Fig. 6.—Henson and Stringfellow’s Model.
Henson and Stringfellow built in 1845 a model which weighed about 30 lbs. ([Fig. 6]); and although its stability was not perfect, it was an interesting machine—a forecast of the monoplane of the future. Here one saw the lifting planes take shape; the body between the wings; the tail-planes at the rear; and, above all, a suggestion of the means by which machines would be driven through the air: the fitting to the model, that is to say, of revolving propellers or screws. When an inventor has fitted an engine to an aircraft, means must be devised for using its power to drive the machine through the air; and to make the wings flap like those of a bird, has been found so complicated, owing to the mechanism necessary to imitate natural movements, that much of the power is wasted. Inventors such as Henson and Stringfellow, realising this difficulty, made wings that were outstretched and immovable, like those of a bird when it is soaring, and relied upon screw propellers—which they set spinning at great speed by means of their engines—to thrust their craft forward through the air.
Fig. 7.
In an early and simple form, the aerial propeller was as shown in [Fig. 7]. Here are two curved blades, so shaped that, when the propeller is made to revolve quickly, these blades will act powerfully upon the air. What the propeller does is to screw itself forward through the air, as one might revolve a corkscrew and drive it into a cork, or force a gimlet into a piece of wood. Each time you twist the gimlet for instance, as you drive it inwards, it forces itself a certain distance through the wood; and in a like manner the air-propeller, each time it revolves, tends to bore its way through the air ([Fig. 8]) and so push, or draw with it, the flying machine to which it is attached. But with air, seeing that its density is small, it is necessary to use a large screw, and to turn it fast, before power can be obtained.
