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30. Assembly

31/07/2012

After that it was off to Theo’s for a concentrated couple of days’ work on assembly of flying surfaces.

The tail of the aircraft is virtually complete as you can see. In fact, the only thing left to do is to silver solder little clips to the tailplane and attach the wooden ribs, which Theo had made some time ago.

Seeing an entire bit of the aircraft assembled is hugely rewarding, and I’ve done it several times in  order to boost our morale. I did it for Theo when I got down on Friday evening, and we both felt much better for it.

We also wanted to get the centre section completed, so that it’s ready to go to the LAA Rally which is only about a month away. The main job here is to fit the four metal fittings where the wings and centre section struts attach.

And finally we wanted to make a start on the additional pieces of ash wood that are going to reinforce the wing spar joints we tested last time we were down at Theo’s.

And as an added extra, I’d bough a length of hickory wood – famous for its resilience in bending, and used as an alternative to yew for longbows – for the tailskid, and I wanted to use Theo’s bandsaw and thicknesser to cut out the blank shape so that it could be carved to shape back at home.

Needless to say, we started on the added extra , and Theo got that completed in very quick time. The hickory is great to work with, and has a beautiful finish. The bits went into the back of the car so they didn’t get forgotten.

Then while Theo made a start on the ash pieces for the wing spar joints (ash provided very generously by Allen Haseldine), I made a start on the metal fittings for the centre section. It’s a complicated spot, with three steel parts, three aluminium parts and two pieces of wood to be bolted together with five bolts – all repeated four times.

I’d folded the part that fits around the rib okay, and they fitted snugly, despite having done so without reference to the actual rib. It’s actually a lot more complicated than it might first appear, since the folded-over parts that lie against the top and bottom faces of the rib are at complicated angles to the vertical bit, which meant that the drawings for waterjet cutting had to be exactly correct too – and they were, thanks to Stan Teachman and Derek Walton.

As you can see in this close up, there are four horizontal bolts (two of them shown fitted in this picture). The holes in those (and the clip that sticks outwards, into which the top wings will fit) had been waterjet cut, but they had to match exactly those in the aluminium angles on the other side of the rib.

It required careful assembly of each joint in the vice and holding one’s breath as one carefully drilled through, hoping the drill point would appear in the right place.

And it did. each one appeared in the middle of the aluminium channel, and missed the eyebolt that goes through the spar.

So the only other drilling was for the long bolt that goes from top to bottom of each fitting. It’s an odd design, the bolt being designed to go right down the join between the rib and the spar, and not actually joining anything except the metal. Initially, we did this using a long drill right the way through the joint, which took ages to set up, and was even more heart-pounding. But eventually we realised that it was far simpler to cut a slot in the end of the spar and simply drill holes in the metal. Much easier, and far less nerve-racking!

If you go back to the upper picture, you can see that there’s an aluminium strap across each spar. This was a modification suggested by Francis Donaldson to help take the landing loads, and was fairly straightforward to install, though we had to carefully cut away the ribs to make room for them.

Finally, the sockets for the struts had to be drilled for the vertical bolt, and washers tapered to fit the angle of the bolt.

And that was it – we did a trial assembly, as shown in the photograph, and it all went together just dandy.

And so we moved on to the next phase, which was brazing. We needed to braze the sockets to the bottom of the rib clip, and the tapered washers to the top, and here, reader, is where I made a goof, and one of them has been brazed the wrong way round… It’s possible we can heat the thing up enough to unbraze it, in which case we live to fight another day; otherwise we’ll need to see what we can rescue from the situation.

But we weren’t finished yet.

We managed to get all the clips silver soldered onto the tailplane, and Theo did sterling work finishing off the rather curious rib fittings, so he’s planning to get them fitted on Friday, so that we can finally say we’ve got the back end of the aircraft completed – apart from covering, of course.

Theo also made most of the ash blocks for the wing spar joints during this couple of days. As with most of these things, it’s not quite that simple – the ribs in way of these blocks need to be altered to make room for the blocks, and he’s well on with that too, so we’ve achieved a lot in a couple of days, and my goof with the brazing may not hold us up too much provided my plan for unsticking it goes okay.

Plan this week is to do everything possible to get ready for a big push to complete ALL the flying surfaces when I’m down with Theo again next week. It’s an ambitious target, but I think it’s achievable. I’ll let you know how we get on, of course.

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