Chapter 19b - making the wings

Jigging the wings

I cut out the recesses for the wing attach points and added the aluminum hard points. Ready to do the sheer web, but out of epoxy. I hope the wing doesn't warp while I'm waiting for materials. I removed the jigs from the right wing and set them up for the left wing. I repeated the "jiggling" process for the left wing cores. As for the right wing, the angles on the cores were not quite perfect. I thought I'd been exact on the measurements. Either the jigs were wrong, or the angles were a little out. I decided that the wings looked straight if I let them follow the jigs, so I filled the 1/8 gaps with micro. Once the left wing cured in the jigs I cut the hard points then removed it and stored it with the other wing in the front room. Hurricane Irene was bearing down on us with 70 mph winds, so I wanted the wings and winglets somewhere where they wouldn't take their first flight without the fuselage. Also, both wings seem very straight and I wanted to keep them that way.

Sheer web & spar cap - left wing

Anyone following this journal must think I'm a complete klutz by now. Rereading I find that it sounds like I make errors everywhere and every job sounds like a disaster. Actually, things are going along very well - its just that my mission statement for this log was to report things that went wrong rather than just retype the plans. Anyway, just to dispell the klutz rumour I will report that, when I did the left wing sheer web, NOTHING went wrong! I didn't run out of anything, nothing didn't fit, nothing exothermed and everything cured correctly.

Reassembling the cores

I love the way these jigs are used for everything by adding or removing parts. I just wish mine were a little more substancial and didnt jiggle around so much. I made mine with 1/2 ply. FAQ says to make them with 5/8 or better. I know. I wrote the FAQ after making my own jigs. [later note - I'm reconsidering that FAQ item. After skinning the wings are a fairly tight fit in the jigs. A 5/8 width would be a problem since the jigs surface is square and the wing is angled. Even with 1/2, I had to sand a slight angle on one of my jigs to get a good fit.] Also, the fit isn't very good. I cut my jigs as accurately as I could, but the cores dont fit perfectly, even where I know the cores are perfect. Other builders have had the same problem. In any case, the jigs do their job admirably. I am quite pleased with the way mine are attached to each other. I used 1/4 bolts and nuts per plans, but found that the wood became threaded and the nuts made no difference. I use my electric drill with 1/4 socket to remove or add a jig part. When removing I stop before the bolt comes out altogether. This way I can change the jig arrangement in a couple of minutes.

As I said, the sheer web went fine. No problems at all. I added the extra 3 BID layup and the metal parts and left them weighted for cure. To get best possible results on the sheer web I used plastic to help the squeege get excess epoxy out, then removed the plastic and peel plyed the spar cap faces. I was a bit worried that the spar cap at the wingtip was too shallow. Plans say it should be 0.075, but mine looked to be half that, so I built a dam with spare blue foam to make sure the cap didnt spread over the wing foam at the wingtip. Compared to the canard spar cap, the bottom wing spar cap was quick and easy. No problems. I had to add an extra strip around BL 65 to get it flush. When the spar cap was done I removed the dam, and found that the cap was perfectly flush until the last few inches. I'll need to contour there with dry micro (but NOT on top of the spar cap). I'd used a 3 inch squeege to do the squeege work. Once the dam was removed I used a 6 inch one to do a final pass and get everything smooth.

Bottom wing skin

I did the flox corner around the attach hole. I'd sanded a joggle here to allow for a BID cover to sit flush. Strange - I can't find anything anywhere in the plans about making a cover for this hole. In fact, the wing glassing instructions don't mention cutting the hole out again. I hope I'm not missing something here.

[Later note: If you think you might be missing something, you probably are! I WAS missing something. You cut the holes out AFTER you've done the wing ribs and the reinforcement which crosses over the attach holes. I shouldn't have made my depressions go all the way to the spar cap because the overlapping glass in this area stays there. Also, I shouldn't have cut the attach holes out until after doing the crossing layup. This way I would have had wing skin under the crossing UNI layup. I added an additional reinforcement to fix this mistake.]

Another item that was bothering me was wing tie downs. I don't see anything in the plans on this either. I'd bought a couple of padlock latch fittings which would do nicely, but before fitting them I needed to know the width of a standard (spam can) tie down. I posted a question to the list and got 10 or more replies, but no one actually gave me a width. What I did learn is that my idea to glass the tie down loops to the bottom skin was a very bad idea. A strong gust and I'd be left with a rope and a wing skin. The airplane would be long gone. Turns out Robert DuBois has designed a really neat tie down system and provided drawings. His approach is simple, structurally sound and doesnt involve carrying I bolts or drilling holes through the spar caps. I'll definately do mine his way.

