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Aviation History
1921
1921 - 0307.PDF
MAY 5, 1921 TESTS MADE WITH CAPTIVE HELICOPTERS * By Professor KARMAN 1. Central Development of Preparatory Work.—The tests in question were consequent upon the acceptance of a pro- posal for the construction of a captive helicopter, offered by 1st Lieut. Stefan von Petroczy, then Commander of Balloon Pilot Instruction, to the Imperial and Royal War Office. Lieut, von Petroczy also requested to be accredited with a certain sum for testing expenses. The first tests were made at the Austrian Aeroplane Factory, Ltd., Wiener-Neustadt. with propellers of rather The Petroczy-Karman captive helicopter in the air. large diameter. The Daimler works at Wiener-Neustadt also received an order from the Aviation Arsenal to hurry on the construction of a light 300 h.p. electro-motor originally intended for giant aeroplanes. As this motor was intended to weigh 250 kg. only, according to the statement of the firm, the possibility of constructing an electro-motor with power provided by means of a cable was taken into consideration. The Austrian Aeroplane Factory proceeded no further than • Prepared by Paris Office, American National Advisory Committee forAeronautics. general drafts. When the present writer was entrusted with the direction of all the tests of the captive helicopter, in the early part of 1917, the work was commenced systematically along two lines. First of all, tests were made at the pro- peller-testing laboratory at Fischamend ; secondly, model tests were carried out in order to throw light on their stability conditions, beginning with very small models worked by rubber cords, then with a heavier 30 kg. model driven by a 5 h p. air pressure motor specially constructed for the purpose. These tests led to the discovery of a special kind of cable which ensures stability, and which was used in all later models. On the basis of the above-mentioned preliminaries, tests were proceeded with along two lines : one by means of electric power, and the other with petrol rotary motor power. We shall now give a short description of these two methods, with a report of the tests carried out. 2. Short JJescription of the Captive Helicopter having Electric Power.—The machine was completely equipped with electro- motor, electric cable and winch before being tested working on the ground. The framework itself is composed of steel tubes, with an observer's car in the centre, from which there is a clear view and firing range in all directions. The lifting power is furnished by four propellers driven by a motor by means of cone gear. Its weight empty, including motor and pro- peller, is about 650 kg. The electro-motor weighs 195 kg. ; according to the Daimler Co., its output should be 225 h.p. (originally 300 h.p. with 250 kg. load), and it has actually yielded 190 h.p., though in that case the motor was heated to such an extent, after 15 minutes' working, that the test could not be carried on. Even with this reduced power, the lifting tests resulted in a carrying capacity sufficient for three men. In consequence of difficulty with the electro-motor, the captive helicopter has not yet been flown with electric power. The electro-motor was built into the machine, which then rose from the ground and attained a low altitude with three passengers. After a run of about 15 minutes, however, the motor caught fire, and had to be returned to the Daimler Aviation Section unaccepted, where it is now undergoing repairs. The advisability of equipping the already completed machine with two rotary motors, which necessitate the instalment of transmission gear, was considered, but the idea was not carried out for want of suitable motors. The machine belongs to the Austro-Hungarian Military Administration. 3. Short Description of the Captive Helicopter having Petrol Motor Power.—The captive helicopter with petrol motor power consists of a ihree-armed frame made of steel tubes, in OOOOOOOO O o The Petroczy- O Karman Captive Q Helicopter : The spheres under the framework are pneumatic shock- absorbers. Each of the Le Rhone engines has its petrol tank mounted concen- trically with it, so that the petrol system should be of the simplest. OOOO O O o o o o o o o o o o OOOO 307
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