Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
2002-10-04
2004-09-21
Dinh, Tien (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
C244S194000
Reexamination Certificate
active
06793173
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an automatic control device for a helicopter, as well as to an automatic control system comprising such an automatic control device.
DESCRIPTION OF THE PRIOR ART
It is known that an automatic control system for a helicopter generally comprises:
a set of sensors for automatically determining the effective values of state parameters of the helicopter;
means of adjustment allowing an operator of the helicopter to choose preset values of state parameters;
a set of actuators which act on control axes of the helicopter, according to control commands; and
an automatic control device which automatically determines control commands for said actuators, as a function of the state parameters and of the preset values, received respectively from said sensors and from said means of adjustment.
The job of the automatic control system is to aid, or even to completely replace, the pilot in the flying of the helicopter. For this purpose, it is capable of slaving one or more state parameters of the helicopter, such as the altitude, the attitude or the speed for example, to one or more preset values chosen beforehand by the pilot. The automatic control system acts for this purpose on one of the control axes (roll axis, pitch axis, yaw axis and collective axis) so as to command the corresponding state parameter or parameters.
It will be noted that both the pitching axis and the collective axis make it possible to control the airspeed (which corresponds, according to the invention, to the speed of the helicopter with respect to the air) or parameters of the vertical plane. It will moreover be noted that the collective axis makes it possible to act on the pitch of the blades (as would the pilot by shifting the collective control stick) in such a way as to apply the same variations in angle of incidence to each of the various blades of the main forward motion and lift rotor of the helicopter. This results in a shift of the helicopter along a vertical axis (upward/downward).
Additionally, the two axes relating to the cyclic pitches (pitching axis and roll axis) produce a cyclic variation of the angle of incidence of the blades of the main rotor, these blades then having angles of incidence which vary as a function of their azimuth. This results in a forward tilting of the rotor (pitching) or sideways tilting (roll) or a combination of these two movements.
The automatic control system comprises various independent modes of slaving. Several of these modes may even be activated simultaneously. These modes are activated with the aim of carrying out a flight without intervention from the human pilot or pilots on the flight controls. Generally, an automatic control system is capable:
of acquiring and of maintaining a specified airspeed, that is to say a specified speed of the helicopter with respect to the air;
as well as of continuing an objective, in the vertical plane (acquisition and maintaining of a barometric altitude, of a vertical speed, of an approach slope or of a “radioprobe height” for example);
whilst ensuring, in a horizontal plane, the following of a flight plan (alignment with a given heading, with guidance beacons, with let-down axes, etc.) and generally, steering along a trajectory.
Such a system for the automatic control of a helicopter which enables the pilot to free himself completely of the task of controlling the helicopter, for almost the entire flight, may exhibit safety problems, generally having two different types of origin:
a mechanical origin due to a malfunctioning of the set of sensors, computers and actuators forming part of the automatic control system; and
a human origin due to a lack of attention or to a lack of knowledge of the automatic control system and of its limitations on the part of a pilot or of a crew member of the helicopter.
For this purpose, it is known that the more the flight management is automated, the more the control task is eased, and the less inclined is the crew to monitor the proper operation of the control system and the consistency of the modes and presets which it itself has displayed. The automatic control system must therefore to a large extent ensure its own monitoring and introduce automatic protections or limitations to cover the risks of ill-use. Such monitoring and protection means are numerous in helicopter automatic control systems. The following will be cited by way of illustration:
a dual architecture of the control loop (sensor, computer, actuator) allowing multiple monitoring;
multiple alarms and signalings presented to the crew, allowing diagnosis of the state of the control system possibly calling for increased monitoring (indication of disparities between sensors, of loss of redundancy, of abnormal alteration or of excessive discrepancy in the event of deviation from the preset displayed, etc.), or even active participation (need for the pilot to regain manual control of the helicopter, etc.); and
flight domain protection elements, such as the limiting of commands heading for the collective axis so as not to exceed the maximum permitted power or automatic leveling-off at the end of an instrument approach using a set of beacons on the ground and of receivers on board the helicopter.
However, all these monitoring and protection means participate in essence in the safety of the functioning of the technical control loop, but do not directly reduce the risks related to the human factor, since the pilot still intervenes in the complete control loop (action on the controls, on the presets, on the selection of modes, etc.).
More especially, it is known that a standard automatic control device comprises:
a single objective law for the pitching axis, namely a forward motion objective law whose aim is to maintain the airspeed with respect to a preset value. To do this, said objective law for the pitching axis determines, automatically, a control command for operating the tilting of the disk of the main rotor of the helicopter. It will be noted that, within the framework of the present invention, an objective law is a means of calculation which determines a particular control command making it possible to bring or to bring back at least one state parameter of the helicopter to an objective (which represents a preset value of this state parameter or of another state parameter); and
two objective laws for the collective axis, namely a vertical objective law and a law of maintaining the recommended power. Each of these two laws determines, automatically, a control command for operating the collective pitch of the blades of the main rotor of the helicopter.
With such an automatic control device, during normal functioning of the helicopter, the acquisition and holding of the airspeed are achieved via the pitching axis (forward motion objective law) and that of the parameter of the vertical mode (for example the altitude) via the collective axis.
However, as soon as the available power becomes insufficient to maintain the airspeed (that is to say the speed of the helicopter with respect to the air) at the scheduled preset value, the vertical objective law of the collective axis hits a top limitation which is calculated by the law for maintaining the power (the object of which is to maintain the power at a recommended value). In this case, the automatic control device still ensures safety in terms of power (maintaining of the power required for the flight configuration), but more in terms of vertical objective (altitude for example), since the vertical objective is no longer commanded by this automatic control device. In such a situation, it is the pilot who must intervene to ensure safety in terms of vertical objective. Thus, when he notes the toggling of law to the collective axis and that the helicopter is still descending, the pilot disengages, manually, the mode for holding the airspeed on the pitching axis so as to release this axis for the achieving of the vertical objective.
This known solution therefore exhibits risks related to the necessary intervention of the pilot who must not
Dinh Tien
Eurocopter
Stevens Davis Miller & Mosher LLP
LandOfFree
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