I have been running my O.S. 46 engine on omega 15% fuel. Well, i am about to run out of fuel, and i was wondering if i would be ok switching to 10% fuel. Is one beter than the other for this engine, or should i stick with 15% since that is what i have been running w/ it. !?!? tHaNks 0.o

I ran 10% when I first got mine and it worked fine. I did notice,however, that in colder weather, it did not run as well. I am running 15% in all of my engines at the present time. I have 2 OS46fx's, Saito 72, OS91Surpass, and an OS61FX.

Thanks! Its getting colder now so i believe i'll stick w/ the 15%.

In Geaorgia the 10% should be fine. I run 10% in all my engines, and don't see starting issues until it gets down to about 35 degrees. Then all it takes is a few clicks richer.
Dennis-

What is the theoretical argument for running more nitro in colder weather? When the air is cold it is both denser and dryer than in hot weather and therefore your engine sucks in more oxygen with each revolution. Thus you need to go a click or two richer so that the alcoholxygen ratio remains as you like it. So I would expect the usual fuel to run better in cold weather than in hot weather.

Jim

More nitro does make an engine run easier in cold weather, and in many engines it will improve idle and trasition. I belive the nitro makes the fuel burn just a little hotter, but I'm not sure.

The theory about cold, dry air having more oxygen makes sense, but the real world experience of many many years of many many guys doing some very cold weather flying has shown that adding nitro helps.

GA just doesn't get cold enough to make a difference, you can use 10% if you want, no problems. It's only when you start to try flying in the snow that it matters more.

10% is all you will need. Get some and just retweak your needles. The extra savings in fuel will allow you to buy more fuel and fly more. In GA there isn't that much elevation that would require more nitro. I only ever used 10% in the mountains of Central PA and never had problems.

Mark Shuman

t1nk,

I used to run 10% in the summer and 15% in the winter and found that my engines ran better with the 15% when it's cold. I now run 15% all the time because my club offers both the 10% and 15% at the same price. It's price is subsidized with club dues. $10/gal for either one.
(Omega)

Either way works well. It is well known that more nitro content increases engine heat, hence when it's cold, the engine is still running warmer than with a lower nitro content.

Something to consider....

The smaller the displacement the higher nitro content typically. I like 15% in everything up to about a .90. My persoanl opinion. I have found that where I lived and flew all the time, Western Washington (cool and humid) the 15% worked best.

The higher nitro content means higher head temps. After many hours of run time with a given nitro, 15% for example, when you start noticing reduced performance then you go to a lower nitro. What this does is reduce the head temp, meaning that the expansion of parts are less, meaning that you have a gain in compression. This is all taken consideration you are flying an ABC,ABN type, 2 stroke, engine.

These thoughts are for general sport type engines. If you look at the pylon racers, 3d, and heli guys, you will see that they are flying high nitro content. Usually 20% and up.