Engineering Wonders of the World
Volume III

CONSTRUCTION OF AEROPLANES AND PROPELLERS. 41 loid—is fastened to the under side of the ribs, and the rear spar and the ribs are enclosed in pockets of the same material, so that no surfaces may be opposed squarely to the passage of the air. This method of con- struction is economical in fabric, but the attachment of the pockets is a somewhat troublesome business. Upper Surface Fig. 2.—A DOUBLE-SURFACED DECK, SHOWING SPARS AND BLOCKS SEPARATING UPPER AND LOWER RIBS. For double-surfaced decks (see Fig. 2) the spars, other than the front one, are enclosed by the ribs and fabric. This form of deck gives a better “ run ” for the air over the upper side, which is much more free from excrescences than the single-surfaced deck, and is therefore more efficient. The fabric must be stretched as tightly as possible over the framework to prevent undue sagging under pressure of the air. At the trailing edge of the deck it is commonly passed round a taut cable running longitudinally from end to end, or round a fine spar. The upright stanchions between the decks of a biplane are of oval or fish-shaped sections, and arranged with their greatest diameter fore and aft. These and the decks are braced together diagonally with piano wires or fine cables drawn tight, and provided with adjust- ments for taking up any slack. It is important that the wires should not be able to vibrate, since a vibrating wire offers more resistance to the air than one that remains quite taut. The girder formed by the deck spars and the stanchions is, if properly designed, very strong. To test a certain glider, weighing only about 150 lbs., and having a 30-foot span, the ends of the decks were supported on stools, and a 14-stone passenger took his seat at the centre. The deflection was only half an inch. Outriggers and the body work of a machine are also built up on the girder principle, so as to be able to withstand sudden and violent strains. A monoplane body is , ill Body Work. given a more or less decided torpedo or boat shape, tapering somewhat abruptly towards the front and gradually to- wards the tail, as shown by our illustrations of the Blériot and Antoinette machines. The covering-in of the body with tightly stretched fabric helps to lessen its resistance to the air. A very important part of an aeroplane is the chassis, or wheeled carriage, which supports most of the weight while the rest, and enables it to run easily over the ground when getting up speed for a start. steel tubing is employed, as wood could not be relied upon to resist the sudden shocks caused by alighting. Two or more wheels, shod with pneumatic tyres, are generally placed under the main decks, and one or two under the tail where a horizontal tail is fitted. Cody and Curtiss use three in front, Farman four, and Voisin two. Voisin and Blériot mount machine is at The Chassis. In the chassis their wheels castor fashion, so as to adjust themselves automatically to the direction which the aeroplane may take, and interpose springs to minimize shocks to the body of the machine. Special springs are provided to bring the wheels into a fore and aft position when the aeroplane rises from the ground. The Wrights, by dispensing with a wheeled chassis, reduced the total weight of their bi- plane and also its air resistance considerably. The Voisin chassis accounts for 250 lbs., or half as much again as the main decks. SCREW PROPELLERS. Good design of aeroplanes and high engine power in proportion to weight are of little avail, if the means of converting the engine power into work are inefficient. Locomo- tives driven over rails and roads are en- abled to transmit their force from the moving