GB1571998A - Helicopter rotors - Google Patents

Description

(54) HELICOPTER ROTORS (71) I, MARIUS GIRODIN, a French subject of La Fontaine Pleureuse - 78 Bazemont, France, do hereby declare the invention, for which I pray that a Patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to helicopter rotors.

In existing helicopters, the rotor blades are attached to the rotor boss by three orthogonal joints or equivalent elastic members when the boss is integral with the rotation axis or by a radial joint when the boss is articulated by two perpendicular axes on the rotation axis.

In addition to steering, piloting with the rotor has two functions: 1. Changing the pitch of the blades overall by directly controlling the incidence thereof to vary the lift; 2. Cyclically changing the pitch of the blades by direct control to incline the rotor plane so as to vary the direction of the lifting force.

This method of piloting by varying the intensity and direction of the lifting force has the disadvantage of causing instability, being slow to respond, and resulting in dangerous zones, requiring an expensive heavy rotor and delicate controls. It is an object of the present invention to provide a helicopter rotor which can overcome or at least reduce such disadvantages.

The present invention provides a rotor for a helicopter including a plurality of rotor blades, a rotor boss and a rotor hub disposed within said boss, said hub and said boss having a common axis of rotation. each blade having a rigidly connected spindle extension connected by spaced respective articulated joints to said boss and said hub, the longitudinal axes of said spindle extensions intersecting at said common axis, each spindle extension being rotatable about its longitudinal axis, and pilot-operated linkage means connected to said boss for lifting and lowering said boss relative to said hub so as to vary the inclination of said blades by adjusting the angle said spindle extensions make with said common axis, said angle always being less than ,. radians.

In a preferred embodiment. each rotor blade, without any other coupling, is attached to the boss by means of a spindle freely rotatable about its own axis, the spindle being located in a plane radial to said boss, and forming an angle in the direction of rotation with the line of foci of said blade, the apex of which is at a distance from the rotation axis such that the torque is, on average, compensated by the centrifugal force exerted on the blade, and the angle of the spindle axis with the rotor boss rotation axis, which is identical for all the blades, is less than x,, radians and can be regulated by the pilot.

Thus, at any given time, the incidence of each blade is the result of the equilibrium of the component of the centrifugal force on the cone of rotation and the lift of the blade.

The centrifugal force being constant for a given number of revolutions, the lift is regulated by adjusting the angle between the blade spindles and the boss rotation axis.

Therefore, the rotor according to the invention makes it possible, without controlling the blades, to obtain a lifting force coaxial with the rotor drive shaft with the cone produced by the blades of a substantially fixed direction.

Piloting in incidence or roll is effected by aerodynamically creating longitudinal or transverse couples. The simplest method is to use the rotor itself to provide these piloting couples.

For this purpose, a cyclic blade control is provided characterised in that it does not impose a position or an angle but creates, on the spindle of the blade, a couple which can be varied with the azimuth and is independent of the position of the incident blade.

In one type of control for creating aerodynamic couples which may be provided the blades are fitted with a lever attached to a cyclic plate or spider arrangement analogous to those on conventional helicopters but wherein the connecting rods are replaced by hydraulic jacks the pistons of which have an aperture adapted to ensure, by an escape fluid flow, a loss of load proportional to the velocity.

Thus, without any piloting activity, the blades are free to orientate themselves to ensure that they have substantially constant lift, whilst the jacks act as vibration absorbers.

The couple exerted on the rotor as a whole is equal to the couple introduced on the blades divided by the tangent of the angle of displacement of the blades behind the axis of the blade spindles.

Since the couple exerted on the blades is itself very much greater than the couple exerted on the controls by the pilot - by the normal effect of the gearing down of the control sequence - it is possible to produce substantial control couples instantaneously without any intermediate inertia effect.

A preferred embodiment will now be described with reference to the accompanying drawings wherein: - Figure I is a section through the rotation axis, on the line I-I in Figure 2, of the boss of a helicopter rotor with three blades according to the invention; and Figure 2 is a section on the line II-II in Figure 1.

In Figures 1 and 2, each rotor blade 1 is attached to the rotor boss 2 by a spindle extension 3 of the blade. Each spindle 3 is in a meridian plane containing the axis of rotation of the rotor boss and externally forms an angle A with the rotor boss axis of less than ,. The axis of each spindle makes an angle B with the axis of each blade, the blade axis being located behind the spindle axis relative to the direction of rotor rotation. The apex 4 of angle B in the direction of rotation relative to the blade and its distance from the rotation axis is such that the bending moments in the plane of the blade are, on average. compensated by the centrifugal force.

The spindle 3 is mechanically free to rotate and abuts with a sperical end zone portion 5 on a spherical cup 6. disposed on the interior of boss 2 with a common centre for all the spindles.

