THE CONCAVED PLANE.--These considerations led to the adoption of the concaved plane formation, and for purposes of comparison the diagram, Fig. 24, shows the plane B of the same length and angle as the straight planes.

In examining the successive stream lines it will be found that while the 1st, 2d and 3d lines have a little less angle of impact than the corresponding lines in the straight plane, the last lines, 5, 6 and 7, have much greater angles, so that only line 4 strikes the plane at the same angle.

Such a plane structure would, therefore, have its center of pressure somewhere between the lines 3 and 4, and the lift being thus, practically, uniform over the surface, would be more effective.

THE CENTER OF PRESSURE.--This is a term used to indicate the place on the plane where the air acts with the greatest force. It has reference to a point between the front and rear margins only of the plane.

_Fig. 24. Air lines below a concaved Plane._

UTILIZING THE RAREFIED AREA.--This structure, however, has another important advantage, as it utilizes the rarefied area which is produced, and which may be understood by reference to Fig. 25.

The plane B, with its upward curve, and at the same angle as the straight plane, has its lower end so curved, with relation to the forward movement, that the air, in rushing past the upper end, cannot follow the curve rapidly enough to maintain the same density along C, hence this exerts

an upward pull, due to the rarefied area, which serves as a lifting force, as well as the compressed ma.s.s beneath the plane.

CHANGING CENTER OF PRESSURE.--The center of pressure is not constant. It changes with the angle of the plane, but the range is considerably less on a concave surface than on a flat plane.

_Fig. 25. Air lines above a convex Plane._

In a plane disposed at a small angle, A, as in Fig. 26, the center of pressure is nearer the forward end of the plane than with a greater positive angle of incidence, as in Fig. 27, and when the plane is in a normal flying angle, it is at the center, or at a point midway between the margins.

PLANE MONSTROSITIES.--Growing out of the idea that the wing in nature must be faithfully copied, it is believed by many that a plane with a p.r.o.nounced thickness at its forward margin is one of the secrets of bird flight.

Accordingly certain inventors have designed types of wings which are shown in Figs. 28 and 29.

_Fig. 28 Changing centers of Pressures._

_Fig 29. Bird-wing structures._

Both of these types have p.r.o.nounced bulges, designed to "split" the air, forgetting, apparently, that in other parts of the machine every effort is made to prevent head resistance.

THE BIRD WING STRUCTURE.--The advocates of such construction maintain that the forward edge of the plane must forcibly drive the air column apart, because the bird wing is so made, and that while it may not appear exactly logical, still there is something about it which seems to do the work, and for that reason it is largely adopted.

WHY THE BIRD'S WING HAS A p.r.o.nOUNCED BULGE.--Let us examine this claim. The bone which supports the entire wing surface, called the (pectoral), has a heavy duty to perform. It is so constructed that it must withstand an extraordinary torsional strain, being located at the forward portion of the wing surface. Torsion has reference to a twisting motion.

In some cases, as in the bat, this primary bone has an attachment to the rear of the main joint, where the rear margin of the wing is attached to the leg of the animal, thus giving it a support and the main bone is, therefore, relieved of this torsional stress.

THE BAT'S WING.--An examination of the bat's wing shows that the pectoral bone is very small and thin, thus proving that when the entire wing support is thrown upon the primary bone it must be large enough to enable it to carry out its functions.

It is certainly not so made because it is a necessary shape which best adapts it for flying.

If such were the case then nature erred in the case of the bat, and it made a mistake in the housefly's wing which has no such anterior enlargement to a.s.sist (?) it in flying.

AN ABNORMAL SHAPE.--Another ill.u.s.tration is shown in Fig. 30, which has a deep concave directly behind the forward margin, as at A, so that when the plane is at an angle of about 22 degrees, a horizontal line, as B, pa.s.sing back from the nose, touches the incurved surface of the plane at a point about one-third of its measurement back across the plane.

_Fig. 30. One of the Monstrosities_

This form is an exact copy of the wing of an actual bird, but it belongs, not to the soaring, but to the cla.s.s which depends on flapping wings, and as such it cannot be understood why it should be used for soaring machines, as all aeroplanes are.

The foregoing instances of construction are cited to show how wildly the imagination will roam when it follows wrong ideals.

THE TAIL AS A MONITOR.--The tendency of the center of pressure to change necessitates a correctional means, which is supplied in the tail of the machine, just as the tail of a kite serves to hold it at a correct angle with respect to the wind and the pull of the supporting string.

CHAPTER VII

ABNORMAL FLYING STUNTS AND SPEEDS

"PEQUOD, a Frenchman, yesterday repeatedly performed the remarkable feat of flying with the machine upside down. This exhibition shows that the age of perfection has arrived in flying machines, and that stability is an accomplished fact."--News item.

This is quoted to show how little the general public knows of the subject of aviation. It correctly represents the achievement of the aviator, and it probably voiced the sentiment of many scientific men, as well as of the great majority of aviators.

A few days afterwards, the same newspaper published the following:

"Lieutenant ----, while experimenting yesterday morning, met his death by the overturning of his machine at an alt.i.tude of 300 meters.

Death was instantaneous, and the machine was completely destroyed."

The machines used by the two men were of the same manufacture, as Pequod used a stock machine which was strongly braced to support the inverted weight, but otherwise it was not unlike the well known type of monoplane.

Beachy has since repeated the experiment with a bi-plane, and it is a feat which has many imitators, and while those remarkable exhibitions are going on, one catastrophe follows the other with the same regularity as in the past.

Let us consider this phase of flying. Are they of any value, and wherein do they teach anything that may be utilized,

LACK OF IMPROVEMENTS IN MACHINES.--It is remarkable that not one single forward step has been taken to improve the type of flying machines for the past five years. They possess the same shape, their stabilizing qualities and mechanism for a.s.suring stability are still the same.

MEN EXPEDITED, AND NOT THE MACHINE.--The fact is, that during this period the man has been exploited and not the machine. Men have learned, some few of them, to perform peculiar stunts, such as looping the loop, the side glide, the drop, and other features, which look, and are, hazardous, all of which pander to the sentiments of the spectators.

ABNORMAL FLYING OF NO VALUE.--It would be too broad an a.s.sertion to say that it has absolutely no value, because everything has its use in a certain sense, but if we are to judge from the progress of inventions in other directions, such exhibitions will not improve the art of building the device, or make a fool-proof machine.

Indeed, it is the very thing which serves as a deterrent, rather than an incentive. If machines can be handled in such a remarkable manner, they must be, indeed, perfect! Nothing more is needed! They must represent the highest structural type of mechanism!

That is the idea sought to be conveyed in the first paragraph quoted. It is pernicious, instead of praiseworthy, because it gives a false impression, and it is remarkable that even certain scientific journals have gravely discussed the perfected (?) type of flying machine as demonstrated by the experiments alluded to.

THE ART OF JUGGLING.--We may, occasionally, see a cyclist who understands the art of balancing so well that he can, with ease, ride a machine which has only a single wheel; or he can, with a stock bicycle, ride it in every conceivable att.i.tude, and make it perform all sorts of feats.

It merely shows that man has become an expert at juggling with a machine, the same as he manipulates b.a.l.l.s, 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 c.o.xVEX 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.