Some practical usesAt the same time there are fields in which the fiving machine may beused to great advantage. These are.Sports--Flyimg machine races or flights will always be popular byreason of the element of danger It is a strange. but nevertheless a trueproposition, that it is this element which adds zest to all sporting eventsScientific--For exploration of otherwise inaccessible regions such asdeserts, mountain tops, etcReconnoitering--In time of war fling machines may be used toadvantage to spy out an enemys endascertain its defenses. Etc

In order to understand the theory of the modem fying machine onemust also understand bird action and wind action In this connection thefollowing simple experiment will be of interestTake a circular-shaped bit of cardboard, like the lid of a hat box, andremove the bent-over portion so as to have a perfectly flat surface withclean, sharp edge. Holding the cardboard at arm's length, withdraw yourhand, leaving the cardboard without support. What is the result? Thecardboard, being heavier than air, and having nothing to sustain it, will fallto the ground. Pick it up and throw it, with considerable force, against thewind edgewise. What happens? Instead of falling to the ground, thecardboard sails along on the wind remaining afloat so long as it is inmotion. It seeks the ground, by gravity, only as the motion ceases, andthen by easy stages, instead of dropping abruptly as n the first instanceHere we have a homely, but accurate illustration of the action of thefying machine. The motor does for the latter what the force of your armdoes for the cardboard- imparts a motion which keeps it afloat. The onlyreal difference is that the motion given by the motor is continuous andmuch more powerful than that given by your am. The action of the latteris limited and the end of its propulsive force is reached within a second ortwo after it is exerted, while the action of the motor is prolonged.Another Simple Illustration.Another simple means of illustrating the principle of fy ing machineoperation, so far as sustentation and the elevation and depression of theplanes is concerned, is explained in the accompany ing diagram.A is a piece of cardboard about 2 by 3 inches in size. B is a piece ofpaper of the same size pasted to one edge of A. If you bend the paper to acurve, with convex side up and blow across it as shown in Figure C, thepaper will rise instead of being depressed. The dotted lines show that theyou may blow, the effect will be to elevate the paper, despite the fact that

In Figure D we have an opposite effect. Here the paper is in a curveexactly the reverse of that shown in Figure C, bringing the concave sideNow if you will again blow across the surface of the card the action of thepaper will be downward-it will be impossible to make it rise. The harderyou blow the greater will be the downward movement.Principle In General Use.This principle is taken advantage of in the construction of allsuccessful fying machines. Makers of monoplanes and biplanes alikeadhere to curved bodies, with the concave surface facing downwardStraight planes were tried for a time, but found greatly lacking in thepower of sustentation. By curving the planes, and placing the concavesurface downward a sort of inverted bowl is formed in which the airgathers and exerts a buoyant effect. Just what the ratio of the curve shouldbe is a matter of contention. In some instances one inch to the foot isfound to be satisfactory; in others this is doubled, and there are a few casesin which a curve of as much as 3 inches to the foot has been used Righthere it might be well to explain that the word plane applied to flyingmachines of modern construction is in reality aomer. Plane indicatesa flat, level surface. As most successful flying machines have curvedsupporting surfaces it is clearly wrong to speak of "planes,aeroplanes. Usage, however, has made the terms convenient and, as theyare generally accepted and understood by the public, they are used in likemanner in this volumeGetting Under HeadwayA bird, on first rising from the ground, or beginning its flight from atree, will flap its wings to get under headway. Here again we have anotherlllustration of the manner in which a flying machine gets under headwaythe motor imparts the force necessary to put the machine into the air, butright here the similarity ceases. If the machine is to be kept afloat themotor must be kept moving. A flying machine will not sustain itself, it willnot remain suspended in the air unless it is under headway. This is becauseit is heavier than air and gravity draws it to the groundPuzzle in bird soaringBut a bird, which is also heavier than air, will remain suspended, in acalm, will even soar and move in a circle, without apparent movement ofits wings. This is explained on the theory that there are generally verticalcolumns of air in circulation strong enough to sustain a bird, but muchweak to exert any lifting power on a flying machine, It is easy tounderstand how a bird can remain suspended when the wind is in action,but its suspension in a seeming dead calm was a puzzle to scientists untilMr. Chanute advanced the proposition of vertical columns of air.Modeled Closely After BirdsSo far as possible, builders of flying machines have taken what may becalled"the architecture" of birds as a model. This is readily noticeablethe form of construction. When a bird is in motion its wings(except whenflapping) are extended in a straight line at right angles to its body. Thisbrings a sharp, thin edge against the air, offering the least possible surfacefor resistance, while at the same time a broad surface for support isafforded by the flat, under side of the wings. Identically the same thing isdone in the construction of the fving machineNote, for instance, the marked similarity in form as shown in theillustration in Chapter I. Here A is the bird, and b the general outline ofthe machine. The thin edge of the plane in the latter is almost a duplicateof that formed by the outstretched wings of the bird. while the rudderplane in the rear serves the same purpose as the birds tail.

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