Each blade is rotationally driven via a bearing 7 with an outer spherical bearing surface 8 carried by the top 9 of the boss.

The top 9 of the boss is rotationally driven by gear teeth 10 in sliding engagement with a base 11 of the boss.

The pilot regulates the angle A defining the lift for a given number of revolutions, by axially displacing top 9 relative to base 11 by means of a control acting on a lever 12 which, via symmetrical rods 13 and a ring 14 suitably held in rotation and a double thrust 15, acts on a central driving body 16 connected to the top 9 of the boss by three radial pins 17 moving in longitudinal apertures 18 in a central cylinder 19 which is integral with the base 11 of the boss.

Each spindle 3 has a lever 20 the end of which is connected to the corresponding end of a spider arrangement 21 by an hydraulic jack 22, the piston 23 of which contains an aperture 24 providing communication between the two chambers of the jack cylinder.

The spider arrangement 21 is centred in the central cylinder 19 by a ball-and-socket cage 25 attached to said cylinder 19 by three arms and thus allowing the passage of the connecting rods of the driving body 16 controlling the angle A. A lever 26 of the spider arrangement 21 receives depth and roll commands at right angles to it.

The base 11 of the boss is centred on a boss support 27 by a central bearing 28 and a double action peripheral thrust 29.

The boss 2 is rotationally driven by peripheral gearing 30 appropriately coupled to the helicopter engine or to the turbine.

In the following equations. the symbols have the following meaning. r : radius of any point of the blade at m, Fc : centrifugal force.

Q : angular velocity, international symbol = N = number of revolutions per minute, 5 : linear mass of the blade (mass per unit length), Me : moment in relation to the axis of the spindle due to the lift of the blade and reducing the incidence, p : mass of one cubic metre of air, international symbol, incidence of the blade at radian, t : depth of the blade at m, A : angle of the blade spindle axis with the axis of rotation, B : angle of the line of seats of the blade with the sindle axis.

Each blade portion dr with the radius y is subjected to radial centrifugal force: d Fc = Q2 Jccdr. 5 being the linear mass of the blade, expressed as a couple, increasing the incidence on the axis of the spindle having the elementary value: d Mc = d Fc cotg A r tg B = Q 4 cotg A tg B 5 dr On the other hand, if i is the actual aerodynamic incidence of the portion of blade being considered, the elementary aerodynamic couple reducing the incidence by the axis of spindle is: d Mi = 5.371 P/2 Q24 2 i r tg B t dr t being the depth of the blade.

In equilibrium we have: 5 cotg A = 5.731 i r t P/2 If 5 is constant we may therefore have point by point equilibrium if irt is constant. This borderline case can only exist when hovering.

In different cases of flight. the angles A and i vary and tend towards point-by-point equilibrium at any given moment and overall equilibrium is established automatically. This eliminates any cyclic pitch control and further makes such control detrimental.

Thus it will be understood that the blade inclination is controlled by the variation of the angle A. a reduction of this angle increasing the blade incidence. There is no cyclic control of the blades. Piloting is effected by introducing a cyclic torque to the spindles, thereby creating a cyclic force on each blade introducing a torque to the hub perpendicular to the axis of rotation. thus making it possible to act directly upon the angle of incidence or the angle of roll in the same way as for aircrat. For that purpose, the pistons 23 connected to the blades are displaced with a leak in the cylinders linked to the spider, thereby creating a cyclic force at the end of the lever. hence a cyclic torque on the spindle translated into the cyclic torque on the shaft. Hence. a resultant piloting torque on the helicopter as a whole.

To control incidence or rolling. the lever 26 is made to act on the spider arrangement 21, which has the effect of creating a cyclic out-flow in the calibrated hole 24 of each piston 23, and this in turn has the effect of producing a difference in cyclic pressure and consequently a cyclic couple on each blade base opposing equilibrium and thus creating an aerodynamic couple the vector of which is normal to the rotation axis and the value of which is equal to that of the couple exerted on the spindle divided by tg B.

The lengths of the levers 20 and jacks 22 are such that the blades 1 may be vertical on stopping under the effect of their own weight, i.e. with the leading edge at the top and the trailing edge at the bottom.

