2 hr
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( 2.8 / 24 )I pulled the clamps from the spar and removed it from the table to inspect it. With the exception of one small area (about 1 inch long out near the tip) I had glue squeeze out everywhere, generally forming a 1/8" fillet. It is also fun to start holding ribs up to it to start getting a scope of the wing size. To me, the spar is exceptionally straight - I can't spot much deviation in the bottom at all, even with a laser. It's hard to tell with the glue drips in the way, but the top has perhaps 1/32" - 1/16" sag along the entire length. That may go away as I plane off the glue drips. (Aug 8 note: after cleaning up the glue drips, the top looks as straight as the bottom)
The images below show the spar before a lite pass through the planer to clean off the excess glue.
1 hr
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( 3 / 20 )I glued the top capstrip, upper cap doubler, tip lower capstrip, and the strut attach filler block into the spar. This required a lot of glue and I had to be quick in the August heat so that I had the clamps in place before the glue started setting. I had opted to do this in one session because I didn't care for all the removal and cleanup of the glue fillets where another piece was to be attached. In the future, however, I will be doing the filler block and doubler in their own session apart from the cap. In my haste I forgot to wipe the excess glue from the inside fillets after everything was clamped up. That's a minor cosmetic bother I suppose, but a bother nonetheless.
The image at left shows the strut attach filler block after the weights and clamps were removed, but before the excess glue was cleaned up from the back face of the spar.
2 hr
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( 3 / 20 )I ripped the spar top capstrip. This had an approximately 10 degree angle on the top to match the airfoil profile. I also made the 1 inch top capstrip doubler. and the strut attach filler block. The strut attach filler block was tapered into the spars similar to the manner in which the root filler block was tapered.
Because of the angular sheared Horner tips, the top cap strip ended up being about 15" longer than the 12' board I had purchased. Although the loads in the cap strips at the tips would be minimal, I decided that the right thing to do would be to scarf on the additional 15" of top cap length. As the glue set on the cap extension, I cut the bottom cap for the tip region from 1/2" thick spar material.
3 hr
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( 2.9 / 16 )I ripped out some 1/4" strips from the 3/4" stock to create the spar intercostals. I also made the 1/2" lower spar cap doubler. With 12:1 tapers at the ends, the lower cap doubler was made just long enough to fill the two bays on either side of the strut attach point. By my calculations, this length was sufficient to encompass the moment envelope peak that occured there. The intercostal locations were carefully marked out, then the intercostals and lower cap doubler were glued into place.
2 hr
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( 3 / 20 )I made the root attach filler block from spar stock and glued it in place. It was made just long enough to completely fill the first 9" bay, plus the length needed to form a proper taper into the spar caps. I made the taper as recommended in Roger's addendum to the RW11 plans by setting the diameter of an adjustable bit to the width of the block, then drilling out the center of the block. This produced a nice half-moon shaped bite out of the end of the block, eliminating the abrupt transition that a squared off block possesses.
1 hr
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( 3 / 25 )After replacing the blade and triple checking the bandsaw setup, I ripped the lower capstrip from one of the spruce spar stock boards that I got from Wick's Aircraft. As nerve wracking as it was to rip such an expensive piece of timber (one board cost almost as much as the saw I was using to cut it), the cut went quite well. I cut it just a scant oversize so that a single pass through the planer produced a perfectly dimensioned piece that required no sanding for finish.
I glued this capstrip in place to the shear web using the fence on the big table to keep it straight.
1 hr
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( 2.9 / 41 )I began work on the starboard wing front spar. A number of changes from the plans will take place. The first is that a 1/4" plywood spar web will be used. 1" inch deep caps top and bottom will be further reinforced over the strut attach point through the use of doublers top and bottom. Rib spacing will be modified to include an additional rib - the first two bays will be 9" and the remaining will be 14". Intermediate intercostals will be used in areas of high shear. A builtup Horner wingtip will be used that adds approximately 15" to the spar length.
Why do these things, you ask? Most of the reasoning has to do with the gross weight increase. When asked about the required changes to support a Corvair engine, Roger responded to increase the shear web thickness to 1/4" and change the cap depth to 1". I checked the design calculations for a normal category, 1200 lb gross weight, with 1.5 safety factor and felt that the spar cap doublers were needed to handle the moment due to aileron deflection. This airfoil appears to have a significant pitching moment change as the flaperon is deflected. The upper doubler is even thicker than the lower doubler to account for the additional compression stress due to the lift strut. The additional intercostals control shear web buckling. As time goes on I hope to post all my calculations in support of these changes, many of which are based on EAA spreadsheets.
The Hoerner wingtip simply seemed like the best looking tip for the labor involved. The look of the cub style bows doesn't appeal to me. I don't feel like investing in the fiberglass droop tips either. Although the efficiency improvements from Hoerner tips are debatable, this chosen design should give me an effective 30' wingspan at the very least.
My first task was to rip the 1/4" birch plywood into strips the depth of the spar with the top edge angled about 10 degrees to match the airfoil shape. I then scarfed them together into one 15' long piece. The bottom of the strip was placed against the aluminum angle fence and clamped tightly as the epoxy set, ensuring a straight spar.
2 hr
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( 2.4 / 23 )I built the big table. I chose to make a 16' x 4' table in two sections. It consists of a ladder frame of steel studs with 1/2" MDF faces on each side. I used an additional pair of steel studs to tie the two table sections together. The whole table is torsionally and flexurally very stiff - I estimate that a section warps by less than a 1/16" when picked up by a corner. I used inexpensive steel folding sawhorses and shims to level the table in our garage. Along one edge, I have affixed 1"x1"x1/18" aluminum angle that acts as a straight edge.
Although it probably wasn't needed, I welded the frame together. This did make assembly a little easier, and also allowed me to practice my acetylene welding techniques before moving on to the rudder pedals or landing gear.
4 hr
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( 3 / 10 )Scarfed up another side panel from 1/16 inch birch ply for the starboard root rib.
1/2 hr
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( 3 / 10 )
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