Chapter 19 - Section 12

Attachment, Wing to Center Section Spar

I purchased my wings from Dennis Oelmann and they arrived in January 2007 while I was still building the center section spar. The timing was good because I was able to verify the exact thickness of the wing root such that my spar mating surface is just a hair narrower. As a result, my center section spar mating dimension is about .2" narrower than the wing root mating surface - giving me about .1" both on top and bottom.

Recognizing the importance of attaching the wings to the spar correctly, I read the plans, sifted through all available web sites and talked to several experienced builders, so that I understood where the critical criteria are throughout the alignment process. I picked up many good ideas from previous builders which I followed. Here's how I approached my alignment and attachment process...

Pilot Holes and Access Holes in the Center Section Spar

I placed the center section spar on the work bench (forward face down) and propped up one end with a large foam block so that the surface being drilled is parallel (flat) to the work bench. That way, I have a much better chance of drilling straight to the surface.

Next, I drew the markings on the spar per plan and I was pleasantly surprised that the pilot hole locations were right on the center line of my hard points. I started with a short 1/8" drill bit on all pilot holes to minimize any drill bit wobbling effect. Once completed, I opened up the holes to 1/4". I did not lay out the same dimension on the front face of the center section spar per plan. Instead, I continued with a 10" long 1/4" drill through the spar, using triangles as a guide and holding the drill as steady as I could. The pilot holes did not turn out perfect, but pretty close to dead center.

Initial Placement of Center Section Spar

Before matching up the center section spar and the wings, I used my cross laser and marked (on the floor) the critical locations of the spar and wings for future reference (Note the masking tape on the floor). For example, I drew a horizontal line for the forward face and a perpendicular line at the center for the spar. Then I drew perpendicular lines at BL 31, 66.3, 130.1 and 169 for the wing placements. These dimensions assure both wings are the same distance from the center line of the center section spar.

I placed the center section spar on a couple wood blocks along the aforementioned lines. I dropped a plumb line from the center of the spar to the pre-marked center line. I also hot glued a bubble level onto the aft face of the spar for a quick vertical reference. With a long digital level, I shimmed the spar level to 0 degrees.

Building the Water Level System

Many builders had good success with the water leveling method (note Clark Canedy and Wayne Hicks web sites) and I decided to follow. I toyed with using laser beams and found they were less accurate (if you use lumber yard, grade lasers). In addition, they are less effective because you can't quite measure water lines both front and back of the wings at the same time. I went to Home Depot and purchased five 1/2" PVC pipes, elbows, 1/2" clear OD tubing, 1/2" barb adapters (by Toro) and pipe clamps. As shown (left), I hot glued a wood strip to the PVC elbow to support the clear tubing (later). The barb adapter is for attaching the clear plastic tubing onto.

My water level system consists of 10 vertical tubings for measuring various wing and spar heights (i.e. 1 to 5 left & right) relative to WL17.4. In addition, I used digital levels for spar and wing levels (DL1 to DL4). Specific measurement locations are shown in above picture. When I was building the spar, I marked WL17.4 along its aft face, thus 1L and 1R (above) will be my datum point for setting WL17.4 for the entire Spar & Wing alignment purpose. DL3 & 4, S & W (i.e. Digital level position 3 & 4 at Spar & Wing) were added to measure the alignment between the matching surfaces of the spar and wing root. You can find most of the alignment criteria in Chapter 19 page 10.

Here's a picture of my water level system. Note the clear tubing being held upright with tie wrap. The entire system is connected as one.

The center funnel and drain station is for filling the water to the exact WL17.4 as needed.

Wing Supporting Fixtures

Again, this was suggested by both Wayne and Clark. To support the wings during the alignment process, I used the bottom halves of Jig#1 and #4 (both left and right wings). However, I have to modify them a bit so that I can raise and lower them by turning a bolt. As shown, I added a small base board to the jig ends by 2 small L-brackets (one on each side). Then I anchored a 12" x 1/2" bolt through the base board. At the plan jig locations, I hot glued them directly onto the bottom of the wings. Later on, I hot glued a couple cross member (boards) at the middle of the jigs to keep them from wobbling. They worked well.

[Hindsight] I ended up using a wedged block of foam at the outboard end of the wing. They both worked, but the foam seems to provide a better 3-point support for alignment.

Establishing the Water Line at Wing Leading Edge

According to the plan (Ch19 p.10), WL17.4 of the wing is tangent to the Leading Edge (LE). After I have the wings leveled (i.e. DL2L and DL2R at 0.0^o), I took a square and ran it along the LE of the wings, marking its tangent points. I connected up the dots - thus established my WL17.4 at the LE of the wings.

Let the Leveling Begin...

