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Old 08-12-2011, 10:41 PM   #10
Rockin Robbins
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Hmmmm. Lack of 3 blade props in Drive Calculator, so first i checked your statement that a two blade 8" is about equivalent to a 3 blade 7". Checked out a 7x4 MAS electric 3 blade against a 8x4 MAS GF and they were very very close. So I began checking out pitch to see what works.

Figuring from that analogy, a 3 blade 7x5.5 with a 3 cell battery with a large C rating should yield 1,508 grams of thrust. That gets the plane off the ground nicely at 9.9A per motor, 107 watts per motor. These guys are only going to be between 65% and 70% efficient there, so cooling might be an issue. Be a bit careful there. Pitch speed is 60 km/h, 37 and a fraction mph. At 10 A per motor your battery can hack it.

If you went to 8" pitch (7x8 3 blade) you'd get 438 g per motor static thrust, 1,752 g total, not too shabby, brings pitch speed up to 54 mph, maybe more appropriate, each motor drawing ehhhhhh....9.8 A. Another doable combination. Different models and manufacturers of the same pitch prop will give somewhat different results but none should be a deal breaker. You have plenty of slop there as you are not near the limits of motor or battery performance.

OH! Flight duration is projected to be about 4 minutes and a bit less than a quarter with a 2200 mAh battery. You might want to think about more capacity.

Where's Denny hawking his Hackers? (that's almost as good as saying the Supertigres can't hack it, isn't it?) This is a golden opportunity to talk about the advantages of getting a more efficient motor. I won't steal his thunder. Listen closely when he speaks.......
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