Chapter 21 - Section 2

Jigging and Assembly of Parts


Establishing Jigging Locations

All the strake ribs and bulkheads are laid out in the plan except its exact location is 'somewhat' vague. I scanned Page 2 into my computer and using my Corel Draw software laid a (1"x1") grid on top of it. The effort was  well worth it because I ended up continuously referring to it throughout the entire chapter.


Establishing the BLs

The two main ribs for the strake are R33 and R57. To make sure I got them parallel to the center line of the fuselage, I did the following:

- Confirmed the centerline of the fuselage (nose tip to firewall) using my laser line;

- Clamped a long straight edge against the Instrument Panel and extended it out to the side of the fuselage (shown left where the laser is sitting on);

- Hot-glued another straight edge against the firewall, extending out perpendicular to the center line of the fuselage;

- Marked BL22, then every 10" outwards, all the way to BL60 on both straight edges;

- Used my laser to line up each pair of BL from front to back while casting a vertical line onto the forward face of the center section spar;

- Add BL33 and BL57 onto the center section spar.


Notice the laser line on the small white block to the side? It's for making sure the laser is square from side to side and front to back.


The WL17.4 was not too hard to mark, between the laser and digital levels, I have it marked from the wing root, along the center section spar and the entire fuselage side. I found my WL to my right wing is almost right on (may be 1/32" off), while the WL to my left wing is ~1/16" off. I figure its good enough for me...


Lining Up R33 and R57 Ribs

I did not build the table per plan right away because I wanted to be able to get to the under side of the top skin when building the 'T-hats' and the table top would be in the way. In addition, with the Feather Lite leading edge, I need to squeeze (clamp) the leading edge surfaces onto the top and underside of the ribs, access space will be much needed. Instead, I used a couple of clamping work benches and straight boards to hold the 2 ribs in place for glassing. 


Note the red cloth at the end of my horizontal beam? Its a danger zone sign I put up after I ran into it with my forehead...after my duck walk under the ribs. Practically knocked me on my butt...The good news was that the plane did not even budge and it stayed straight and level.




To establish the forward tip location of the ribs, I used a 1"x3" beam and a plumb line. I placed a masking tape on the plumb line string (5.6" below the bottom of the beam) - that's the WL17.4. Then I placed the plumb line in-line with the laser beam. That establishes where the tip of the rib should go. All I need to do is to line up the tip of the ribs to the plumb line, with its WL17.4 marking to the same height as the masking tape. I glassed the ribs onto the center section spar with 2 layers of BID on each corner.


After the glass cured, it put my 4' digital level against the WL17.4 at the tip of the ribs as well as the fuselage - they registered 0.0 degrees.





Temporary Stabilizing Stringers

Since I did not have a table top to support the ribs (after they are glassed in), they tend to flop sideways a bit when bumped. To stabilize them for fitting the Feather Lite LE, I added a couple of temporary stringers which helped quite a bit. They will be removed after the LE is installed.









Additional Rib at Wing Root

Since I will be using the Feather Lite leading edge, I will need some kind of a template to clamp my leading edge to. I decided to add an end rib, with the same curvature profile as the wing root for this requirement.


Notice the dental floss I learned from Wayne Hicks' web site to confirm my WL17.4 at the tip of all the ribs?




From here, I jumped to Chapter 21 - Section 2A - Mounting the Feather Lite Leading Edge...


Returning from Chapter 21 - Section 2A...


T-Hats for the Top Skin

One of the highly recommended deviations from plan is the addition of T-Hats along the upper edges of the ribs and bulkheads. These T-Hats should reduce the chance of air leaks in the fuel tanks. To be able to get to the under side of the TOP skin and fabricate the T-Hats, one must first glass in the ribs and bulkheads before installing the bottom skin. Its somewhat of a challenge to mount the bulkheads in mid-air - i.e. without the help of a table per plan. In addition, I don't think the table will help me much especially with the Feather Lite Leading Edge.


Glassing in the Bulkheads

Fortunately, the WL17.4 on all the bulkheads can be extracted from the M25 drawing and the plan. I decided to glass in the bulkheads without the table. I pre-marked WL17.4 on all bulkheads.


Next, I beveled the bulkhead ends to fit flush against the ribs and fuselage sides. Then I performed a trial fit with tapes and clamps. Some of the bulkheads are just a bit taller than the R33 & R57 ribs (due to fitting and jigging). I trimmed off the excess and proceeded with the bulkhead installation.


Since holding the bulkheads in place for glassing without the table and bottom skin is a kind of a challenge - here's what I did...

