Chapter 20: Winglets & Rudders

Just starting this chapter while I wait for my shear web inspections (canard, main spar and wings).

Here's a shot of me working on my winglet templates. Spray glue my paper copy and attach onto formica, use the bandsaw to rough cut (within 1/16"), use bench sander to trim most of the way, block sand hard to reach corners and areas needing touchup and then buff a bit with 220 grit. Sounds like alot of steps but each one only takes a few minutes.


Robin helped me hotwire the upper and lower cores in about 2 hours.



Here's one completed core after a light sanding. Each of the upper cores had a wire burn in it so they got a little pour foam applied/squeegeeed into the low spot and then sanded down to profile. 2 part urethane is much nicer than micro because it doesn't get displaced while glassing. It's not as porous as the blue PVC foam so I brush it with pure epoxy prior to glassing over it. The other alternative some people have used is what's called "hardshelling". Nat was always against this - I think because he hadn't tried it. Marc Zeitlin did his wings with it and he hasn't fallen out of the sky yet - or at least not from that. I verified that urethane bonds well to wing foam if it's pressed in with a squeegee so that's what I use for dent repair.



After getting all the cores cut/smoothed I grabbed 2 pieces of 1" urethane sheet, spray glued the tip template to each in turn and sanded it down to profile. Here's what that looks like.




Next I micro'd the core sections together and micro'd the tips on top. I let that cure overnight and then started sanding the tips to the plans specified "pleasing shape" - that could be interpretted a whole bunch of ways! I guess I'm just not adventurous enough as I choose something wingtip-ish. Here's the comparison of pre and post shaping.



 Following shaping of the winglet tips I put reference lines on for the 2 UNI layers and the 3rd ply BID area (NOTE: if you look at the drawing in the plans the BID layup looks longer than it is tall. The text description though is 18" tall by 14" horizontally). I also put a couple reference marks on for where the rudders will be so I could place the com antenna then once I was happy I wouldn't interfere with hinges or cross the rudder cutout I markered on the antenna placement and coax route down to the front of the winglet. I routed a shallow channel for the foil and routed a deeper channel for the coax. I pushed each of the torroids in a bit to mark the placement and then used the dremel router to deepen the hole. I also ramped the coax channel down a bit because it has to descend into the torroids to keep everything below the level of the foam.

Here's what the core looked like prior to starting the glassing:



To glass the outboard side I made a plastic template and marked on the fiber orientation. I cut all my glass and then wet each piece out on plastic and then transfered to the core. This is what the template looks like:



The plans dont' say anything about how to handle the rounded tip and I made the assumption that it should be glassed similar to the leading edge (allowing overlap from the inboard side). The problem is keeping the glass down as it goes around the tip. I used a bit of peel ply and tacked it on the urethane on the other side. I was initially worried that the outboard side would pop off but it stuck ok. Here's what the peel ply looked like with the tacks stuck underneath:



I applied the 3rd ply (BID) to the base of the winglet and peel plied that section and applied the micro to the trailing edge. For that I used a squeegee tight to the cloth on the front and loose on the back. That will give me a bit extra that I can then sand to profile. I used a knife to score the micro at the trailing edge to make it easier to cleanup after cure. I should be able to dremel off anything behind that line. I then left the winglet to cure overnight.



After cleaning up the trailing edge I flipped the winglet over and built my com antenna. There was something in the Cozy email archives about putting the center conductor to the top pole so that's how I did it. I also decided it made more sense to have the solder connections UNDERNEATH the copper foil. To do this I stripped off 1" of the backing from each foil and cleaned off the adhesive with an acetone soaked Q-tip. Then tinned the foil and wire and soldered them together. I used 5 minute to secure the antenna coax - use a small blob every couple inches for best results. I then mixed up some pour foam + micro (see chap 19 learnings) and squeezed it into the coax channel with a large syringe body. If the coax is not secured it'll be pushed up by the pour foam and you'll hae to rip it out causing damage to your nice core. Oh ya, I then remembered to check the resistance between the coax and antenna tips - everything checked out ok.



Prior to glassing the inboard skins you need to remove the fishtail and the imbedded 1" peel ply to expose the trailing edge glass. After marking the 1" on each end I used a straight edge and knife cut the foam and then cut sideways to that cut line. After most foam was removed I just pulled the peel ply up to expose the glass. I looked through the email archives because you can't achieve the nice taper shown in Chap 19 Fig 39 without significantly altering the shape of the foam. Archives said taper it down and fill later. Here's the profile I ended up with (sorry for the washed out photo):



Next step was to glass the inboard skin and then put the winglet back into it's off-cuts for cure. Both my winglets had a bow in the trailing edge after the 1st skin was on so I used the ruler/level and clamps to keep it straight - turned out nicely.



Here's what the two upper winglets looked like at this point:



After glassing the upper winglets I shaped the lower winglets. There's no specific instructions, just a diagram that shows the forward edge and bottom edges rounded. The bottom edge has a bend up to the rudder so I split the problem into two. First I marked the center point at the leading edge, the bend and just ahead of the trailing edge. Then I used those three points to draw two straight lines. I then sanded the sides inwards towards those center lines with a 50 grit block to start and then 80 grit. The outboard side has more camber so you'll sand more off that side using this method. Once I was happy with the bottom I rounded the transition from the leading edge to the bottom. All this took about 20 minutes - not bad for free hand work.



