Chapter 20 - Winglets & Rudders

Foam cutting

While we were on a roll [see chapter 19 foam cutting] I decided to carry on and cut the winglets. The top winglets came out fine, but I hit a problem with the lower winglet templates. I followed the plans and set the undercamber [that is the "bottom" of the airfoil] inward at the top and outward at the bottom. Everything seemed correct for the right winglet, but it said "left - reverse numbers for right" on the bottom tip template. I found in the archives that others had similar problems. I think the template is mislabeled, but one builder said it depends on interpretation. Best advice seemed to be to make sure the fishtails line up, the camber is correct and that the sweep is in the right direction and you'll be fine.

By the way - don't confuse the "tip template" with the "bottom tip template", otherwise you'll have really small bottom winglets, as happened to one builder.

Glassing the outboard side - with plastic peel ply

I'd recently visited a local builder and saw his beautiful fuselage done with what he called the poor mans vacuum bag technique. I decided to use the winglets to try it before doing the wings. I layed out the top and bottom winglets and prepared for glassing. Got my glass cut and ready and also cut a sheet of 4 mil plastic [home depot] to about 1 inch oversize. There had been some discussion about epoxy "distribution" techniques, and I wanted to try the "pour and squeege" technique rather than my normal "brush it on lightly and quickly" approach. I mixed 5 squirts (about 5oz) of epoxy and poured most of it on the piece. It ran downhill like water and I lost some of it off the edge before I could catch it with the squeege. I think my MGS at 112 degrees F is too liquid for the pour approach except on really big layups, and then only with great care not to pour too much. I'll use this technique to save time on the wings in combination with lightly brushing the epoxy on. Plans don't mention to put the 1 inch peel ply strip along the trailing edge [as with all fishtail layups]. I remembered to do this just in time.

Once the third BID ply was wetted out I put the plastic sheet on top and smoothed it down by hand. I'd bought the stuff that comes folded, so I had small lines where the folds were. Next time I'll get it on a roll to avoid this. [Later note: I found that a hair dryer used carefully eliminates these lines - which is good because I couldnt find plastic on a roll] I wrapped the plastic around the leading edge and used masking tape to hold it (and the layup underneath) in place. I started to squeege. Wow! Excellent. I've tried lots of different methods, but this beats the lot. ALL the excess epoxy and ALL the tiny air bubbles are pushed easily to the edge. Of course the squeege slides really easily without the usual tendancy to disturb the cloth. You can watch the air and epoxy accumulating in front of the squeege. After a short time you're left with a very "tight", totally smooth layup with absolutely no air. After cure the stuff comes off with no trouble at all. Much easier to remove than peel ply. The cured result looks like it came out of a mold. Some say the smooth shiny surface is a problem. Has to be sanded to get a bond to glass or paint. My "mentor" in this uses a sand blaster. I used 120 grit sand paper both by hand and with a palm sander. It only took a few minutes before I had one of the winglets nicely roughed up and ready for paint. No sign of the fibers at all. There are a lot of naysayers on this method. My personal opinion is that it produces the best finish and lightest parts of all the methods I've tried. If you haven't tried plastic peel ply yet, try it on one part. I don't think you'll ever go back to the "old way". I certainly won't. I'm very glad I discovered this before doing my wings.

Glassing the inboard side

To ensure really straight trailing edges I taped the winglets to my eight foot aluminum extrusion using double sided tape. This should be simple. I noticed a few nicks I needed to fill with dry micro. Mixed the dry micro, filled the nicks and proceeded to micro the entire surface. OK. Place the glass and off we go. I'd just layed down the second ply and was taking a quick break while it soaked up epoxy from the first ply. Damn! Antenna! I've forgotten to install the antenna! OK. I'm using all slow hardner. We can do this. I'd guess we've got an hour before the epoxy is to far gone for the hair dryer. I grabbed Char and we swung into action....

one minute...

Put some plastic sheet on the hot tub lid. Char - get some gloves on! Help me roll up this wet fiberglass and put it on the plastic. OK. Now - you find the solder and soldering iron and plug it in. I grabbed the copper foil and cut 4 strips 20.25 inches long. While I marked out the position and layed the copper foil on the wet micro surface, char mixed up [her first] dry micro. (came back four times to ask if this is dry enough).

four minutes...

I found my 12 inch long 1/4 bit, drilled from the center of the antenna toward the leading edge, stuffed the RG58 coax up the hole and trimmed the end. Char - find me 6 torroids! Little 1/4 inch donut things. OK. torroids on, shrink wrap and solder the connections. Dig a hole for the connections. Char buried the lot in micro while I drilled up from the root along the trailing edge. Wish I had a 3 foot drill bit. Never mind. I quickly dug a trench to connect the coax to the hole and fed the coax through. Char - fill the trench with micro while I start on the other winglet.

twelve minutes...

