The Aeroplane Speaks [38]
but this is only part of their work. They must keep the planes apart, so that the latter are in their correct attitude. That is only so when the spars of the bottom plane are parallel with those of the top plane. Also, the chord of the top plane must be parallel with the chord of the bottom plane. If that is not so, then one plane will not have the same angle of incidence as the other one. At first sight one might think that all that is necessary is to cut all the struts to be the same length, but that is not the case.
Sometimes, as illustrated above, the rear spar is not so thick as the main spar, and it is then necessary to make up for that difference by making the rear struts correspondingly longer. If that is not done, then the top and bottom chords will not be parallel, and the top and bottom planes will have different angles of incidence. Also, the sockets or fittings, or even the spars upon which they are placed, sometimes vary in thickness owing to faulty manufacture. This must be offset by altering the length of the struts. The best way to proceed is to measure the distance between the top and bottom spars by the side of each strut, and if that distance, or ``gap'' as it is called, is not as stated in the aeroplane's specifications, then make it correct by changing the length of the strut. This applies to both front and rear interplane struts. When measuring the gap, always be careful to measure from the centre of the spar, as it may be set at an angle, and the rear of it may be considerably lower than its front.
BORING HOLES IN WOOD.--It should be a strict rule that no spar be used which has an unnecessary hole in it. Before boring a hole, its position should be confirmed by whoever is in charge of the workshop. A bolt-hole should be of a size to enable the bolt to be pushed in, or, at any rate, not more than gently tapped in. Bolts should not be hammered in, as that may split the spar. On the other hand, a bolt should not be slack in its hole, as, in such a case, it may work sideways and split the spar, not to speak of throwing out of adjustment the wires leading from the lug or socket under the bolt-head.
WASHERS.--Under the bolt-head, and also under the nut, a washer must be placed--a very large washer compared with the size which would be used in all-metal construction. This is to disperse the stress over a large area; otherwise the washer may be pulled into the wood and weaken it, besides possibly throwing out of adjustment the wires attached to the bolt or the fitting it is holding to the spar.
LOCKING.--Now as regards locking the bolts. If split pins are used, be sure to see that they are used in such a way that the nut cannot possibly unscrew at all. The split pin should be passed through the bolt as near as possible to the nut. It should not be passed through both nut and bolt.
If it is locked by burring over the edge of the bolt, do not use a heavy hammer and try to spread the whole head of the bolt. That might damage the woodwork inside the fabric-covered surface. Use a small, light hammer, and gently tap round the edge of the bolt until it is burred over.
TURNBUCKLES.--A turnbuckle is composed of a central barrel into each end of which is screwed an eye-bolt. Wires are taken from the eyes of the eye-bolt, and so, by turning the barrel, they can be adjusted to their proper tension. Eye-bolts must be a good fit in the barrel; that is to say, not slack and not very tight. Theoretically it is not neces- sary to screw the eye-bolt into the barrel for a distance greater than the diameter of the bolt, but, in practice, it is better to screw it in for a considerably greater distance than that if a reasonable degree of safety is to be secured.
Now about turning the barrel to secure the right adjustment. The barrel looks solid, but, as a matter of fact, it is hollow and much more frail than it appears. For that reason it should not be turned by seizing it with pliers, as that may distort it and spoil the bore within it. The best method is to pass a piece of wire through the hole in
Sometimes, as illustrated above, the rear spar is not so thick as the main spar, and it is then necessary to make up for that difference by making the rear struts correspondingly longer. If that is not done, then the top and bottom chords will not be parallel, and the top and bottom planes will have different angles of incidence. Also, the sockets or fittings, or even the spars upon which they are placed, sometimes vary in thickness owing to faulty manufacture. This must be offset by altering the length of the struts. The best way to proceed is to measure the distance between the top and bottom spars by the side of each strut, and if that distance, or ``gap'' as it is called, is not as stated in the aeroplane's specifications, then make it correct by changing the length of the strut. This applies to both front and rear interplane struts. When measuring the gap, always be careful to measure from the centre of the spar, as it may be set at an angle, and the rear of it may be considerably lower than its front.
BORING HOLES IN WOOD.--It should be a strict rule that no spar be used which has an unnecessary hole in it. Before boring a hole, its position should be confirmed by whoever is in charge of the workshop. A bolt-hole should be of a size to enable the bolt to be pushed in, or, at any rate, not more than gently tapped in. Bolts should not be hammered in, as that may split the spar. On the other hand, a bolt should not be slack in its hole, as, in such a case, it may work sideways and split the spar, not to speak of throwing out of adjustment the wires leading from the lug or socket under the bolt-head.
WASHERS.--Under the bolt-head, and also under the nut, a washer must be placed--a very large washer compared with the size which would be used in all-metal construction. This is to disperse the stress over a large area; otherwise the washer may be pulled into the wood and weaken it, besides possibly throwing out of adjustment the wires attached to the bolt or the fitting it is holding to the spar.
LOCKING.--Now as regards locking the bolts. If split pins are used, be sure to see that they are used in such a way that the nut cannot possibly unscrew at all. The split pin should be passed through the bolt as near as possible to the nut. It should not be passed through both nut and bolt.
If it is locked by burring over the edge of the bolt, do not use a heavy hammer and try to spread the whole head of the bolt. That might damage the woodwork inside the fabric-covered surface. Use a small, light hammer, and gently tap round the edge of the bolt until it is burred over.
TURNBUCKLES.--A turnbuckle is composed of a central barrel into each end of which is screwed an eye-bolt. Wires are taken from the eyes of the eye-bolt, and so, by turning the barrel, they can be adjusted to their proper tension. Eye-bolts must be a good fit in the barrel; that is to say, not slack and not very tight. Theoretically it is not neces- sary to screw the eye-bolt into the barrel for a distance greater than the diameter of the bolt, but, in practice, it is better to screw it in for a considerably greater distance than that if a reasonable degree of safety is to be secured.
Now about turning the barrel to secure the right adjustment. The barrel looks solid, but, as a matter of fact, it is hollow and much more frail than it appears. For that reason it should not be turned by seizing it with pliers, as that may distort it and spoil the bore within it. The best method is to pass a piece of wire through the hole in