Recent developments in what may be called rotary wing flight, as distinct from flight with the fixed wings of. the aeroplane, show a steady advance towards a practical application of this method to aviation, permitting more or less vertical ascent and descent. The disadvantage of the aeroplane, that it requires large aerodromes with ample landing and takingofE areas, is overcome by the rotary wing machines, which can. rise from limited spaces and descend to them in comparative safety. The performances of the autogiro are already well known, and some years ago one of the earlier forms of this machine—the "windmill aeroplane"—was seen in New Zealand. A noteworthy achievement was its rising from Eongotai in heavy rain with lowsailing clouds when no ordinary aeroplane dared leave the ground. This capacity for flight in dirty weather with low visibility is another very distinct advantage of the rotary wing machine, which can reduce its horizontal speed to under 20 miles an hour and still keep aloft. No aeroplane in still air can yet show any comparable performance. DIRECT-START AUTOGIRO. Remarkable improvements have been made in the autogiro, and in a recent lecture the inventor, Senor Juan de la Cierva, described a new method of direct-start, giving a vertical ascent capable of clearing any ordinary obstacle about an aerodrome. This take-off without a preliminary run is accomplished by spinning up the rotor blades by a coupling to the engine until the energy stored in the revolving rotor —as in a fly-wheel—is sufficient to lift the whole machine off the ground. As soon as this is done the power of the engine is transferred by declutching from the rotor vanes and clutching to the forward airscrew, and the autogiro then functions normally. Though details were not given, the inventor sketched the idea of the device as the hinging of the rotor blades vertically, the upper ends of the hinge pins being tilted outwards to provide an automatic variation of pitch. While the drive from the engine remains an accelerating force, the rotor blades, owing to their inertia, lag behind the central rotorhead, and in so doing decrease their angle of incidence and consequently their lift. When the clutch is disengaged, the blades assume their normal position and pitch angle, and this positive angle at high speed gives rise to a lift sufficient to raise the whole craft into the air. The energy stored in the rotor slows down, and ultimately the whole machine would sink slowly to the ground again were it not for the fact that in the meantime the thrust of the air-screw has given the aircraft a 1 horizontal speed sufficient to allow auto-rotation and to keep it in the air. The inventor added, in conclusion, that it would be possible to design an autogiro to attain a speed of 160-170 miles per hour, and that the high maximum speed and direct takeoff would enable the autogiro to compete with both, the aeroplane and the helicopter.. ASBOTH HELICOPTER. While Senor de la Cierva was disposed to doubt whether the helicopter proper would really work, extraordinary claims are made in the same, issue of "Flight," which publishes his lecture for the type of helicopter designed by Mr. Oskar yon Asboth, and built experimentally in England. The difficulty- with the helicopter is not so much the lift that may be obtained with an air-screw set on a vertical shaft, -as with stability and control, due to torque reaction, which tends to turn the fuselage of the .machine in the opposite direction to that of the propeller. This Mr. Yon Asboth gets over by having two air-screws or sets of rotor blades revolving in opposite directions on the same shaft, cancelling out their reactions. As far back as 1928 the original Asboth helicopter, as first flown and as subsequently modified,- made, in all, 182 flights, with a maximum single flight of 53 minutes' duration and a total flying.time of 29hr 7min. It is intendeH to construct a side-by-side two-seater cabin helicopter provided with a 300 h.p. watercooled engine. It is hoped with this to attain a vertical rate of climb of 1500 feet per minute, a maximum speed in horizontal flight of between 110 and 130 miles per hour, and a flight duration of two hours at full load, including pilot, passenger, and 1001b of luggage. The take-off and landing, it is considered, can be managed on a platform 21ft square. The advantages of the helicopter for direct soaring and hovering flight, if these expectations are realised, are obvious. THE CYCLOGIRO. Lastly, there is the c'yclogiro, in which both the supporting and propulsive agents are to be found in light paddle-wheels projecting from each •side of a normal aeroplane type fuselage. These wheels are provided with blades or vanes which feather in such a way as to give lift and drive, and when the powfir is cut off, to rotate automatically. This is not in nearly so far an advanced stage as the helicopter and the autogiro, but it is considered by experts in aerodynamics to be feasible from a technical point of view. While it is unlikely that any of these forms of rotary wing aircraft will supersede the aeroplane for general military and commercial aviation, there is ample room for them in their own field where space is limited for manoeuvring, as on flat roofs, lawns, and narrow stretches of water. In this direction they would appear to have a distinct future.
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