Once you have the cores you use the same process to glass the non-fishtail side, apply micro to the trailing edge, allow to cure, cut the fishtail off and then glass that side. Here's the completed lower winglets curing:

When I was done the wings I used the winglet trim template to trim the upper winglet to shape and then positioned it on the wing to satisfy the three distance criteria from the WPRP. I used string with loops on one end, to go over my WPRP nail, and then made a pen mark at the other end at the specified distance from the WPRP. This method presumes you can reproduce a consistent pressure on the string because it does stretch bit. Once I was satisfied with my positioning and confirmed the distances with a measuring tape (several times) I marked the footprint of the upper winglet on the wing and cut the top skin with a dremel multimax and then cut the foam beneath it away. I then marked the bottom skin with marker and cut it as well. Finally I cut through the shearweb piece with the dremel using a rotozip "sabrecut" bit - looks like a drill bit but it cuts sideways. Here is what the cutting looked like prior to removing the bottom skin.

I setup my strings again and used sharpened craft sticks rammed under the upper skin to hold the winglet in place. I used about 6 sticks and that provided enough support. I hotmelt glued a block to the top skin and winglet as well as a long brace piece. I then made a micro fillet at the intersection to temporarily hold everything in place. I let that cure over night. The plans call for blobs of bondo to secure the winglet but these then have to be sanded off later. The micro fillet is required later, for the interior reinforcements, so adding it now helps secure the winglet in position and saves you the effort of sanding off bondo later.

I flipped the wing over and made the triangular pockets for the interior layups and secured the rudder cable conduit in place with 5-minute. I also pre-cut a bunch of foam wedges on the bandsaw, which you can see sitting on the wing. Lots of flox is required for the corners and filling the triangles, even with the wedges.

After getting the pocket glass (pre-wet) in place, adding flox and ramming in the wedges I trimmed the wedges and placed on the last interior layup and allowed that to cure rather than adding the urethane blocks called for in the plans.

Instead of the urethane I made a block from blue wing foam. First I used the winglet root template to get the shape in the horizontal plane. I then used the winglet trim template to match the curvature of the bottom of the upper winglet. I required a little touch-up sanding but turned out pretty well. Here's one side prior to sanding it to form the racetrack shape.

I sanded the blue foam blocks to shape prior to bonding them in. I covered with a layer of micro and then weighted them down for cure. After a few hours I added the "racetrack" layups shown below.

Sanding the lower winglet to match to my racetrack took alot time with much trial fitting. Eventually I was happy with the basic fit. I covered the upper and lower winglets with 4mil plastic and then dropped in some pour foam while holding the bottom winglet mostly in place. Cleaned up the outside with a bit of sanding, added a bit more foam and then did a bit more sanding to get a good match with the lower winglet positioned where I wanted it (see Cozy Builder's FAQ). I used a stick hotmelt glued to the upper winglet to help keep a consistent position for the lower winglet. By positioning sticks on both wings at the same place I was assured some consistency between wings.

Once happy with my urethane "shim" I buttered up both sides with micro and attached the shim and lower winglet to the upper winglet. I was originally going to apply the 1 BID attachment glass right away but ran out of time that day so I added peel ply and left it to cure. Next day we left for a week of vacation.

When I got back into the shop I roughed up the micro with 36 grit, applied a bit of epoxy and then applied the BID attach tape between the upper and lower winglets. Nat says to use 2" tape but my shim is almost 2" wide in one spot so I used a tapered piece that goes from 2" at the trailing edge to about 3 1/2" at the front.

After the lower winglet tape cured I trimmed the excess and marked/cutout the rudder. Remember to measure twice and cut once. Visually check the lines on both sides to ensure they match - I caught a mismatch that showed I had the inboard top of the rudder 4 1/2" long - not sure how I did that but at least it was fixed before cutting! I then used the dremel with a router bit /router base to remove 95% of the foam from the rudder channel. Cleaned things up with sandpaper on a tongue depressor sized craft stick. I trial fit the hinge halves to ensure I had sufficient foam removed. I also cleaned up the exposed glass for a good glass-glass bond.

Same story with the rudders themselves. The dremel router workes even better here because there are no inside corners that require hand sanding. The foam looks like it's been machined - I guess it has :)

Last step before glassing is to make provision for the CS301 bellhorn backing layups. These required "conical" depressions in the rudder foam. Unfortunately it's right where you've got a nice micro and glass joint - bit of a pain digging out foam, glass and micro. Dremel with the flex extension and a few different bits/sanding drum seemed to work for me.

To glass the interior of the rudder I clamped it to a saw horse and laid in wet glass to the schedule called for in the plans. The bellhorn depression got more than it's share where it overlaps the bottom hinge location so I sanded that even before installing the hinges.

Trial fitting the rudders ensures everything is lined up properly before drilling out the holes for the AN525 screws.

How you're supposed to bond the hinges to the rudders isn't specified so I used the same basic technique as with the aileron hinges. I used the cleco clamps as posts, wound up the rubber band and then pushed in the blade segment. I found I had to put a hook on the hinge end to get sufficient pressure against the rudder while the 5-minute epoxy cured. For the final install I sanded off the 5-minute and used flox/rivets.

Completed rudder. Neither ACS nor Wicks carry the countersunk rivets so I used standard BSPQ rivets. If they impede finishing I may drill them out and replace with something with a lower profile.