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Old 02-22-2008, 07:09 PM
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BMatthews
 
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Default RE: Avionnette HM-8 build thread.


ORIGINAL: ProBroJoe

Oh, darn you Bruce - you're not going to make this easy on me, are you? ........
Easy? WHat's that???????

ORIGINAL: ProBroJoe

The G-Mark only spins a 7x4 in the low 13's, and it does have a throttle, ......
-Joe
I had no idea that this was all it would do.

OK, you win. 360 sq's isn't that bad. As long as the engine looks "scale" to the plan then go for it.

The wood usually isn't where the weight comes from. Generally it's the hardware that can add on the avoirdupois quickly. But stick to lighter grades and plan on using something light for covering and go that extra mile to get lighter hardware and it should be practical to hold it to 24 to 28 oz.

If you're going to use functional rigging then a LOT of the need for our classical structural strength ceases to be an issue. Wing spars can then be made quite a bit lighter. Also the center A frame wing mount can be done quite lightly but you still want some good flexibility in there, Not for flight loads but for twisting and "arrival" loads. Carbon tubing would be a very good choice for this. And the wing mount only needs to locate the wings rather than withstand all the bending loads since the flying and landing wires will take care of that.

I still need to dig out that wire. I'll make it a point to look for it tonight and let you know. But even if it turns out that my wire is all twisted and shot Brodak has control line sets. But let me check my parts box first.

I'd also suggest that you alter the airfoil to round that nose a little. Sharp nose shapes like that one are often known for having a harsh and abrupt stall.

I'm not sure what the wood sizes are that they call for. A good indicator that it SHOULD be quite light is the fact that it was intended for .049 and Scale Texaco flying. The rules called for a minimum 8 oz/sq ft loading. I'll bet it can be built pretty close to that and then you just add the Gmark. But pick that wood carefully so it hits the mark. With some superhuman care it may even come out at 10 oz/sq ft.....