Nevertheless, experimenting has proceeded on lines which seek to recognize nature's form only, while avoiding the best known and most persistent type.
SHAPE OF SUPPORTING SURFACES.—When we examine the prevailing type of supporting surfaces we cannot fail to be impressed with one feature, namely, the determination to insist on a broad spread of plane surface, in imitation of the bird with outstretched wings.
THE TROUBLE ARISING FROM OUTSTRETCHED WINGS.—This form of construction is what brings all the troubles in its train. The literature on aviation is full of arguments on this subject, all declaring that a wide spread is essential, because, —birds fly that way.
These assertions are made notwithstanding the fact that only a few years ago, in the great exhibit of aeroplanes in Paris, many unique forms of machines were shown, all of them capable of flying, as proven by numerous experiments, and among them were a half dozen types whose length fore and aft were much greater than transversely, and it was particularly noted that they had most wonderful stability.
DENSITY OF THE ATMOSPHERE.—Experts declare that the density of the atmosphere varies throughout, —that it has spots here and there which are, apparently, like holes, so that one side or the other of the machine will, unaccountably, tilt, and sometimes the entire machine will suddenly drop for many feet, while in flight.
ELASTICITY OF THE AIR.—Air is the most elastic substance known. The particles constituting it are constantly in motion. When heat or cold penetrate the mass it does so, in a general way, so as to permeate the entire body, but the conductivity of the atmospheric gases is such that the heat does not reach all parts at the same time.
AIR HOLES.—The result is that varying strata of heat and cold seem to be superposed, and also distributed along the route taken by a machine, causing air currents which vary in direction and intensity. When, therefore, a rapidly-moving machine passes through an atmosphere so disturbed, the surfaces of the planes strike a mass of air moving, we may say, first toward the plane, and the next instant the current is reversed, and the machine drops, because its support is temporarily gone, and the aviator experiences the sensation of going into a "hole."
RESPONSIBILITY FOR ACCIDENTS.—These so-called "holes" are responsible for many accidents. The outstretched wings, many of them over forty feet from tip to tip, offer opportunities for a tilt at one end or the other, which has sent so many machines to destruction.
The high center of gravity in all machines makes the weight useless to counterbalance the rising end or to hold up the depressed wing.
All aviators agree that these unequal areas of density extend over small spaces, and it is, therefore, obvious that a machine which is of such a structure that it moves through the air broadside on, will be more liable to meet these inequalities than one which is narrow and does not take in such a wide path.