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Old Jan 07, 2016, 03:41 AM
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An amp meter would be the best way to tell. The general rule is " add a blade and reduce the diameter by 1"." so theoretically the 7x4.5x3 should work. 6x4.5x3 would still fly it great and be a safe bet if you do not have a amp meter.
Mike
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Old Jan 07, 2016, 12:34 PM
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Thanks for the reply Mike,

After several hours digging through different threads about prop selection, and a whole lot of technical data, a few points stand out:

While a common misconception about the number of blades selected for most warbirds is ground clearance, increasing blade count to compensate for the smaller diameter needed, the true reason, in most cases, was tip speed. The engines were so powerful that the prop tips would break the sound barrier, causing many problems, sometimes fatal failures. (Not to mention the constant sonic boom!)
By adding blades, more power is absorbed, giving the equivalent thrust, or sometimes better, with less rpms.

I was reading some threads also where bench tests would give sometimes twice the thrust even when using more blades, and while true, this doesn't mean better efficiency or speed, but is more like a low gear in a car, great torque, but lower speed, more fuel burned, equals less airtime.

What did I take from all of this? In this particular case, the only reason to use the 3 blade here, would be looks. While also being a bit quieter and smoother, I could lose pitch speed, resulting in a slower top speed, but higher torque at lower rpms. The latter helps in shorter take off rolls, and also seems to make it a more suitable prop for 3D. (Anyone tried a 7x4.5x3 on a FF Edge 540T or Yak?)

The main thing I got out of all this, is that I should just go out and try the different props, and see what I like best!

So, I've got a 7x6x2, a 7x4.5x3, and a 6x4.5x3 to try, the latter being red, would be the best looking.
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Old Jan 11, 2016, 01:22 AM
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Managed a short hop on Saturday before this oddly Fall-ish weather hit in the afternoon.

CG was right on the KF step, seemed a bit tail heavy still, so I kept going forward, until it was just slightly nose down balancing on the mark, still squirrelly in the air, and quite beaten about by the motor torque, tons of pull.

She likes to rock back and forth quite alot in the roll axis, needing at times, quite extreme rudder corrections to get level...

Still seems I need to trim better, I never really learned how to fly 3 channel either, this is new...
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