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Old Feb 14, 2013, 10:59 AM
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Jim in the Desert
United States, NM, Las Cruces
Joined Aug 2007
1,263 Posts
Quote:
Originally Posted by jjkupinski View Post
I just love reading some of these discussions: castor vs. synthetic, 2 stroke vs. 4 stroke, gasoline vs. methanol. In this particular discussion, in any engine size, gas is more economical to operate for the same sized engine. In terms of power, methanol provides more power in the same sized engine. If you adjust engines sizes in order to match power, gasoline (larger but initially more expensive) is still cheaper than methanol to operate. Take your pick; simplicity with a glow plug and more operating cost; or gasoline with an ignition system and more initial and less operating cost.

Why? Basically, our engines are air pumps. Given two engines of the same size and style: they will both pump (intake) the same amount of air. The difference between them in this example is the amount of fuel needed to burn efficiency and the amount of power in the fuel. Gasoline has 125,000 Btu/gl energy, methanol has 64,600: a 93% advantage. But then factor in air/fuel combustion ratios of 14.7:1 for gasoline; 6.47:1 for methanol: methanol now gains a 17% advantage. Adjust downward for oil content: 5% for gasoline, 17% for methanol. Methanol still has a 3% advantage. Add nitromethane to the mix: all bets are off as to power advantage, but then at the expense of cost.

Jetmech05: FYI, I have a 11# Katana, 71" wingspan, rated for up to a 1.6 ci engine. It has a Super Tigre 2500 (1.5 ci), 16x8 prop, 5% fuel, and it will do what you say it can't do. I have an IMAC pilot who maidened it to verify it.
This confuses me, because I am not experienced.

Is methanol = nitro?


" Gasoline has 125,000 Btu/gl energy, methanol has 64,600: "

" But then factor in air/fuel combustion ratios of 14.7:1 for gasoline; 6.47:1 for methanol: methanol now gains a 17% advantage. "

Can you define what "advantage" means in this sentence? More power for same sized engines? I think what you are trying to say may be obvious to some but it's not clear to me. Because same sized gas / nitro engines are passing through the same amount of air/fuel, and there is 3 times as much nitro as gas passing through (air fuel ratios), and that nitro has half the power of gas inherently, the power of the air/fuel is 1.5 times greater for the nitro engine?

I don't see how you get the 17% or the 3%. Sorry for the elementary questions.

I don't think I recall seeing anybody say a gas motor has more power than a nitro motor. I think the advantages have more to do with fuel economy and flight time, since the motor will use less fuel to fly. At least that's what I have gleaned so far.

Also, there is the issue of engine weight. If you go up in size to equal the power of a glow (methanol?), now you have a heavier engine and all the issues that causes, plus the extra battery possibly.

Thanks for any clarification.
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