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62. Cabane

04/08/2013

The chassis was done on the Wednesday; almost all the work was done by Theo, since I’d been up until late on Tuesday night trying to count our stock of nuts, bolts and other fittings, since I knew we had a good many superfluous items, and were lacking shackles to enable us to make up the rigging cables that hold the whole aircraft together.

On the Wednesday morning, I headed off to Light Aero Spares in Okehampton to return the surplus items and hopefully to collect the order of stuff I’d placed the evening before. I’d had many conversations with their manager, Scott Powell, over the years, and it was a very great pleasure to be able to put a face to the name. LAS are a mail order organisation so they aren’t geared up for visitors off the street, bu they made me feel very welcome and sorted out my order with astonishing speed.

A handful of shackles for the flying wires. Guess how much they cost... Would you believe over £700!

A handful of shackles for the flying wires. Guess how much they cost… Would you believe over £700!

It’s a two hour journey from Dorset, and much of the journey took place in thick fog along the coast near Lyme Regis, so it was lunchtime before I got back and having taken a photograph of progress on the chassis, we dismantled it and turned the fuselage over to begin work on the Cabane.

The major worry here was the length of the cabane struts, since this determines the angle at which the top wing sits in relation to the fuselage which is absolutely critical to the way the aircraft handles in the air. We had no original drawings apart from Barnwell’s sketches for the 1913 prototype, so I’d done some detailed calculations and in fact these more or less agreed with the sketch, showing that this was something that hadn’t been altered in the major redesign from the B to the C model.

You do have to be extremely careful about which information you use; at an early stage we wanted to find out how high the top wing should be above the lower, and consulted the American drawings done in 1917 when they investigated the Bristol Scout as a possible primary trainer to be manufactured under licence. It said the height should be 40 9/16 inches, and when we measured this up in the workshop, the top wing would barely have cleared the top of the fuselage! Thankfully, when we looked in the 1915 Bristol drawings, we found it given as 1300mm which looked much more like the aircraft in the photographs!

It’s not the only case we’ve come across where they’d converted the original metric dimensions incorrectly. I think I’m right in saying that the USA and Liberia are the only countries in the world that haven’t adopted the metric system, which is odd, since the metric system was developed by France under Napoleon, as you know, and the US also declared war on the UK in 1812…

Making the scrap struts was altogether more straightforward; although they slope forwards, they are all set at the same angle and are in a vertical plane viewed from the front. This means that once you’ve carved and sanded the ends to fit the sockets, its a single cut at a particular dimension and angle at each end. So we had the whole thing assembled pretty smartish, and using string instead of cable to brace it, we were delighted to find the calculations were correct, and that it sat exactly where it should.

Having congratulated ourselves on the speed with which we’d achieved such accuracy and precision, it now occurred to us that we – that it Theo – was going to have to set to and make up the 8 cables that brace the cabane. That’s 16 splices, at around an hour per splice.

So for the whole of Thursday and Friday Theo was pretty much chained to the bench splicing cable, being let out only in order to make the lunch and dinner, while I got on with a variety of other smaller tasks that  needed doing; fitting the round engine former to the front engine mount, finishing off the heel troughs, gluing the seat supports, making funny little brass fairleads under the seat support to stop the control cables rubbing. These last were a bit frustrating – they took most of Friday to make, and could have been equally well replaced with a little block of fibre. In fact, there are three different designs for these; the first (which we’ve used, of course) have  bits of brass bolted to the beam on which the cable rubs lightly, with a little channel to keep it in place. Later on they changed to little pulleys, one for each cable, and finally they just had a single rotating bar.

But we ended up with a cabane that is perfectly straight and true, and – critically – with the wing centre section at exactly the right angle of attack.

The cabane with the top wing centre section. NB. The struts are only temporary to check the lengths. Rupert Wasey is making the proper ones!

The cabane with the top wing centre section. NB. The struts are only temporary to check the lengths. Rupert Wasey is making the proper ones!

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