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Aviation History
1950
1950 - 0470.PDF
FLIGHT, 9 March 1950 The Nord 1700 has an unusual tail-rotor arrangement. HELICOPTER DEVELOPMENT IN FRANCE . . . partments forming the flexible suspension permits free differential movement between the two rotor shafts, while simultaneous movement of the two is damped as is neces- sary in order to transmit longitudinal and lateral control movements. The rotors are attached to the drive shafts by universal joints, the drag hinges of which are damped by two hydraulic dampers common to the two blades, one of which damps simultaneous movement while the other damps any differential movement between the blades. Pitch change of the blades by rotation about a pitch-changing hinge is provided by a combination of torsion bar and mechanical and rubber buffers. Lateral and longitudinal control are obtained by cyclic- pitch variation of the blades of the two rotors. Pitching control by movement of the control column causes corres- ponding tilting of the two swashplates governing the blade angle. Displacement of the column to the right causes a greater lateral tilt of the swashplate of the starboard rotor. This is to ensure that the blades of one rotor cannot foul the hub of the other rotor. Directional control by pedals is obtained by differential variation of the collective pitch of the two rotors, and by longitudinal and lateral tilt in opposite senses of the virtual axes of the rotors. This is done in order to suppress all interaction between the directional control and the control about the other axes. A single lever controls simultaneously the pitch ami throttle opening by an electrically operated linkage. In the event of power-unit failure, the reduction in engine torque, indicated by a torque-measuring device, operates a small e'ectric jack which moves the single control back to the zero setting. The pilot can over-ride this control. In addition the blade attachment is so arranged that there is a reduction of incidence when the coning angle of the blades increases, so eliminating any danger of loss of rotor speed. NORD 1700 This is an experimental two-seater undertaken as a private venture by the Societe Nationale de Constructions Aeronautiques du Nord, under the direction of M. Bruel. tThe object was to test a number of novel. arrangements llesigned to simplify both construction and flying. 1 Principal characteristics of the Nord 1700 are: All-up weight, 2,090 lb ; engine power, 160 h.p. ; rotor diameter, 32.8 ft; length (without rotors), 23.94 ft; height overall, 10.S ft; undercarriage track 8.5 ft. In the interest of simplicity and lightness a iwn-bladed rotor is used. Each blade, in which chord and aerofoil sec- tion are constant from root to tip, is built up of a soli<l spar, ribs, nosepiece and a thin sheet skin, all in duralumin. These components are assembled by clamping together, and 110 rivets or bolts are used except at the hubcattach- ment. The engine is a SVlathis G7.R air-cooled radial developing 160 h.p., and mounted with its crankshaft vertical. The Nord 1700 is the first French helicopter to have the engine installed in this attitude. At the after end of the helicopter is an unusual arrange- ment—the subject of a Bruel patent—a fan to blow a current of air to the rear over vertical and horizontal control sur- faces. This fan is mounted inside a cowling ring which screens it from gusts when hovering and from variations in the rotor dowmvash, so increasing its efficiency, and at the same time giving protection to ground personnel. This tail arrangement is used not only to compensate: the torque reaction from the rotor ; the vertical surfaces provide direc- tional control, and the horizontal surfaces longitudinal control, and it is thus possible to eliminate the disadvan- tages of complicated arrangements such as cyclic-pitch control. Another advantage is that the helicopter can he taxied with the main rotor stopped. Deflection of the vertical surfaces is controlled by a hydraulic torque measuring device so that the rotor torque- reaction is compensated automatically. The rotor is fully articulated and without drag-hinge dampers. Vertical vibration is damped out by a pneumatic system located at the top of the rotor. On starting up, and until a predetermined rotational speed is reached, the blades are held rigidly in forks and at zero pitch, so minimizing the effect of gusts. When r.p.m. reach the safe figure the blades rise, free themselves from the forks and auto- matically take up the correct pitch-setting. This same arrangement also automatically puts the rotor into auto- rotation if the engine fails. Rolling manoeuvres are affected very simply by displacing the rotor head parallel to itself laterally. Auxiliary blades, called " pilot blades " are fitted qo dcir A twin tail-rotor system is employed in the S.E. 3110. (Right) Close-up of main rotor head.
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