Danger Eliminated
One of the lessons learned from the operation of the air mail service during the year is that the element of danger that exists in the training of aviators in military and exhibition flying is almost entirely absent from commercial flying. Second Assistant Postmaster-General Praeger, in reporting to the postmaster-general the operations for the year, says that the record of the air mail service, which includes flying at altitudes of as low as 50 feet during periods of marked invisibility, throws an interesting light on this question. During the year, more than 128,000 miles having been travelled, no aeroplane carrying the mail has ever fallen out of the sky, and there has not been a single death of an aviator in carrying the mail. The only deaths by accident which have occurred were that of an aviator who made a flight to demonstrate his qualifications as an aviator and that of a mechanic who fell against the whirling propeller of a machine on the ground. But two aviators have been injured seriously enough to be sent to a hospital. Other accidents consisted mainly of bruises and contusions sustained by planes turning over after landing. Of the three types of planes operated regularly in the mail service, one type was more given than the others to turning over on rough ground, and it was principally on planes of this type that pilots were shaken up or bruised by the plane turning turtle. One type of machine in the mail service which has performed almost half of the work has never turned turtle. The record of the air mail service with respect to accidents will compare favorably with that of any mode of mechanical transportation in the early days of its operation.
One of the first studies to be taken up by the air mail service was to determine whether visibility is absolutely necessary to commercial flying. The first step necessary was the refinement of the existing radio direction-finders so as to eliminate the liability of 3 to 5 per cent of error. This has been successfully worked out by the Navy Department on an air mail testing-plane. The second problem was that of guiding the mail plane after it had left the field to the centre of the plot for landing. This problem has been solved by the Bureau of Standards in experiments conducted on the air mail testing-plane in connection with the radio directional compass. This device is effective up to an altitude of 1,500 feet, and with the further refinements of the device another thousand feet is expected to be added. Aeronautical engineers are working upon a device for the automatic landing of a mechanically flown plane which would meet the condition of absolute invisibility that could exist only in the most blinding snow-storm or impenetrable fog.
A year’s flying in the mail service, with all types and temperaments of aviators, has established the fact that 200 feet visibility from the ground is the limit of practical flying, although a number of runs have been made with the mail between New York and Washington during which a part of the trip was flown at an altitude as low as 50 feet. The objection of aviators to flying above a ground-fog, rain, snow, or heavy clouds with single motor-planes is the possibility of the motor stopping over a village, city, or other bad landing-place, with the radius of visibility so little as to afford no opportunity to pick out a place for landing. It is generally accepted that with two or more motors, forced landings under such conditions can be avoided.
Flying in Roughest Weather
A number of severe gales have been encountered during the flights between New York and Washington. Gales of from 40 to 68 miles an hour have been encountered and overcome. Pilot J. M. Miller, who was formerly a naval flier, made the flight from Philadelphia to New York in a Curtiss R4 with a 400 horse-power Liberty motor, rising from the field against a 43-mile gale and arriving in New York through a blinding snow-storm with a wind velocity reported by the Weather Bureau to be 68 miles an hour and which was 15 per cent greater at the altitude at which he flew.
Mr. Praeger says in his report that from experience it is learned to be useless to send against a 40-mile gale a plane having a top speed of no more than 75 or 80 miles. “The two types of planes in the air mail service of this speed,” he said, “are the Standard JR 1 mail plane, having a wing spread of 31 feet 4 inches, and the Curtiss JN 4, having a wing spread of 43 feet 7⅜ inches. Each plane of this type is equipped with a (Hispano-Suiza) 150 horse-power motor, which does not provide enough reserve power to combat the disturbed air conditions at the surface in a wind of more than 40 miles an hour, especially if the wind comes in descending columns or gusts. Under these conditions it is possible to make headway only with a Liberty engine, which has plenty of reserve power. A plane equipped with a 150 horse-power motor, if it succeeds in breaking through the surface winds, can make only slow and laborious headway against a full or a quartered head wind of about 40 miles. There have been many instances where the planes equipped with 150 horse-power motors have been held down to a speed of between 30 and 37 miles an hour; and also many instances where a hundred-mile-an-hour plane equipped with a Liberty motor has been held to between 55 and 60 miles. A few wind-storm conditions were encountered where the planes at the height of the gust were actually carried backward.”
The same six planes that were in operation at the inauguration of the service, and have been in continuous employment during the year, are in operation to-day, and the one which made the initial flight from New York to Washington, May 15, 1918, made the flight May 15, 1919. This is regarded as throwing a new light on the question of the life of an aeroplane and as demonstrating that the mechanical requirements and the operation in commercial flying are more economical and safer and in many instances more practical than in exhibition or military flying.
The fact that there were only 37 forced landings due to mechanical troubles during flights makes a record not heretofore approached in aviation and is creditable in the American-built aeroplane and mechanics who keep them in fine condition. Especially is this record a strong tribute to the American-built Liberty and Hispano-Suiza motors.
The transportation by aeroplane is ordinarily twice as fast as by train, and on distances of 600 miles or more, no matter how frequent or excellent the train service, the aeroplane mail at the higher rate of postage should equal the cost of its operations. Wherever the train service is not as frequent or as fast as it is between Washington and New York the aeroplane operations should show an immense profit on all distances from 500 miles up.