Aeroplane Construction and Operation

by John B. Rathbun

Mechanical Flight. Although the elementary principles of mechanical flight are not of recent origin, the practical development of the flying machine is confined almost entirely to the present century. Gravity propelled gliders and small models have been flown with success from a comparatively early date, but the first actual sustained flight with a power driven machine was performed by the Wright Brothers in 1903. There was no single element on this first successful machine that had not been proposed many years before by Langley, Chanute, Montgomery, Henson, Mouillard, and others, but this first flight must be attributed principally to the fact that the Wrights started carefully and painstakingly to learn how to operate (By practicing with gliders) before starting on the first power machine. If Langley had studied the operation of his machine as carefully as he did its theory and design, he would have been flying long before the Wrights as his original machine was afterwards successfully flown by Curtiss.

When once actual flight was achieved, and the success of the Wright Brothers became generally known, the development proceeded with leaps and bounds. All the resources of science and engineering skill were at once applied to the new device until our present scientific knowledge of the aeroplane compares very favorably with the older engineering sciences. In the few years that have elapsed since the first flight, the aeroplane holds all records for speed, endurance, and radius of action. A great deal of the success so rapidly acquired can be credited to the automobile and motorcycle industries, since it was the development of the light internal combustion motors used on these machines that paved the way for the still lighter aeronautic motor. Again, the automobile industry was responsible for the light and powerful materials of construction, such as alloy steel, aluminum alloys, and also for the highly important constructional details, such as ball bearings, pneumatic tires, carburetors, magnetos, steel tubing, etc. The special methods developed in automobile work have helped to make the aeroplane an immediate commercial proposition.

Curtiss Type JN4-B Primary Trainer

Types of Flying Machines. In general, flight apparatus may be divided into two classes, (1) The Lighter Than Air Type, such as the balloon and dirigible, and (2) The Heavier Than Air Machine, represented by the aeroplane, helicopter and ornithopter. The lighter than air machine is supported in flight by "buoyancy" in much the same manner that a piece of wood floats in water. When a balloon or dirigible, because of its large volume, displaces a volume of air equal to its own weight, the device will float. When the weight of air displaced exceeds the weight of the balloon or dirigible, it will continue to rise until it reaches an altitude where the diminished air density again results in an equality between the weight of the device and the air displaced. At this point it rests, or is in equilibrium. The flotation of such a device is entirely due to static forces and hence (1) is often called an "aerostat."

The sustenation of a Heavier Than Air Machine is due to an entirely different application of forces. Forces in motion (Dynamic Forces) are essential to the support of a heavier than air machine, and it is the resultant of these forces that performs the actual lifting operation, this resultant corresponding to the buoyant force of the aerostat. "Dynamic" flight is obtained by an apparatus in which an arrangement of surfaces are moved in such a way as to cause an upward component of the forces generated by the impact of the air on the surfaces. The surfaces drive the air down and when the force necessary for the continuous downward deflection of air becomes equal to the weight of the machine it is sustained in flight. Dynamic flight therefore depends on the continuous downward deflection of masses of air, and when this motion ceases, sustentation also ceases.

An aeroplane is provided with a deflecting surface that is fixed rigidly in regard to the body of the machine, and the motion necessary for its support is provided by driving the machine forward, the forward motion being produced by the horizontal pull of air screws or propellers. It is at once evident that the forward horizontal motion of the aeroplane must be maintained for its support, for the surfaces are fixed and there is no other possible way of producing a relative motion between the wings and the air.

To overcome the objection of forward motion, several other machines have been proposed in which the surfaces are moved in relation to the body, as well as the air, thus making it possible for the device to stand stationary while the revolving or reciprocating surfaces still continue in motion in regard to the air. One type of the moving surface machine, the "Helicopter," is provided with revolving surfaces arranged in the form of vertical air screws or propellers, the blades of the propellers being inclined so that they drive down a continuous stream of air and produce the continuous upward reaction that supports the machine. While such machines have succeeded in raising themselves off the ground they are not yet practical flying devices. The "ornithopter" or "orthopter" is a flapping wing machine that maintains flight after the manner of the bird (Ornis). Like the helicopter, the ornithopter has not yet proved successful.

Fig. 1. Comparison Between the Kite and Aeroplane; Fig. 2, Showing the Lift and Drag Forces Produced by the Air Stream. The Propeller (P), Acts in a Manner Similar to the Kite String (S) in Producing Relative Motion Between the Air and the Lifting Surfaces.