Chapter 24 - Section 9

Strake Fairings


As far as I can tell, there are three sets of fairings for the Cozy - the lower strake fairings, the upper strake fairings and the main gear fairings. Instructions for the strake fairings are provided in this section. However, I was not able to find instructions for the main gear fairings. After searching through the Cozy forum and other builder's web sites, I gathered enough information to build the main gear fairings. Since it is not discussed anywhere in the Plans, I decided to document my build in Section 11.


Shaping the Lower Strake Fairings

The lower strake fairings are made to cover up / blend in the fuel sump under the strakes. Since this is not a structural or shape critical part, you can see more variations among Cozy builders than you can count with your fingers and toes! I decided to follow the Plans recommendations as close as possible. Actually, I followed Nat's fairings (per the Plan's picture at the back of the Chapter). However, I did not carve out the fairings from a bunch of foam blocks. Instead, I followed Norm Muzzy's approach by hot wiring them out from a block of blue wing foam. Since the Feather Lite's sump is somewhat straight in the middle section but curved at both ends (like a lemon wedge), I decided to divide the fairing into three different sections as shown.





Mid-Section Templates

I started with the carpenter's widget and extracted the surface profile of the sump. since the profile has ridges and valleys, I rounded it off with my graphics software. I also measured the angle between the fuselage sides to the bottom of the strake - its greater than 90 degrees. Remember the bottom of the strake slopes up from the wing root to the wing tip? Connecting the angled sides to the sump profile, a pair of hot wire templates can be made. I made two (2) for both ends of the center section. the picture shows the 2 templates for the mid section and the end template. The mid section foam is about 7 1/2" in length.






Front Section Template

The Front section hot wire templates consists of 1 mid section template and a point source. My point source is just a small slot (pencil lead size) at the end of a wood block. I made the small slot by lightly touching a wood block with the band saw. For hot wiring, I just rest one end of the wire on the slot while the other end travels over the rounded edge of the mid-section template. The length of my front section (tip to sump flow valve) is 38".


Tail Section Template

The tail section consists of 1 mid-section template and the triangular shaped section of the fire-wall.



After carving a cavity in all three sections to accommodate the features of the sump, I 5-min. epoxied all three sections in place. Then I sanded the entire fairing for a smooth flow. After micro and patching up all the dents in the foam, I glassed both fairings with 2 layers of BID. I was able to stretch a single strip of BID to cover the entire length of the fairing.


Before I glassed the fairing, I removed the fuel drain valve, taped over the hole with duct tape and marked the hole location on the top of the foam.






Fuel Drain Valve 

After cure, I located the pre-marked hole location (on the foam). Then I drilled and sanded a tight fit opening for the fuel drain value. The size of the hole was large enough to accommodate the diameter of a socket wrench.










After the opening was rounded off nicely, I removed the fuel drain valve, re-capped the opening with duct tape (to keep the dirt out), then applied wet flox all along the gap inside the hole and peel-plied.











Upper Fairings

I delayed installing my upper fairings until I completed the cowling installations and baffles (Chapter 23_Section 12). The reason for the delay is to make sure the upper fairing provides a smooth transition connecting the front canopy to the cowling. I do not believe it is structurally significant but it make the plane's line 'flow' right.


Based on my limited experience with pour foam, I doubted I could sand down a symmetrical set of upper fairings by hand. I think I can do a better job by hot wiring instead. I started by making a hot wire template for the fairing 'ears' both front and back. Then I nailed them at both ends of the blue foam and cut out the fairing core.









Here's the hot wire result. Note that the foam cut out is solid at the core, therefore, I have to hollow it out to fit around the canopy and turtle back lip (as shown in the above picture).










Note that I have Princeton fuel probes mounted on hard points - right above the fuel sump opening and inside the foam cores (both pilot and passenger sides). My concern is accessibility down the road? Most builders told me that these probes hardly fail and that they plan to dig it out when the time comes (if ever). I was not comfortable with that thought and decided to build in a fall back access door for them.


Instead of glassing the fairing with the foam core in place, I decided to make a glass cover / fuel probe access door combination. Picture left shows the duct tape as release for the 4 BID cover.






I used a large piece of paper and traced out the fairings such that I can wet out the glass and cut to fit on the bench. This works out well.











