Month: September 2014

Rear Spars

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Started building the rear spars for the main wing. Since two spats are needed I plan to build them one on top of the other just like the fuselage sides. The only difference between the right and left spars is what side is sheeted with plywood.

I started by cutting the root end of the RS-9 spar caps to three degrees then gluing the doublers.

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Root end of spar cap cut to 3 degrees
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RS-7 rear spar doubler

Once the glue was dry I assembled the frame of the spar using RS-5 and RS-9 verticals as shown on the plan.

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Root of rear spar

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Then I cut the RS-11 diagonal to 30 degrees and glued it in place.

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Strut attachment point on rear spar

Once this is dry I plan to build another one directly on top of this one so they both ends up identical.

Even at twelve feet long this spar was pretty simple to build.

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Rib trailing edge

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The taking edge of the ribs need trimmed to match the RS-15 taking edge piece. They also need to be trimmed to the same length.

The RS-15 is an odd shaped piece, using a piece of RS-15 scrap I measured the angle that the ribs need set to, a whole 2 degrees. Setup my guide on the sander to this angle.

Next I cut an RS-1 to act as a stop so I can easily sand all ribs to the same depth. I clamped a piece of plywood to the front of the rib, note that it is necessary to tell trim the horizontal RS-1 flush with the vertically RS-1 on the front of the ribs first.

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Now I clamped the RS-1 stop piece to the rib placing it flush with the plywood piece.

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Then I held the bottom of the rib flush with the guide and sanded until the RS-1 stop stick hit the guide.

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They may not all be exactly perfect but they are close enough for as fast as this bird will fly.

Wing End Caps

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Making the wing end caps was fairly simple, ensuring they are aligned with the aileron properly was not so simple.

Used the aileron cap to drill the location of the center pivot.

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Then used the first wing cap as a template to make three more.

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There is a 1/8″ gap between the wing and aileron, this is perfect since my circle cutter has a 1/8″ bit. However the aileron is sheeted with 0.060″ plywood so it is necessary to increase the circle cutter radius by that amount.

To align the aileron and wing sheeting I need to keep track of where the center is. Since the center is being cut off of the wing plywood this is a little difficult.

Cut a little of the radius.

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Then stapled a plywood sheet over the cut, then cut part of the radius on the other side.

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Added another plywood strip and finished cutting the radius.

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Here you can see how the aileron moves.

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Now it’s time to build a rib and glue these plywood pieces on.

Aileron End Caps

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The root and tip ribs are covered with plywood, making the plywood pieces for the aileron section was fairly simple.

I used a rib as a template to mark the outer edges of the aileron section onto the RS-535. With a little measurement I marked the center pivot hole. Used my circle cutter, setup to same dimension as the aileron nose ribs, to cut the radius on the front.

Once one was completed I used it as a template to make the other three. The center hole needs to be accurate, I used the first one as a drill guide to make sure all were identical.

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Making aileron end cap for mini-max

All four turned out great.

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Aileron nose ribs

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There are a total of thirty aileron nose ribs, twelve are 1/4″ thick and the remaining only 1/8″.  All of these need to have the same radius so the sheeting that covers them will have proper support.

I setup my dremel with the circle cutter to cut 1 3/4″ radius circles. Drilled a 1/8″ hole in the RS-672 for the pivot and cut out a half circle.

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These ribs a glued onto the 1/8″ sheeting on the aileron spar so this thickness must be subtracted from the nose ribs. To accomplish this I drilled out the pivot hole to 1/4″.

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Next I drew a straight line that intersects the edge of the hole.

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I then sawed off the excess wood and sanded the edge flat right too the point that none of the 1/4″ hole remained. Here you can see where I was almost completed.

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The angle of this straight edge is not important, what is important is that its straight and you stop sanding at the edge of the 1/4″ hole. I kept sanding little by little until the hole dissapeared.

All of the 1/4″ nose ribs, except for two, need. Cut to fit inside the ribs. To accurately mark these cut lines I stapled a 1/8″ scrap plywood piece to a rib.

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Then placed the nose rib against this plywood, centered the nose rib and drew the lines at the edge of the RS-1.

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Mini-max aileron nose rib fitting

Hinged Ribs

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Three ribs on each wing are reinforced for the aileron hinges. Two areas of the rib are filled with 1/4″ plywood RS-672. I removed the cams on the jig in those areas so I could assemble the ribs with plywood.

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Wing rib with hinge reinforcements

I cut six of each plywood piece.

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Rib plywood reinforcement
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Rib plywood reinforcement

Rib number five on each wing needs these plywood pieces and gussets added to both sides like the other ribs. I built both of those and now only have four ribs remaining.

The last four ribs are the root and tip ribs, each one is unique and requires some additional components.