She'd already lifted the glass. Repeat the routine with the drill and coax. Make the connections. Char - you bury the coax in micro while I put the glass back on the other winglet. Cleaned off the bits of foam which had stuck to the [still wet] micro and layed the layup back down. Have you ever tried to reposition a wet two ply layup four feet long? Eventually, despite the rush, I had to seperate the plys and work the first one down slowly pulling the threads straight using gloved hands pushing in opposite directions.

twenty three minutes...

I'm still working on the first ply. Char - would you like to try to do what I'm trying to do on the other winglet? We work on the two winglets together. I got my second ply down and smooth, added the third local BID ply and layed the plastic on the top. Hmmm. plastic and hair dryer don't mix. Took the plastic off again and used the hair dryer to warm everything up. Layed the plastic back down and squeeged with a little gentle heat. The layup is still wet. Excess epoxy and air comes out fine.

fourty six minutes...

Char has finished relaying the glass on the other winglet. Wow. She did it quicker than me. I layed the BID ply, hair dryed, added plastic and squeeged. Everything smooth, leading edges tucked nicely underneath and taped. No air.

fifty eight minutes...

Done. What you need in a crisis is a good team and a clear head. Of course, a clear head is also what you need to avoid a crisis in the first place. Nothing was lost but pride and much experience was gained. Funny thing is - it took me almost a whole day to lay out the antenna in the fuselage. Today I did two in about 12 minutes flat. I suppose that proves something.

Moral of today's story... put your antenna in before glassing the inboard side - just like it says (in bold) in the plans.

Next day I microed the trailing edges and removed the winglets from the aluminum straight edge. The trailing edges couldn't be straighter. I highly recommend using the aluminum to get the TEs right.

Plastic Peel ply experiment

I decided to do an experiment with the lower winglets to test the 4 mil plastic. After the layup of the inboard side cured I weighed the lower winglets. Each weighed 12.75 Oz. Then I did the outboard sides using plastic on one and not on the other.

Left lower winglet. 2 squirts of epoxy were just enough to wet up the first ply. Using hair dryer, second ply soaked up enough epoxy to be wet. Added one additional squirt of epoxy to complete wet up of cloth that wraps around LE and stipple entire surface to ensure complete wet up. Added plastic film, then squeege.

Right lower winglet. As above except no plastic film. Exactly the same amount of epoxy used.

Comment - squeege was more difficult because of tendency to disrupt cloth and need to keep cleaning excess off the squeege. With the plastic you just keep going to the edge of the piece. I think that what happens with the plastic is that the layup gets compressed as the air and excess epoxy is removed because there's no way for air to get back in. You can prove this to yourself by making a fully wet layup under plastic, then lifting the plastic. You can watch the layup go dry as the cloth "expands" and sucks air back in.

BTW - be careful not to get too enthusiastic with the squeeging on plasic. Since it doesn't move the cloth you can easily overdo it. It's possible to make the layup too dry and air can suck back in from the sides of the job or up through the foam.

Time to complete - roughly 20 minutes for each. Maybe a couple of minutes more without plastic.

After cure, weights of the completed winglets were 17.75 for the one without plastic and 17.00 for the one with plastic. i.e. using plastic saved 15% of the layup weight. (Remember that the parts themselves weighed 12.75oz). On top of this, the one without plastic will need filler to fill the weave. I'd guess that this will be at least another 10% i.e. 1/2 oz. Contouring beyond that will be the same for both. Measurements were done with a mechanical postage scale. Error range is probably 1/4 oz +/-. Once the two winglets were cured I sanded the shiny plastic one to a dull finish in about 10 minutes. There were no signs of the threads.

The plastic doesn't go around compound curves at all well, but for flat surfaces I've proved to myself that it produces much better results. I used this method on the wings where the large relatively flat surface gave me even better weight savings and much reduced finishing work. I learned later that its easy to peel ply where needed, then add the plastic and squeege through everything. Also, I found that cutting the plastic and using multiple sheets works well when the curves are too much for the plastic to lay flat.

I just learn a couple more uses for 4 mil plastic.

1. Ever tried to fill a nick in bare foam with dry micro? The micro sticks to the squeege and refuses to lie down in the curveyou want. 4 mil plastic on top of the micro lets you squeege the micro all you need without sticking. After cure the plastic peels off and you have an even finish.
2. Plastic removed from a layup makes great masking material for the next job - much better than newspapers.
3. Plastic is better than wax paper for preparing BID tape layups.