Once the fairings are cured, I stuck packing tape at the fuel probe location and made an additional 4 layer BID cover (approx. 3" x 3") - as shown in the picture. This will eventually be my access door.


Once the access door cures, I popped it off, removed the packing tape, and I cut out a small 'window' on the fairings - showing my fuel probe. Since my fairing cover is removable (not yet glassed permanently to the fuselage), I can be more attentive to make a clean cut window.







Once cut, I slapped the access door BID back in place and traced the window pattern onto it. After cutting and trimming, I ended up with a seamless access door for my fuel probes.


Before glassing the upper fairing to the fuselage, I hot glued the access door to the fairing and glassed a flange behind the access door. Adding a couple of nut plates onto the flange (not shown), I can now have a removable access door for the fuel probes.







Here's a picture of the pilot side upper fairing. Notice the masking tape for cutting the fairing into the strake section and the canopy section.











Once I cut the fairing into its appropriate sections (shown left), the challenge is to blend the fairing with the rest of the fuselage.


First, I made a foam plug to cover up the ends of the upper fairing. Recall my fairing is hollow inside? In order to connect the fairing to the front of the fuselage, I decided to use pour foam to blend it in. Picture shows the cardboard fence I made - ready for the pour foam.








Once the foam cured, I reshaped and glassed. I did the same for the pilot side as well.











As for the forward end of the upper fairings, I tackled the pilot side first because it going to be easier than the hinge side. I used a bit of pour foam and micro for shaping. I also extended the canopy lip (~3/4") down the pilot side of the fuselage. The intent of the extension is to help the sealing of the cockpit besides the sealing tape. Incidentally, it also helps to keep the canopy in position.








Upper Fairing (Hinge Side)

Making a nice seam on the hinge side was difficult because of the position of the forward hinge and the way the canopy opens. In addition, my original canopy edge is kinda crappy (picture left). You can see my hinges are showing and the canopy edge is crooked. I made a couple of attempts but was not successful. Notice the pour foam along the side the fuselage? That was one of those approaches.


I ended up staring at the problem for an extended period of time...pondering.


I finally did the following:





I removed the canopy and sat it flat on the table. Then put packing tape along the edge of the table. Then I used extra hinge halves to fill the open knuckle of the hinges, covered them with electrical tape, and packed the entire canopy edge (including hinges) with West micro.


Once the micro cures, I popped the canopy off the table and carefully pulled the electrical tape from the hinges. The elastic characteristics of the electrical tape is most helpful in this application. Unfortunately, this approach lowers the micro baseline to the same height as the bottom hinge (or the top surface of the ailerons). This will cause the canopy edge to bind when opening the canopy. So I have to sand the baseline up just a hair. I took care to sand the edge nice and straight. Then I mounted the canopy back on the fuselage.





One of the toughest tasks is to open the canopy (a bit at a time) and sand off the excess micro - to make sure the canopy swings freely. Fortunately for me, I have a remote actuator control canopy (ref. Chapter 18 Section 22A). This allows me to raise and lower the canopy remotely while I pay close attention to any obstruction.


This step took a lot of time and patience. Between careful sanding and measuring the gap with a spark plug gauge, I finally was able to open and close the canopy with no obstruction. I added 2 layers of BID to protect the micro at the edge.






My next step was to build up a fence to hide the seam along the canopy. This is one of those areas most Cozy builders find challenging. After observing how the canopy edge 'swings' as it opens and closes, I decided to put a 2 layer BID with the canopy at open position. This forms the 'inner' surface of the fence.


Once the fence cures, I closed the canopy and marked the canopy edge onto the BID fence. That way, I know exactly how high the fence needs to be to minimize the seam.






After the fence is trimmed, I added pour foam to 'fill in' and match up the fuselage curvature. Since the forward edge of my hinge sticks out past the fuselage (per Plan), I decided to use a bit more foam to blend it in - at least to the first knuckle. It turned out I have to 'extend' my blending past the hinge a bit (shown left).


After shaping, I glassed over the pour foam with 2 layers of BID. Do not forget to use flox corners at the top edge where the outer glass meets the inner glass..











Here's a picture of my completed fairing and seam. So far, I have only done the pre-fill. A final fill on the entire canopy and fuselage shall be performed in Chapter 25. I intentionally left this picture the original size because it is difficult to see the seam line.