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Aviation History
1933
1933 - 0958.PDF
FLIGHT, NOVEMBER 9, 1933 THE ROHRBACH ROTATING WING AEROPLANE By W. S. SHACKLETON (Concluded from page 1090) JV last week's issue of FLIGHT Mr. Shackleton dealt with the history of revolving surfaces as a means of obtaining lift. This week he turns his attention to what has been done more recently in France, the United States and Germany, concluding with some par ticulars of the proposed Rohrbach machine. As readers appear to have been a little puzzled by the diagram published on page 1088 last week, the follow ing explanation of the symbols used may be of assistance. They are .'— rfK Resultant wing force. dv Vertical component of dR. dH Horizontal component of dR. u Peripheral velocity of rotor. v Translational velocity of machine. Mr Resultant velocity (and direction). a Angle of attack. Tests and Experiments on Modern Revolving Wing Aircraft in France An article in the French technical journal, Les Ailes (of May 11, 1933), gives particulars of a series of tests which recently have been carried out with satisfactory results in every respect by the well-known aircraft manu facturers, Messrs. Liore et Olivier, with a wing-wheel aircraft designed by the Swedish inventor, Strandgren. A motor-driven wing-wheel produced a satisfactory lift force (800 kg.) with relatively small power, and with a reasonable forward impulse (corresponding to a speed of 100 km. per hour). With the motor stopped, auto- rotation produced sufficient lift forces from the wing- wheel. These results prove the possibility, with a properly constructed aircraft, of vertical ascent, of hover ing without forward movement and of a safe descent with the motor power cut out. Also, these tests have shown that the centrifugal forces and oscillations, even with a number of revolutions 50 per cent, in excess of normal, are transmitted by the wheel structure with a satisfactory factor of safety. American Tests During the annual meeting of the National Advisory Committee for Aeronautics (N.A.C.A.), in the first half of May, 1933, a report was delivered on a series of wind- tunnel tests made with a full-size set of Piatt wing-wheels, similar—it was said—to the design developed by Dr. Rohfbach. In the course of these tests smoke was used in order to observe the movement of the air. The American tests have also shown that the wheels produce great lift forces when the aircraft is flying normally or when hover ing without forward movement. The following report is taken from Aviation, June, 1933. N.A.C.A. Report " The Cyclogiro." ' Lift without speed ' was the text of the opening portion of the talk by J. W. Crowley, Jr., chief of the Flight Research Section, who has been conducting a special study of rotating wing systems of all types. It was Mr. Crowley who introduced to the audience the ' Cyclogiro,' the paddle wheel rotor design, sponsored in this country by Haviland H. Piatt and in Germany by Dr. Adolph Rohrbach. Computations indicate that a 3,000 lb. air plane utilising this principle, with constant velocity rotor and cams, would attain a speed of approximately 100 m.p.h. with an engine of 300 h.p., assuming that 270 h.p. remained after gear friction losses. The power required would be a minimum of 45 m.p.h. and increase 60 per cent, at zero air speed, and 90 per cent, at 100 m.p.h. The vertical rate of climb computed was 700 ft. per minute and the maximum rate of climb 1,500 ft. per minute." The computed maximum rate of climb is approximately 30 per cent, better than would be likely with a con ventional aeroplane of the same power loading. The efficiency of the gearing would not be lower than 93 per cent, or some 15 per cent, better than would be possible with an airscrew working under optimum conditions. In a technical note issued by the National Advisory Committee for Aeronautics and entitled *' Simplified Aero dynamical Analysis of the Cyclogiro Rotating-Wing System," by John B. Wheatley, of the Langley Memorial Aeronautical Laboratory, the summary states: — " The aerodynamic principles of the cyclogiro are sound; hovering flight, vertical climb, and a reasonable forward speed may be obtained with a normal expenditure of power. Auto-rotation in a gliding descent is available in the event of a power-plant failure." German Tests Dr. Rohrbach's extensive research work, submitted to the competent judgment Of the Deutsche Versuchsanstalt fur Luftfahrt, more than confirms the excellent results obtained in America. His machine shows marked superiority in the relatively large span and high aspect ratio of the wings, together with an adequate peripheral velocity and diameter of the rotor, resulting in overall efficiencies comparable with a conventional aeroplane. It is, however, in the wing oscillation control that the Rohrbach machine shows the greatest technical advance over other types of rotating wing machines. The effective angles of incidence at all speeds are positively and pro gressively controlled throughout the circle of revolution to produce forces of the required direction and amount with the least expenditure of power. The wing oscillation controls have been reduced to such a simple form that the pilot can quickly and easily adjust the effective incidence and feathering action to suit any required speed or inclination of flight within the capacity of the machine. Some data relating to the Rotating Wing Machine A machine similar to the type illustrated in the photo published last week has formed the principal basis for calculations and design of details. It is fitted with one engine of 240 h.p., driving the rotor-shaft through a worm- or bevel-gear—a one-way clutch or free wheel being inter posed. The wings, which have a mean aspect ratio of 14:1, project 14| ft. on each side of the fuselage. Three wings are fitted to each rotor, these being separately carried on steel struts and streamline section tie rods. These members carry all centrifugal and aerodynamic loads between the wings and the rotor-shaft. The wings revolve with a maximum r.p.m. of 420, corresponding with a peripheral speed of 260 ft. per second. The minimum rotational speed to produce sufficient lift forces is 270 r.p.m. (peripheral speed 167 ft. per second). Each pound of weight produces a centrifugal force of 362 pounds at 420 r.p.m. and 150 pounds at 270 r.p.m. The greatest possible aerodynamic forces amount to only some 12 per cent, to 18 per cent, of the centrifugal forces, which latter are of a uniform and steady character. Conse quently violent manoeuvres do not overstress the wings to anything like the same degree as with fixed-wing aero planes, where the ratio between normal and maximum wing forces can be as great as 7 to 1 or even more. If specially required, the revolving wing aircraft, with a temporary sacrifice of its ability to climb vertically, would safely carry considerable overloads. This is clearly shown in the weight data. With the total loaded weight increased to such an extent that the minimum air speed is 21 km./hr. (13 m.p.h.), the estimated disposable load is 76 per cent, of the empty weight. The wings make 7 complete oscillations per second at 420 r.p.m. and 4.6 at 270 r.p.m. Investigations have shown that the torsional deformation of the wings can be kept very small, thus avoiding incorrect angles of attack through twisting- Each of the two sets of revolving wings, right and left oi the aircraft fuselage, forms a stable structure with regard to any kind of loading. Without any experimenting the pilot can adapt the oscillation control to any practical operating condition, so that a maximum efficiency is obtained. The pilot is also in a position to vary the direction and the amount of the generated air force at any moment, to meet any requirements according to his judgment. In order rapidly to reduce the translational speed of the aircraft the pilot can temporarily give to the resultant air-force a backward inclination without losing any lift. A diagram shows on page 1123 the air forces acting on the revolving wings in various positions and under different operating conditions. The air forces resulting iQ one revolution of the wheel are also shown. As indicated 1122
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