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47. Cogitation and Action

03/02/2013

Monday

When we come down to Blandford Forum for a week’s working on the Scout, progress on the first day is usually quite impressive. We have had a plan in mind, and we make an enthusiastic start on it.

This week, for example, I made a good start on the last mechanical process on the wing fittings – those vital but horrible brackets to which the flying wires are attached, and into which the struts fit. They are horrible because there isn’t a right angle on them anywhere, and trying to line things up correctly is consequently very difficult. This final operation involves angling the ends of the holes where the bolts fit so that the bolts sit down flat – because the bolts down come through at right angles. I’d tried doing it freehand with a powerfile, but needless to say that wasn’t good enough. I’d bought a set of spot facing tools, but they were a smaller diameter than the washers we were using, and had to be put down as another expensive mistake. Finally I’d managed to source what was known as an aviation spot facing tool, which came in a variety of diameters, and I picked the one that was right for the job.

It worked fine for most of the batch (about 24 of the 32 holes, but finally went blunt, and my efforts to sharpen it met with no success.

Meanwhile Theo and Rick were getting on with the much more important business of assembling the fuselage, and by the end of the first afternoon had come up with a generic plan of assembling each side first, and then joining the two sides together. Rick marked out the shape of the fuselage side on the worktop, with blocks of wood to hold everything in place. But the more he thought about it the less easy the whole thing seemed; all the little metal brackets that hold the joints together would raise the wood away from its datum plane, and one or two of them have bits sticking out that would make it necessary to set everything a long way off the table top.

Tuesday

The cogitation continued throughout the Tuesday morning, with the result that visible progress by lunchtime was noticeable by its absence. And further discussion over lunch seemed to throw up other problems with the whole approach; we became concerned that the fuselage sides would twist or just come apart when they were removed from the table top. So we came up with a different way of doing things; use the marked out table top to make all the wooden bits for the fuselage, but not actually try to assemble them. Then start assembling the fuselage upside down on the table. The top of the fuselage frame is flat, and by assembling from a this nice firm starting point, we can introduce all the wire and cable braces as we go along, making sure that everything is held together firmly before having to remove it from the table.

A side view of the fuselage showing the method of manufacture

A side view of the fuselage showing the method of manufacture

And by the afternoon, we were under way again. Rick started making the splice joint in the longerons (you may remember that the longerons are the four wood pieces that run from front to back of the fuselage and that the front is ash and the back is spruce, and the slanting glue joint is known as a splice). This is the joint that was originally held together by the copper rivets that are used in traditional boatbuilding, but we’ve decided in the interests of safety to use modern glue which is far stronger and more reliable. Once they were done, it pointed up just how long the fuselage is. We could read off the drawing that it’s 5 metres, and roll out the tape measure to check it would fit in the workshop, but it’s not the same as seeing the actual bits of wood!

I worked out how to get all the short pieces of wood for the fuselage using the minimum amount of timber, and suddenly things started to come together.

And Theo was making good progress with his wire splices (at which he is now not only good, but quick too). For the internal fuselage bracing there are 24 to do. Quick means about 2 in an hour and a quarter, so you can see what Theo’s going to be doing all week!

Wednesday – a day of slogging on.

Rick did the really tricky stuff – marking out the fuselage side (which involves a HUGE amount of cross-checking and worry, and asking the rest of us to double check). By the end of the day, he’d got all of the vertical frame members (the short pieces of timber in the fuselage sides) cut absolutely accurately to length. And why could we not just get the lengths off the drawing and cut them? Because although the top of the fuselage is straight, the bottom is curved, and one of the things you quickly learn is that it’s very difficult to predict exactly what curve the timber will take up, which means that you can’t predict exactly what angle to cut the frame unless it’s laid out against the longeron first. And it’s really important to make sure the frames sit absolutely flat on the surface of the longeron, as any misalignment will weaken the overall structure very considerably.

Once I’d finished cutting timber to length, and using the thicknesser to get it to the right, um, thickness, and cleared up the enormous pile of shavings from the floor (it seems like most of the timber you’ve bought ends up in piles of chippings on the floor), I was allowed onto the router, since most of the fuselage frames have large grooves taken out of two faces in order to reduce weight. Both Rick and Theo are experienced routers, and know the destructive power of it when it goes astray, and I had all sorts of dire warnings about keeping the thing under control. But after a bit of practice, we seemed to have the thing more or less sorted, and I made a start. It’s amazing how much weight is saved by routing (pronounced ‘rowting’, as opposed to ‘rooting’, which is spelt routeing, and is something completely different!)

Theo – well, you can guess what Theo was doing. For some reason, the internal bracing cables are spliced directly onto the airframe, which means he has to work directly onto the metal brackets. This is possible (but inconvenient) before the airframe is assembled, but would be quite impossible if a repair was required. Then you’d have to use a shackle, and you wonder why they didn’t specify this in the first place.

Thursday…

… continued where Wednesday left off.

There was a minor drama, however, when I discovered I’d cut all the pieces that go across the fuselage at the front too short, in a classic case where I assumed I knew the fuselage width and didn’t double check… Happily, we had enough material to spare, so it caused a delay, rather than a halt, and as punishment I was on tea duty for the rest of the day.

Rick meanwhile was making excellent progress with cutting the vertical parts of the fuselage frame, and by mid afternoon had dismantled the blocks marking out the fuselage side, and replaced them with those for the top. We had originally planned that the tail of the fuselage would stick out over the end of the table, but we decided that wasn’t workable, so he also had to build an extension to the table.