Attaching the winglets to the wings

I took a trip up to Aerocad to "borrow a cup of micro", pick Jeff's brains and take pictures of a part finished airplane. You can only see so much when you look over a finished bird. If you can catch one that's not closed up yet you can learn a lot more. Ended up spending the day with Jeff learning how to do finishing. Next day I did the other aileron recess layup and started on the winglet attachment.

Cutting the winglets and wing to shape was fairly easy, but I didnt cut all the way through. I cut the skin on one side, removed the foam, then cut the skin on the other side. This helped me get an accurate cut. I tried it the plans way first, but my ability to cut straight with a coping saw is limited. I propped the winglet in place with foam and wood and moved it around until I had it perfect. Not hard too do without a helper. Once I had the two lower dimentions exact and the upper one close I bondoed the winglet to the wing. Before the lower bondo fully cured I made fine adjustments to the angle to get the upper measurement right, then bondoed a board from the winglet to the bench. Great! Everything is fixed in place. Now - on to the next instruction... Now turn the wing over. Hmmm. I'd bondoed the board supporting the winglet to the bench. Helps to read ahead, doesn't it? I bonded a second board to the winglet, and this time bonded the other end to the wing, then removed the first board and checked all the meaurements for the eighth time. Jason & Char helped me turn the wing over and support it so I could get at the root inside layup area. I started cutting the foam wedges out, then kicked the winglet. Nice thing about bondo when it cracks away is that you can see exactly where it broke and put it back in place. I called for my helpers and we inverted the wing once again. I took the opportunity to cut out the rest of the foam wedges while the winglet was flat on the bench. Much easier. I'll do this work first on the other wing, that way I won't have to break the bondo half way through the job. [Note: Don't do this. See right winglet attach below]. I reattached the winglet and support board, rechecked the measurements and called for my helpers yet again to invert the wing. The layup looked simple, so I started it just before leaving for thanksgiving dinner. Opps. Not so simple. We were an hour late. I had trouble figuring out what to do with the rudder conduit. Its installed near the TE per RAF hidden bellhorn plans. In the end I understood what was needed and made a 1 inch hollow in the wing root for the nylaflow to move in. Plans don't say anything about the wing LE which is forward of the winglet attach area. (at least I didnt see anything about this). I floxed here also and ran two ply of BID out to the wing LE as for the winglet TE. This where the nav light goes, so there's not much structure involved.

Attaching lower winglet

When I came to hollowing out the pocket for the hidden bellhorn to reach the rudder conduit I had to do hours of "arthroscopic surgery". On the second winglet I'll do the following...

Before attaching the lower winglet, I will hollow out foam for where the bellhorn goes and where it attaches to the rudder and where it mounts in the winglet. I'll order the steel rudder cable and fittings in advance, cut off the conduit just inboard of the edge of the wing as shown in the RAF plans diagram, thread the cable and attach the fittings. Then I'll remove foam from the lower winglet to make a pocket which goes from where end of the bellhorn is going to be to about an inch forward of where the conduit exits the wing. This pocket will be about 9 inches fore and aft, about an inch deep and all the way from side to side. Now I'll glass the three sides this pocket. I'll use a piece of cured 2ply bid tape to build a "roof" over the pocket level with the top of the lower winglet and put some bid tape inside the pocket to hold the roof in place. After I attach the lower winglet and cut out the rudder I'll be able to tunnel through to my ready made pocket, snatch the rudder cable and attach it to the bellhorn. I'll be testing this method on my second wing in a few days. Check back to see if it worked. PS. It didn't! Well, not very well anyway. My "ready made pocket" turned out to be in the wrong place and at the wrong angle. I still ended up poking wet glass down a 7 inch by 2 inch hole and working with a flashlight to make sure I got rid of the bubbles. I won't be suprised if I have to cut a small door in the inboard side of the winglet to finish of the rudder cable fitting. So, if you can think up a better way to do this, try it. I got it done, but my way wasn't much to shout about.

