28th September 2013 - Left Wing Top Surface UV protected and Primed

Today I started the task of painting the wings. As I've covered in ceconite I need to hide the fabric edges. The picture shows the way the lower fabric wraps round the wingtip. This creates an edge along the cut surface. Following advice from Jason at Stewart, I started by appying the usual three cross coats of EkoFill which provides the UV protection to the fabric (I'll reduce this to 2 on the underside of the wings). Then EkoPrime was applied along the leading edge and sanded, prime and sand, prime and sand... until the edge of the fabric was completely masked. The rear joint in
the fabric is on the trailing edge behind the flap/aileron so that needs no particular attention.

27th September 2013 - Left Wing Covering Complete

I decided that I would try and get the second wing covered as quickly as possible - so I put in a 10 hour day today and it is finished! - next to paint the wings.

26th September 2013 - Right Wing Covered, Left Started

I finished off the right wing today and then it was my wife's turn to help me re-organise the garage. The wings are awkward but not too heavy. First the left wing was removed from the garage, then right wing was stored against the wall, finally the left wing could be placed on the saw horses for covering.
I won't bother repeating the same pictures for the covering of this wing so it will be a few days before the next post.

25th September 2013 - Right Wing Bottom Covering Glued

Today I shrunk the bottom covering into place and then glued it in the same way as the top. The tips and trailing edges have been made off so tomorrow I can finish the leading edges.

24th September 2013 - Right Wing bottom fabric

First job today was to make good the leading edge of the top covering and the rear section of the wingtip. Then another piece of fabric was cut ready for the bottom covering. This was cut out to fit round the strut attach brackets. Then a 1" strip of EkoBond was applied round the edge of the bottom wing surface and allowed to get tacky. The bottom fabric was then applied and glued round the edges. Tomorrow this can be shrunk and stuck in place.

23rd September 2013 - Covering the right wing top surface

With the help of my neighbour Daryl I re-organised the garage to allow access all round the right wing which was placed on a couple of saw horses. I had previously called Jason at Stewart Systems to get advice on how to cover a fully sheeted wing and followed his approach. First a piece of the lightweight Ceconite was cut to size to fit the top surface of the wing.  Then a glue line (EkoBond thinned 10% with water) about 1" wide was painted around the edge of the wing. When still slightly tacky the cloth was laid over the wing and smoothed out as far as possible. More glue was then brushed over the glue line and, as always with the Stewart System, any excess was removed with paper towel to leave it matt looking. Once this was set the cloth was shrunk with the iron to remove any wrinkles and looseness.
Then it was a case of brushing (using a foam brush) more EkoBond, thinned 10% with water, over the entire surface of the wing and, as before, all excess glue was removed. I found that gluing about 2 sq ft at a time was about optimum to ensure that the excess glue could be removed easily.
Finally I made off the ends of the wing. and the trailing edge. The cloth will wrap round the leading edge and overlap the bottom cloth by 3". However no finishing tapes are required as the cloth will be completely bonded to the wood. According to Jason,  it should be possible to avoid the join being visible by using a small amount of primer on top of the EkoFill to level out the cloth edge. I used about 300g of glue to fix the cloth and as much of this is wiped off the approach looks like being lightweight. All together covering the first wing surface took about 3 hours - not too bad!

22nd September 2013 - Inner door skins installed and painted

The lightweight Ceconite arrived a couple of days ago so I was able to glue this to the inner framework of the door using the standard Stewart Systems approach. The cloth was then shrunk and filled with EkoFill and then topcoated in white. The topcoat had a couple of runs so I've sanded these out and will needed to respray a light tack coat and gloss coat at some later date.

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.