AEROPLANE. The main problem that. confronts the de signer of any means of transport is to find a working compromise between the various demands of those who maintain and use the service. There is no conflict between the interests of the operator and those of the user. Their common requirements are safety, speed, comfort and adherence to a published time-table. While it cannot as yet be maintained that air transport is as safe, or as reli able as other comparable methods, it is rapidly reaching that goal. As regards both safety and reliability, recent improvements in radio, the establishment of radio beacons, the installation of de icing apparatus, tremendous forward strides in instruments and aeroplanes, and improvements in operating facilities have had great effects.
The cost of air transport is comparatively high and it is in terms of cost only that all the four requirements mentioned above can be expressed. That the slight extra cost, however, is balanced by time saving and ease of travel, is being demonstrated by the ever increasing passenger traffic.
For reasons which are explained in the article AERODYNAMICS a normal aeroplane cannot be maintained in flight at a speed less than a certain minimum "stalling" speed, which for a modern commercial aeroplane varies between 4o and 75 miles per hour. On the other hand, it is possible to give it enough engine power to drive it at between 90 and 25om.p.h., while leaving a margin of some 20% of its total weight for passengers or goods. The aero plane's permanent way, the air, is the only medium of transport which connects without interruption all places on the globe. It may be anticipated that the consequent possibility of transit free from the necessity of making transfers may prove to be as valu able as the speed which can be maintained.
From the point of view of DESIGN, with which this article deals, safety is discussed below, comfort is comparable to that of other types of travel and in the opinion of many air travel furnishes superior comfort; and reliability (in so far as it depends on de sign) presents no special problems.
In what follows we shall discuss (r) the Minimum Speed of Flight and its influence on the design of aeroplanes,• (2) The Power Required for Flight, including both that necessary to drive the aircraft through the air and also—the unique feature of trans port by aircraft heavier-than-air—that expended in sustaining it in flight; (3) The possibilities of Improvement of Performance by reduction of resistance; (4) the Origin of Aerodynamic data of Design; (5) the Distribution of Weight among the component parts; (6) the External Form of Aeroplanes, commenting on the most conspicuous features of modern aircraft; (7) Stability and Control and their influence on (8) the Safety of Air Travel; con cluding with notes on (9) Structural Design and (fo) Materials used in Construction.