Thread: Build Log CMP Spitfire 50 - 54"
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Old Jan 09, 2010, 04:06 PM
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TMO
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Stonington, Ct.
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I have an update:

Bob brought it over to the shop today to program up the radio etc. I took another look at the CG issue. The instructions call for 82-86mm (3 3/8") from the leading edge, but measured way out on the wing- approximately the last invasion stripe outboard on the wing. Since it is an elliptical wing, the leading edge has already moved aft significantly at that position.

The long and short of it is, the stock recommendation, if measured from the wing root, is 100mm (4"). In that position (which looks "right" if you know what I mean), we removed ALL the weight (12oz is what it took to get it to balance at 3 3/8" measured at the root!), and now the plane sits perfectly with 14g weight in the tail. The overall weight dropped back down to 6lbs.

I'm much happier now, since I probably have to maiden this thing, and I was looking at that 3 3/8 CG saying to myself- no way! Plus, at 6 lbs, 800 watts will give a respectable 133 watts/lb. I was puckering a bit thinking about launching this thing at 7.5 lbs. Not that it wouldn't fly, but it wouldn't pull itself out of much of a hole either at that weight.

Carrera GTSCS:
There is room to go up in both motor and battery size. I'd say a 41mm motor will fit no problem and that should really be the "stock" electric motor for conversions. I chose this motor(the U3620-6) because I wanted to stay with packs Bob already had- and it's hard to find 41mm motors that are "hot" enough to get this thing's speed up on 4s voltage. As far as battery, we're running the 4s 3600's, but we weren't really constrained by size. Our pack is 133mm (7 1/4") long, 42mm (1 5/8") wide, and 32mm (1 1/4") thick. Alot longer than that, and you'll have trouble getting the hatch closed, but if you went with a different battery box setup, I don't think think there's anything stopping you from going up to 5s, or up to ~5000mah on 4s.

Hope it helps,

Tim
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