Friday, 20 May 2011

Matty laird had a sense of humor

Once all the ribs had been glued in place, it was time to pre varnish the wing sections which would receive fittings, wires, etc, and at this point the varnish really brings out the beauty of the spruce and the mahogany plywood.
I imagine the only way that every drag anti drag wire could hit a rib diagonal or upright was by careful pre planning in the design phase.

And they do.

Well that is not exactly correct, as they do miss ribs # 6 and 9, but only barely. And since brushing up against most of the ribs was not good enough, the wires actually go directly through the uprights in ribs
# 3,8, and 13.
Matty must be having a quiet chuckle over this.
Of course the wires contacting the ribs in so many places creates issues. Every location needs to be braced, then the cut out determined and shaped to allow the wires a clear run. The uprights were braced either side, and then the hole drilled directly through the center upright.

I had the wires made up by a company in new Zealand, Vintage Aero, run by Russ Ward. Russ specializes in recreating wires as they made them back in the 30`s and even earlier. The wires are beautiful, and very different from a modern stainless drag wire. Each steel wire has 1 LH and 1 RH rolled thread, a square section for tightening and they have a hot dipped finish. The wires are really nice, and they arrived in the exact lengths as ordered, which was great as there is no room for error.
It is nice to have another source for wires beyond Bruntons. Russ also does streamline wires.

Onward with the lower right hand wing, once all the ribs were glued in place, next step was corner blocking, and putting the spar strips in place top and bottom.

The metal fittings had arrived back from the powder coaters, so I was able to bolt various fitting in with the correct hardware. The Aileron hinges are placed in position at this point, but I do not want to attach them until the ailerons are completed to ensure everything lines up perfectly.
Once all of the wires and fittings were installed, next was the wing tip bow installation, (version 4) which went pretty smoothly, using the measure 50 times, cut once technique. I could not even think about having to make wingtip bows version 5!
Sometimes the biggest challenge is working out effective clamping solutions, and when dealing with tapered and curved surfaces this can be quite entertaining, with clamps on clamps. One can never have enough clamps, either in number or variety.
My main concern was shaping the bow, as it is not a symetrical radius, due the low chord line of the wing. This means the bow is constantly changing radius, from a 2 inch height at the leading edge, to less than 3/4 inch at the trailing edge, but multiple passes with an air angle grinder, and finishing up with a long block sander  produced the desired results.

The Lower right hand wing is now essentially complete, still to be installed are the various plywood sheeting, at the tip, root and along the leading edge, it is all cut to size, but I shall wait until the lower left hand wing is completed to the same stage, as I would like to have this wing as a reference.
The next lower wing will go much quicker, as while I have been building the right hand wing, I have also made all parts for the left hand wing. The spars are shaped, and drilled, the ribs are ready to glue in place, all steel fittings are complete and pre located, the wires are on hand, and the wingtip bow is ready. Below is the left hand wing in kit form, ready to assemble.

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