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25. Consultation

15/07/2012

Having come across some potential issues with the all-important wing joint when we tested it, it was clear we needed to consult the experts.

I had a long list of about 14 items raised when we’d first registered the project with the LAA, most of which had been sorted out, but THAT wing joint was one of the outstanding ones, together with a few more, and on a day when I happened to be in at the LAA on other business, I managed to find some time with Francis Donaldson to go through them.

First on the list was the wing joint of course, and I’d proposed a pair of metal brackets on the sides of the wing spar to straighten the whole thing up. Francis, whose experience of different types of aircraft is possibly unique in the world, suggested a similar idea, but using pieces of ash hardwood. It’s a solution adopted in another type with which he’s familiar, and so it’s got the inestimable advantage of proven history!

It’s a solution that won’t be visible once the wing is covered, and retains all the original parts. It does make assembly a bit more of an exercise, however, because you won’t be able to thread the ribs on and off the spar in the way you currently can. I don’t think that’s a particular problem – once we’d got the wing assembled finally the ribs all have to be glued in place, and it’s not as if we’l be wanting to take them off again ever – so we now need to find quite a lot of straight-grained ash in lots of little pieces (48 to be exact) for these parts.

We’re still slightly mystified how the original design seems to have worked successfully. Are we being over-fussy? Or was it simply that most of the original aircraft didn’t survive long enough for this problem to come to light?

The next problem was what happens in a heavy landing. You can imagine that when an aircraft is flying along, the weight of the fuselage, and the engine, fuel and pilot, are all tending to pull downwards, making the wings want to bend upwards, and of course that’s the main job the wings are designed to resist. But every time you land the aircraft, suddenly the loads are reversed, and the wings try to bend downwards.

Francis has had experience of similar vintage aircraft (like the Sopwith Pup) and they hadn’t made sufficient allowance for these loads, and a modification was introduced to strengthen things up a bit. He looked at the Bristol Scout design and noticed that we had a similar shortcoming, and suggested that we should look to build in some reinforcement during the build process, and that’s what we did. We’ll hide a couple of aluminium straps inside the wing centre section (the short bit of wing over the fuselage) which should take these landing loads and stop everything else stretching.

Finally we took a look at how the tailplane is fitted to the fuselage.

Here’s a picture of Leo Opdyke’s machine at Yeovilton. At the back the green tube is bolted to the fuselage and that’s that. At the front, on the right, is a strange sort of hook which is bolted to the fuselage and hooks over the tailplane. It’s got a series of holes in which allow one to adjust the height of the front of the tailplane above the fuselage, and it’s important for adjusting the trim when it’s being flown. You can also adjust the length of the metal struts that come out from the bottom of the fuselage to the outer ends of the tailplane.

But if you look carefully, you can see that there’s a bracket connecting the spar (the main wooden member going across the tailplane from side to side) to attach it to the fuselage, and on the drawings that bracket is (a) very hard to make, (b) not very strong, and (c) not adjustable. This means you can adjust the height of the tailplane at the front, but since the back and the middle are fixed, it would have to bend like a banana. Anyway, we agreed with Francis a very small change to the design of the bracket that will improve its strength enormously and make it easier to manufacture and fit. And, although it’s not shown on the drawings, we believe it will be possible to drill extra holes to make the whole thing adjustable.

All of which means we’ve got clearance to go ahead and finish off making the wings and tailplane. Then we’d only got to do the fuselage and we’re nearly there…

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From → Building, Technical

2 Comments
  1. Great project – a long and difficult process, no doubt, but it will result in a wonderful piece of flying history. Love the history and nice to follow your progress. Keep up the good work!

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  1. 30. Assembly « Bristol Scout

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