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Old Feb 12, 2002, 01:50 PM
Dereck is offline
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Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
12,788 Posts
Hi Dan
You have to look at the entire package, and often past glow experience won't help all that much - they are usually so vastly overpowered, it doesn't matter as much what prop is used.

Basically - fast models will use a direct driven smaller prop, a slower model will prefer a larger, slower revving prop. My two 300W models are opposite ends of that spectrum - one burns the sky up behind a 8.5 x 7 on direct, the other acts like a slow Sumo-parkflier on a 12 x 10 geared 3.7:1. Both use the same battery packs, BTW. The fast one is an Aveox Embat - sleek, thin winged and hand toss launches real easy for a 54oz model. The other is my design, with a fat, stubby wing, UC, open cockpit fuselage and much bulkier all round.

Low thrust at low speed is embarrassing if the model only flies at a very high speed. The FAI class pylon racers are a fine example - they take the first lap of a race to get going enough to unstall their little, high pitch props and start really hauling. Not a fun model to fly for fun, I'd reckon, and an Olympic level javelin thrower may be essential for launching to stand a chance.

If you have wheels on a model, you can stand slower initial acceleration - the ground doesn't mind holding the model up a little longer (unless the runway is short ). If you can't hand toss a model to a speed it can reasonably fly at, misery and rebuilds await you.

Props are interesting devices. My beloved CAP 232 is a converted glow model. As intended, it would normally fly with around a 10 or 11" prop on a two cycle, maybe a 12" on a fourbanger. My usual 14 x 10" (geared MaxCim brushless) barely rates a second glance in an e-power setting, but wet power fliers are amazed at that much prop on the model. I once flew it - very well, too - on a 12 x 11 at an electric site and was ribbed for flying with a tiny little prop! With a 14 x 10, the initial take off roll is slow, but things soon get fun and the wings take over real fat. Good job - hand launching 6.5lb would be overly taxing.

Best tip - rely more on examples seen in reality than in *calc programs!
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