And by the evening I had cut out all the timber to replace the too-short ones and Rick was pretty much done with cutting the horizontal fuselage members.

And Theo? You guessed it.

By now he had a goodly pile of finished splices, so after dinner I load tested all of them in our test rig and sat down in front of the television and whipped them (no, not that. Whipping is thin cord that’s wound round the splice to stop the cut ends of wire catching your fingers.)

Friday

You can see from the drawing below how everything’s assembled – there’s a steel angle on the outside and wires go across the diagonals everywhere – the top, bottom and sides, and, behind the pilot, transversely as well.

View looking forward through a typical fuselage joint, with the steel bracket on the outside, the end grain of the longeron, the vertical and horizontal frames, the aluminium angle on the inside, and the bolts - one of which is an eyebolt for the diagonal wire bracing.

View looking forward through a typical fuselage joint, with the steel bracket on the outside, the end grain of the longeron, the vertical and horizontal frames, the aluminium angle on the inside, and the bolts – one of which is an eyebolt for the diagonal wire bracing.

So having finished off the horizontal frame pieces, we carried on making the top and bottom ones in the same way; the thickness and routing was already done, so once the top longerons were secured in their correct positions on the worktop, they only had to be trimmed exactly to fit and the holes drilled for the bolts. Most of this Rick did, while I worked on the steel corner brackets, fitting pop rivets and peening them over for the bracing wire to go through.

But we’d decided that the curved lower longerons, while they had formed a slight curve when sat in the jig for a month, weren’t curved enough, and they needed a bit of steaming.

So Theo had gone to his partner’s to borrow a wallpaper stripper, which he and Rick connected up to an old piece of plastic guttering downpipe. This they rigged up in the upstairs toilet, with the end of the plastic pipe poking out of the window. Into the downpipe they stuck one of the lower longerons.

The steaming apparatus - wallpaper stripper connected to the downpipe, all arrranged over the toilet to catch the drips...

The steaming apparatus – wallpaper stripper connected to the downpipe, all arrranged over the toilet to catch the drips…

... and the ash longeron poking out of the toilet window.

… and the ash longeron poking out of the toilet window.

And twenty minutes later, disaster struck! The steam was coming out close to the glued splice joint between the ash and spruce, and the heat softened the glue. Thankfully, the timber wasn’t affected, and so the faces were cleaned up and the steaming process continued, after which the ash was put back in the jig. Then in the evening, they re-did the glue joint, leaving it all clamped up overnight to set.

Saturday

Work had to stop at lunchtime, so we spent the morning continuing yesterday’s assembly work.

There was one potential problem. Every wire and cable has a turnbuckle in it so that it can be adjusted for length and tension. For the cables at the front end of the fuselage, the turnbuckle is fitted to the metal bracket at one end, and the cable runs from its other end to the metal bracket. We have had long discussions about which goes at which end, because of this strange requirement to splice direct onto the fuselage fittings. And then we had a similar problem for the wires aft of the seat. The drawings seem to indicate that they are fitted in the middle of each piece of wire. Apart from requiring twice as many joints in the wire (not good from a reliability perspective and more time-consuming to make) having the weight of the turnbuckle in the middle of the wire makes them more susceptible to fatigue as a result of the engine vibrations, and so we’re planning to do the same as for the cables – fasten the turnbuckles to the metal bracket at one end, and run the wire from the turnbuckle to the other metal bracket.

But we found that some of the brackets were too small to allow the turnbuckle to fit without taking a chunk out of the longeron – probably not a good idea! In the end, we went through all the fittings and found there was only one set of wires where there was no room at either end for the turnbuckle, and these we will do according Bristol-fashion. But that will have to wait until next time we’re down. For now, we’ve each got a list of jobs to do before we meet up next.

David and Theo clearly enjoying working on the fuselage

David and Theo clearly enjoying working on the fuselage

The three of us naturally form an excellent team, and while there are plenty of discussion about how to do things, they are animated, good-humoured and constructive, and between the three of us, we usually come up with satisfactory solutions. It’s also a huge pleasure. The work itself is physically demanding, and by the end of a week we are completely cream crackered, but apart from the satisfaction of working on such a wonderful, fulfilling project, we’ve spent a thoroughly enjoyable week in each other’s company, which would be sufficient reward on its own.

This is where we're up to. The fuselage is upside down on the worktop, with most of the top and side frames temporarily fitted. You can see the routing on some of the side frames. Rick is carefully lining up the tailplane to the fuselage - they have to be made to match so that the one can bolt onto the other. And on the floor you can see the lower longerons, steamed and waiting in the jig until they can be fitted to the rest of the fuselage next time. The glue joint that came apart has been cleaned and reglued, and is being left with the clamps on until next time.

This is where we’re up to. The fuselage is upside down on the worktop, with most of the top and side frames temporarily fitted. You can see the routing on some of the side frames. Rick is carefully lining up the tailplane to the fuselage – they have to be made to match so that the one can bolt onto the other. And on the floor you can see the lower longerons, steamed and waiting in the jig until they can be fitted to the rest of the fuselage next time. The glue joint that came apart has been cleaned and reglued, and is being left with the clamps on until next time.

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One Comment
  1. Absoluter netter Blog. Werde jetzt öfter die Seite besuchen Vielen Dank und Grüsse aus Hamburg

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