The next task is a dreaded step for many builders: the canopy's fiberglass fairing, which provides a transition from the aluminum canopy frame to the plexiglass canopy. Fortunately, I attended an EAA Sportair workshop titled "Fiberglass Techniques for RV Aircraft" led by Scott Vanderveen, who had us do a complete process for a mockup canopy fairing over the 2 day class (along with 2 other RV-relevant projects). Scott's method differs from Van's quite a bit; I've provided many of the steps below, but unless you already know how to work with fiberglass, I highly recommend taking Scott's workshop. The major differences are: 1) the Van's-supplied templates to outline the fairing or cut the fiberglass pieces are not needed; 2) instead of cutting umpteen fiberglass pieces, some on the bias but most not, simply cut enough fiberglass all on the bias (important!) for 4 strips of BID fiberglass, 2.5" wide; 3) a strong structural adhesive is used to bond the fiberglass to aluminum (epoxy doesn't adhere well to bare aluminum), 4) all filler and fiberglass layers are tinted, so the result is a deeper black than the Van's method that has only the first layer or so of fiberglass tinted; and, 5) the finishing layer is Aeropoxy light - a wonderful epoxy paste that is strong yet can be easily sanded and shaped (unlike epoxy/flox/micro). So far, I've completed half the process - i.e., up to the point right before the second application of dual-layer BID fiberglass. I've delineated each step with pictures, following these details from the past week:
- match-drilled #27 (w/reamer) all holes common to canopy and canopy frame; deburred holes; dimpled #27 holes in side skins; started prepping for interior paint
- painted interior of canopy frame assembly; deburred and machine-countersunk holes in canopy; separated seal retainers; cut notches in rear seal
- painted top of glare shield matte black; painted seal retainers gray; primed contact surface of canopy handles; installed safety wire (to eventually pull canopy latch switch wires, when avionics are installed)
- placed canopy back on canopy frame assembly; clecoed left side skin, loosely attached hardware on left side, and tried to “fish” 0.041” safety wire though the channel
- loosely attached screws/hardware on right side of canopy; riveted side skins to canopy; fished 0.041” safety wire through wire channel using thread and needlenose pliers; attached screws/hardware and seal retainers on aft part of canopy (tightened inboard 14 screws); fabricated and installed canopy wear strips
- separated and fit hinge covers; tightened screws in “zone 2” of canopy with my wife’s help; fabricated canopy clips
- riveted canopy clips to canopy frame assembly; sanded canopy (80 grit) and aluminum (220 grit); followed Scott Vanderveen’s canopy fiberglass transition, Day 1 (structural adhesive; flox/micro/tint epoxy fillet; 2 layer tinted BID fiberglass cut on bias, pre-preg)
- Day 2: sanded fiberglass (80 grit); brushed on thin layer of epoxy; used tinted dry micro/epoxy paste and a bondo spreader to form center fillet and fill some of the low spots
Final #27 drilling of the canopy and canopy frame:
Scuffed canopy frame, prior to priming and painting:
Painted the interior of the canopy frame:
Other side:
Cut the aft canopy seal to match the hole pattern in the seal retainers:
Painted the glaresheild matte black:
After drying:
Riveted side skins onto canopy frame assembly, and attached the screws to the canopy very loosely:
Here is how I pushed safety wire to the canopy switch. First, straighten the wire completely - and I mean completely (that's over half the battle)! Then, thread it all the way back until it pokes out the back. Attach a bit of thread, which has been inserted through the hole hear the canopy switch and pushed to the back (with a thin piece of wire) where the safety wire is. Tie the thread tightly around the safety wire, and then ease the wire back until the end is visible through the hole next to the canopy switch.
Here you can see the safety wire being pulled inboard by the thread. Grab the wire with needlenose pliers and voila! The safety wire has been threaded, waiting for the avionics kit to be installed (which includes the wires that connect to the canopy switch).
Installed the seal retainers and tighten only Zone 1, leaving Zone 3 very loose:
Completed canopy view:
Another view:
Fabricated and attached canopy wear strips:
Fit hinge covers:
Reattached canopy assembly to fuselage, and lock into place. Weighed down canopy as done previously, and then final torqued Zone 1 (screws on the lateral aspects of the canopy):
Fabricated and installed canopy clips where the forward canopy bulges away from the aluminum skin - I had 6 areas that needed attention:
THE START OF THE FIBERGLASS FAIRING: The first steps are to mask off an area approximately 2.8" wide using blue masking tape (1.4" width) on both the canopy and aluminum. No need for templates if you just use the double width of the tape! Next, place a layer of yellow electrical tape alongside the masking tape (or whatever color is easily discernible from black) - this will define your fairing, so take care to install it well.