WHAT I CLAIM IS: 1. A rotor for a helicopter including a plurality of rotor blades, a rotor boss and a rotor hub disposed within said boss, said hub and said boss having a common axis of rotation, each blade having a rigidly connected spindle extension connected by spaced respective articulated joints to said boss and said hub, the longitudinal axes of said spindle extensions intersecting at said common axis. each spindle extension being rotatable about its longitudinal axis. and pilot-operated linkage means connected to said boss for lifting and lowering said boss relative to said hub so as to vary the inclination of said blades by

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. r : radius of any point of the blade at m, Fc : centrifugal force. Q : angular velocity, international symbol = N = number of revolutions per minute, 5 : linear mass of the blade (mass per unit length), Me : moment in relation to the axis of the spindle due to the lift of the blade and reducing the incidence, p : mass of one cubic metre of air, international symbol, incidence of the blade at radian, t : depth of the blade at m, A : angle of the blade spindle axis with the axis of rotation, B : angle of the line of seats of the blade with the sindle axis. Each blade portion dr with the radius y is subjected to radial centrifugal force: d Fc = Q2 Jccdr. 5 being the linear mass of the blade, expressed as a couple, increasing the incidence on the axis of the spindle having the elementary value: d Mc = d Fc cotg A r tg B = Q 4 cotg A tg B 5 dr On the other hand, if i is the actual aerodynamic incidence of the portion of blade being considered, the elementary aerodynamic couple reducing the incidence by the axis of spindle is: d Mi = 5.371 P/2 Q24 2 i r tg B t dr t being the depth of the blade. In equilibrium we have: 5 cotg A = 5.731 i r t P/2 If 5 is constant we may therefore have point by point equilibrium if irt is constant. This borderline case can only exist when hovering. In different cases of flight. the angles A and i vary and tend towards point-by-point equilibrium at any given moment and overall equilibrium is established automatically. This eliminates any cyclic pitch control and further makes such control detrimental. Thus it will be understood that the blade inclination is controlled by the variation of the angle A. a reduction of this angle increasing the blade incidence. There is no cyclic control of the blades. Piloting is effected by introducing a cyclic torque to the spindles, thereby creating a cyclic force on each blade introducing a torque to the hub perpendicular to the axis of rotation. thus making it possible to act directly upon the angle of incidence or the angle of roll in the same way as for aircrat. For that purpose, the pistons 23 connected to the blades are displaced with a leak in the cylinders linked to the spider, thereby creating a cyclic force at the end of the lever. hence a cyclic torque on the spindle translated into the cyclic torque on the shaft. Hence. a resultant piloting torque on the helicopter as a whole. To control incidence or rolling. the lever 26 is made to act on the spider arrangement 21, which has the effect of creating a cyclic out-flow in the calibrated hole 24 of each piston 23, and this in turn has the effect of producing a difference in cyclic pressure and consequently a cyclic couple on each blade base opposing equilibrium and thus creating an aerodynamic couple the vector of which is normal to the rotation axis and the value of which is equal to that of the couple exerted on the spindle divided by tg B. The lengths of the levers 20 and jacks 22 are such that the blades 1 may be vertical on stopping under the effect of their own weight, i.e. with the leading edge at the top and the trailing edge at the bottom. WHAT I CLAIM IS:

1. A rotor for a helicopter including a plurality of rotor blades, a rotor boss and a rotor hub disposed within said boss, said hub and said boss having a common axis of rotation, each blade having a rigidly connected spindle extension connected by spaced respective articulated joints to said boss and said hub, the longitudinal axes of said spindle extensions intersecting at said common axis. each spindle extension being rotatable about its longitudinal axis. and pilot-operated linkage means connected to said boss for lifting and lowering said boss relative to said hub so as to vary the inclination of said blades by

adjusting the angle said spindle extensions make with said common axis, said angle always being less than S radians.

2. A rotor according to claim 1 in which the axis of each spindle extension forms an angle with the line of focus of its respective blade said line of focus being behind the spindle extension axis relative to the direction of rotation of the blade.

3. A rotor according to claim 2 in which the distance between the apex of said spindle-blade angle and the said common axis and the size of the spindle-blade angle are such that the flexural couples in the plane of the blade are, on average, cancelled out by centrifugal force.

4. A rotor as claimed in any preceding claim including means for applying cyclic couples to each said spindle about the spindle axis, said couples being variable in value and phase.

5. A rotor as claimed in claim 4 wherein said couple applying means includes for each spindle a sliding connecting rod of variable length with internal resistance acting on a lever coupled to each spindle.

6. A rotor as claimed in claim 5 wherein each sliding connecting-rod of variable length comprises an hydraulic jack having an internal fluid escape such that the movement of the piston of the jack relative to the cylinder of the jack creates a desired loss of load and hence a desired pressure.

7. A rotor as claimed in claim 5 or 6 wherein the sliding connecting-rods are connected, at their ends remote from the spindles, to means controllable by a helicopter pilot.

8. A rotor as claimed in any of claims 1 to 7 wherein said means for applying cyclic couples are such that in a stationary position, the weight of each blade causes the blade to be disposed in a vertical plane.

9. A helicopter rotor substantially as described with reference to the accompanying drawings.