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Cox Engine of The Month
Geared Twin using 2 Golden Bees
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Geared Twin using 2 Golden Bees
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.
Jason_WI- Top Poster
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Posts : 3123
Join date : 2011-10-09
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Location : Neenah, WI
Re: Geared Twin using 2 Golden Bees
You should cut your losses now and sell me the whole shebang for $30.00
lousyflyer- Gold Member
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Age : 64
Location : Garden City Ga
re: 3 piece cox piston
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
happydad- Rest In Peace
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Re: Geared Twin using 2 Golden Bees
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.
Re: Geared Twin using 2 Golden Bees
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.
ahrma_581- Gold Member
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Re: Geared Twin using 2 Golden Bees
For your drooling pleasure.
Jason_WI- Top Poster
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Posts : 3123
Join date : 2011-10-09
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Re: Geared Twin using 2 Golden Bees
El Coolo !!!! Drool-Drive engaged !!!!
Kim- Top Poster
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Posts : 8528
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Location : South East Missouri
Re: Geared Twin using 2 Golden Bees
Fire it up!!!!!!
But only if you really want too.....
But only if you really want too.....
Cribbs74- Moderator
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Posts : 11895
Join date : 2011-10-24
Age : 50
Location : Tuttle, OK
Re: Geared Twin using 2 Golden Bees
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.
Jason_WI- Top Poster
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Re: Geared Twin using 2 Golden Bees
Looks like you picked a winner.
lousyflyer- Gold Member
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Re: Geared Twin using 2 Golden Bees
i have seen plans to make one of these geared twins, but were? can someone help me?
mitchg95- Diamond Member
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Re: Geared Twin using 2 Golden Bees
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?
Cribbs74- Moderator
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Re: Geared Twin using 2 Golden Bees
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.
Jason_WI- Top Poster
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Re: Geared Twin using 2 Golden Bees
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?
Mebbe less pitch on the prop, or not enough lash in the gears?
ahrma_581- Gold Member
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Re: Geared Twin using 2 Golden Bees
Here is another run with 7x4 MA prop.
Jason_WI- Top Poster
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Re: Geared Twin using 2 Golden Bees
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?
Ron
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?
Ron
Cribbs74- Moderator
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Re: Geared Twin using 2 Golden Bees
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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RknRusty- Rest In Peace
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Re: Geared Twin using 2 Golden Bees
The engine is heavy at 6.5 oz.
Jason_WI- Top Poster
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Re: Geared Twin using 2 Golden Bees
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.
PV Pilot- High Tech Balsa Basher
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Re: Geared Twin using 2 Golden Bees
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.
Jason_WI- Top Poster
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Re: Geared Twin using 2 Golden Bees
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?
Ron
Cribbs74- Moderator
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Re: Geared Twin using 2 Golden Bees
Maybe some of Bernies TD sets and high comp heads.
PV Pilot- High Tech Balsa Basher
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