Fuel Choices for my Pantera

[Flyer2004]

Since getting back into nitro helis I've been running Power Master 30% nitro in my OS Hyper. Was looking for more economy so I'm considering cool power 15% nitro. Not doing 3d just enjoying sport flying. So the PM has 23% oil the Cool Power has 17% oil, and OS recommends 18% oil. So my question is should I even consider Cool Power? Also why do most heli fuels use synthetic oil, vs synthetic/castor blend?

[helihammer]

I'm not sure why they use what they do (synthetic vs. real castor), but I personally don't care for CoolPower. I used it with an old Shuttle and it left deposits inside the engine. I have, however, used Byron's Rotor Rage 22.5% with good results. It's a bit cheaper than 30% and the engine was always very clean. I was sure to keep it well oiled with Marvel Mystery Oil, however (gotta love that air filter snorkel!).

[tealc]

I agree with KB3TO on the Cool Power and deposits. I discover that same thing. I personally only used 30% when I had my OS 50 but with the YS I can go down to 15%. I have recently been using Cool Power because it is what is found locally. I am looking to see how I can get Byron's again. It is what I have used in the past but my LHS stopped carrying it. Last time I looked (Feb 2016), it was going to cost $50 to ship a case to my house and that is a hard pill to swallow.

[jbeech]

I've synthesized what follows from the FAQ section for an engine-DVD we offer . . .

I like fuel with a bit of castor for the added protection during a lean run, e.g. if I make a mistake on the needle valve setting. However, I'm a pretty experienced modeler and this really no longer happens to me. However, experience doesn't protect me from mechanical failure when the little bit of castor oil is like an insurance policy.

Examples of mechanical failure are a pin-hole leak in the line, or a tiny leak at the fuel filter body, or when a line begins splitting where it attaches to the carburetor nipple. Any of these may allow air into the fuel line. In turn this results in a leaner fuel mixture than you set with the needle valve. And if it's lean enough that it the oil cooks off instead of lubricating, it'll kill an engine.

The reason is the castor oil has a higher flash point than the synthetic oil but more importantly, and as it begins burning (and any oil will burn once it gets hot enough) it forms longer chain molecules (the reason it stains mufflers with brown spots and splotches) that make it thicker and thicker just before it flashes off. However, like the synthetic, it too will cook off. Hopefully, however, in becoming thicker it may present enough drag on internal components to slow the engine to a halt before it's damaged. This, plus the film it makes often protects an engine. Pain in the hind end to subsequently disassemble and clean up but better than slagging an engine in my opinion.

Thus, at it's most basic, castor oil can protect an engine better than synthetic. However, as others have mentioned, the downside is it forms a stain on metal surfaces over time, which can be tough to remove. This is especially troublesome at the start of the next flying season when you, for example, discover the carburetor's throttle valve won't turn in the carb-body because it's gummed up by the residual castor oil. However, a lot of modelers don't like the staining and gumming and manufacturer's responded by offering a full synthetic. As long as the engine never runs so lean the oil in the fuel begins flashing off (burning) there's no downside to a full-synthetic and the upside is the engine stays spotless inside and out.

Regarding oil content. As a practical matter, 17% vs. 18% oil content doesn't mean squat in the real world. Remember, the oil in the fuel doesn't burn, or isn't supposed to. However, it will during a lean run when it's no longer lubricating but instead is burning up - just like the alcohol in the fuel. This is bad, very bad because then it's not doing its job. However, lower oil content won't hurt a thing - except - if you run the engine too lean when you face a greater likelihood of ruining the engine. Lower oil content is 17% vs. 23% . . . not 17% vs. 18% which is really a rather inconsequential difference in the real world.

As for why some fuel has 23% versus 17%, in some cases it's the manufacturer's choice of oil, e.g. Cool Power first popularized the high oil content fuel. In their case, they were using a thinner oil and made up for the difference in lubrication capability by using more of it. They made up for the power loss by adding more nitro. Power loss? Yes because what burns to make power is the alcohol, not the oil. Remember, the oil is part of a total loss oil system. It just flows through the engine while lubricating and cooling but doesn't burn. Anyway, this is where using 30% nitro first became popular.

Basically, you reduce the alcohol (what burns to make power) by adding oil (to lubricate and cool) and you have to recover the power somehow. The 'somehow' is the added nitro, which bonds with oxygen molecules in the air and this is what allows more fuel to burn within the combustion chamber. After all, alcohol won't burn without oxygen, remember? Added nitro results in more oxygen and this allows a richer mixture to make more power to compensate for the added oil as a percentage and thus, make more power. Think of the nitro as chemical supercharging, which lets you run the engine richer yet still burn the alcohol completely.

Meanwhile, as a practical matter, I have run engines with as little as 12% oil content. However, while this gives you almost no margin for error, the engine will run happily enough 'and' make great power. Why? It's because there's more alcohol burning within the combustion chamber (instead of oil flowing through for cooling purposes). But no margin whatsoever for a mistake in fuel mixture. Understand?

Finally, I have flown many, many flights with 5% nitro fuel. Why? it's because I don't give a darn about 3D-flight which needs as much horsepower as you can throw at the rotor blades. Basically, I never need the ultimate in power making ability from my engine because my flying style is big air maneuvers with lots of slow hovering maneuvers thrown in to replicate scale like flight.

That, plus I'm an old hot rodder and thus, I simply opt for a much bigger engine in my model when I want more horsepower. Why? It's because I prefer a big engine loafing instead of a small one screaming its guts out.

In closing, I would say I've written the book on model engine operation but I haven't. Instead, I made the definitive video on the subject. Hubris on my part? Perhaps, but I doubt there's a better one available in the whole world. Want a copy for your library? That's easy . . .

aboutENGINES - http://www.audacitymodels.com/Produc...3/Default.aspx

Finally, in terms of fuel, I like a bit of castor oil in it for the insurance value. This, despite the fact it will stain my engine and gum it up over time. Moreover I especially LOVE how it smells when I catch a whiff of exhaust because it shouts model airplane fuel and this is part of the experience.