Service Aviation, Aeronautical Engineering and Commercial Aviation 270068
INFLUENCE that the research and development work done in aeronautics by the naval and military services has had in the advancement of design and construction of airplanes and aircraft engines suitable for commercial operations is pointed out and exemplified by citing a few instances of direct adaptability of military types of airplane to commercial uses. Nearly all of this work would have been done much later or not at all if the airplane had been purely a commercial vehicle, but the constructor for purely commercial purposes and the commercial operator have had the benefit of it. Major fundamentals, such as speed, safety, reliability and economy, are the same in both types of aviation; divergencies between the requirements for the two kinds of service begin to appear in materiel, personnel, or methods of operation only at a somewhat advanced stage of evolution.
Although it is inadvisable, as a rule, to combine military and civil functions in one design, the methods of design and construction created for the naval service are largely suitable for commercial purposes, as many elements that enter into the designer's work are independent of the use to which the finished machine is to be put. Progress grows out of specific knowledge, and the same procedure that suggests to the designer means for improving the performance of a military machine can point the way toward production of a safer and more comfortable passenger-transport airplane.
The author discusses the general question of the desirability of a specifically commercial type of airplane engine that shall be less refined and less expensive than the military types and indicates that safety, reliability and economy are objectives alike of commercial and military aviation. The problem of economy in first cost is tied up with economy of operation. By simple financial analysis it is shown that an engine which weighs 2 lb. per hp. and costs $24 per hp. is on a commercial parity with one weighing 3 lb. per hp. and costing less than $12 per hp. A 10-per cent increase in weight of the airplane structure will be justified only if accompanied by a 20-per cent decrease in total cost. The economic penalty on excess weight is too heavy at present to sanction any appreciable lowering, on behalf of air-transport operators, of the standards established by the naval and military services for the selection and working of materials used in airplane construction.
Since privately owned airplanes, on the other hand, are likely to be in the air relatively few hours per year and as first price rather than economy of operation and upkeep is decidedly a factor in their purchase, an undoubted need exists for rugged, reliable and cheap powerplants for such machines, even though the low price is obtained at considerable sacrifice of efficiency. This is the field of low power and small size.