I carved the lower winglet as best I could. The plans say make the attach layup flat, but it's flat along a complex curve so the shape you have to cut the winglet isn't really flat. I messed with this for quite a while. The plans are not very specific about how the lower winglet fits. The angle of the lower winglet is different from that on the upper winglet (at least mine are - and they're both the same), so there's no way that both sides of the rudder can be straight. All the EZ's I've seen are straight on the outboard side, so I settled for this. Another thing that caused me some puzzellment was the angle of the winglet. By this time you have a flat glass surface along the bottom of the upper winglet aft of the wing. Makes sense that the lower winglet sits square on this flat surface, which puts the leading edge of the lower winglet about an inch below the leading edge of the wing. This effects the final height (depth?) of the lower winglet. Only way to get the lower winglet flat on the glass of the upper one would be to change the angle of the skin at the back. This didnt make sense to me, so I let the flat glass guide the positioning. My lower winglets may be a little longer than others because of this. I can always sand them down later with a few bad crosswind landings.

When the winglet is carved plans say to use foam wedges and micro to fill the gap. I fixed the lower winglet in place with a screw at the LE and clamps at the TE, taped the outboard side and poured pour foam down the gap. Note that my leading edge was about 1 inch below the LE of the wing. I couldn't see how it could go anywhere else, so I had voids to fill on both sides. The pour foam worked well and filled all the voids. (but I've since backed away from using pour foam for anything. It sometimes shrinks or expands.) I sawed off the pour foam at the edges, then microed and added the single BID ply tape per plans. One ply of BID doesn't seem much to hold the lower winglet on, and 2 inch tape only leaves 1/2 inch coverage over the foam wedge. I widened the tape to 3 inches.

Next day I did the inside layup, cut out the rudder and proceeded to dig a tunnel through the foam to find my rudder conduit. I found it eventually. Now I have a 7 inch deep, 2 inch wide foam pocket to glass, and it has a rudder conduit near the end of it. Glassing this was fun. I covered the conduit with duct tape and taped it to the glass. Then I used a mixing stick to poke the glass into place. The result was a bit scrappy, but it'll do. If anyone wants to look at my bellhorn installation, I'll steer them to the right wing. (later correction - They can pick which side they want to look at - it won't matter!)

Right winglet attach

I tried my idea of carving out the foam first. Bad idea. This makes the winglet and even the wing skins flexible. I had to stuff foam wedges back in to stop the skins moving. I had a lot of trouble getting the position right on this wing. First I found that to get the aft postions correct the winglet tip was sticking up about 1/4 inch above the wing. That can't be right! I checked the template against the winglet and decided that I'd cut off 1/4 inch too much. Strange. I thought I'd been very accurate with that cut. Only way I could see to fix this was to put the piece back and cut again. Plans say to discard the piece when you cut it off, so I had. Couldn't find it anywhere, so I taped some thin foam, bent it to the curve and layed up 1 ply BID to extend the skin. Next day I recut the curve and... it still didnt match. After quite a bit of fiddling I reasoned that the center of the curve was too shallow, so I sanded it down a little and got a much better fit. I added a few dollups of bondo. Once the bondo cured I found that the measurements were off, so I removed the bondo and tried again. I repeated this cycle 3 times before finally getting the winglet in exactly the correct position. Plans say you need to be within 0.05 inches on A & B. I don't have the equipment to measure to that level of accuracy. I settled for as close as I can get with a ruler on all three measurements.

I did the inside layup, then ran out of epoxy. Once epoxy was delivered by my happy UPS guy, Ed, I prepared to do the outside layup. I'd made my A block with pour foam. It had shrunk to a crust. I don't trust this pour foam anymore. I made a new A block with urathane foam, carved it to shape and microed it in, then did the outside and inside winglet layup.

Right winglet attach

I carved and attached the lower winglet and stood back to admire my work. Strange - the rudder TE has a slight kink in it. I looked at the other rudder, now on the bench waiting for hinges. It also has a kink. After checking plans and archives, I called Jeff Russel - he know's his stuff and he's local. Jeff said that he thinks I'm OK, but maybe I should post the problem to the maillist group. I did, and got the following back from Nat.
Not to worry. Because of the airfoils and the different chord lengths, you
can't have both the outside surfaces in the same plane and the trailing
edge straight. Either by itself would probably be okay, but for sake of
consistency, follow the plans.
I asked which way is preferred - a bent TE or a canted winglet. Answer was:
Bent trailing edge.
Now - wasn't that lucky! That's what I have.

Cutting the rudder

I clamped the left rudder in place over the right winglet and cut the right rudder out with a hacksaw using the edge of the left rudder as a guide. They may be "bent" and they may be the wrong shape, but at least my rudders will be the same. :)

I did the rudder and aileron hinges at the same time. Added the "teflon" spaghetti from Gary Hall and riveted them in place. I left the bellhorns and springs until I get the rudder cable in Chapter 16.

Working alongside the wings, this chapter took me nearly three months and (including the wings) 220 hours work. I'ts gotta be downhill from here. Yea, right!

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