AVIATION'S FUTURE.

Auckland Star, Volume LXX, Issue 53, 4 March 1939, Page 8

AVIATION'S FUTURE.

GIANT "PLANES.

HOW FAST AND HOW HIGH?

What may we expect from aviation during the next thirty years? The answers to this question (says the scientific correspondent of the "Manchester Guardian") provide some of the data upon which the development of human affairs will depend.

A conservative review of the immediate prospects of aviation has recently been given by Igor I. Sikorsky, the famous RussianAmerican aeroplane designer, in his Steinmetz memorial lecture at Schenectady, Xew York. Sikorsky is the pioneer of the design of large aeroplanes with multiple engines. He dismissed in hifl lecture the possibilities in speed, altitude and size.

The present speed record is about 440 m.p.h., or 645 ft per second. This is half the speed of a revolver bullet. A heavy object dropped from a height would have to fall more than 6400 feet before it would acquire such a speed. The practicable operating speed of aeroplanes at present is about 200 m.p.li.. but during the next decade it may Tisc to 300 m.p.h. Sikorsky does not believe that the prophecies, of regular 1000 m.p.h. flying within the next thirty years are probable. It has been discovered that the flow of air past moving objects is changed in an abrupt way at the velocity of sound, which is 760 m.p.li. This effect begins to be noticeable at 500 m.p.h. The efficiency of the propeller also falls noticeably -at speeds greater than 500 m.p.h. Thus aeroplanes will not function with the same efficiency above 500 m.p.h., and this 6peed will tend to be a practical limit unless new methods of generating power are discovered. Efficiency of Engines. The present balloon height record is 72,935 feet. At this height the balloonist has 95 per cent of the atmosphere beneath him, so that further ascent is very difficult. Ascents to 54,000 feet have been made in aeroplanes by pilots wearing special suits and breathing oxygen. The average person cannot fly comfortably for a considerable time in the rarefied air at heights of much more than 10,000 feet. The efficiency of the engines also falls off, but may be restored by supercharging. An air-compressor is attached so that air at sealevel pressure may be supplied to the engine. This provides it with the normal amount of oxygen for the combustion in ite cyclindere, and hence the normal output of power. At great heights petrol evaporates more easily, so it must be kept in tanks under pressure. These tanks must be heavy in order to have the strength requisite to bear the pressure. A propeller which is efficient at sea-level pressure is less efficient at the low pressure of high altitudes. As passengers cannot travel long distances in comfort at heights of more than 10,000 feet, long-distance high flying requires the super-charging not only of the engines but of the cabin.

Limits to Size. Sikorsky believes that aeroplanes driven by internal-combustion engines and propellers will probably not rite above 10,000 feet, at which speed they will fly at 500 m.p.h. Aeroplanes weighing up to 1000 tone and carrying thousands of passengers arc possible. The limit of size is not dictated by engineering possibilities, but by economic factors and traffic requirements. These factors will not demand during the next thirty years machines weighing more than 100 to 250 tons. Five Atlantic air liners carrying only 100 passengers each will replace one steamer carrying 2500 passengers, because they will be able to cross the ocean five times while the steamer is crossing once.

One-hundred-ton Atlantic flying boats should be built quite 6oon. They will contain fifty staterooms, a large dining saloon which may also be used for dancing and games, promenade decks, smoking lounges, a library, and comfortable quarters for the crew—but no swimming pool. New inventions may entirely transform these possibilities. If liquid hydrogen, which is very light, could be economically and safely used as fuel, a nonstop flight around the earth along the equator would be possible. Some of the problems of large aeroplanes have been discussed by Professor J. Small in his recent inaugifral lecture at Glasgow University. He mentioned that a fleet of flying boats capable of carrying as many passengers across the Atlantic in a year as the Queen Mary would cost only onethird as much as the ship and would use less than one-sixth as much fuel.

Small steam engines with boilers are much heavier than internal-combustion engines of equal power, but the ratio of weight to power steadily falls with increasing size. At 20,000 h.p. the ratio of weight to power for steam plants falls to a figure which makes them conceivable for aircraft. There are serious difficulties, but the appearance of steam power in big aeroplanes is not inconceivable.