11th November 2013 - Painting, painting, painting...

Despite the lack of posts I have been working over the last few weeks. The left wing has been completely painted and once fully hardened wrapped in bubble wrap and transported to my friend Paul's house for storage. The doors have been finished inside and out. Also, all the flying surfaces have now been finished to a good standard.
The learning points from doing this are interesting, First, the EkoPoly has a very definite shelf life. Trying to use it beyond this is doomed to failure! The newer EkoPoly Premium paint is much easier to apply without runs.
I'm painting in Insignia white, it is hard to get a full colour coverage over the grey EkoFill or charcoal grey EkoPrime. However, a thin coat of the smoke grey EkoPrime makes it much easier to get an even, high gloss, white finish.

11th October 2013 - Left Wing Painted

Over the last few days I have finished applying the EkoFill and EkoPrime to the left wing and have now sprayed it with the white EkoPoly. This hasn't been simple, it seems that as soon as I get enough paint on to get a gloss runs start to appear. The bottom of the wing actually sprayed up quite nicely but my first attempt at the top was so bad with multiple runs that I washed the paint off completely before it had time to harden - thank goodness for water based paint!

Thinking about it, my suspicion is that there had been some surface contamination in areas of the surface. So I sanded the whole wing with 320 grit open coat sandpaper and then washed and rinsed it thoroughly. My next attempt at the top surface was better but I was too sparing with the paint and didn't get a full gloss so this was cut back with the sandpaper to create a key, cleaned with isopropyl alchohol, and then today another coat was applied. This time I got a good gloss. Note the way in which all the fabric edges have completely disappeared. There are a couple of small runs that will need sanding and polishing out but basically the left wing is now finished. I'll let the paint harden for a few days and then I can get on with the right wing.

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.

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.

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.