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32. Preparation

14/08/2012

The next week was the one we’d allocated for completing the flying surfaces (except the ailerons, which will come later).

I went down to Dorset again with Theo and we made an all-out effort to get the job done in the eight days, Saturday to Saturday, we had available.

The first day was mostly dedicated to painting – you need to leave enough time for paint to dry, so we’ve needed to get a whole lot of etch priming done early to ensure (a) the parts are dry when we need to use them, and (b) they don’t go rusty! The etch primer is horrible stuff; it’s a two-pack paint, meaning you have to mix two liquids together, and use them relatively quickly – and that means you need to estimate how much you’re going to use. Like a lot of paints, one of the liquids needs vigorous stirring to thoroughly mix the yellow colour. By the time you’ve done that and mixed it with the clear liquid, it’s a pretty runny sort of colour, and given that you’re painting lots of little complicated metal fittings, it’s not possible to do a nice even coat. Unlike normal paint, the colour gives you uneven and incomplete coverage – on most parts, you can see through to the metal underneath, even when you’ve painted it properly, and the amount of colour is variable. So you slap it on, and like most paints it looks a bit better when it’s dry and the bright yellow colour has turned to a murky green. But not much.

The great advantage of etch primer is that it does stick to the metal like crazy, and I was able to test this when I needed to sand some off a fitting. It takes a LOT to remove it.

After that I put a coat of black paint on the rudder, so that it’s ready to go to the LAA show in a month’s time.

It’s not the most beautiful finish, but I don’t think that’s particularly high priority, since the whole thing is going to get covered in fabric eventually, and no-one will ever see it again. The critical thing is to stop it rusting!

Meanwhile Theo was trying to sort out the metal fittings for the centre section.

I’d bought down some captive nuts to go on the inside of the centre section, so that you can undo the bolts on the outside after it’s all covered in fabric without the nuts falling off inside. It’s all a horribly cramped situation – tucked in the shadow on the right of the picture – and as usual, we immediately thought of ways to do it better, but resisted the temptation to introduce more modifications, and in fact we decided to sleep on it and see if we could come up with something better.

So he moved on to making the spar reinforcements recommended by Francis Donaldson ready for gluing to the spars.

The spar runs from top left to bottom right of the picture, and the bits glued on to each side of it to make it wider are the modification.

They are made of ash, which is a hardwood, and behaves quite unlike the spruce from which the spar is made.

From a structural point of view, there are probably only two joints that need reinforcing in this way, since the majority of the loads pass through the one on the rear spar, top wing, but it seems to make sense to do them all the same – partly from a sense of symmetry, but also because the unreinforced joints could wiggle and wear out in service, even if they weren’t likely to break from overstress.

So Theo did that, and by the end of Saturday, we’d got one pair of spars glued up, and loads of painted metal bits hanging up from the washing maiden in the downstairs loo.

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