RCU Forums - Glow engine hesitates when going to full throttle.

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Quote:

Originally Posted by Hydro Junkie (Post 12214912)

Actually, something some do with boat motors to break them in is to run them on the bench without cooling, other than an oversized aircraft prop, and use the needle to actually regulate the engine's temperature. By running the engine rich, you actually cool the engine. .............

Yup, break in instructions for OS Max engines nowadays describe much the same. Except they do most of it in the first tank of fuel. And with the engine installed on the plane. Well, they've recommended it at least a decade actually. A 46AX bought back in 2010 or thereabouts is still running like a clock, a powerful one. They have you run it a minute or so rich, then needle it to full, then rich, then full, etc.

Having the right alloys and modern manufacturing works.

I just love the way we have taken this thread totally in a different direction, using relevant and go to know information to do it. Do you guys think we have helped Doug out with all this minutia about fuels, nitro and all the rest?

Quote:

Originally Posted by HighPlains (Post 12214933)

Nitromethane is an interesting energy source, but there is a lot of nuance in what it does and why.

It can cool the inside of the engine - somewhat true, since it takes roughly twice as much heat energy to vaporize nitro than methanol. On the other hand it in high percentages can send the piston right out the exhaust in just a few seconds after an engine goes lean. This then requires a new piston, sleeve and head.

Low BTU output - true compared to methanol.

Makes it's own oxygen - somewhat, as it does have oxygen in the molecule. But it still needs oxygen from the air to burn. The big difference is the air/fuel ratio. Methanol needs about 5 to 6 lbs of air for each lb of fuel to completely burn, while nitromethane only need 1.7 lbs of air for each lb. This is known as the stoichiometric ratio, which is about 14.7 for gasoline.

So why does it make so much power? It is mostly due to the amount of mass of heated gases you get on top of the piston that does the work. Since you can run about three times as much fuel through an engine (comparing 65% to 15% nitro fuel), the power goes up considerably. My racing .40's used about 3 oz of fuel a minute on 65%. They also used up a glow plug each flight. And you had to adjust the load and the head clearance based on the density altitude, temperature, and humidity. High pressure days at low altitudes at about 70 degrees and 30% humidity engines ran really strong.

It's interesting to read your comment about having to adjust head clearances as that was how my head and piston got beat up was lack of clearance. I've had to add several shims to get the clearance high enough to prevent detonation and preserve the parts in my engines. That's one of those little details that most take for granted when they buy an engine, that it will run right out of the box without having to look at anything other than setting the needle and filling the tank