cox dragonfly

Hi Ron,

 Thanks for suggestion.
I'm still building the kit, the listed flying conditions are just a manufacturer's suggestion, I don't know why they suggest 10% nitro fuel but maybe thats the minimum requirement they suggested.
I believe that most of Cox engine love a lot of nitro, anything lower than 15 % and it will not performing. 20% to 30% are common for good flying.

There's an exception in my case though, I have one weird older Cox production engine , which is non-booster port in its cylinder. Its from a plastic plane and never run. I put it on my computer desk for more than 10 years, when I'm free, I just like to flip its 3 blade prop several time, just for fun. until last year , I plan to test run it , and after 4 oz of 0% nitro, with 20% castor oil, ( I use FAI fuel for break in because thats the only fuel that contain castor by that time)
I purchased Sig Champion, It run smoothly on 10% Sig Champion fuel, at 13400 rpm using Master air screw 6 X 3.
I try to fuel it with any fuel that higher than 15% nitro and its RPM drop. I keep this little engine for further investigate. Someone say, older engines are different slighty, and capable of running at lower nitro. and some others say, this Cox engine that break in by using low nitro fuel , will "blueprint " its running condition into low nitro condition. I don't know, but just love this easy to start reedie.

Back to the topic, Its a shame that I I'm a Cox reedie engines user for the past 20 years, but never have any TD series, nor 020 , 010 etc.  Main reason is , back in 20 years ago, I can't find any other cox engine in my country, just basic U shape back plated engine.  I did purchase several others engine on ebay in recent years , might try to purchase some TD for future project.

 You did mentioned TD high comp. glow head. Thats a good idea, any idea how many RPM gain if you use TD hi comp. head on normal reedie?

Tough to say on RPM gain as it's specific to the condition of the engine. All I can say is try it and see.

As to your RPM loss when adding nitro. You have to add a head gasket for every 10% of nitro. I bet your old bee was over compressed.

Cox tuning is a lot of trial and error. When I want an engine to run a certain way it takes me a week or so of fiddling before I happen on the right combination. Good luck and post back with your results and if you need more help

Hi Ron ,

As you said, I think the best answer will be experiment with it.

I owned several Cox reedie for the past 20 years, but I just flip it and fly , never care about how it perform , till recent years, and Several forums talk about Cox engine's performance and mod, drill out venturi, high comp head, etc.

I will try to add copper shim on my old reedie, you got the point there, it might be over compressed.

Thanks for the tips and will get back in here once I test it again.


Ew