I started microing the cores at 3pm using fairly think micro because there were a few nicks I wanted to fill. Took about an hour to get it all done. I decided to give the micro an hour to set a little so that squeeging the first ply wouldn't just lift it out of the nicks. I started laying out the glass at 5pm. Jason held one end while I positioned the glass. {Jason, Chars son, is an A&P with composite experience). I smoothed and pulled the threads straight using rubber gloved hands. Once everything was smooth and straight I mixed up the first cup of epoxy - and the phone rang. An old friend I hadn't spoken to in years. I'd mixed almost a whole cup and knew it would exotherm in a few minutes. While I was on the phone Jason poured the epoxy and spread it around. Just to help me catch up, he mixed three more cups while I poured and squeeged as quickly as I could. Had to be careful pouring because the MGS is so thin it runs off the part. The last cup was used to lightly brush any dry areas. I squeeged the air out and moved on to the second ply. Again, I had a little help laying the cloth, but then I was on my own. The second ply wet up almost by itself. I little stippling and hair dryer work and I only had a few patches to touch up. Next the UNI and BID reinforcements. It would have helped if I'd precut the BID, but cutting when I needed it didnt take much time. The temperature was 74 and dropping slowly. My epoxy was at 110 in the hot box. No problem squeegeing the second ply. The epoxy was still very wet. After squeeging the part all I could I peel plyed the areas specified per plans, then put my 4 mil plastic sheet over the entire thing. This worked very nicely and I was able to pull out a LOT more air and epoxy working along the wing with the hair dryer. Squeeging through the peel ply made no difference.

I looked at the trailing edge and noticed that it dipped slightly between the jigs. I was prepared with a new 2 * 1 * 10 alum extrusion ($8 from home depot - sold as screen room framework). I clamped this to the TE to pull the TE up flat. The clamps I used dug into the fishtail foam a little, but I'll be cutting this off in the next step anyway. I finished the work by 8:30. Total time was about 1 hour for the micro and about 3 1/2 hours for the layup. Next morning I did the knife trim (temp overnight was in 60's) and left the wing to cure for the morning. The wing looks great and it really wasn't a problem to do it mostly by myself. The plastic gave me a very nice smooth finish and, I'm sure, a light part. Thanks, Bulent.

Left Wing continued

Ever done a knife trim after 4 days cure? I don't recommend it. My dremel and hacksaw did the job eventually. I nicked the rudder conduit while trimming the outboard end. I'll wait to see how to fix this when I add the winglets and rudder controls. I added a little dry micro to the trailing edge and bondoed a level block to the skin. Plans don't say WHERE to put the incidence level, so I put it close to the edge so that the supporting block would be in the way of the crossing layup for the attach points. Duh! Later I had to knock the supporting block out, but managed to do this without disturbing the level. Had no helpers that evening, but manhandled the wing off the bench and onto its trailing edge (on foam supports) by myself. I dug out the foam for the rib using a small drum sander on the dremel. There has to be a better way to cut away 0.7 of foam, but I got it done. I wasn't happy with the reinforcing layup on my inboard hardpoint. It had a few dry spots and a couple of bubbles. I sanded it down and added another two ply.

Wing Ribs

Right Wing

Sorry for the error - sending UPS overnight today (Thursday).  You will receive Friday
Linda

I did the bottom skin with no problems, but when I turned the jig over I noticed a bump along the foam joint nearest the wing tip. I put my 10 foot straight edge on the sheer web and it rocked at the bump. The same thing happens on the forward and trailing side of the sheer web. The bump is only about a 1/16, but this translates into about 3/16 at the wing tip. Let me put it another way, my wing is bent. Actually its not my wing, its Char's wing - but dont tell her. I broke the wing off the jigs and tried the straight edge on the other side. Yep. I have about 1/8 gap in the middle. The bump is really an angle where there shouldn't be one. All is not lost. The wing can flex until the top spar cap is done. I triple checked for level on the jigs, put the wing back, lifted the tip a little and weighted it down in the middle. Of course the bending I get from this will be along the entire length, not just at the angle, but it will move me in the right direction. Next day the wing seemed perfectly straight. I used bondo to stick it back to the jigs, then sanded away the bump as much as I could without damaging the sheer web. After checking for level and zero twist at least three more times I did the top spar cap. The trough was a bit overfull, so I took the opportunity to shorten one of the plys so it ended just before the bump in my sheer web. Before the spar cap cured I checked the wing again for straightness. Perfect. After cure I found that the spar cap was definately a bit proud of the foam. Sanding spar caps is my least favorite part of airplane building. If I were doing this again I'd double check the depth of the spar cap trough in a few places and sand it down if necessary.

I was out of slow hardner, so I had to wait for more before doing the top skin. Wouldn't dream of doing it with all fast hardner. The slow hardner took 4 days to get here (maybe thats because its slow hardner), so I had lots of time to prepare for the "big job" of skinning the wing top. I installed the rudder conduit (per hidden bellhorn plans from RAF) and filled the channel and other dings with dry micro. Plans say to do this just before glassing, but I've found that this always leaves a small depression. I prefer to let the micro dry, at least partially, and then "top it off" just before glassing. As with the left wing I did the micro, then took an hour's break before starting in on the glassing. With the left wing I cut the glass as needed. This time I had precut all the glass for the UNI plys, BID ply and other reinforcements. This saved me quite a bit of time during the layup, but did cause some confusion. When I came to lay the second ply I had no idea which way to lay the folded precut glass for the inboard piece. A little planning might have helped here. I layed it on the job, unfolded it and moved it around until I had it in position. Total time for the layup was about 7 hours. Actual glassing time including my 4 mil plastic ply, was about 3.5 hours. I had no help with the layup. Next day I did the two ribs and added some micro to the training edge. I now have a set of wings.

BUGS