plywood wing skin

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djschwartz

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Joined
Jun 21, 2008
Messages
982
Location
Portland, Oregon
No, the scarf joints can be anywhere. The whole point of a properly done scarf is that it maintains the strength of the material across the joint.

The best grain direction is at 45 degrees to the spar. That will give you the most torsional rigidity. But that is expensive to do. The next best is to have the grain of the outer plies approximately parallel to the spar so the skin will form to the curvature of the leading edge. That is how the skin is done on my Stephens Akro.
 

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Vector

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Joined
Dec 4, 2010
Messages
343
Location
Pacific
dj,
Can you kindly explain to me the function of the white strips you have over your wing surface. I think I know what it is but don't want to assume.

Thanks, Vec
 

djschwartz

Well-Known Member
Joined
Jun 21, 2008
Messages
982
Location
Portland, Oregon
dj,
Can you kindly explain to me the function of the white strips you have over your wing surface. I think I know what it is but don't want to assume.

Thanks, Vec
Vec, they are nailing strips to provide pressure on the joints while the glue cures. They are made of cheap lathing from the hardware store and are nailed through to the underlying structure using fine aircraft nails. I used FPL-16 epoxy adhesive which requires very little clamping pressure, just enough to hold the parts in place.

Dave
 

djschwartz

Well-Known Member
Joined
Jun 21, 2008
Messages
982
Location
Portland, Oregon
How thick is the skin on Stephens Acro...I see it it is 820 lbs empty.
The skin is 3/32", approximately 2.5 mm. And I have my doubts any Akro was ever built that that met the original design weight. The original assumes a 180 HP Lycoming with no electrical system and a fixed pitch prop, and nothing but the very basic flight instruments. Even at that I have my doubts. 850 lbs is typical for a Pitts S1S. My Akro wieghed 1250 Lbs empty when I got it. It was definitely built heavy with a 200 HP AEIO360, full electricals, and a constant speed prop. It also had 600x6 wheels and brakes and a tooled leather interior. But even that doesn't begin to add up to 400 lbs difference, and the structure of the aircraft is per the plans with the exception of the fuselage being widened 2" (5 cm) at the firewall and cockpit. But that's very typical of homebuilt specs, especially for designs from that era. Most of those specs are wildly optimistic and it's very important to look carefully at completed aircraft to get the real picture. Even that requires some care as many builders are reluctant to face the whole truth about where their pride and joy ended up. That doesn't make them bad aircraft or bad builders, it just means one has to be careful in making assumptions about the actual "state of the art" when thinking about the level of improvement that is possible. In todays world some of the kit makers, such as Vans, are pretty accurate in their claims and it shows in the success of their designs, both by the number completed and the number of hours typical owners put on their planes. Others are not so good and the usual result is that fewer of those designs actually get completed and flown, and those that do are flown much less often.
 
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