Chapter 21 - Section 1

Fabrication of Parts


What's UP

In this chapter, we will be building the strakes - the structure that holds the fuel tanks between the fuselage and the main wings. The leading edge of the strakes must be straight and should blend with the main wings naturally. This is one of the most noticeable locations if you do a lousy job.  



Leveling the Fuselage

The first thing I did on this Chapter was to level the plane fore & aft and side to side. Then I hot-glued two (2) wood blocks against each wheel such that there can be no movement with the plane.


Glassing the Ribs and Bulkheads

The next task was to make the ribs and bulkheads for the strakes. I followed the general consensus in joining two 48" x 32" H45 PVC foam, then applied 1 BID layer on both sides. This part was pretty straight forward except it is a large piece of foam to micro and glass. I did one side one evening and the other side the next. After cure, I traced/drew out all the rib and bulkhead patterns per M25 and plans. I noticed some surface imperfections from the peel-ply, I decided to paint another layer of pure epoxy and peel-plied one more time.


Since I was planning to use the Feather Lite leading edge, I did not cut out the BLE, TLE and OD bulkheads - not yet anyway. However, I made sure I have enough glassed foam for them if I need them. I connected the R33 to the B33 as a continuous piece and its 46.8", just an inch shy of 48".


Instead of using the band saw, I just used the FEIN tool and cut out all the ribs and bulkheads with little problem. Then I sanded the edges down to its outline with a sanding block.


Preparing the Notches

There are 16 half-moon notches among all the bulkheads. They are necessary for keeping the fuel from sloshing  around too quickly as the plane banks and dives. It has been pointed out in the archives that the airplane fuel would not affect the exposed foam, therefore, no foam surface preparation at the notches is necessary. However, I have yet to find a Cozy builder who did not prep those notched surfaces. Well, I am not taking any chances either. Per Randi's (Cozy Girrrls) suggestion, one good way to prep it is to auger out some foam and then fill it with wet flox.


Since the foam is sandwiched between the glass (1 ply on each side), I need to be careful not to damage the side edges. I took a 1/4" x 1/2" Dremel grinding wheel and ground it down to 3/8" in length (same thickness as the H45 foam). With a Dremel and this shortened grind wheel, I removed a slight trench inside the half moon notches. It worked perfectly...









I made some wet flox and 'whipped' it well before use. The reason for whipping the flox is to remove the cotton fiber lumps such that they will lay down smoothly. Once I filled the trenches with flox, I further smoothed it out with pure epoxy and peel-plied.










I did the same for the sight window on B33 as well though I did not cut these sight windows until later on.











Top and Bottom Skin

I decided to wait until I completed the leading edge before making the skin because I do not know how much surface area the Feather Lite leading edge will cover. I shall return to this section later on...


From here, I jumped to Chapter 21 - Section 02...



I returned to this section after installing the  the leading edge...


Since I am using a pre-fabricated leading edge, the top skin dimension in the plan would not work for me. So, I taped up a few large wrapping papers and traced it out (left). I also decided to make the top skin in a single piece of foam instead of two separate pieces per plan. 









I was able to make the entire top skin with a single piece of 48"x32" foam though I have to do a little bit of joining (3 pieces of foam all together) - the main piece next to the fuselage, the triangle piece at the wing tip and a small triangular piece (gray in color) at the forward tip of the top skin. Actually I messed up when cutting the top skin (the first time), I ended up a bit short with that small triangular piece. I did a much better job on the bottom skin though. since the Feather Lite leading edge took most of the LE curvature, I still have to lance 4 lines along the foam to make a smooth transition between the LE and the top and bottom skin. 







I beveled the trailing edges of both the top and bottom skin to fit onto the center section spar per plan. Note the duct tape along the trailing edge? The duct tape kept my sanding straight and kept me from over sanding. Once I was happy with the trial fit, I glassed the inside surface with 1 ply of BID and peel-plied.









I repeated the same procedure with the bottom skin. The joint along the fuselage turned out nice - practice makes perfect. However, I did not flox it in place at this time because I need the access from the bottom to make the T-Hats first.









[Hindsight] My first top and bottom skin had A LOT OF delamination - I certainly do not know what I did wrong here. I suspect the peel-ply wrinkles were pulling the glass too much...but not sure. I ended up re-doing both top and bottom skins. Then I sealed the glass with a plastic sheet & hair dryer to squeegee out all the bubbles. Once it cured, I squeegeed on another layer of pure epoxy and then peel-plied. They turned out much better.


Lancing Foam at Leading Edge

Though I am using the FeatherLite leading edge, I still need to lance the foam at the leading edge joint. I lanced both top and bottom skin - 4 lines, 1/2", 1/2", 1" and 1" respectively. It helps to fold the foam nicely.