Sir Hiram in condemning the airship was ready with a substitute. On looking round on the patterns of Nature, he concluded that, inasmuch as all things that fly are heavier than air, the problem of aërial navigation must be solved by a machine whose natural tendency is to fall to the ground, and which can be sustained only by the exertion of great force. Its very weight would enable it to withstand, at least to a far greater extent than the airship, the varying currents of the air.
The lifting principle must be analogous to that by which a kite is suspended. A kite is prevented from rising beyond a certain height by a string, and the pressure of the wind working against it at an angle tends to lift it, like a soft wedge continuously driven under it. In practice it makes no difference whether the kite be stationary in a wind or towed rapidly through a dead calm; the wedge-like action of the air remains the same.
Maxim decided upon constructing what was practically a huge compound kite driven by very powerful motors.
But before setting to work on the machine itself he made some useful experiments to determine the necessary size of his kites or aeroplanes, and the force requisite to move them.
He accordingly built a "whirling-table," consisting of a long arm mounted on a strong pivot at one end, and driven by a 10 horse-power engine. To the free end, which described a circle of 200 feet in circumference, he attached small aeroplanes, and by means of delicate balances discovered that at 40 miles an hour the aeroplane would lift 133 lbs. per horse-power, and at 60 miles per hour every square foot of surface sustained 8 lbs. weight. He, in common with other experimenters on the same lines, became aware of the fact that if it took a certain strain to suspend a stationary weight in the air, _to advance it rapidly as well as to suspend it took a smaller strain_. Now, as on sea and land, increased speed means a very rapid increase in the force required, this is a point in favour of the flying-machine. Professor Langley found that a brass plate weighing a pound, when whirled at great speed, was supported in the air by a pulling pressure of less than one ounce. And, of course, as the speed increased the plate became more nearly horizontal, offering less resistance to the air.