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42. Hibernation

12/12/2012

We’ve had another week working on the aircraft and proving the old saw that once an aircraft build is 90% complete, there’s only 90% to go.

Last time Theo and I were working on it together, we’d finished assembling the wings. Since then, Theo’s had to spend some time redoing the ailerons, which hadn’t all worked out quite right. Assembling them was something that required about a dozen hands in order to keep everything aligned while you set the clamps. Then, when we mated them to their wings, we found that some had adopted a banana shape and needed to be carefully dismantled and reset.

When I came down this week, we carried on the unspectacular work of titivating the wings, with no major new assembly to show off at the end of it.

We found that a couple of the ailerons still weren’t quite right – the gap between the inboard end of the aileron and the wing wasn’t correct on a couple, and Theo, acknowledged woodmaster, took charge of the surgery required (in between mugging up for his final flight test in order to upgrade his licence from a microlight to a light aircraft. The test was scheduled for the Wednesday morning, but although the sky was clear blue, there was a strong northerly wind, and the runway at Compton Abbas was flooded, so it was postponed, much to his frustration).

Meanwhile, the wings – and the ailerons as they became available – needed to be sanded down, the glue touched up, and a coat of paint to the woodwork, so I made a start on the sanding while Theo did the painting.

Painting the wings - in 5 degrees of frost!

Painting the wings – in 5 degrees of frost!

Slowly we made progress, though the lack of an exciting conclusion in prospect, the cold – indeed freezing – weather, and the lack of daylight meant that breakfast was later, tea breaks longer, and the evenings shorter than during the summer.

But by the Thursday, we’d got the ailerons to fit, the surfaces sanded down, a start on the touching up of glue joints, and a coat of Danish Oil on all the woodwork. We’re using Danish Oil because it soaks right into the wood before setting, as opposed to varnish, which forms a skin on top. We’re hoping that this will provide protection to the wood even if the surface gets rubbed and scuffed. Oh, and it can be applied to rougher surfaces, so that we don’t have to spend so much time carefully preparing surfaces which won’t be seen once the fabric covering is in place, and it doesn’t drip, which is another big advantage to those of us who are by nature slapdash painters!

The plan had been to get the wings completely finished before starting on the fuselage, but much of the final titivating is really a one-man job, and so we decided to put them on one side for Theo to finish off in his own time – to let the process ferment naturally, his house being an old pub and the workshop where they had their own micro-brewery.

Meantime, we started to look at the fuselage.

The most important parts of the fuselage are the longerons – the four long pieces of timber that go from front to back, forming the four corners. All four are made of ash at the front (which is strong enough to take all the loads from the engine, undercarriage, wings and seat) and spruce at the back (because it’s light). The two are joined by a long sloping joint called a scarf joint (and no, I don’t know why). In 1915, the glues available were weak and unreliable, so this joint was made by rivetting – holes were drilled vertically through the joint, and thin copper rods were pushed through and the ends hammered over. The whole thing was then bound with whipping twine. These days, we can use modern glues, which will be stronger and more reliable.

The aft fuselage longerons after tapering. Finding four pieces of absolutely straight-grained spruce of such a length is NOT easy, so putting them through the band saw was a sweat-inducing experience. The thinner ends go to the rear of the fuselage.

The aft fuselage longerons after tapering. Finding four pieces of absolutely straight-grained spruce of such a length is NOT easy, so putting them through the band saw was a sweat-inducing experience. The thinner ends go to the rear of the fuselage.

The spruce pieces are tapered down from 30mm square at the front to 18mm square at the back, and this long tapering cut – over a distance of 3m – had been exercising our minds since the start of the build project. We’d come up with all sorts of fancy ideas for jigging this up, but in the end, Theo suggested we stick to the normal method, and mark the cut with a pencil line and stick it through the bandsaw. We set to about teatime on the Friday, and it worked absolutely fine, the sawn faces just requiring a little finishing off with a belt sander which we did on the Saturday morning.

The fuselage longerons are ash at the front and the lower ones have to be curved. They are clamped into the correct curve and will be left for a couple of months to see if they take a permanent set without the need for soaking or steaming.

The fuselage longerons are ash at the front and the lower ones have to be curved. They are clamped into the correct curve and will be left for a couple of months to see if they take a permanent set without the need for soaking or steaming.

The other challenge in making the fuselage is that the lower longerons are curved at the front (the ash part). We weren’t sure, ash being so much stiffer than spruce, how easy it would be to form this curve, so we set up a temporary jig on the worktop, and it proved possible to form the curve by main force without overstressing it. The normal method of forming curves in wood is to wet the fibres through – either by soaking for a long time, or, more commonly, by steaming it, but we believe that this shouldn’t be necessary, and we’ll simply leave them in a jig with the curve applied for some months until they are need, and that should be enough.

We had visualised actually starting to assemble the fuselage this week, but although this hasn’t been possible, we both feel we’ve made good progress, even if there isn’t as much to show for it as on previous weeks (apart from the stiffness in my back and legs from so much unaccustomed exercise). We’ve both got a list of jobs to do on our own – Theo on woodwork as usual, me on metalwork – and we’re looking to a week at the end of January when we can make a start on assembling the fuselage…

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