In an aeronautical vehicle, such as a helicopter, a vehicle operator uses control inceptors to control the vehicle. Position changes of each control inceptor causes changes in orientation of aerodynamic surfaces and engine generated output power of the vehicle. In a helicopter such changes usually include the pitch of the main and tail rotor blades and the angle of a horizontal stabilator.
Traditionally, for helicopters, a dominant trend has been for a vertical control inceptor to predominantly be used in adjusting the pitch of all main rotor blades, which is commonly known as collective pitch, and in adjusting engine output power. A two axis longitudinal and lateral control inceptor is predominantly used in adjusting pitch of the main rotor blades as a function of blade position, which is commonly known as cyclic pitch. In using the stated convention, the vehicle operator can control the vertical velocity of the vehicle by adjusting the vertical inceptor and he can control the pitch and roll attitude by adjusting the longitudinal and lateral inceptors. By controlling the pitch and roll of the vehicle the operator can control the longitudinal and lateral acceleration and velocity of the vehicle.
A vehicle operator can maintain a constant altitude or vertical velocity, hereinafter referred to as a vertical state, by positioning the vertical inceptor in an appropriate position. The correct vertical inceptor position for maintaining the desired vertical state changes with changes in the acceleration and velocity along the longitudinal and lateral axes, requiring the operator to reposition the vertical inceptor.
Advanced vehicle control systems currently exist in the art for maintaining a specific vertical state. For example, a vehicle may have a control system capable of maintaining one or more vertical states, including constant vertical velocity state, a constant altitude state, or a constant flight path angle. Such vehicle control systems can function by automatically adjusting the vertical control inceptor position or by adding an electronic input in series with the vertical inceptor position.
Although vertical inceptor positions required to maintain a desired vertical state may currently be determined, since the vertical inceptor positioning effects power output of the engine as well as the collective pitch of the main rotor blades, there are many mechanical and aerodynamic limits associated with vertical inceptor positioning, which can limit the ability to maintain the desired vertical state.
Examples of such vertical axis limits are actuator limits, transmission torque limits, rotor over-speed and under-speed limits, rotor stall, rotor vortex ring state, and engine performance limits such as temperature and gas generator speed. These limits can be represented as minimum and maximum limits for vertical inceptor positioning.
Difficulties arise when, as a result of other vehicle operator actions such as commanding longitudinal and lateral accelerations, the vertical inceptor positions required to maintain the vertical state exceed one or more of the vertical axis limits. Depending on methods used in maintaining the desired vertical state and the methods used in limiting vertical inceptor positioning, the exceedance of a vertical axis limit may result in disengagement from or inability to maintain the vertical state or exceedance of the limit(s).
To maintain the desired vertical state and avoid exceedance of a limit a vehicle operator must continuously monitor vehicle instrumentation and vehicle performance, which distracts from the operators other tasks. Also, in order to be able to monitor instrumentation while navigating the vehicle, extensive training is required, which costs time and money. Also, the vehicle operator to maintain the desired vertical state and not exceed a limit, typically, operates the vehicle in a conservative manner and does not utilize full performance capabilities of the vehicle.
A related problem for vehicle operators occurs if the desired vertical state changes and the airspeed must be reduced to enable the vehicle to maintain the new state. In this scenario, the vehicle operator must determine how quickly to decelerate the vehicle to allow the new state to be maintained and when desiring to maintain a maximum airspeed the operator must avoid reducing speed of the vehicle more than required to maintain the new state.
It is sometimes necessary for the vehicle operator to require sudden deceleration or acceleration of the vehicle due to, for example, dangerous or hazardous situations. At the same time, it is often necessary during such situations to maintain a certain vertical altitude or state (for example, to prevent detection or ground contact). During these situations, the maximum and minimum limits of various operating conditions of the vehicle should not be exceeded in order for the vertical state to be maintained. However, it is often difficult for the operator to do so due to distractions and other concerns.
It is therefore desirable to provide a vehicle cueing system that is capable of cueing a vehicle operator to the maximum accelerations or decelerations that may be performed while maintaining a constant vertical state without exceeding any vertical vehicle limits or without disengaging, interrupting, or causing the vehicle to no longer be able to maintain the vertical state. Also, it is desirable that the vehicle cueing system cues a vehicle operator in a nondistracting and nonobstructing manner and minimize time required of the vehicle operator in monitoring vehicle instrumentation and aircraft performance.
Additionally, it is desirable that a vehicle cueing system operates in conjunction with existing vehicle control systems. For an aeronautical vehicle, relationships between a control inceptor position and corresponding vehicle response are control characteristics of the vehicle, which are carefully designed. Altering vehicle response characteristic can result in time consuming and costly testing of a vehicle and re-training of vehicle operators. Thus, a newly introduced vehicle cueing system should not significantly alter this relationship.