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Geared Twin using 2 Golden Bees Empty Geared Twin using 2 Golden Bees

Post  Jason_WI on Sat Aug 18, 2012 4:11 pm

I got the geared twin today that used 2 Golden Bees. To my surprise one of the Golden Bees has a 3 piece piston. It makes sence as it has the brighter colored backplate and the darker golden color. I think this will cause a balance problem with the pistons being a different weight. It is set up to fire at the same time during rotation.
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Post  lousyflyer on Sat Aug 18, 2012 4:15 pm

You should cut your losses now and sell me the whole shebang for $30.00 tongue
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Geared Twin using 2 Golden Bees Empty re: 3 piece cox piston

Post  happydad on Sat Aug 18, 2012 4:24 pm

Jason_WI wrote:I got the geared twin today that used 2 Golden Bees. To my surprise one of the Golden Bees has a 3 piece piston. It makes sence as it has the brighter colored backplate and the darker golden color. I think this will cause a balance problem with the pistons being a different weight. It is set up to fire at the same time during rotation.

i'll give you $31.00 Chinese for the piston. LOVL. hope you have fun tearing apart the "twin". you should work with chris74100 and build a real twin between the 2 of you. happydad Small Cox Logo

Futaba Radio RC Plane
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Post  Admin on Sat Aug 18, 2012 5:27 pm

Cool! A hidden surprise inside! I cant wait to see it run! You could either swap the piston out or run it the way it was, whatever you think works best. You should play with the gearing and compare the firing at the same vs firing one after each other.

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Post  ahrma_581 on Sat Aug 18, 2012 7:13 pm

Jason_WI wrote:I think this will cause a balance problem with the pistons being a different weight. It is set up to fire at the same time during rotation.

Piston weight is probably 3rd or better down the list of balance considerations. First, if the cranks were intentionally balanced by Cox, they were done so for a single cylinder engine running by itself. Two engines geared together require a different (theoretical) balance factor.

Second, geared twins like this can actually be balanced quite well if the two cranks are geared directly together. Not so good with an intermediate gear (so both cranks turn the same direction), as Kawasaki found out with its initial design of the KR250 racing engine.

Course that's all theoretical considerations, interesting to see how it does work in practice.
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Post  Jason_WI on Sun Aug 19, 2012 2:23 am

For your drooling pleasure.

Geared Twin using 2 Golden Bees 7c6dcd7c
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Post  Kim on Sun Aug 19, 2012 7:30 am

El Coolo !!!! Drool-Drive engaged !!!!
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Post  Cribbs74 on Sun Aug 19, 2012 7:33 am

Fire it up!!!!!!

But only if you really want too.....
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Post  Jason_WI on Tue Aug 21, 2012 8:15 pm

cribbs74 wrote:Fire it up!!!!!!

But only if you really want too.....

Heck ya! Used an APC 8x4 prop which I think is a bit much. Will try a MA 7x4 prop tomorrow. Using Sig Champion 25%. Getting one Cox to run nice is sometimes a PIA geting 2 to run in synch I think is going to be an art.



One side ran out of fuel at the end and the RPM really dropped.
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Post  lousyflyer on Tue Aug 21, 2012 8:23 pm

Looks like you picked a winner.
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Post  mitchg95 on Tue Aug 21, 2012 8:41 pm

i have seen plans to make one of these geared twins, but were? can someone help me?
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Post  Cribbs74 on Tue Aug 21, 2012 10:37 pm

Very nice Jason. Thanks for running that up. They ran well but I assumed the RPM would be higher. I wouldn't think a 8" prop would load it down that much. Are you going to try a 6x3 sometime?
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Post  Jason_WI on Tue Aug 21, 2012 10:45 pm

I have a MA 7x4 on it now that I will try tomorrow. Ran out of light today. One needle is slightly bent so I will replace that also. I was hoping for more RPM also but I did not have it dialed in and with the large prop I do not think it could wind up.
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Post  Admin on Tue Aug 21, 2012 10:59 pm

SHE RUNS! Didn't sound bad either!

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Post  ahrma_581 on Wed Aug 22, 2012 4:14 pm

What's the gear reduction? I counted something like 18:24 but probably am off a couple teeth either way. So the GB's are turning about 1/3 higher rpm than the prop. It spiked at 9K so they were doing around 12K then.

Mebbe less pitch on the prop, or not enough lash in the gears?
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Post  Jason_WI on Wed Aug 22, 2012 7:48 pm

Here is another run with 7x4 MA prop.

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Post  Cribbs74 on Thu Aug 23, 2012 6:52 am

Sounds like they are balanced really well, I could only hear one engine.

I never thought about the ratio of the gears and you may be turning much higher RPM than the actual prop is spinning. A 6x3 is probably the smallest you can safely go.

How much does that whole thing weigh?

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Post  RknRusty on Thu Aug 23, 2012 7:58 am

Now you're cooking. That sounded like it would actually fly a plane. Does the same engine always run out of fuel first?

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Post  Jason_WI on Thu Aug 23, 2012 8:00 am

The engine is heavy at 6.5 oz.
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Post  PV Pilot on Thu Aug 23, 2012 11:55 am

Jason_WI wrote: Getting one Cox to run nice is sometimes a PIA geting 2 to run in synch I think is going to be an art.

One side ran out of fuel at the end and the RPM really dropped.

Was wondering that. If both needles are not perfectly matched, one motor just drags the other along. Possible constant hydrolock condition, ramming the fuel thru the one that is late.
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Post  Jason_WI on Thu Aug 23, 2012 10:54 pm

The gear ratio is 18:22. If the prop was at 12,200 then the engine is at 14,911. Not too bad for a golden bee with #2 cylinders.
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Post  Cribbs74 on Fri Aug 24, 2012 6:00 am

Jason_WI wrote:The gear ratio is 18:22. If the prop was at 12,200 then the engine is at 14,911. Not too bad for a golden bee with #2 cylinders.

Yeah that is pretty good. I wonder what #1 cylinders would turn? Do you have any plans to mount it too an aircraft or would it be impractical?

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Post  PV Pilot on Fri Aug 24, 2012 6:23 am

Maybe some of Bernies TD sets and high comp heads.
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