Chapter 19 - Wings
Templates built, it was time to build jigs and bondo them to the floor:
Gettin' jiggy with it
Cut the foam blocks to size and lay templates on them:
Then hot-wire a perfect core, if I do say so myself:
The right wing in the jigs, with the wing attach bolt fitting layups just knife-trimmed:
Shear web and spar cap I have no photos of.
Finally, my brother and I skinned the bottom of the right wing. Even at 60 degrees F in the hangar (IR lamps kept the work at 70-75), we had to work fast!
After a lifetime of squeegeeing:
Whereupon a problem became evident: for the #5 jig, the jig is misaligned -- the trailing edge is 1/4" high! Hadn't actually noticed it before, but I sure did now! Oops; had I re-read some of Dave Orr's helpful hints and tips, I'd have known about it ahead of time. Yes, the per-plans jigs are a bit off. Hey, I guess that means I did it right....
Well, I'm certainly not going to have my inboard section that far out of true...it'll create drag! So when it came time to put the bottom jigs on and flip the wing so as to skin the top, first I cut down the #5 jig at the TE. Then, I bondoed the whole thing to the table. With luck, this'll hold the wing in the CORRECT position while the top skin cures, locking everything into place....
It almost worked. What we did wrong was we bond'ed jigs to the lower skin, and flipped the wing, after only 36 hours or so of cure. It FELT fully cured, but the strong tension force pulled the bottom skin away in a couple of 1" patches. It's repairable; just inject a little micro and weight it down....but for the left wing, I'm waiting longer. And I'm starting with the jigs in the correct orientation!
Notice, though, that the TE is die-straight and the wing looks beautiful. Rapture!
While waiting for things to cure, we amused ourselves by hot-wiring the left wing.
Most of the foam is old; came with the project. But here I used some recently-purchased stuff from Aircraft Spruce. At first I wasn't impressed; the stuff looked like it had been cut to length with an axe! On further examination, though, I noticed that it was oversized in every dimension. Hooray! This came in very handy; it completely eliminated some of those "scrap foam piece" placements, and just cleaned up the hot-wiring immensely.
This is the right wing with aileron removed, the well glassed, and ribs glassed. Note the additional wing pin near the front edge of the wing; this it to prevent the leading edge from wiggling up and down during full aileron deflection. With the aileron lengthened 20", this pin is probably needed to keep the wing from flexing.
A close-up of the wing pin. It's an AN4-11A bolt; the head is buried in the foam inside a 1/4" thick piece of aluminum; the D-shaped piece you see here goes over the rib layup and is 1/8" thick. Later, it receives a 1-ply BID cover (NOT shown here). Much later, I plan to grind it to length and to a rounded tip; it will mate to a socket on the outboard side of the strake.
An industrial accident claimed the photos of left wing construction. (Lesson: if you're the sort of person who's dim enough to snap away with a 35mm camera with no film in it, you must NEVER leave that camera unloaded, at any time. Alternatively, spring for a digital camera like a normal person.)
Suffice it to say the left wing looks a whole lot like the right one, except that it's considerably yellower. This is actually due to a minor change in the formulation of Safe-T-Poxy which has recently taken place. Temperature and humidity were much higher during left wing layups than they were for the right. Both are still in the tolerable range, so strength will not be affected.
With both wings built and ailerons installed, it was time to mount them to the spar!
These days, the fashion is to mount the wings to the spar, THEN mount the spar in the fuselage. I didn't know that; I was silly and did things per plans. Fortunately, the spar went on straight and level...more or less. At the time of writing, the right wingtip is 1" low, and 3/4" further away from the pitot tube. These numbers are well within tolerance, but I'm going to see if I can bring them to zero before mounting the wings permanently.
In the meantime, some photos of the wings mounted with Bondo:
The wing supports are makeshift (sawhorses, lumber, foam...in one case, a table saw). But they're sturdy, so they work.
During this process, I fiddled with the wings until they were exactly level and even in sweep and fore-aft, within the limits of my measuring ability. It took a lot of maneuvering, but I made the error mentioned above disappear. Measure thrice, cut once...it was time to drill holes for the wing attach fittings.
