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33. In Praise of Right Angles

17/08/2012

On Sunday we concentrated on the remainder of the spar reinforcements. They are quite a complicated shape, and there are sixteen of them required. Oh, and those on the top wing are upside down, and the ones for the rear spar are different to those on the front wing. The result is that you spend an inordinate time making sure that you’ve got exactly the right pieces, and that they don’t get muddled up!

Theo is master carpenter, and so this was mostly his job, with me offering help wherever required.

I’m in charge of metal fittings, so I was mostly preparing the fittings for the all-important wing spar joints, and then – heart very much in mouth – drilling the holes through the spar reinforcements.

The reason for the worry is that the bolts are only about 2mm from the spar itself. They are about 3in (75mm) long, and if the drill wanders off and into the spar itself, you’d have to scrap the spar…

In addition the holes must all be parallel to each other, otherwise the fittings on the other side wouldn’t fit.

And here’s where I really started to appreciate the sheer sensual pleasure of a right angle. You see, instead of designing the wing with rectangular spars, Frank Barnwell decided to make the biggest ones that would fit inside the profile of the wing, so that because of the curvature of the profile the top and bottom surfaces are all at different angles. Then for some reason he made the front and rear spars different thicknesses. The result is that every part of every fitting is set at slightly different angles, and woe betide you if you get them muddled!

The most critical part was to drill the holes in the ash pieces, and making sure the drill was running exactly parallel to the vertical face of the spar was tricky and frustrating. The spar naturally wanted to sit with its bottom face on the bed of the drill, which (because it wasn’t at a right angle) would have led to the holes going wonky, and despite any number of clamps and bits of aluminium channel, I had to keep a VERY careful eye out for things shifting.

There’s that moment when you’ve stated drilling, the point has disappeared inside the wood, and all you can do is hope that it’s going to come out in the right place.

And although every hole was nerve-wracking, they all ended up where they should be.

But that wasn’t the end of it. Because those holes aren’t at right angles, the faces on which the bolt head and nut sits have to be filed off, each to their own individual angle. Basically it’s taken a day and a half to get all eight spars completed, and I shall be glad never to have to look at them in detail again.

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From → Building, Technical

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