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Aviation History
1950
1950 - 0469.PDF
FLIGHT, g March 1950 HELICOPTER DEVELOPMENT JN FRANCE Current Types Reviewed by a French Air Ministry Specialist : Assorted Approaches to the Auto-rotation Problem : Progress with Jet-driven Rotors . ••-.,• > AREMARKABLY informative paper on French heli-copter development as exemplified by current con-struction was given before the Helicopter Association in London on February 25th. The author was Colonel R. M. Garry, who is engineer in chief of the rotating wing section of the Service Technique Aeronautique of the Ministere de l'Air. The paper was read by Captain R. N. Liptrot (now of the B.E.A. Helicopter Unit and formerly Deputy Director of Helicopter Research, Ministry of Supply) who, we understands was also responsible for the admirable translation Lest the uninitiated should assume from the paper that rotating-wing progress across the Channel has been unim- peded by any of the difficulties encountered elsewhere, it should be remarked that not all the designs mentioned are, in fact, in an advanced state of development. This, however, does not detract from the technical interest of Colonel Garry's review of the various types, which is given in the following pages in slightly abbreviated form. (In the original lecture, it should be added, certain rather detailed descriptions of linkage systems and other mechan- isms, here omitted, were illustrated by diagrams.) BREGUET G.11E The Breguet G.11E, a helicopter with two co-axial rotors, is the logical successor to helicopters built by the Breguet Company before the war. Weighing 3,o8olb with pilot, two passengers, and 26^ gal of fuel, it is fitted with a fan- cooled Potez 9E, nine-cylinder air cooled radial engine developing 260 h.p. It has a tricycle undercarriage. The rotors are three-bladed, each of 28.2ft diameter. The front fuselage is a light-alloy monocoque structure with two sliding doors, the cabin glazing giving excellent visibility. The rear fuselage, of steel tube, fabric-covered, carries a vertical fin, and a tailplane coupled to the control column in such a way as to suppress once-per-revolution flap in forward flight. A semi-automatic single-plate clutch controlled by a lever in the cockpit, carries the cooling fan and a roller-type free-wheel. Then follows a double- splined universal joint the shaft of which drives two spiral gears through two pinions. The reduction ratio is 6.5:1, the maximum rotor tip speed being 574 ft/sec. The gears drive the two rotors through concentric shafts carried in ball bearings. Of the blades, which are very stiff, each consists of a steel tubular spar, tapered both as to diameter and thickness, and carrying ribs attached by special clips. There is a dural leading edge and the main covering is by Plymax, which is a three-ply sandwich with an outside skin of light alloy. The blades are tapered and have 4 deg twist. Axes of the napping hinges intersect at the rotor axes, and hydraulic drag-hinge dampers are fitted. The control column gives cyclic-pitch control by means °i two coupled swashplates. the controls for the upper rotor passing inside the shaft. Differential collective-pitch variation necessary to com- pensate the residual torque reaction, and to give directional The N.C. 2001 as it appeared at the last Paris Show. A noteworthy feature is the use of closely " meshed " rotors. control when hovering, is not obtained by the swashplates but by displacement of the control support sleeves, which carry an intermediate link. Directional control from the pedals is thus very stable and forces quite normal. A governor driven by the rotors and sensitive to both angular speed and positive acceleration, controls a hydraulic jack which moves the swashplates axially. Centrifugal force acts on bob-weights, and the angular acceleration on a wheel driven ait high speed by a planetary train of gears. By controlling a secondary hydraulic distributor the wheel immediately increases pitch on the slightest acceleration of the rotors. In addition an over-ride mechanism allows the main distributor of the governor to be used as a servo to increase collective pitch at the will of the pilot, but not to reduce it. A separate "over-ride pitch lever" is provided for this purpose. This arrangement not only permits the rotor kinetic energy to be used in a forced landing, but also prevents collective pitch being reduced below a predeter- mined level in the event of power-unit failure close to the ground. When set at the limit of its travel it still permits the governors instantaneously to reduce pitch to the auto- rotative setting in the event of engine failure, or complete closure of the throttle. A linkage with the throttle lever, by acting on the governor spring, provides for reduction in rotor r.p.m. when the throttle is reduced. N.C. 2001 The N.C. 2001 helicopter has been designed by the rotat- ing-wing department of the Societe Rationale de Construc- tions Aeronautiques du Centre under the direction of the chief engineer, M. Rene Dorand. It is of the symmetrical configuration with two intermeshing, laterally disposed two- bladed rotors, either driven by the engine or turning freely in auto-rotation. It provides side-by-side seating for a crew of two, and a cabin accommodating three passengers. Total weight is 5,9401b, and weight empty 4,5501b. The hovering ceiling outside the ground cushion is 8,200ft. The undercarriage is of the tricycle type, the wheels being fully castoring through 360 deg. Power for the N.C. 2001 is provided by a Gnome Rhone type 12S developing 575 h.p.. at take-off, and the reduc- tion-gear ratio between engine and rotors is 15:1. The normal reduction gear of the engine is replaced by a special gearbox driving two oblique shafts, in a vertical plane and parallel to the rotor axes, through a clutch, free-wheel and two sets of bevel gears. The two drive shafts, each of which has a universal joint at each end, convey the drive to two rotor gearboxes symmetrically disposed about the vertical, and containing a double-pinion drive to the two rotor shafts which carry the pitch-control swashplates. The rotor shafts are suspended hydraulically in a mounting whose inclination longitudinally with respect to the fuse- lage is automatically adjusted as a function of forward speed. An oil connection between the two diaphragmed com-
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