I first filled the water level to my pre-determined WL17.4 per the center section spar (1L & 1R). I shimmed the center section spar to make sure its 17.4 Water Line matched the newly filled water levels. I also placed a 4' digital level on top of the center section spar and it was at 0.0^o - Digital Level 1 position (DL1). Turning the digital level perpendicularly against the aft face of the spar and determined that it is at 89.9^o- not bad...

With Susann's help, we placed the wings at their appropriate positions (per the laser lines we drew earlier). After many hours of adjusting the bolts up and down, up and down again, then up and down some more... we finally got the wings to seat at plan levels as follows:

	Left	Right	Plan	Comments
1	17.40	17.40	17.40	Datum point on spar, spar leveled
2	17.40	17.40	17.40	LE Ch19 p.10
3	17.40	17.40	17.40	LE Ch19 p.10
4	17.25	17.40	17.50	TE Ch19 p.10 at BL31
5	18.30	18.35	18.35	TE Ch19 p.10 at BL169

Results looks great, only slight variation from plan at position 4 and 5. The problem, however, was the 'fit' relationship between the spar surface and the wing root surface.

Outboard (L)	Inboard (L)	Spar (center)	Inboard (R)	Outboard (R)
+.04"	+.2"		+.56"	+.0"

+ means wing root surface above spar surface at mating point

- means wing root surface below spar surface at mating point

Note the inboard wing root surface sticks up above the spar by ~.56" - way too much to fill up later on. That means I have to raise the wing tip (on the right) which in turn, lowers the inboard wing root. Placing a digital level at DL4S and DL4W respectively, I raised the right wing tip slowly, until they read the same (.6^o). Then I measured the height of the LE to the WL17.4 and it measured at WL18.6 (1.2" above plan waterline!!!). I was glad to learn from the plans, the Cozy web sites (including Nat's comments) and several experienced builders that - dihedral is not a real critical factor as far as flying characteristics (for the Cozy) is concerned. Its mostly aesthetic - what a relief...

[Side note] The most difficult part with my alignment task was keeping the wing tips 3L & 3R at WL17.4 while maintaining a good match between the mating surfaces (DL3 & DL4). When I built the spar in Chapter 14, l kept the thickness of the spar very close to the thickness of the wing root (i.e. 0.1" above and 0.1" below). In a sense, it gives me very little maneuvering room to keep the spar within the thickness of the wing root matching surface. With the variances of spar and wings, it became clear to me that I have to make a few compromises.

I was glad that I had adequate water level measuring points that allowed me to gather many wing/spar positions such that I can determine the best compromise... and I made many, many, many sets (in excess of 10) of measurements...

After wrestling with all the pros and cons from Wayne Hicks and Clark Canedy, I followed most of their recommendations with just a slight deviation. I averaged out the dihedral between both wings and tried to keep their positions symmetrical while keeping the wing root/spar interface within acceptable level. As a result, here's the alignment I ended up with:

Water Line Measurements

	Left	Right	Variance (L&R)	Plan	Variance (plan)	Comments
1	17.40	17.40	0.00	17.40	0.00	Expect good fit with fuselage
2	17.40	17.40	0.00	17.40	0.00	Must meet requirement
3	18.21	18.31	0.10	17.40	~0.91	Dihedral at both wings but symmetrical
4	17.10	17.25	0.15	17.50	~.40	Most deviations between L & R wings
5	19.03	19.03	0.00	18.35	0.68	Dihedral at both wings but symmetrical

Outboard (L)	Inboard (L)	Inboard (R)	Outboard (R)
0.0"	+.10"	+.25"	0.0"

+ means wing root surface above spar surface at mating point

- means wing root surface below spar surface at mating point

Digital Level Measurements

Location	Angle	Comments
DL1	0.0	Center section spar is leveled
DL2L	0.0	Left wing incidence (critical requirement)
DL2R	0.0	Right wing incidence (critical requirement)
DL3S	0.4	Spar level (left)
DL3W	0.4	Wing root level (left)
DL4S	0.4	Spar level (right)
DL4W	0.9	Wing root level (right)

I also made a measurement between the center point on the spar to the wing tips - they both measured 181 7/8" exactly - an added symmetrical dimension.

In summary, the wing incidence are at 0.0^o, which is a must. I will have dihedral at both wings but they are symmetrical. The one deviation I'd rather not have is at the inboard TE of the left wing that is .40" below plan. The matching surfaces between the spar and wing root are all within tolerable levels.

Drilling the 1/4" Pilot Holes

Once the wings were aligned, I secured them with clamps and small dabs of bondo - bridging the hard points together. I drilled the 1/4" pilot holes through the wing roots, using a 12" long drill bit. I drilled all the holes to the right wing first, then the left. I drilled the inboard hole first, then the outboard bottom, then the outboard top. As I completed each hole, I bolted the wing and spar together with a 1/4" bolt and nut. This part was not too difficult. However, not all the holes came out perfectly centered at the wing root hard points, because I have to tilt the wing tips for alignment above. However, the hole locations should clear the bushings, bolts and nuts.

