SPEED IN THE AIR

Grey River Argus, 6 August 1937, Page 8

SPEED IN THE AIR

Limit of 60 m.p.h, DESIGNER’S CALCULATIONS. “Nature’s unclimbable fence,” in the arresting phrase of Mr. H. E. Wimperis, president of the Royal Aeronautical Society, sets the limit of speed attainable by’a man-carrying aeroplane at six hundred miles an hour. The fastest speed yet recorded in level flight is 441 m.p.h. and speeds in the neighbourhod of 500 miles an hour have been reached in terminal velocity dives. In his presidential addess to the society Mr. Wimperis set out clearly his reasons for selecting the 600 m.p.h. limit. He defined the “fence” as the natural limit to the speed with which the air is able to get out of the way of the advancing aeroplane. He continued: “The speed at which air can move when pushed is the same as the velocity' of sound, and once the aeroplane speed approaches this boundary, it becomes more and more difficult to push away the air in front. And there is nothing we can do to increase the velocity of sound. “When a body' moves it compresses the air just in front of it, and the resulting pressure is communicated to the air further ahead. This communication is achieved at the velocity of sound in the medium. In air of normal sea level pressure and temperature, this velocity is 750 m.p.h. . . . In the stratosphere it is only 650 m.p.h. “When the speed reaches this limit what is coming. This leads to as the air ahead cannot be ‘warned’ of many shocks and collisions as if an un lighter motor-car tried to get through a crowd of deaf people on a dark night. When an aeroplane moves as fast as, or faster than, the velocity' of sound, collisions with the air particles are inevitable and there will be enormous loss of energy, through conversion into heat of the resultant shock waves.” Mr. Wimperis added that drag, or head resistance, was enormously increased, and a much less efficient aeroplane, characterised by a low ratio of lift to drag, resulted. Hence, an aeroplane flying near the velocity of sound would require approximately two thousand horse-power for every' ton of weight; but a present day engine of this power would require the whole of the weight allowance and none would be left for the rest of the machine. “If speeds such as these are to be attained,” commented Mr. Wimperis, “it cannot be by the engine as we know it to-day.” He continued: “In point of fact, the limit of speed is reached even more rapidly than these considerations indicate, because the air speed just above the top of the wing is appreciably higher than the air speed of the machine itself. Hence the critical boundary will be reached _ while the air speed of the aeroplane is still substantially below the velocity' of sound. Taking everything into consideration, there is much to be said for assessing the maximum possible speed of level flight with the present type of engine as over 500 but less than 600 miles an hour.” Mr. Wimperis quoted calculations to show that a height of 61,000 feet should be attainable in the light ot present knowledge by' a specially-built aeroplane, or 11,000 feet higher than the world record established last year by' Squadron-Leader F. R. D. Swain, and that the ultimate range of nonestop Hight might be extended to 12 500 miles —sufficient for any spot on the earth to be reached in one hop from any other.