Main Wing Spars

Wing construction begins with the preparation of the main wing spars. These spars are the structural backbone of the wings, holding all of the load from the weight of the aircraft during flight. The spars are partially constructed at the Vans factory. Their thick reinforcement bars come riveted to the main spar channel and the entire assembly is anodized (treated with Alodine) to resist corrosion.

The first task is to rivet on all of the tank skin attachment platenuts. There are 120 of them. These platenuts are used so the fuel tanks can be attached to the wings using screws. This allows the fuel tanks to be removable in case they need to be serviced for leaks or other problems.

The rivet holes for the platenuts (there are 240 of them) all needed to be machine countersunk so that the rivet heads are flush on the outside surface. The flush rivet heads allow the fuel tank skins to sit nice and flat against the wing spar for a smooth, aerodynamic surface.

I used a screw with a nylon sleeve as a tool to hold the platenuts in place for riveting. I found that this was more effective than clecos for holding the platenuts flat against the spar flange.

Tank Skin Platenut and Sleeved Screw for Mounting
Platenut Held in Place
Cross-Section View
Rivets Ready to be Set
Riveted Platenuts
The Flush Side of the Spar Flange

Once the tank skin platenuts were all mounted, twelve more platenuts per wing need to be mounted on the bottom side only. These are for screws on the three access plates on the bottom of the wing that may be removed to inspect and service the interior components.

Tank Skin and Access Panel Platenuts

With all of the platenuts installed, the screw holes (the center hole for the platenuts) must be machine countersunk to make room for the dimpled skins and the screw heads. These were deep countersinks and I found that running the drill very slowly produced the best results.

Machine Countersinking the Screw Holes
Countersunk Holes Cleaned Up

Finally, there are a pair of platenuts on the inboard ends of the main spars that are used when the wings are mounted to the fuselage center section.

Platenuts held in place with Clecoes
Main Spars with the Inboard Platenuts Installed

This completes the first set of wing tasks. There’s one thing I need to do still. That is to spot-prime the big countersunk holes where the anodizing has been cut away and raw aluminum is exposed. I will do this after the next task because that task will involve a couple of parts that will need to be primed. That way I can do both things with a single patch of primer.

The next project will be to fabricate, prepare, and install the tie-down anchors to the main spars. The tie-down anchors hold the large eye bolts that are used to rope the aircraft to the ground when it’s parked outside.

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