Drilling the 5/8" Holes

After reading the Cozy archives, I bought 3 hole saws and an adapter that accommodates a 12" pilot drill from Grainger. I made a test run with the hole saw on a 1/4" thick aluminum. The hole turned out to be a bit over-sized for the 5/8" bushing. There are two obvious contributors - protruding teeth and wobbly body. First, I brushed down the protruding teeth with my Dremel, confirmed its diameter with my caliper and performed a re-test. The new hole still turned out a bit over-sized.

I took the hole saw to the belt sander and rounded off its body a bit and performed a re-test again. This time the hole was under-sized. With my Dremel and a sanding drum, I opened up the hole to size. This time, the bushing fits fine but the hole was a bit out of round. I was a bit frustrated...

I was talking to Gilbert (owner of a machine shop, a few units from me) regarding the above-mentioned challenge. He said he'll give it some thought. The next day, he returned with a funny looking tool (left).

He took a 5/8" drill bit and ground the first inch or so into a 1/4" pilot drill. At the shaft end, he drilled a 1/4" hole with 2 set screws such that I can slip a long 1/4" extension shaft (with 2 flat surfaces) into it (shown left).

To use the tool, I first held up the tool with a magnet and slipped it inside the spar (through the big hole at the bottom). Butting the shaft end against the pre-drilled 1/4" hole at the forward face of the spar, I slipped the 1/4" extension into it. Then I pushed the tool's pilot tip into the pilot hole at the hard point. A slight push and twist will cause the tool to 'dig' into the hard point surface a bit, anchoring the tool in place. With an extended Allen wrench, I tightened the two set screws in place. Grabbed onto the extension shaft with a power drill and I was ready to start the 5/8" hole.

This tool allows me to use both the pre-drilled (forward and aft) 1/4" pilot holes in the spar as a guide throughout this drilling step. Since this is a drill bit, it generates a lot more metal shaving compared to a hole drill. However, I do not have to be concerned with the donuts plugging up the drill shaft. Regardless, this step took a long time - the first hole took me an hour, because the drill was getting really hot and I had to stop and cool everything down with my air compressor. Once I changed out to a more powerful drill, the last hole took me ~20 minutes. Again, once I finished one hole, I tightened a 5/8" bolt and nut through it to keep the wing and spar in position.

I can't say if this drill tool is any better than a hole saw (since I did not use a hole saw). However, the holes turned out nice and clean. I got a slip fit between the bushing and the hole with NO slop. A slight nudge gets the bushings into the holes. This drill tool is available for any fearless builder to use... just send me an e-mail and I'll send it out to you. Bare in mind - use it at your own risk...

[Hindsight] Use a heavy duty hand drill for this task. I ended up using a 7.8 amp DeWalt instead of my 3.5 amp Black & Decker variable drill. The DeWalt didn't get very hot and NO SMOKE.

Shaving the Bushing to Length

Once I completed the six holes, I removed the bondo and separated the spar from the wing. The plan suggested making a small measuring tool for determining the depth of the holes. I made one of those tools by shaping a stir stick per plan. After transferring the first hole depth to the bushing, I got a simpler idea.

Instead of transferring the hole depth from the tool to the bushing (using a caliper), I assembled a collapsible magnet stick, a flat washer and the bushing as shown. I also numbered the bushings to the holes.

I just 'thread' the magnet stick through the hole and, with the help of the washer, pull the narrow end of the bushing through the hole - exposing the extra length. I took a pencil and traced out a circular line (on the bushing) along the hole surface. Since the plan calls for .01" shorter than hole depth, I just grind the bushing down to and including the pencil mark. No measurement is required and it will be exact as long as I keep track of the bushing # and hole #.

To make sure I ground the bushing flat (90 degrees to the longitudinal axis of the bushing), I drilled a 5/8" hole through a long piece of 1/4" aluminum strip. Then I clamped the strip against my belt sander as shown. By slipping the bushing through the hole and grinding it down to the pencil mark, they came out nice and flush every time. The tough part was to hold the bushing in place while it's getting hot by the second.

After the bushings were trimmed to length, I floxed them in place per plan. I re-measured everything one more time to make sure nothing moved in the process. Once confirmed, I bolted the spar to wings (through the bushings) and allowed to cure. (Don't forget to wax the bolts, nuts and washers).

Additional Level Boards

My next step is to install the center section spar to the fuselage. Though the center section spar is integrated to the main wing (leveled), I doubted I'll mounting the center section spar to the fuselage with the wings attached. I decided to add a couple small level boards onto the center section spar at this time such that they have the independent level indicators (as the wings). As shown, these two level boards allows me to level the center section spar fore & aft and side to side.

[Hindsight] These level boards proved to be useful again when I mount my upper firewall in Chapter 18 - Section 7.

Now, back to Chapter 14 - Section 10 - Installing the spar onto the fuselage...