SOCIETY OF AUTOMOTIVE ENGINEERS, INC. 485 Lexington Avenue, New York 17, N. Y. Helicopter Rotor with Flexible Hub Rene Dorand Societe Giravions Dorand SOCIETY OF AUTOMOTIVE ENGINEERS International Automotive Engineering Congress Detroit, Michigan January 11-15, 1965 memDownloaded from SAE International by University of British Columbia, Monday, August 20, 2018driven by a fluid exhausting from the slotted nozzle (4). Fig. 1B - K B effectABSTRACT The paper discusses an improved control system for a helicopter or VTOL aircraft equipped with a rigid lift rotor integral with a flexible hub. The proposed method consists in suitably arranging the knuckle joints on the ends of the blade pitch control levers to create a complementary cyclic deflection effect which is dependent upon the rotor's attitude and is superimposed upon the pilot's control. The reduced dynamic instability of the helicopter with the control column locked, and the calculated improvement in the rotor's response to the control column facilitates pi- loting. The control of such a helicopter compares with driving an automobile equipped with servo-assisted controls.Helicopter Rotor with Flexible Hub Rene Dorand Societe Giravions Dorand PURPOSE The control sequence mechanism enables the relation Eq. 2, representing the flap deflection, to be written as fol- Figs. lA and 1B schematically illustrate a rotor (1) with lows: blades set into the hub. A resilient spherical joint represented by a rubber ringK = 0v--tg•(2) enables the hub to tilt through an angle and imparts 13v A B ea restoring moment AM to the blade. The elastic restoring coefficient K on the flexible hub e is defined by the relation (1).O = The flap deflection.v OM To fix ideas in the more general case, a flap with tan-Ke = A l3 (1) gential blowing is represented, as applied to a rotor jet The novelty resides in a special arrangement of the swash- plate control sequence, as shown in Fig. 1B. If the blade (1) flaps through an angle A , this produces 5 a complementary control effect which increases the thrust. This control effect is represented by a downward deflec- tion of the flap (3). Fig. lA - Elastic hub(2) where: Downloaded from SAE International by University of British Columbia, Monday, August 20, 2018+ cd13 + KB = f (t) dt2 dtId26If conventional means are used to control the blade pitch where: 0, the Eq. 2 takes the form of Eq. 3:2 To facilitate setting down the calculations, it will be assumed that control is effected by blade pitch variation. Considering next the flap, it will suffice to increase KS in the proportion N V, as defined by Eq. 4 K13 = Nv K13 (4) N represents the flap deflection, expressed in degreesv providing the same increase in CL as a 1 deg variation in airfoil incidence. In the case of a blown flap, N approxi- mates to 4. In what follows, the role of this sequence coupling will be termed the "K effect."13 The purpose of this paper is solely to evaluate the im- provements to be derived from the "K effect" combined5 with the hub elastic restoring effect Ke, in the area of heli- copter stability and control. It is felt that it would not be amiss to stress once again the ensuing simplification of the hub and the fact that a sup- ple suspension system is provided for protecting the heli- copter structure against certain inadvertent mishandlings of the control stick, an example being excessive movement of the stick when the machine is still on the ground.w = Angular velocity of rotor, rad/sec AF = Blade thrust variation due to a variation in thezoairfoil incidence, Aio d = Distance of pivot from center of pressure of blade K = Overall restoring coefficient exerted on a blade, broken down as follows: classic centrifugal restoring effect, Ica 2 6 elastic restoring effect, KeB negative aerodynamic restoring effect due to the K B effect: KB Ka 8 NOTE - The value of K 8 is limited by the blade's static balance: K < — + Ke Ica2 K K (7) a a RIGHT-HAND SIDE OF EQUATION Sustain