After talking with Smizo today I thought I'd pass this along for the wing builders here.
The neat thing with Acro Sport is that the hole that pins all the spars together is in the same relative location on all 6 spars that make up the top wing. All you have to do is lock in that location and then drill the remainder of the holes. The wing attach plates are used for the location device for the holes that go through the spar.
The first step would be to true the center section spars to exactly the same length. Then cut the plywood plates and install them with 1/2' long aircraft nails. About 4 along the top and bottom is sufficient. Sand them so they are a good fit to the spars.
You will need a fixture like the one in the drawing. This block can be made from steel or a really good hardwood as long as you can create a sharp corner and accurately locate a hole that has a good fit for a 3/8" dowel pin. This one fixture will locate the wing attach hole for all 6 spars by pushing the dowel through to accommodate either left or right. With the plates located it is easy to pick up the holes in the attach plates with a brad point bit.
The whole point of using this fixture is to assure that every spar will match when the wing is assembled. Even if there is a small error in the fixture, that error will repeat on every spar and alignment will be maintained.
All of the holes in the spar should be drilled with a drill press. (Not including the aileron hinge or bell crank holes)The reason for nailing the spar plates on is so they can be removed after the drilling is complete. That will allow you to install all the ribs and then you can glue the plates in place. The plywood plates can be glued on at the "I" strut locations before the wing is assembled and all those holes drilled in the drill press before wing assembly. For these holes I have found Forstner bits or brad point bits to work well. Clamping the spar to an angle plate on the drill press table with a support under the end of the spar assures a good vertical hole for the "I" strut bolt.
This "I" strut location was built up before the wings were assembled. The photo is a trial fitting and the ribs were removed and the holes drilled
The neat thing with Acro Sport is that the hole that pins all the spars together is in the same relative location on all 6 spars that make up the top wing. All you have to do is lock in that location and then drill the remainder of the holes. The wing attach plates are used for the location device for the holes that go through the spar.
The first step would be to true the center section spars to exactly the same length. Then cut the plywood plates and install them with 1/2' long aircraft nails. About 4 along the top and bottom is sufficient. Sand them so they are a good fit to the spars.
You will need a fixture like the one in the drawing. This block can be made from steel or a really good hardwood as long as you can create a sharp corner and accurately locate a hole that has a good fit for a 3/8" dowel pin. This one fixture will locate the wing attach hole for all 6 spars by pushing the dowel through to accommodate either left or right. With the plates located it is easy to pick up the holes in the attach plates with a brad point bit.
The whole point of using this fixture is to assure that every spar will match when the wing is assembled. Even if there is a small error in the fixture, that error will repeat on every spar and alignment will be maintained.
All of the holes in the spar should be drilled with a drill press. (Not including the aileron hinge or bell crank holes)The reason for nailing the spar plates on is so they can be removed after the drilling is complete. That will allow you to install all the ribs and then you can glue the plates in place. The plywood plates can be glued on at the "I" strut locations before the wing is assembled and all those holes drilled in the drill press before wing assembly. For these holes I have found Forstner bits or brad point bits to work well. Clamping the spar to an angle plate on the drill press table with a support under the end of the spar assures a good vertical hole for the "I" strut bolt.
This "I" strut location was built up before the wings were assembled. The photo is a trial fitting and the ribs were removed and the holes drilled
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