Chapter 20: Winglets and Rudders

Step 1: Cutting the Cores

Not having a protractor, I thought I was stuck at how to lay out the 78.64 and 101.36 degree angles per Figure 1.  I scratched my head for a while until I stumbled upon a revelation that the rudder blocks are cut at the same exact angles as the wings.  So I merely laid out the dimensions from Chapter 19, page 11 onto a tabletop and then cut the foam blocks accordingly.  I was basking in my genius until I saw the note stenciled as plain as day in Figure 1: “Angles same as wings”.  Guess somebody thought of it first.  You’d think by now that I’d have learned to read the plans more closely J   I was pre-warned about hot-wiring the winglets.  The tip template is so small and the wire moves so slowly that it’s easy to get excessive burning, which leads to gouges in the foam.  Well George and I must be charmed when it comes to hotwiring.  All we did was lower the wire temperature and slow down the cadence (move the wire slower).  The cores came out great. 


Step 2: Glassing the Skins


What’s with adding that 1-inch urethane cap piece?  I had thoughts about deleting it and simply shaping the blue foam, but I followed the plans anyway.   Here’s a picture of the port winglet.  I used reference lines for laying out the UND cloth absolutely straight.  First, I used a chalk line and snapped in lines from leading edge root to aft tip, and from leading edge tip to aft root.  Then I cut the two pieces of UND cloth, arranged them one at a time over the winglet, then drew in reference lines onto the cloth with a fine tip marker to line up with the chalk lines on the foam.  Once the foam was slurried, it was easy to align the UND lines with the line on the foam.  You can clearly see the copper foil tape and coax cable for the port antenna in the photograph above.  Remember to do continuity and isolation checks on the antennas before committing to glassing the winglets.  You want to ensure that there is continuity between the copper tapes and the other end of the coax cable.  You also want to ensure isolation between the tapes by making sure that only one tape talks to the center conductor and that the other tape talks only to the shield.



Step 3: Jigging Upper Winglet to Wing


I ran into a slight problem when trying to place the winglets onto the wings.  No matter how I measured from the “WPRP” (winglet positioning reference point, see Figure 8 on page 20-2), I could not get the winglet’s 102.15-inch leading edge measurement to be 4.5 inches behind the wing’s leading edge.  My winglet ended up being well aft of the spar caps, which I knew to be very, very wrong!   So, I made a new WPRP.  I made the 4.5-inch mark at the wingtip, then measured 102.15 inches back toward the inboard hinge to find the new WPRP mark.  (As it turns out, the new mark is only 0.2 inches inboard of the other mark.)  


Don’t throw the wing cut-off piece away!  After cutting the piece off the wing tip, I screwed it back into place with dry wall screws to help provide a base for supporting the winglet.  I also used a jig at the trailing edge to hold the winglet in place.  I didn’t have to worry about finding an additional set of hands.  And to be different J, I mixed some 5-minute glue and smeared a very small fillet at the junction between the top skin and the inside winglet surface.  In addition to holding the winglet root in place, it also prevents epoxy and flox from leaking through the junction and running down the winglet when the wing is inverted.  (Don’t use duct tape.  I tried that on the first winglet and I had hell getting the tape’s adhesive off the winglet.)  I also anchored the supporting 1x2 stringers to the winglet and wings using drywall screws.  I can’t ever get the bondo to stick properly, or keep it from breaking off at the most inconvenient times.



Step 4: Inside Layups

This picture is just after I've inserted and trimmed the wedges.  There is a tendency to CRAM the wedges into the interior webs.  Don't do that!  You can easily delaminate the skins from the wing/winglet foam cores!  So BE CAREFUL.  The wedges DON'T have to fit perfectly either.  They are there to take up space and to avoid an exotherm from too much wet flox. 


Step 5: Outside Layers

Do not “overthink” when the plans say to “sand Block A at a flat diagonal, not rounded.”   Actually what you end up doing is sanding from the concaved edge of the bottom skin to the convex edge of the outer winglet skin.  There is just no way that the resulting surface can be “flat”.  So what you shoot for is “flat, point to point.”  With a little imagination, Block A ends up looking like a high-banked turn at a racetrack!  I used the wingtip cutouts as templates to help shape the foam block to exact shape.  I used blue wing foam instead of urethane.  Blue foam is more stout and the glass adheres better to it than urethane foam. 


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