Hi Frank,
Depends if you are running a reed or TD 0.49. For reeds, I find anything less than 15% is a bit rough running and needle valve is tricky. I personally would not go above 25% for a reed engine, but there are people that do try to make the last ounce of power. In my experience, TDs like at least 25% to get them humming. In my part of the world, nitro is a touch expensive so I don't go higher than 25%. I am a fly for pleasure guy, if you are competitive then the more nitro the better!

Regards.

Andrew.

Not that I'm recommending this, just relaying an experience. I'd never even started an .049 until I was given a few of them so I decided to run some just for fun. I tried a Babe Bee, one of those product engines with the two transfer ports and a TD. Fuel was my usual 80/20 all castor because I don't use nitro. Once I found the right needle setting they all started with one flick and hummed along very nicely and were easy to richen up into a 4 stroke although the reedies were slow to react to the needle. The TD though was a delight and I was amazed at the ear piercing shriek. I guess my main reason for running them was because I'd often read that without nitro they'd run too cool which would put out the glow and they'd stop running. This obviously didn't happen and there was no rev drop at all when I disconnected the battery.

I also in agreement that 25% nitro and 20% oil, at least half of which is castor, is about the optimum for Coxes. Yes, they will run on any amount of nitro, even 0%, but their happy place for sport flying is 20-25%. In cold weather, near sea level to 1000', you might use 3 head gaskets with 20-25% nitro, and in hot weather, it probably will run better with 2. If you use the new drop-in plugs with the head clamp like the ones that Cox International(Bernie) and Ex Model Engines(Matt) sell, then you will need one or two, sometimes even 3 more shims, as those are very high compression heads. They are also my favorites. They're almost identical to the Norvel Big Mig head/plug combo. In fact they are interchangeable.

Rusty

I was always happy with about 25% N in my Tee Dees (Missle Mist or Cox red can). When I used Babe Bees (back in Jr. High), we usually ran Blue Blazer, because it was cheapest our local department store carried. I think Blue Blazer was about 5%, but could be wrong.

I know that 65% nitro, 5% propylene oxide and 4% nitro benzine with 20% UCON oil will result in a broken Babe Bee. No, I didn't do it, but gave some leftover speed fuel to my protoge Marc Sexton to use in one of the BMA contests. He in turn gave a tankful to a kid with a CG 1/2A Blazer/Babe Bee. One tank was all it took...clank.  Steve

Hello again,
Just to clarify, you can certainly run both the reedies and TDs on zero nitro. They make less power and they become very fussy on the needle valve. My reference to rough running is not absolutely the truth. IF you get the NV "dead on" they run smoothly. Most times when you are flying , you don't get the NV correct, then they run roughly! In my neck of the woods, using 5% is sufficient to broaden the NV response, so it is much easier to get the setting correct. The reedies don't make much power anyway, even on 25% nitro, so you can ill afford to loose a significant amount of power by using 5%! It is just too windy in the UK and you need all the power you can get to keep the lines tight. I am too old and infirm to run backwards quickly enough!!

Regards,

Andrew.

Just to clarify, you can certainly run both the reedies and TDs on zero nitro. They make less power and they become very fussy on the needle valve. My reference to rough running is not absolutely the truth. IF you get the NV "dead on" they run smoothly.

Just for the hell of it I made a glow plug head for a Cox reedie, with as much compression as I could fit.  I could hear the detonation before I put in any head shims.

The engine runs great on low nitro.  Not loads of power, but it has a nice wide needle setting, and it runs like a charm.

Note that I'm not advocating anything here -- I'm just reporting a factoid from the flying field.