It merely shows that man has become an expert at juggling with a machine, the same as he manipulates balls, and wheels, and other artifices, by his dexterity.
PRACTICAL USES THE BEST TEST.—The bicycle did not require such displays to bring it to perfection. It has been the history of every invention that improvements were brought about, not by abnormal experiments, but by practical uses and by normal developments.
The ability of an aviator to fly with the machine in an inverted position is no test of the machine's stability, nor does it in any manner prove that it is correctly built. It is simply and solely a juggling feat—something in the capacity of a certain man to perform, and attract attention because they are out of the ordinary.
CONCAVED AND COXVEX PLANES:—They were performed as exhibition features, and intended as such, and none of the exponents of that kind of flying have the effrontery to claim that they prove anything of value in the machine itself, except that it incidentally has destroyed the largely vaunted claim that concaved wings for supporting surfaces are necessary.
HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.— When flying "upside down," the convex side of the plane takes the pressure of the air, and maintains, so it is asserted, the weight of the machine. This is true during that period when the loop is being made. The evolution is made by first darting down, as shown in Fig. 31, from the horizontal position, 1, to the position 2, where the turn begins.
Fig. 31. Flying upside down.
TURNING MOVEMENT.—Now note the characteristic angles of the tail, which is the controlling factor. In position 1 the tail is practically horizontal. In fact, in all machines, at high flight, the tail is elevated so as to give little positive angle of incidence to the supporting planes.
In position No. 2, the tail is turned to an angle of incidence to make the downward plunge, and when the machine has assumed the vertical, as in position 3, the tail is again reversed to assume the angle, as in 1, when flying horizontally.
At the lower turn, position 4, the tail is turned similar to the angle of position 2, which throws the rear end of the machine down, and as the horizontal line of flight is resumed, in an inverted position, as in position 4, the tail has the same angle, with relation to the frame, as the supporting planes.
During this evolution the engine is running, and the downward plunge develops a tremendous speed, and the great momentum thus acquired, together with the pulling power of the propeller while thus in flight, is sufficient to propel it along horizontally, whatever the plane surface curve, or formation may be.