This was WORK! I opted to use the per-plans spot-face tool, despite which the spot-face tool isn't really designed to drill a 5/8" hole through that much aluminum and fiberglass. As a result, it got HOT! Hot enough to delam the final layer of glass, in fact. Fortunately, this was an inboard hole, so re-attachment was easy. After that, I went MUCH slower, with frequent breaks to cool the tool. In fact, it took me over a week to drill the holes. Eventually, they were done.
After a not-so-quick detour to Chapter 20 to attach the winglets, I was ready to re-attach the wings!
This was MUCH easier said than done. Whoever billed this as a "trailerable" airplane was stretching things; certainly it's not easy for ME. Alignment went fairly well, but I overestimated the depth of four of the six holes, and so had to wait for additional bolts. That done, I found more problems. Many more.
The inboard attach bolts are almost easy. I can reach both sides at once; I can see at least one side at a time. It only took about two hours to get these down to a science.
The lower outboard attach bolts are harder, but workable. I can see the front (nut) side through the lower hole in the spar, and reaching both sides isn't TOO hard. About four hours, per bolt.
Alas, reaching the upper outboard bolts gets harder! Worse, I found that on the right side I'd drilled my holes just slightly too close to the top edge. What that meant was that, with the nut held in a socket wrench, it won't quite align and allow itself to thread onto the bolt. No, I have to hold the nut in place with a monkey wrench, turn the bolt until it starts threading, THEN switch to the socket wrench, which works fine. Guess how many times I dropped the nut out of the monkey wrench? And of that million and one times, how many times do you suppose the nut fell out the hole directly underneath it? Zero, of course...the nut always went flying into the interior of the spar, and did NOT want to come out! Murphy strikes again...and again.... I estimate about half a million man-hours per bolt. With practice, I ought to be able to cut that time almost in half!
Happily, the wings are on. I plan to remove and re-attach them as few times as humanly possible:
Very satisfying; it almost looks like an airplane!
At this stage, I also hooked up the aileron control rods (Ch 17). The left side rubs on the rudder pulley, and will need some adjustment of the bracket next time the wing is removed, but overall, it works well.
Update 16 Jul 01: the wings are removed, the left side bracket HAS been adjusted to prevent rubbing, and the wings are getting sanded and filled. A long process!
Update 16 Oct 01: the wings get a multi-ply carbon layup in the aileron well. Why would I do this? Well, I was a bit concerned about the possibility of the upper wing skin flexing in high-speed flight. Should aerodynamic forces move the upper skin, with the attached aileron hinges, enough, the aileron could possibly contact the lower skin. This could cause rubbing, or possibly even control lock! It may already have caused an EZ accident. We can't have that.
What to do? I'd already built the aileron wells per plans except for the 20" aileron extension. I couldn't thicken the skins appreciably, especially the hinges were already attached; it would destroy the fairing line of the ailerons.
What I did was, first, I sanded off 1 ply layer at the hinge attach points ONLY.
Then, I added carbon. I chose the carbon for its strength and stiffness; a little bit would keep the skin from flexing. The downsides: expense, the fact that carbon acts as a metal for purposes of antenna reception (not really a factor; my antennae were far enough away) and corrision (add a thin ply of fiberglass to keep from corroding the hinges!). Also, the stiffening of the aileron well will also change the structural characteristics of the wing, possibly undesirably. Since the aileron well layups aren't integrated with the rest of the structure and don't run to the wing root, I think the structural effects will be minimal.
The new aileron well, before the final thin ply of fiberglass on the hinge areas:
Net result: same thickness at the hinge attach points, minimal added weight, and I can no longer move the top skin by squeezing against the top and bottom, as I could when it was only glass.
I should have done this as an original build, replacing some of the original layup schedule. Save weight and time. Well, next time I'll know.
This "mod" should keep me safe during high-speed flutter tests, Vne calculations, and other intentional violations of the handbook's maximum speed.