Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
1998-04-07
2001-05-15
Poon, Peter M. (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
C244S017270, C416S235000, C416S115000
Reexamination Certificate
active
06231005
ABSTRACT:
The invention relates to a device for the individual control of the blades of a rotor with at least four blades for the rotary wing structure of an aircraft, particularly a helicopter main rotor.
Although the individual blade-control device according to the invention is not restricted, in its application, to helicopter main rotors, the invention is described hereinbelow in the context of this specific application, for which the invention seems to present the greatest benefit.
The pitch of the blades of a helicopter main rotor is conventionally controlled by a swashplate device comprising a set of two swashplates surrounding the rotor mast. One is a rotating plate, rotated with the rotor about the axis of rotation of the latter. This plate, connected to each of the blades of the rotor by a pitch rod, can rotate on the other plate, which is non-rotating because it is held by anti-rotation means attaching it to the stationary structure of the aircraft. The set of two plates can be translated along the axis of rotation of the rotor, to transmit a collective pitch to the blades, and can be inclined in any direction to transmit to the blades a cyclic pitch which varies according to a sinusoidal law (fundamental or 1st order) as the rotor rotates, under the action of three operating actuators each articulated to the non-rotating plate and to the stationary structure of the aircraft.
In a device of this kind, the operating actuators are control means generally comprising rams which operate quasistatistically.
In order to improve rotor performance, particularly from the energy point of view, it has been proposed that harmonics (2nd and higher order) be introduced into the law governing the variation in angle of incidence of the blades.
This has been achieved by giving the set of swashplates a “height” (translational movement parallel to the axis of the rotor) and an inclination which can be varied over time, but which are predetermined, using non-rotating hydraulic rams that can be computer-controlled and afford a multicyclic control.
It has also been proposed for such a multicyclic control system to be improved using sensors arranged on the blades for measuring their movements and/or the aerodynamic forces to which they are being subjected and for delivering signals allowing the angle of incidence of each blade to be controlled automatically independently of the others, and in a closed loop, thus getting around the idea of harmonics of the rotor rotational frequency.
Such individual control of blades must make it possible to obtain any arbitrary variation in the angle of incidence of each of the blades, which are considered as being independent of one another, because they may encounter random aerodynamic disturbances which vary from one blade to another.
To achieve individual control of the pitch of each blade, making it possible to improve rotor efficiency, and reduce vibration and noise, it is necessary to give each blade, within a reference frame which rotates with the rotor, any variable angle of incidence, and this requires active control means capable of operating according to more complex laws which take harmonics into account.
It is known that such individual control of each blade of a two-bladed or three-bladed rotor is possible using a conventional swashplates device controlled by three rams mounted in a stationary reference frame associated with the body of the aircraft, and in which the swashplates which have three degrees of freedom can control up to three blades and give them any three pitch movements whatsoever independently of each other under the effect of complex control of the rams, taking the azimuth position of the blades into account.
It has been proposed that this type of individual blade control be generalized to cover rotors which have more than three blades, using hydraulic rams mounted in a reference frame which rotates with the rotor, there being as many of these as there are blades, each of them respectively controlling the pitch of one blade.
However, this development, with rams located in a rotating reference frame, is difficult to optimize and expensive in terms of maintenance, especially as far as the rotating hydraulic seals needed for supplying the hydraulic rams from the helicopter hydraulic circuits are concerned.
EP-A-0,451,218 discloses a system for the individual control of the pitch of the blades of a helicopter four-bladed lift rotor. It comprises a conventional swashplates device, as outlined hereinabove, with two of the four pitch-control rods driven by the rotating plate and which are each connected to a respective one of two pitch rods of two diametrically opposed plates via respective one of two levers pivoting on the rotor mast.
The other two pitch control rods, driven by the rotating plate, are each connected to a respective one of the two pitch rods of the other two diametrically opposed blades by a respective one of two other levers pivoting on a rotary differential sleeve rotated by the rotor mast and translatable parallel to the axis of the rotor by a fourth actuator servo controlled using signals from blade-mounted sensors.
This known individual blade control therefore consists in adding, for two diametrically opposed blades, a pitch of the collective type, provided by the rotary sleeve with controlled axial sliding, to the conventional collective and cyclic pitch transmitted to the four blades by a conventional swashplates device.
In this system, the rotary and translatable sleeve introduces just one additional degree of freedom, even if it controls two blades. This means that for a rotor with more than three blades, it is necessary to introduce as many rotary and sliding concentric sleeves as there are blades in excess of three, and the study into the individual control of the blades needs to be entirely reworked.
The principle employed by this known system is of acting differentially on one or more blades, in particular on two diametrically opposed blades for reasons of symmetry. However, there is no decoupling between the blades, because the conventional set of swashplates acts on the four blades whereas the differential sleeve acts on two of them.
The system described in EP-A-0,451,218 is a system with full authority for which, in the event of a breakdown in the individual control, there is not explicitly provided any system that will allow operation in control mode with reduced authority, especially since in normal operation, the three rams that operate the conventional swashplates in addition to providing the monocyclic function, fulfil the function of individual control, without there being any decoupling between these two functions.
The problem underlying the invention is that of remedying the drawbacks of the known systems for individually controlling the blades with rotary actuators or according to EP-A-0,451,218, and of proposing a device for the individual control of the blades for a rotor with at least four blades, using operating actuators which are situated in the stationary reference frame, using reliable and well-known technology, there being at least as many of these actuators as there are blades to be controlled.
Another object of the invention is to propose a device for the individual control of the blades which, from a control configuration which, in normal operation, has full authority, can adopt a control configuration with reduced authority, applying a conventional monocyclic control law in the event of a breakdown in the individual control device. This device can be readily applied to devices for the individual control of blades for two-bladed or three-bladed rotors.
Finally, another object of the invention is to propose such an individual control device of this kind, which allows complete decoupling between groups of blades, so that vibration can be controlled, it only being possible for significant vibration of one blade, which may have been damaged by a projectile, to be transmitted to the group of blades to which this blade belongs, which means that it will be easier for these vibrations to be compen
Dinh Treu
Larson & Taylor PLC
Onera (Office National d'Etudes et de Recherches Aerospatia
Poon Peter M.
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