8th September 2013 - Tidying up the doors / 3D printing

I need to order some ceconite, glue, and paint to cover the wings so while that arrives I did a bit of work to tidy up the inside of the doors. The Wittman plans give the basic outline of the doors and the door latches but no information on internal finishing.
My intention is to cover the inside of the doors with fabric but that left the issue of how to tidy up round the door latch mechanism.
I started off by making two box structures, each out of two pieces of aluminium to cover the mechanisms and then pop-riveted these to the door frames. Next these were covered in ceconite. The leading edges of the doors had had the aluminium skins bent round them and the gaps were filled with a slurry of vinylester resin and microballoons (I'm only allergic to epoxy resin). The same mixture was then used to bond small strips of wood left over from the wings to the wing skins. This adds almost no weight and should reduce any risk of "oil-canning" in flight.
Whilst I haven't been building the Wittman over the last few months, I have been building myself a 3D printer! This is now fully debugged and prints very reliably. I use Google Sketchup to draw the 3D part and then this is saved as a .STL file. Slic3r is then used to convert this into the gcode instructions for the printer which is driven using Pronterface. Gcode files can also be saved on a microSD card and printed directly from a card reader built into the printer electronics (Ramps 1.4 with Marlin firmware)
The printer is a Prusa Mendel V2 design with additional cross bracing and home designed filament spool holders and LCD display mount. This was used to "print" a pair of door handles and backing plates in white ABS. Once the ceconite for the  wings arrives, I will also finish the insides of the doors and then they will be ready for final painting. Another little job ticked off.

5th September 2013 - Wing Construction Finished!!

Yesterday I finished preparing the inner leading edge and glued the outer leading edge strips into place. That was the last time I would be using epoxy thank goodness. Today, the leading edges were sanded to profile. I used a rotary sander/polisher with 120 grade sandpaper to get the edges flush with the wing skins. Then a plane was used to get the basic shape. Finally it was hand sanded to finish. Some fine surface filler was used to get a perfect blend between the front root panel and the rest of the wing. It is no wonder that the Tailwind flies so well the Wittman designed wing is truly a thing of beauty and the plywood skin creates a perfect surface.
Given my problems with epoxy I will be using lightweight ceconite as the covering secured and painted using the Stewart system.

3rd September 2013 - Front wingroot skin panel

To fit the last bit of the top skin, I started by chamfering the main skin along the main spar and the first main rib to conform with the shape of the curved section that would be glued in place. Then, yesterday, the leading edge was glued into place leaving the outboard edge and the rear edge loose. This anchored one edge and ensured that when the outboard edge and trailing edge of the piece were pulled down the panel would take up a nice curve. Today, the rest of the panel edges were glued and the section clamped into position while the glue dries. Meanwhile the topskin was trimmed around the rest of the leading edge, the wing tip and the trailing edge ready for the front section of the leading edge to be glued into place.

30th August 2013 - Right top wing skin

With the invaluable help once more of my friend Paul, the right top wing skin was glued into position using West Systems epoxy with the slow 206 hardener and 6% by weight of microfibre in the same way as for the left wing. The skin was stapled to the wing structure through strips of sacrificial scrap ply and clamps applied along the root, leading edge and tip where the bend radius was greatest. The inner front section cannot be glued as part of the single piece as the bend radius is too severe so this was cut out and a separate piece will be applied later. I was completely covered up for the gluing process and other than getting incredibly hot suffered no allergic reaction.

29th August 2013 - Nav and strobe cables installed

Just a few minutes work today to install the cables for the wing tip navigation light and strobe head. The nav wiring is a twisted pair of 22 gauge Tefzel. The strobe wiring is screened 3 core 20 gauge wire.

Tomorrow is the big day when the wing top skin is glued into place.

22nd August 2013 - Sealing the right wing interior

The interior of the wings are sealed to avoid any risk of the wood deteriorating over time with moisture. As before two pack Randolph Epoxy varnish was used. The top skin was masked so that the glue lines can be kept free of varnish.
The right wing contains the VOR/glideslope antenna. This is a dipole with a tuned balun. It was made based on instructions from Bob Archer.

19th August 2013 - Wing leading edge

I've become very allergic to epoxy, the least exposure and I get reactions like swelling round the eyes such that I can hardly see out. This has certainly dampened my enthusiasm for moving forward with the build. However, I have now invested in sealed goggles, filtered mask, and disposable suits to allow me to make progress. I think the look is very flattering :-)
The first test of this last week was to glue into place the small section of wing skin forward of the spar and between the root rib and the first main rib. I seemed to survive this without a reaction so today I cut to length and glued into place the 1/2" thick spruce strips that will be shaped to form the leading edge.
Once the glue was set the edges were then blended into the upper and lower skins and a reference line drawn to mark where the forward edge of the leading edge would be located. Then, with a combination of very fine cuts with the power plane and much sanding, the final shape of the leading edge was created. The left wing is now finished ready for covering.