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48. Continuation

23/02/2013

Here’s a picture of where we’re up to with the fuselage.

Fuselage Assembly

Fuselage Assembly. It’s currently upside down, with the front in the foreground. When it’s complete it will be turned over, the undercarriage and wheels attached at the front, and things like the fuel tanks and the curved turtle deck fitted to the top.

 

 

Of course it depends what you mean by ‘assemble’. We may have thought all the metal brackets were cut and folded and welded and brazed, but then we’ve found that some of them need to be riveted and all need to be painted. Then, because for some reason Bristols didn’t use shackles on internal bracing cables, they need to be spliced onto the fittings themselves. Goodness knows what happens if a cable needs to be replaced in service – one can’t imagine a rigger sitting inside the fuselage knitting wire!

And although the wood frames are sized, routed and cut exactly to length with the correct angles at the ends, there are bolt holes that need to be drilled with the joints temporarily assembled.

And you would have thought that by now we knew every inch of the assembly of the fuselage by heart, but the fact is that we seem to spend longer and longer agonising over every additional hole to be drilled, every additional cut to be made, because the consequences of an error are so much greater.

The top longerons are held exactly in place on the bench with wooden blocks. The rear engine mount goes on first, since it has to be slid over the top longerons. Drilling the holes to locate it took a great deal of courage, given the time and effort that had gone into making the longerons. Then the front engine mount, and all the frames with their metal fittings assembled, painting Danish Oil on the wood in way of the joints first. Then the lower longerons were taken out of the jig holding the curve in place and laid on the frames, and the lower joints assembled.

This bald statement hides all the dashing to and fro to the computer to see how things were supposed to be assembled, the agonising over the drilling of holes, where one wrong move would wreck days and days of work, the sorting out of bolts of exactly the right length, the ordering of extra bolts when there were none. Oh, and then the drilling of the little aluminium angles that go on the inside of each joint.

Aft of the cockpit, each frame has diagonal bracing across it (you can’t do that at the front, or there would be nowhere to put your legs). They are attached to eyebolts, so each joint has one ordinary bolt and one eyebolt. And one eyebolt has to be suitable for attaching the strainer and one for the wire. And it wasn’t clear whether the eyebolts should go in horizontally or vertically. In the end, where they went was determined largely by the configuration of the joints and it’s some and some.

In other words, progress was pretty slow and painstaking.

You’ll see in the picture that there are clamps and straps at stations C and D (A is the front). This is because the lower wings are attached to the fuselage at these points, and the wing fittings are a complete nightmare to align. Obviously the lower longerons are bent at this point, so the two fittings don’t line up with each other. The two bottom frames need very careful making, because the ‘rock tube’ (part of the controls) is fitted in bearings mounted on them, and that determines their alignment. But the ends have to be made to fit the curve of the longerons… In addition the  front ones (CB) have to match up with two frame pieces and the complicated bottom frame, there’s a very large cable running inside the cable joining the left and right fittings together, and the back and front fittings have to be exactly the right distance apart, otherwise the wings won’t fit on! The front fittings also have a socket for the undercarriage legs…

In the picture we’re getting all of this set up with another jig to replicate the ends of the wings, then with everything held in exactly the right place, it all gets very, very carefully marked up and clamped and taken away to be welded.

To be fair, once we get this bit done, the rear fuselage is much simpler, since we’re using wire rather than cable. But that’s for next time.

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