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Johns Web Site
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Date: 10-8-2014
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Number of Hours: 24.00
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Manual Reference:
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Brief Description: Strong Enough?
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From the begining the underlying question has been there. Are the wings strong enough?
Ronin (the bastards that screwed me out of 7K) said the wing had serious flaws. Hense why they said they where designing a carbon fiber spar.
Many people (people familiar with areobatic aircraft) said put carbon caps on it. Why, if it's strong enough. I have heard T-Bird put 30 layers uni-fiber on their prebuilt wing. Why, if it's strong enough.
I did my own calculations. Gross wt 2000lb - 135lb wing/2 = 932.5lb per wing
Wing bending moment = 62.269" based for formulas by Jim Marske (Composite Design Manual)
Moment of Inertia I=Mc/s, 9400 psi spruce at 6Gs (no safety factor) = 127.4055
Width of beam b=12xI/h to the 3rd. 12xI/324.9512 = 4.7 in.
This means the spar should be 4.7" wide at 62 1/4" from the root. Mine is 3 1/16"
BUT - I followed the plans.
There are other factors. It is laminated perfect pieces of spruce and it is a carry thru spar. Does that make the difference? I don't know. But what matters is I dont like it. I'm am adding carbon. Its gonna be my ass in it when we find out at 260 mph in a 6G vertical pull.
I am concerned about putting 30 layers of carbon fiber. Not the strength of it, but the application of one person doing the work without air bubbles and keeping the fibers straight.
I'm adding carbon graphite rods. 13 retangular 0.092 x 0.22 on top. and 18 round 0.125 rods on bottom. These alone should cary a gross 2000lb aircraft at 6Gs plus the strength of the spruce spar to start with.
Yes. I'm adding wt, cost, and time. But I now have peace of mind and can move on.
10/15 wetted out channels, brushed all 4 sides of rods, put 1/32 epoxy in bottom of channel, 3 rods per channel, tapped in rods, covered top with 1/32 epoxy
10/16 remaining two channels on top installed
10/17 routed channels on bottom of spar
10/18 4 rods per channel
10/20 all rods on bottom of spar in.
Spar Wt before 102.6 Lbs. With carbon rods added 106.6 Lbs.
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