13th January 2013 - Left wing top skin

The wiring is in, the inspection hatch is in, the plumbing for the pitot is in, the remote compass is in, and the inside of the wing is fully sealed with epoxy varnish. I hope I haven't forgotten anything because today with the essential help of my friend Paul (the fastest stapler in the west) the top skin was glued onto the left wing. It simply isn't possible to apply the glue fast enough with just one person before it starts to gel in the pot. The glue was the usual mix of West system epoxy with the 206 slow hardener and a 6% addition of microfibres. This was spread over the ribs, spars, and leading and trailing edges of the wing structure and then onto the wing skin completely filling the gaps left in the varnish by the masking. Actually the latter statement is not exactly correct. Applying the Randolph EV-400 epoxy varnish thinned to soak into the wood also resulted in it soaking straight through the masking tape and varnishing the protected areas almost as though the tape wasn't there! Still I enjoyed the hour spent sanding it off where it shouldn't have been in the first place. Note for next time use a plastic tape.
The glue can now set overnight before I remove the clamps but even with them and the nailing strips in place the aerofoil already looks superb. It is no wonder the Tailwind is so fast with such an elegant thin section wing.

11th January 2013 - Left wing plumbing and wiring

The final job on the wing before gluing on the top skin was to install all necessary plumbing, wiring, and components. This comprises the tubing to the pitot, the remote compass and its wiring, and the cables for the wingtip strobe and navigation light. 5/8" holes were drilled through the three sheeted ribs to take SB625-8 plastic bushes. The holes in the inboard rib were positioned so the wires and tubing will pass directly into the rear spar cover and connect to the wiring in the fuselage. The wiring to the remote compass was kept separate from the strobe wiring to ensure that no interference would take place. Wires were secured to the lower skin using self-adhesive cable tie bases and were protected as they pass over the ribs using spiral wrap.
The second picture shows the pitot mount with the pitot installed. The mount is screwed to the back of the spar with 1/2" stainless steel #8 screws and glued to the lower wing skin with a slurry of epoxy mixed with microballoons. This provides a light but stiff seal between the shape of the lower skin and the straight bottom plate on the pitot mount. As the picture shows it will be easy to check both the pitot and the strut attach as well as the general condition of the inside of the wing through the access panel.

7th January 2013 - Sealing the inside of the left wing

I hate painting! probably because I'm so bad at it but it has to be done. Yesterday and today I gave two coats of Randolph Epoxy Varnish EV-400 to the inside of the left wing. The first coat is thinned about 50% to ensure it soaks into the wood. It is important to keep the surfaces to be glued free of varnish so the top surfaces of the wing ribs and spars were not varnished.
The varnish takes about 7 days to fully set and then is impervious to pretty much everything.
The top surface of the wing is still to be glued on and of course can't be painted when it is in position. It was first rough cut from one of the scarf jointed lengths of 3/32" mahogony ply  then masked off  to match the ribs and spars. The glue will be spread to fill the gaps in the varnish.
Next job is to fit out the internal components in the wing: the remote compass, the pitot, and the wiring for the nav and strobe lights, then it is a case of varnishing the inside of the top surface and gluing it on.

3rd January 2013 - Under wing access panels

It is inevitable that at some time access will be required to the inside of the wings so I decided to install an access panel in the underside of each wing just behind the strut attach bracket. In the left wing, this will also give access to the pitot connections.
I used the CNC router to cut out two 60mm radius disks out of 3/32" aluminium with six holes spaced radially on a 55mm circle. These will form the access panels. Then two rings were cut with matching holes and a centre 50mm radius hole and outside diameter of 140mm. Next a 120mm diameter hole was cut in the wingskin using a flycutter and a cutout for the pitot mount was also made. The mounting rings were then drilled for 6 platenuts which were flush riveted into place. The access panels were countersunk to take #8 screws. One ring was then bonded to the inside of the left wing and clamped into place for the epoxy to set.

5th December 2012 - Lower right wing skin

The picture shows the left wing after the clamps were removed and the wing turned upside down. I'm going to leave the stapling strips on until eveything is finished to provide a bit of protection to the wing skin. There are a lot of staples to be removed !
The left wing was then stored against the wall and the lower skin of the right wing glued onto the structure. Next job is to varnish the inside of the two wings to protect the wood. Then I'll install the various cables and tubing for the pitot before installing the top skin.

4th December 2012 - Left lower wing skin

Today it was time to glue the first of the lower wing skins into place. First job was to cut the  4-1/2" x 8' piece of ply cut off yesterday into 8 strips using the bandsaw. 4 of these will be used to staple the skin onto the two spars and leading and trailing edges of the wing. The rest will be cut up and used to staple the skin to the ribs.
A batch of West Systems Epoxy was made up with the slow 206 hardener. Even with the slow hardener the epoxy reaction is exothermic and in the confines of the mixing cup can get hot and gel quickly, so enough was made in the first batch to coat inside the lines marked on the skin itself.
Once the glue is spread out the working time is considerably extended so another batch was then made up to coat the wing structure itself.
The wing was first placed on the bench upside down and once all the glue was applied the skin was slotted over the strut attach brackets and into place. Working from the middle out the skin was then stapled onto the main spar. Then, again from the middle out, the skin was stapled to the ribs between the two spars. Next the skin was stapled to the rear spar and then the rearmost section of ribs and the trailing edge.
This process was repeated with the front section of ribs and the leading edge with the exception of the innermost stub rib.  As the curve of the skin is greater at the front, clamps were also used to ensure the staples would hold. The wing was then turned over to check that the joints looked properly glued and clamped.
Then the skin was clamped onto the innermost stub rib. This is easy enough behind the main spar but in front of it there is a significant bend in the skin. Multiple clamps were
 required to hold the skin to the tapered section of the main spar and to the stub rib itself as staples did not have enough holding capability. The front section of skin was also painted with epoxy which when fully set should help it to hold shape and reduce the stress on the glue joint. I think I will also install some fillets of wood in the joint before closing up the wing.
Next job a full 24 hours for the epoxy to set.

3rd December 2012 - Preparing the wings for the lower skins

Over the last few days I have glued the scarf joint for the other top wing skin and fastened the lower skin to the wingtip of the right wing. Today was spent sanding the scarf joints into the edges of the lower wingtip skins so that the main skins can overlap them. A 12" sanding block was prepared with sandpaper on 4" or so of the surface and then a smooth area over the rest of its length.. This allowed the block to rest on the penultimate rib whilst sanding the wingtip skin to create a flat level with the rest of the ribs. Easy enough to say but a long and laborious process! However, finally both wings were prepared ready for gluing the main skins. Next the full sheets of plywood
for the lower skins were cut down to a width of 42.5" which reaches neatly across the width of the wing. The offcuts will be used for making more sacrificial stapling strips.
A cardboard template was made to fit over the strut attach brackets. Then for each wing in turn the lower skins were positioned and the locations for the cutouts marked. The template was then used to trace the outline and a rotary rasp used in the Dremel to cut to the outline. Following a bit ot trial and error the hole was then made to fit snuggly over the brackets and the wings skins positioned ansd clamped into place. The wings were then turned over and the positions of the ribs and spars marked in pencil - just visible in the picture. These markings will allow the glue to be applied in the right places without too much excess. Like the wingtips, the markings were also then transferred to the outside of the skin to allow correct positioning of the attachment staples into the ribs and spars. Next job to glue one!