matador_24

Hello guys, I am building a twin plane (c160), I got a couple of new OS 25FX. I was told to break them in with 15% nitro but after that, to go below.

What should I use to fly 5% or 10%? The guy at the LHS adviced me 10% but he did not seem sure......

thanks!

P.S. What happens if I attempt to fly it with 15%?

JohnBuckner

My Feedback: (1)

Hi Matador, You could not have picked a better engine for multi's than the 25FX. I use thirteen of them and need more, all but one are on Multi's. My normal fuel is 15% nitro and never use anything less but do on occassion use 25% when I want to turn some heads or fly in Flagstaff not far from here and 7000 msl.

10% will work fine also but don,t think I would care to use 5% which may affect starting and throttling negatively.

John

Lifer

My Feedback: (1)

Have 2 25FX engines. The only fuel I use is 5% Rich's Brew with 18% synthetic. The engines run fine. Nitro adds oxygen molecules and that is why it adds power. Try a tuned pipe instead. You only pay for it once. My 25's turn a 9x4 APC in the mid-fifteens and glow plugs last for years. Good luck.

JohnBuckner

My Feedback: (1)

Or both.

matador_24

wow, very nice!!!!
I think I'll keep the stock muffler, It is a scale, so, it does not matter if it is not a speed machine,
I'll be using 10% then but if there is more people who can recommend 15% would be nice, that way I do not have to have al time 2 different gallons of nitro! (I always use 15% with my OS46 plane)

Wayne22

My Feedback: (2)

Honestly, you wont see any difference until you get up to 15%...it idles better and a bit more top end. It is a good idea to stick to one % of nitro for the life of the engine. They operate in different heat ranges. changing mid stream can alter the internal tolerances and wear patterns due to the expansion properties of the different metals used in the engine...

victorzamora

Stick to 15%. Engines just seem to be happier running on 15%.

matador_24

I heard somebody said once: 'small engines such as the 20 or 25 should use always 10% or below, the are too small engines and can be damaged using 15%"

That is why I was worried about, my engines are new, I would not like to burn them out!

JohnBuckner

My Feedback: (1)

More incorrect heresay and actually quite the opposite, most half A engines will not function on less than 25%. That is simply someones speculation with no experiance.

Do not confuse your OS 25FX with certain russian and primarily eastern Europeon engines that are intended to run on zero nitro and have much higher compression ratios.

Your engine (OS 25FX) will be perfectly happy using anything from 10 to 25% period. There is no problem in using a different percentages at different time either. As alway its just a matter of proper needle setting which can be screwed up just as fast with 10% as with 25%.

Use what works for you. Agine you have an ideal new engines for your application Do not be afraid to let them shine and do the job for you. Agine your engines will be fine on anything from 10 to 25. Just a hundred miles to east of us their field is 7000 feet which easily reachs a density altitude of 8500 feet in the summer time and all the two stroke flyers always use a minimum of 25% and the fourstroke flyer use 35%. When a flatlander shows up with 15% eve3ryone lands and huddles up to watch the takeoff attempt.

Nitro is a tool to be used appropriately and not just for speed.

John

Sarah

Hi Matador,

Whereas in the USA higher percentages of Nitro are used, in England the tendency is to use lower nitro fuels.

I've run the OS25FX's on 5% and they have run very well indeed. I do use 5% nitro fuel in all my two strike engines up to an OS120AX and soon an OS160FX. By using 5% nitro it allows a less critical mixture setting than with no nitro at all. However after more research I am going to move over to 10%, as this should allow a little more latitude on mixture setting without significantly increasing the cost of each gallon of fuel. Fuel, as with most things, is more expensive in England! (10% Nitro will cost an extra $4.5 dollars more than 5% nitro)

Another of the important things to consider with your fuel is the oil content, at least 18% for the OS engines.

matador_24

Thanks a lot guys for your answers, 15% will be then!!!!
I already have enough with buying 15% planes and 15% helis fuel, I would not like to have to buy in addition 10% nitro, and therefore carrying 3 gallons of fuel to the field!

Thanks!