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Old 01-20-2009, 06:21 AM   #1
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4 stroke twin

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I must be trying to think about this to much

Anyway, if a 4 strock twin (I will use a 120 for an example) is two 60 size engines using one crankshaft putting out the power of a single 120 or a 60? I believe that they fire alternately, so it would then act more like a 2 stroke, making the power the same as a 90 or so 2 stroke??? I also think it would have more/smoother power output than a same size single.
I know that twins sure sound great.
What started this all is that I am thinking of putting a twin in a 1/4 size cub and do not want it under powered.
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Old 01-20-2009, 08:45 AM   #2
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Re: 4 stroke twin

Back in the day when OS made their first version of the 1.20 Gemini engine, there were people using them in Sig 1/4 scale Cubs, both full span and clipped wing.

Having seen them fly, I would say that there was adequate power for realistic Cub flight, including the aerobatics which the clipped wing versions are capable of.

The second generation of the OS 1.20 Gemini was a more powerful engine and worked better. A present alternative is the OS 1.60 twin.

The power you will get out of the 1.20 twin will be less than a 1.20 single. There is much more internal mass and friction in the twin. It takes power just to run it. The twin is also considerably heavier than the single.

Years ago I had a G-Mark.30 twin (2 stroke). It had an output roughly equivalent to a .20 single cylinder two stroke.

The smaller your engine displacement, the greater the difference in output between the twin and the single of the same displacement.
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Old 01-20-2009, 11:09 AM   #3
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Re: 4 stroke twin

I had a quarter scale cub (full span) with the original Gemini 120 twin (still have both) and it was very scale type flying. It had the power of a first generation OS 90 4 stroke.

Super smooth running and very quiet too. You can start it on one cylinder and then put the glow plug connector on the other cylinder to get it going.

The 160 Gemini is a much more powerful engine. I will be using one to power my 1/4 scale Stinson Reliant.
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Old 01-20-2009, 12:34 PM   #4
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Re: 4 stroke twin

A few years back, around 1994, I had a Balsa USA 1/4 Scale J3 Cub with the origional Gemini 1.20 twin. The Cub was built light and the 1.20 had more than enough power to fly the plane.

I am currently building another BUSA 1/4 Cub and as DO335 knows, I have a beautiful new OS Gemini 1.60 Flat Twin for power. It will have way more power than it will ever need but as has been said, its the only twin four stroke close enough in size to power the plane. I had origionally thought of using a Saito 182 Twin but its not a flat twin and the carb barrels stuck out the top and would have looked awful protruding out the top of the cowl.

A twin does sound awsome and does run somewhat smoother than a single but the single of the same displacement will always have more power than a comparable sized twin. As stated above, power is not the issue, with me anyway. Having a twin with the cylenders sticking out of each side of the Cub cowl will look beautiful and so much more scale than a single cylender on one side and a dummy cylender on the other. And the sound of a four stroke twin is hard to beat, unless of course you have a radial FS with multiple cylenders.

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Old 01-21-2009, 06:47 AM   #5
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Re: 4 stroke twin

Thanks for feedback
With the info you provided and my budget I will stay with the pre surpass 120 I have in it for now. Will start saving funds to get a twin for a later date, love that sound and yes, I do think a twin would also look a lot better with the heads sticking out both sides.
Thanks again
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Old 01-24-2009, 12:31 PM   #6
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Re: 4 stroke twin

hello Don,10 years ago I built a sig 1/4 scale cub full span (clipped wing paint job,green & cream) installed a saito 182 twin.the carbs did cowl up it looked so good that i glassed up the two piece abs cowl.the heads look great out in the wind.the exhaust pipes run staight down and out, very clean. runs strong,super on floats.(lots of power)
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Old 02-01-2009, 10:10 PM   #7
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Re: 4 stroke twin

due to the shorter stroke of twins they only generate aprox 2/3 the power of the same displacement single.and weigh mutch more .but the sound is to die for .LOL
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