Did my searches and been reading everything I can find, still confused. Looking at the Eflite power series, they say the power25 with 4s 4000mah is the same as a 25 glow for RC but we use it in place of a 40? then someone else tells me the power15 with 3s 3300mah is big enough. There's another motor called a 35 because it's 35mm dia. Reading the "List your set up" thread, there must be many ways to do the same thing and the advise I'm getting is all over the map. How do you pick a motor and battery for your plane? Copy someone else, blindly stick with one mentor or is there a way to calculate the optimum system? I'm looking at planes with 550-600 Sq.In. that would use a B40 or LA46.
The motor is rated at 58 amps burst current. With a 4-cell pack (14.8V), that works out to 755 watts peak.
Figure on 11 watts/ounce for peak power, and that leaves you with a maximum plane weight of 68 ounces (!).
The batteries will deliver 59 watt-hours of energy from full charge to fully depleted. You want to use just 70% to 80% of that. Say 45 watt-hours. You're going to fly for six minutes (at least, that seems to be what people set up to do). 45 watt-hours for 1/10 of an hour leaves you at 450 watts average.
Figure on 7 watts/ounce for average power, and the battery pack should be good for a 64 ounce airplane.
Unless you build as heavily as I do, you're slightly, but not terribly, over-batteried and over-motored for your size range of plane. I'd stick with that motor, build a plane with extra space in the battery compartment to allow for playing with different batteries, and run with it. And I don't just mean I'm suggesting it -- I mean, if I had that combination of stuff, I'd probably build a 600 square inch plane to go with it (well, 599, to be sure to fit into Bob Hunt's new class).
The 11W/oz and 7W/oz figures came from a study I did a year or two ago on the airplanes in the "list your setup" thread; they showed a strong trend, and that was it.
I'm not so sure about props, but I suspect that you'll be happier with a 12 inch prop than 11 -- but you'll want to fiddle around with different combinations to see what makes sense for you.
The rating system that eFlight uses is, I am convinced, designed so that no matter how absurdly high-performance a 25 you have, their eFlight 25 will match it. Stunt engines get run well below their power potential, and aren't 35000 RPM racing screamers to start with. Which is why the number on the motor tells you how to order another one just like it, or one that's one step bigger or smaller, but not a whole lot about exactly what glow engine to replace with it.
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