Geared Twin using 2 Golden Bees

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

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.

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.

For your drooling pleasure.

El Coolo !!!! Drool-Drive engaged !!!!

Fire it up!!!!!!

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

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.

Looks like you picked a winner.

i have seen plans to make one of these geared twins, but were? can someone help me?

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?

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.

SHE RUNS! Didn't sound bad either!

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?

Here is another run with 7x4 MA prop.

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

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

The engine is heavy at 6.5 oz.

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.

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 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

Maybe some of Bernies TD sets and high comp heads.