Roee Kalinsky's RV-7A Project

2009.01.24: (0.0) I've been working on the canopy for weeks and weeks and needed a break.  So I took a detour for a couple of days and fitted the flush light lenses to the wing tips.  These lenses come from Van's as a single molding of acrylic that has to be cut in two, and then each half trimmed to fit its respective wing tip.  Similar process to fitting the canopy, but much easier due to the smaller size and simpler geometry.

After trimming, I match-drilled the lenses and wingtips.  I've seen many RV's with only a screw in each corner (i.e. two screws per lens), but that felt a little flimsy.  I went with six screws per lens: the corners, plus one 3" forward of the corner and one 3" outboard of the corner, top and bottom.  That feels pretty secure.  I then enlarged the holes and countersunk the lenses to accept flush 6-32 screws and tinnerman washers.  Following the advice of several RV builders, I used an abrasive "PermaGrit" countersink bit.  This worked ok, but left a pretty rough countersink surface.  The imperfections are concentric of course, not radial, so there shouldn't be a tendency to crack.  But still, a clean countersink would be better.  Not worried about it here, but I plan to look into alternative methods of countersinking plexi for the canopy.


Rather than just riveting nutplates to the fiberglass wing tips, I decided to make a thin aluminum "L"-shaped backing strip or each set of 3 nut plates (i.e. one for top, one for bottom).  This will later be epoxied and/or riveted into the wingtip, which will be much more secure.

2009.03.07: (0.0) Again, taking a quick break from the canopy, and trying out a process in miniature on the wing tips before doing it on the canopy.  This time: composite work.  I bonded the nut plate backing strips into the wing tips.  The process I used is as follows: First I drilled a bunch of 1/16" holes in the backing plates to give the adhesive more to grab onto.  I then prepped the bonding surfaces (the wing tips and the backing plates) by cleaning with acetone, abrading with 150-grit aluminum oxide sand paper, and again a wipe with acetone.  Mixed up some epoxy (West Systems 105 resin & 206 hardener) and wetted the mating surfaces with "neat" epoxy.  I then took the remaining epoxy and mixed in flox to a consistency somewhere between mayonnaise and peanut butter.  I needed it thickened because the inside of the wing tip has a fairly uneven surface, so the gaps between it and the nut plate backing strips needed to be adequately filled.  I spread a generous amount of the flox mix on the wingtip surface, and installed the nut plate backing strips.  I secured the nut plate backing strips simply by putting in the screws, which I first coated with wax to prevent them from bonding.  Tightening things down made the flox ooze through all the 1/16" holes and around the edges of the backing strips, which is exactly what I wanted.  I then used some popsicle sticks to remove the excess and form nice filltes around the edges.  I also coated the inside (i.e. non-bonding) surface of the backing strips with a thin layer of the flox mix to basically encapsulate it, strengthening its retention and sealing it against corrosion.

2010.02.25: (0.0) Now that the wing skins are fully riveted, I'm starting to fit the fiberglass wing tips to the wings.  The initial fit is pretty bad.  The contour of the leading edge doesn't match the wing.  The length (chord) of the tips is about 1/4" longer than the wings.  The aft 1/3 of the tips are substantially bowed.  And the tips have some twist to them, apparently due to simalignment when the tip halves were bonded together at the factory.  Another example of poor quality composite parts from Van's.  Argh...  It'll take a lot of surgery to get a good fit.