on almost this exact premise for the past couple days. my plan was a single row 9 cylinder radial based on almost the same mounting setup. advantages of the radial are as follows:

single drive gear, no worries about trying to make one gear removable since their is only one.
easier back plate mounting. all engines mount through a single plate using screws.
cool factor doubles with the 9 cylinder radial. think about it. you can build anything that takes a scale 9 cylinder radial
size! 9 049s come out to .441


in reference to the removable gear issue of the geared shaft on the flat 4 design, make the entire shaft removable. capture the bearings on the shaft between the gears, solder them on. split the bearing sleeve so that it bolts together like a main journal on a regular engine block.

build light

I don't know if this is the first twin like this but I remember seeing a video less than 2 months before the first post on this thread. In this video it showed this twin being fired up one cykinder at a time.it was way cool. I have been trying to figure out where in the world I saw it. Any one know about this motor and video? Same twin or different? It is a much longer video than the one linked on the first page here.

Robert

BMatthews

BL, the basic geared Cox twin concept has been around for years. It first showed up in my time as an article in the old American Modeler back in the mid 60's and it's resurfaces on occasion now and then. So it's quite possible that you've seen one here or there.

subarubrat

My Feedback: (1)

I just thought of a radial plan that even I might be able to pull off. Using 8 sure starts I think I can make this happen. I am thinking a 2mm duraluminum plate cut to shape (8 sides) with a centered hole. The engines are clustered about that centered hole wiht a gear on each one. A central gear on a 1/4 shaft will mesh with all gears and will have the prop hub just ahead of the gear. With a nice stiff backplate that tricky front plate should not be needed. An aluminum tube will pass through that centered hole and hold a bearing in the front and some sort of flanged thurst bearing in the rear. Should be light and sturdy. A hole can be drilled behind each engine and have a short riser tube that comes up to meet a circular intake manifold.

Bipe Flyer

This all seems familiar.

Here are a few old threads where lots of these ideas were discussed and tested. It might save you some time re-inventing the wheel, so you can build a better mousetrap, (or whatever cliche you prefer).


[link=http://www.rcuniverse.com/forum/fb.asp?m=1462938]Poor mans radial [/link]
[link=http://www.rcuniverse.com/forum/fb.asp?m=309377]Texaco 5 cylinder radial [/link]

Tim Wiltse-RCU

If I remember right AJC said that the Cox twin you see on eBay is one he made and gave to the guy. He then was a slimeball and drew up plans for it and is selling them on eBAy.

LAter,Tim

subarubrat

My Feedback: (1)

I suppose there are only so many ways to do this, so the odds of hitting on something new is slim. I do think I can pull it off though so I am ordering 8 sure starts and thanks to the fellow who posted the WM Berg website I have found the shafts, bearings and such that I need. There are so many nice lightweight electric ARFs, many suited for radials that I am sure I can come up with something nice to bolt it to.

revkev6

another idea on the radial front. I've seen a couple conversions of the cox engines to run on a side port setup where they braze a venturi into the port on side of the cylinder. using this setup, would you need to have the crankcase pressurization to draw fuel into the cylinder? I'm thinking, if this is the case and just the individual cylinder will draw through that port then an actual radial would be possible with a master rod.