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13. Wire winding

04/02/2012

If you look at the Sopwith Camel, you can see that there are masses of wires bracing the whole thing.

Sopwith Camel fuselage showing all the wire bracing

The wire used for this is specially ordered – we’d got the details from the Shuttleworth Collection – to a specification that ensures they are strong enough, yet flexible enough.

Sopwith Camel wire termination

If you look closely at the ends, you can see that they are pushed through a little ferrule made of the same wire, wound into a tight spiral, and by now it won’t surprise you to learn that the Scout uses exactly the same system.

You might think making those little spirals would be easy, since you could just wind them round something the right size, and off you go. But it ain’t as simple as that. The spiral isn’t round – it’s an oval shape – and it’s got to be just big enough to fit two wires through.

So why not wind it round something that’s just the size of two wires? Because when you bend metal beyond its elastic limit, it still springs back a small amount when you let go. So if you make something the size of two wires and wind the spiral round it, when you let go, the spiral springs back and forms an oval shape, but with a long spiral to it, and it would be quite impossible to feed the two straight wires through it, even if you could get it off the former, which you can’t!

Even the Shuttleworth admitted they had problems making these up, but we decided to go about it another way.

We did some experimenting, and made up a round spiral, using a small bolt as the former (also called a mandrel). Because there were so many to do, Rick made up a simple tool to mass-produce them. The springback meant that they came off the mandrel easily, and he then made another little tool so that they were all trimmed off to exactly the right length.

Finally he welded up a little box in steel with a lid on the top into which the round spiral was fitted, and squashed the spiral to give it its oval shape. Did it work?

No, it didn’t. The force required was so great that the steel of the box simply distorted.

So he made another box, but this time with hardened steel (old bits of broken file, if I remember correctly) in the top and bottom, and finally we were in business. The height of the box made sure we didn’t over-squash the spirals, and the length of it matched that of the spirals so that the spiral didn’t squash lopsidedly.

A Fly Press

A friend down the road has a fly press which made short work of the squashing, and now we’ve got a box full of spirals (properly called ferrules) ready for use when we start rigging.

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From → Building, Technical

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