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Post  TCLyon on Fri Jan 08, 2021 11:07 pm

Hi and Thanks for Feedback,

I have a Dragonfly (below), but am interested in CL now. I bought this engine circa 1990 for a sailplane. Somewhere along the way, I lost the muffler spring. A couple of questions (I did search the forum, but didn't see them answered):

-Is there any benefit in using this engine for CL? I'd have to fix the throttle somehow so it wouldn't move in-flight.

-What purpose does the missing muffler spring serve? This really perplexed me because even mufflers with an extension have the spring, so the spring's purpose can't be to cover the exhaust port opening since the extension covers it on those engines and I can't see any openings in the indentations surrounding the muffler.

I love the Golden Bee and Black Widow, so I'll probably go with those for CL. My planes will be radial mount and I am required to use a muffler at our club.

Dragonfly for CL and Muffler Spring Question - Thanks!  Dragon11
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Post  emanuel on Sat Jan 09, 2021 12:53 am

Black Widow and Golden Bee have SPI cylinders. That's not good for a muffler because you lose a lot of power. The Dragonfly is built especially for silencers.
The spring can be opened to adjust the volume and to inject fuel for start-up. It is the same spring as the standard silencer. I had used the Dragonfly in a glider with a fixed throttle. Since you don't have the spring, I would get the standard silencer, which is without a throttle.
Without the spring the engine is almost as loud as without the muffler.
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Post  KariFS on Sat Jan 09, 2021 11:57 am

Tom, I am not sure how a clunk tank would work in C/L. The tank is also pretty big so you’d get long flights. I have very little experience on this but I guess there is a reason why most people use the Bee-type engines or ”horseshoe” engines in C/L.

There is a Cox engine that would fit your application, the ”QRC”. It has the 8cc stunt tank and a muffler. I think a high compression ”Tee Dee” glowhead too. The output is supposedly equal to a Golden Bee. Despite the R and C in the designation, it does not have throttle control. The QRC was available separately, with a red fuel tank, and it also came with many Cox RTF foam RC models. The RTF version was plain aluminium.

Dragonfly for CL and Muffler Spring Question - Thanks!  8c0f2910

You can also take any Golden Bee or Black Widow and install a ”Sure Start” type cylinder, it doesn’t have SPI and works well with a muffler. This same cylinder was already installed in late model Golden Bees and Babe Bees. Below is a picture of a Sure Start engine with that type of a cylinder. Cylinders, high compression heads and silencers are available new from Matt @ Ex Model Engines and Bernie @ Cox International. And of course there is a lot of them in the second-hand marketplaces.

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Post  TCLyon on Sat Jan 09, 2021 3:40 pm

Wow, this is so helpful and exactly what I think I will do. Although I certainly “could” repurpose the Dragonfly, I can see now that I’d be better off letting it go to a new home and getting an engine that is well-suited for CL.

And thanks for clarifying the Sure Start aspect. I got to thinking myself that it had to be something in the cylinder that affected performance with the muffler because the crankcase appears to be identical on the non-Tee Dee engines.
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