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104. AWOL

17/05/2014

Tuesday 13 May

I had to go to London today and so left the business of setting up the wing alignment to Rick and Theo. It’s a fiddly business, since the wings can move forwards and backwards or up and down, or twist from the middle to the edges – and the same applies to each of the four wings!

The main thing is to be systematic about the whole thing. You start off with the centre section, adjusting the side wires until the spar fittings are exactly 430 mm in front of the equivalent point on the lower wing spar fittings. Do this on each side separately. Make sure both wires are as tight as you can get them. Then adjust the front and back wires until the centre section is exactly central. The easiest way to do this is to measure the diagonals at the back and front and make sure they are exactly the same. Finally you need to crouch down and sight from the top edge of the engine mount to the leading edge of the centre section to make sure they are exactly parallel. If you’ve done the other stuff properly, this shouldn’t be out. Finally, check that the angle of incidence is correct. On the Scout, the two wings are at the same angle, so you need to use a digital clinometer on each side of the centre section to check this. If there’s anything wrong, you’ll need to undo all the adjustments you’ve made, add shims into the centre section strut sockets, and start all over again…

Next, attach the wings, leaving all the rigging adjusters a little loose. Then check the sweepback. In our case, the wings are exactly square, so you fix uprights to the rear edge of the lower wing spars at the tips and the middle, and sight along to make sure they are in a perfectly straight line. Now make sure they are at right angle to the fuselage by running a tape measure from the centre of the rudder post. Any inaccuracies are corrected using the internal bracing wires inside the wing. Because there are three lots of bracing wires, it’s quite easy to end up with slightly bent spars, so you need to start at the centre wires and work outwards, making sure the spars remain straight.

Done the bottom pair of wings? Now do the same for the top ones, but also adjusting the wires between the interwing struts.

Once that’s done, we need to sort out the dihedral – the upward slope of the wings from centre to tip. They used  laser level to do this, measuring the height drop in the centre line (in the case of the early Scout C, the slope is 3 in 100, so each wing, which is 3700mm long, the rise is 111mm. Each side must be exactly the same. It’s easiest to do this usually by adjusting the landing wires. Then carefully check the washout of the lower wing – that’s the difference in angle of attack between middle and the tips. In the Scout’s case, this should be zero, so check the angle of attack at root and tip to see if there’s any difference, and adjust the interwing strut diagonal wires if necessary.

After that, you need to go through everything again to see if anything’s shifted, and the final check is to use the digital clinometer on the inboard and outboard ends of the wings to make sure they are all at the right angle (in the case of the Scout, they are all at the same angle, which makes life relatively simple). If the centre section is set up correctly, you’re basically checking that the outboard ends are right, and any corrections will need to me made with shims in the strut sockets, as before.

Rick and Theo were convinced that the two rear wing struts were significantly short – and that one was shorter than the other, so there was an element of worry overnight as we left the Scout tucked away in the hangar2014-05-13 In the Hangar.

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