Chapter Two - Wings

I know. It's been a while since I last posted.  But I'm back.  Since the wing kit arrived ten weeks ago I completed Section 13 (Spar Assembly) and Steps 1 and 2 of Section 14 (Sub Spar).  I'll just catch up by hitting the highlights.  Step zero, of course, was to inventory the shipment, organize parts, and demolish the crates (I saved one of the crate lids).  But instead of demolishing the square crate, I thought perhaps someone in the neighborhood could use it for a backyard sandbox for a toddler.  So one morning I set the empty crate out at the end of the driveway with a FREE sign on it and did some driveway sweeping.  A minute later the driver of a landscaping truck turned down my street, drove by, stopped, backed up, and asked if he have it.  I said "Sure! Take it!" and helped him load it in the back of his pickup.  Turns out his dog just had a litter and with appropriate lining the sturdy crate was perfect for corralling the pups while letting mom hop in and out to attend to business.  Win-win!


So I started doing the inventory and at first thought I only received wing ribs for the left side, since all the ribs were tagged "L".  For a while I thought perhaps I received ribs for two left wings and that some other builder somewhere received ribs for two right wings (which would have meant having extras in case I bungle a rib - not necessarily a bad thing).  Closer examination, however, revealed that L & R ribs were stacked as pairs and that the "R" rib labels were simply hidden by the "L" ribs.     

The first thing in Section 13 is to separate the rib clips with the band saw (snips work too) and debur and remove the connecting material with a scotchbrite wheel.  Then I lined up a bunch of small nails on the salvaged crate lid to hang the clips to give 'em a coat or two of self-etching o.d. primer "just because".

Next step was to drill and tap 3/8" x 16 tpi holes in both ends of the AEX (I think it stands for Aluminum EXtrusion) bracket that came pre-riveted onto each wing spar with the over-sized rivets.  No drama with broken tap handles this time.

One of newly threaded holes will be for an eyelet bolt to serve as a wing tie-down point.  I'm not sure yet what the hole on the other side of the bracket is for.  Pilots use tie-downs 'cause you don't want your plane taking off without you when a bit of wind comes along.  At AirVenture last year either a gusty wind or a windy gust lifted a WWI replica plane up and on top of another plane parked at the event (Oshkosh follies).  Another time as a student pilot I watched the rotor wash from a big Skycrane helicopter lift a plane not tied down at the Madera airport off its gear and into the plane parked next to it (Madera follies).

With drilling and tapping the AEX brackets completed, on Page 13-03 we

1.  Cleco the rib clips to the wing spars;

2.  Cleco the outboard attach clips to the wing spars;

3.  Rivet the outboard attach clips;

4.  Rivet all the rib clips; and

5.  Rivet all the factory-installed rib clips as marked in the plans (mostly LP4-3's, and a few of the slightly longer LP4-4 blind rivets). 

Once again the pre-punched rivet holes are close to the 90-degree angle on the rib clips making it impossible to get the pop-rivet tool barrel square onto the rivet, so again we used the little wedges to pop the mandrel from the rivets at an angle.  In case you're wondering what the circle thingy is in the picture, that would be one of the two wing spar bushings.  Here's a picture of what it looks like when it's removed.  Due to thermal expansion of aluminum I can remove and insert these when it's hot, but not when it's cold.                            

                                            Eventually large pins will go through the brass bushings to transfer up to several thousand pounds of load (or lift) from the wings to the fuselage (and vice-versa) depending on g's, so the spar bushings and pins are definitely of the DO NOT REMOVE DURING FLIGHT variety, not that you could. 

Counting up the used mandrels from all the pop-riveting indicates that about 150 rivets were installed in steps 3, 4 & 5 to fasten 20 rib clips, the outboard end clips, and the rib clips partially installed at the factory (they did the big outside rivets but not the small inner ones).  Just 11,000 more to go, give or take, but who's counting. 

Wrapping up Section 13 I hung the spars up out of the way with the assistance of a neighbor across the street.  I'm amazed at the engineering on these things - relatively light yet very strong.

Moving on to Page 14-02 Step 1 we simply cleco on the inboard doubler plate to the stub spar which becomes a good place to apply a clamp to keep the piece stable on the work bench while drilling countersinks in Step 2. 

In Step 2 we use a countersink bit to countersink holes in the stub-spar.  There's 42 holes on each side (as all good science-fiction geeks know, the number 42 is also the Answer to the Ultimate Question of Life, The Universe, and Everything).  Both sides times two wings gives 168 countersinks.  That took a couple of work sessions and gave my drill battery a good workout.  Until now I've checked each of my countersinks with a flush rivet to test for "flush-ness".  In this case however there's no rivet to test with.  Later on in Section 17 wing skins will be attached directly to the stub spar with CS4-4 rivets that will form a very shallow dimple to make the wing's inboard leading edge as smooth and round as practical.  So to get the depths right Vans has us drill a ¼-inch hole in a piece of scrap aluminum to use as a depth guide.  When the countersink is exactly ¼-inch in diameter the depth is correct.  Just be sure you check the guide hole with your micrometer before you start.  My first guide hole was too big so I had to go down one bit size (15/64ths).  The second hole was slightly oval-ish, but the "skinny" side of the oval was exactly 0.25 so I marked and used that as my guide.  In the end a few of my 168 countersinks came out a teeny-tiny bit oval-shaped due to the drill not being perfectly square-on, but I think they're okay.  Good news is that the guide worked just as well as a rivet would have for checking depth and I don't think I under- or over-countersinked any of the holes.