Partially mask the yellow electrical tape:
Finish taping and masking the fairing zone on the sides:
Add protective visqueen or similar 4 mil plastic around the work zone, since epoxy has a tendency to go everywhere:
Add a sacrificial layer of black electrical tape directly over the yellow electrical tape. This layer will be replaced each time a clean line is needed (e.g. after adding filler) or after each time the fairing is sanded. Not shown: scuff the hell out of the plexi and the aluminum with 80 grit and 220 grit, respectively - if you think you've scuffed enough, scuff some more! Vacuum the dust, and clean both with isopropyl alcohol (99%) - you can use water for the canopy if you think isopropyl alcohol has a chance to craze the plexi (it shouldn't, btw):
Mix ES6247 structural adhesive and apply a skim coat to the aluminum. Yes, the shit is expensive ($83 for the quart size, but you'll only use a couple ounces once), but it is very important to get a good bonding surface for the epoxy. We stress-tested the stuff in the EAA workshop and it has amazing adhesive properties. Well worth the money, especially if you can find someone else to split the cost.
Apply a thin layer of structural adhesive:
Mark a template for your fiberglass using silver sharpie (so you can see it over fiberglass that's been tinted black) on visqueen on whatever 4mil plastic you have (I used a Uline product). A 16" by 10" pattern yields four 2.5" wide strips once cut, for a total of 64" of length. Since the canopy fairing is only about 61" from one side to the other, you'll have approximately 3" left over:
Cut two layers of BID fiberglass on the bias (i.e. 45deg to the weave) a little oversized from the template. Lay both layers of fiberglass on another piece of plastic, so the double layer of fiberglass is sandwiched between two layers of plastic:
Mix epoxy (West System, slow hardener), black tint (I used a little over 3% w/w, but it can be up to 5% w/w), flox and microballoons to a consistency of peanut butter to be used as a filler paste, and apply along the transition zone using a sandwich bag with a hole cut in one corner. Smooth the transition layer with a tongue depressor/popsicle stick to about 0.75" wide (not shown). Don't do what I did, and leave a large amount of the remaining filler in the plastic bag - a highly exothermic reaction, that was too hot to touch!
Mix epoxy and tint (3% w/w), and pour all over the fiberglass - let it start to soak in, then cover with the plastic layer with the template on it (shown below). What's not shown (because my hands were messy) is to use the putty spreader to push the epoxy around to cover all areas within the template. Then, cut along the template so you have four 16" L x 2.5" W strips. For a double layer of BID fiberglass that is 16" x 10", 3 "squirts" of West System epoxy is perfectly adequate to cover the templated area.
Remove the plastic on one side of each strip, and apply to the fairing, starting from one side of the canopy and working toward the other. Remove the remaining plastic layer. Trim the final piece of fiberglass so it abuts the penultimate piece of fiberglass. Use gloved fingers to gently push out the trapped air bubbles and move the fiberglass around so it is ~1/8" away from the top edge of the electrical tape (the bottom edge isn't as critical, but NO fiberglass should overlap any electrical tape). Blot with paper towels, which precludes the need for Dacron peel-ply. Cutting BID fiberglass on the bias enables you to place the pieces around compound curves - something that was emphasized in Scott Vanderveen's EAA workshop, since it simplifies you work greatly:
Let the fiberglass cure overnight, and then sand the fiberglass - if you reach the yellow tape, stop. The amount of sanding at this point isn't critical, since there are several additional steps, all of which need to be sanded. However, take care to sand down any high spots or metal tabs, if applicable, and sand enough to take the shine off the epoxy. Remove the sacrificial black tape:
Replace the black electrical tape and wipe fiberglass with 99% isopropyl alcohol:
Make a dry epoxy filler paste with tint (~3% w/w) and microballoons; approx. 3.5:1 by volume of micro. This stuff is thick, and will form peaks that don't curl over. Apply using a bondo spreader to create a large fillet in the center, feathered toward the sides. This will make the central trough slightly shallower, while also filling in many of the low spots from the previous steps. Remove the black tape to leave a clean line and let it cure overnight. In an effort to fill as many low spots as possible, my filler was slightly too thick toward the edges of the fairing, so I have a little extra sanding in my future. While the fiberglass process can be a PITA, the benefit is that it doesn't have to be precisely applied to the structure. Some spots are a little too high? Sand. Some areas are a little too low? Fill the low spots, and re-sand. You think another layer of fiberglass might let you sleep at night? What the heck, apply one more! The only aspects that should be as precise as possible are the boundary edges of the fairing (i.e. yellow tape) and the ratios of whatever epoxy you are using to its specific hardener.
NEXT TIME: I'll be sanding the filler layer, possibly adding a little more filler in the low spots, and then doing the second double-layer of fiberglass, followed by a final skim coat of Aeropoxy light and other appropriate finishing steps will filler primer and bondo.
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