THE HELICOPTER

Wanganui Chronicle, Volume LXXXI, Issue 18787, 22 May 1923, Page 9

THE HELICOPTER

EMPHASIS OF DEFECTS.

BASED ON FIRST PRINCIPLES. EXTRAVAGANCE OF POWER. An interesting paper on the helicopter type of Hying machine was read recently before the Royal Aeronautical Society by Major F. AL Green. The topic is of special interest now in view of the oiler by the Air Ministry of large prizes for successful trials of such machines. Major Green is frankly sceptical. The Air Alinistry, whose prizes total £50,000, outlines the following tests: The machine must rise 2000 feet and alight in five miles of wind, and also in from five to twenty miles of wind; also make a vertical ascent of 2000 feet, remain hovering for half an hour; also fly a circuit of twentj’ miles at a speed of sixty miles an hour, and, lastly, mar«oeuvre over a given point, and then, shutting off the engine, descend from 50'0 feet into an area of 100 feet.

The prize will be divided as follows: £5OOO for a stright-up ascent, and descent; £15,000 for hovering. £20,00 for a circular flight, and £lO,OOO for t!he descent without the engine. In addition to the pilot, the helicopter must carry petrol for an hour's flight and a load of 150 pounds. Several machines have al ready been designed, one having great revolving vanes driven by a 1000 h.p. engine. The lecturer’s paper was chiefly of interest because the lecturer, working from fundamental principles, came to the conclusion that the helicopter could scarcely compete with the ordinary type of aeroplane. To begin with, he gave an ele-> mentary calculation showing in largo diameter air-screws required—i.e., between 35 and 40ft. for a weight of 10001 b., and a power loading of 53 lb. per horse-power. In order to bring the size of lifting screw to a reasonable figure it was, he stated, necessary to increase the downward velocity of the air, and consequently the lift in pounds per horse-power must be less. It therefore seemed to him that the power required for keeping the aircraft in flight was likely to be much greater in the helicopter than in the aeroplane. Concluding his considerations of the problem of power required, the lecturer stated:

"From the foregoing reasons I am convinced that the power expended in flight in a helicopter, flying at speeds found to bo useful tor aeroplanes, will be very much greater than for the aeroplane, and I believe that, apart from all other disadvantages, this fact alone will render the machine quite impossible for passen ger-carrying, at any rate until engines of much less weight per horsepower and materials with much greater specific strength are available. With present-day materials it is my opinion that it is extremely unlikely that it will be possible to make a direct lift machine carrying any useful load which will be able to fly as fast as 80 m.p.h., which is the slowest cruising speed that makes flying worth while in most cases.” One of the chief merits usually accredited to the helicopter is the possibility of rising vertically and alighting vertically. Major Green pointed out that these advantages were unlikely to be as great as might be supposed, and concluded that in any case it seemed that as a means of ajr travel the helicopter had little future, so that its ability to rise and land in confined spaces was of little value if the ability to fly from place to place at a reasonable speed was absent.

Major Green also referred to the case of engine failure in a helicopter, and pointed out that even neglecting all difficulties of stability, the machine. would descend at a high rate, as the propellers did not offer very much more resistance when spinning

than they did when stopped. Continuing, he said: "A reference to the experiments on the resistance of an air screw on an aeroplane will show that the increase of resistance, is only of the order of 10 per cent, when it is spinning at the velocity which gives the maximum resistance, as against When 11 is stopped. It is possible that a specially-designed screw would have a somewhat, higher resistance than this, but there seems no reason to suppose that such can be gained. The helicopter, therefore, if unchecked. will strike the ground much faster ihan is convenient or can be readily dealt with by even an elaborate form of shock absorbing gear. In addition, the -whole machine will be moving relative to the ground at or nearly the velocity of the wind." In conclusion, Major Green refer red 'O the experiments being made by tho Research Department of the Air Ministry on helicopters. He did not. he said, know the precise arguments which led the Air Ministry to undertake work of this description, bu’ ho did not think it. probable that any useful results would be obtained unless we could make vast improvements in the technique of the production of power and the making of light structures. Such advances would also, he pointed out, improve the design and performance of the ordinary aeroplane. As for the actvantage of being able to hover in the case of a machine intended for war purposes. Major Green suggested that a balloon or an airship was a la- more promising method of obtaining tho required results. It was, ho said, likely to cost less and to bo safer. Commercially, the object, of air travel was to get from place to place, and it seemed to him highly unlikely that the helicopter type of machine would ever afford a useful means of doing this.