Sunday, February 7, 2016

Finishing the wings

After all the test fitting, it was finally time to start prepping (cleaning, deburring, and priming) the wing components for final assembly.  Many hours spent deburring and cleaning the ribs, as well as taking the edge off some of the sharp corners on the spars.  The test-fit also highlighted a few places where the holes in the ribs and/or skin were of different sizes and required drilling out for proper fit.
Wing ribs, channels and rear spar primed.

Main spars primed
Match-drilling rear spar doubler and rib holes
Match-drilling rear spar and spar doubler.
Final assembly began with the individual ribs - affixing brackets and doublers as required - and the rear spar.

Assembling individual ribs
All wing ribs assembled
Riveting the rear spars - I ended up drilling out a number of rivets joining the rear spar
and the rear spar support channel - the channel interferes  with the riveting of the rear of
the ribs, so it is easier to rivet at the end as opposed to earlier on.
Next steps were setting the spars on the wing jigs and riveting the ribs. It takes a bit of planning for the ribs in the wing step area - be sure to do a dry run first to ensure you can access the rivets with your hand or pneumatic riveter.  I also riveted the ribs in place with the bottom skin clecoed in - thought that would help ensure proper lining up of all the components.  Also need to remember that nose ribs will be added to the outboard ribs, so some holes will need to stay open for riveting at a later time.

Left wing main and rear spars on the wing jigs.

Left wing ribs clecoed to spars and bottom skin.
Riveting left wing ribs.
More left wing ribs riveted.
All left wing ribs riveted.

All right wing ribs riveted.
Next step was to verify that both the top and bottom skins still fit, and that the fuel cell, leading edge, and flaps and ailerons all fit all aligned properly.  Once proper fit was verified, the riveting of the bottom skin began.  The top skin was not riveted yet as none of the pitot/static tubing or wiring had been installed.

Verifying alignment of left wing skins and flap.
Testing fit of left wing fuel cell and outboard leading edge.
Left wing bottom skin riveted - last few holes at rear of wing step (right side of photo)
were not riveted because the top skin folds over in this location.

Next step was running the wiring and the pitot/static lines.  The wiring runs (for the wing nav/position/strobe lights  and the taxi/landing lights) were initially roughly laid out.  After the final routes were determined, the wire was then placed in expandable sleeving and the sleeve was attached to the frame.

Right wing rough wiring run.
Wire run to the wingtip and to the taxi/landing light - note the various techniques used for
securing the wire - bushings, Adel clamps, tube stand=offs, and brackets that had been
permanently affixed to the skin surface.  The idea for the vertical bracket holding the
wire run for the taxi/landing light came from Peter and Des - builders in Australia.
After inspection by a local EAA Technical Counselor, the top skin, fuel cell and outboard leading edge were then clecoed together and riveted. I riveted the fuel cells,leading edge and top skin at the same time.  Doing it this way allowed easy access inside the wing to tighten the fuel cell bracket bolts and also ensured all the components aligned before setting any rivets.

Left wing leading edge ribs ready for riveting.
Technique for removing the plastic coating from flat sheets.  Starting at one edge, pull up about
2-3 inches of plastic and start to wrap around a small diameter tube.  Using vice grips clamped
 to the tube, start rolling the plastic off by wrapping it around itself on the plastic tube.  This
 method is much easier than trying to do it all by hand.
Left wing top skin, leading edge and fuel cell clecoed and ready for riveting.

Left wing skins, fuel cell and leading edge riveted.

Right wing top skin, leading edge and fuel cell clecoed and ready for riveting.
Skins on both ribs riveted

Like a few other builders, I decided that I would fill in the pull rivet heads for a cleaner appearance once painted.  I used a mixture of epoxy with microballoons. Droplets of the mixture were placed on each rivet head using a syringe with a very fine blunt needle.  After the epoxy set, the excess was easily sanded flat.  An issue that frequently ran into with this process was that air bubbles would get trapped in the epoxy and would leave gaps after sanding - necessitating a second pass of epoxy.  This was a bunch of extra work, but the final product will look a lot cleaner.

Filling rivet heads with epoxy/micro.

Filled rivet heads after sanding

The final step for the wings was attaching the wingtips.  The location for the wingtip light brackets was measured on each wingtip and holes were drilled for the wiring and for the rivnuts used to attach the brackets.  My lights used a different size screw than that suggested in the plans - be sure to check the screw sizing for your lights to ensure you use the correct rivnut size in this step.  I used epoxy/micro to smooth out the seam between the wingtip and the wing  skins.  A thin coat of epoxy was also smoothed over the entire wingtip to fill in any pinholes.  After sanding, this left a nice surface for future painting. 

After finishing the wingtips, it was time to build a wing stand for storing the wings while completing the fuselage.  I just sort of free-lanced the wing stand.  I had seen many photos of wing stands with the carpet sling for the wingtips and a solid frame for the wing root, so I just sketched out something that I thought would work.  Wheels were added to allow the stand to be easily moved in the workshop.

Location for wingtip light brackets marked off on both wingtips.
Wingtip light brackets installed.
The front edges of the wingtip rib required some trimming to fit without denting the skin
Left wingtip rib installed
Left wingtip clecoed on and ready for riveting.
Smoothing the seam between the skin and the wingtip using epoxy/micro.
Completed wings on wing stand. 


Hilliary said...

How many rivets are there in one wing??? Impressive!

Gordon L said...

Hey Hilliary - I didn't count, but the wing kit inventory says I got just over 6000 rivets, so maybe just under 3000/wing when you take overage into consideration!