- I made a small amount of wet flox and mixed in some 5-minute epoxy;

- I smeared the mixture to the beveled edges of the bulkheads;

- I positioned the bulkheads in place, lining up WL17.4 of the mating parts;

- I held the bulkheads in place by hand, tape and clamps;

- once the 5 minute epoxy took hold, I could let go and proceed to floxing the corners and glassing all joints with 1 ply of BID and peel-plied per plan.


With the underside of the strake un-obstructed, I can now proceed with the T-Hats.



Making the T-Hats

Once the bulkheads were glassed in place, I trimmed off the excess BID and smoothed out the edges. I placed the top skin back in place and made several alignment marks along its edges - such that I can place the top skin back at the same location next time. Then I weighed down the top skin onto the ribs and bulkheads.


With a pencil, I stooped under the strake and traced the profile of the ribs and bulkheads onto the underside of the top skin. Then I removed the top skin and put a 2 " packing tape over the pencil marks.


I wet out 2-ply 2" BID strips (the top strip of the T-Hat) with peel-ply on one side. I centered the BID tape at the pencil mark with the peel-ply side to the packing tape. I then applied a thin layer of wet micro on top of the ribs and bulkheads. With Susann's help, we laid the top back onto the strake and weighted it down to cure.


Since I can access the under side of the top skin at this time (remember, I am not using a table per plan), I added a 4-layer BID under the Leading Edge (to stiffen up a slight sag at the middle of the Feather Lite Leading Edge). I also added glass strips directly to the bottom of the top skin at the fuselage side and the forward face of the center section spar (by my left hand in the picture).


After all glass strips were installed, I stooped under the strake and lightly scraped off the excess micro with a skinny stir stick (thanks Starbuck). After cure, I popped the top skin off. I was pleasantly surprised how easy the top skin came off.


Since I trimmed the BID strip prior in the previous step, they looked pretty straight after they were applied to the ribs and cured.











But I have to do something to make it look crappy again...I made a bunch of wet flox and 'whipped' it really good during mixing. The reason for whipping it is to get rid of the lumps normally formed with the cotton. Since we wanted to get a good seal, whipped cotton is less lumpy. I floxed all edges and corners, then I added the 2" 'T' glass strip joining the top sides of the ribs/bulkheads to the underside of the top strip. Actually there were many strips. By the time I came back to do the peel- ply, the glass was already curing...








Here's a picture of the T-Hats completed and trimmed.











Here's a picture with T-hats completed on both sides of the strakes.











Fuel Drain Viewing Window

I did not cut out the fuel drain viewing window until now because I wanted to make sure I can see the fuel drain location. As many Cozy builders before, I moved the sight window an extra 3" forward per plans dimension. Actually, I wished I moved it up 1" higher as well - a bit late for me though. Regardless, I can see the fuel drain from the fuel filler cap location fine. Note the small target I placed on top of the white board? That represents my fuel drain location. The only problem with this approach is the limited space you'll have to cut the fuel drain window this late in the game. 







Supporting the Bottom Skin for Floxing

Whatever it is, I just had a real difficult time in building a sturdy table to support the bottom skin. To make things more complicated, the Feather Lite LE takes its own form and just does not fit well with the table. By the time I fit the table in place, I lost all visibility on the bottom skin - just won't know how the bottom skin fits until its all cured and done - or worse, after it is too late.









I decided to abandon the table and try other simpler supporting methods. Again, I turned back to my angle aluminum beam, C-clamps and clamping work benches. Here's a picture of my alternative approach. I did measure the slope of the bottom skin sideways (same as the center section spar) and forward and backwards as the fuselage. This way, I can inspect and feel the bottom skin when it is in place for floxing. I can check for any sagging, the straightness of the seams between the LE and bottom skin and the trailing edge of the bottom skin. This set up just looks simpler to me - will see how it turns out.


[Hindsight] I never did use the table for the rest of the Chapter and the strakes turned out fine. Flipping the fuselage over to do the bottom skin is the way to go - in my opinion.   


When its finally time to install the bottom skin, I decided to flip the fuselage over for the effort. (Refer to Ch21 Section 7 where I build the clamshell structure for flipping the fuselage over). I just do not feel the above methods assure bottom skins with identical profiles. I need to see them and compare them as I build them!!!


Here's a picture of my bottom skins after I flip the fuselage over with the clamshells. This approach allows me to see the bottom skin surface and profile nicely before floxing it in place. 


To assure identical wing root profiles, I measure out the profile of the top and bottom skin relative to the 17.4 WL from the right side and traced the same onto the left side.


A more detailed description on attaching the bottom skin in in Section 3.