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30 Dec 1913. Tuesday


Today, Frank made a start on the wings, producing no less than five sketches, aided, no doubt, by the relative quiet in the office in the period between Christmas and the New Year!

522 Wing Spars 30 XII 13

The main structural elements are the spars, and Frank designed them to be as strong as possible by making them the full depth of the wing, less the capstrips on the ribs. The result is that while the vertical faces are vertical and parallel, the top and bottom aren’t, and each one is very slightly different to the others. Sketch 522 is the basic outline of the spars only; there’s a great deal more work to be done on them before they are ready to be assembled. You can see that he’s referred to sketch 523, 528 and 535, which wasn’t signed off until a week later. Did he allocate sketch numbers before he used them? I doubt it; I suspect he added the note about the weights after signing and dating the sketch.

523 Position of Inner End Fittings on Spar Inner Ends 30 XII 13

Sketch 523 is the complex shaping of the inboard ends of the spars where they fit to the fuselage or cabane. There’s a metal cap that fits over the end of the spar, and the wood is made to be a very close fit inside the metal fitting. In fact, here is another indication that there is another sketchbook with designs on it- at the top right it refers to SK423? For the metal fitting itself. One particularly difficult feature to manufacture is the 1 in 50 rake to the centre line. Most aircraft use a small amount of dihedral (the tips are higher than the centre) to improve the handling, and it’s common to adjust the dihedral during flight testing. In that case, it would make sense to attach the wing spars with a horizontal pin, so that the dihedral angle could be adjusted. But for some reason Frank decided to use a vertical pin, and 1 in 50 you can see in the middle of the sketch is the dihedral angle he’d decided to use, and because it’s carved into the wing spars, you can’t adjust it at all. This feature survived all the later redesigns, and when they decided to increase the dihedral angle on later models, it meant making a completely new set of wings.

524 Wing Leading Edge 30 XII 13

Sketches 524 – 526 show the leading and trailing edges, made of steel tube with little clips soldered on to which the ribs are attached. The method of construction stayed the same throughout the production run, although the dimensions altered when the wing size was increased.

525 Wing Trailing Edge 30 XII 13

526 Wing Detail - Aileron Trailing Edge 30 XII 13

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