Vertical control system for rotary wing aircraft

A flight control system for a helicopter having:

• sensors which provide signals indicative of the helicopter's actual altitude and actual altitude rate of change, a sidearm controller which provides a vertical lift command signal indicative of the desired lift along the vertical axis, and a collective stick which provides a collective command signal indicative of desired collective pitch;
• the flight control system controls vertical lift of the helicopter by providing to the helicopter's main rotor a set point signal indicative of the desired collective pitch of the helicopter's main rotor blades, the flight control system comprising:
• means for providing, for each value of the vertical lift command signal presented thereto, a vertical rate of change command signal indicative of a corresponding desired value for the helicopter's vertical rate of change;
• means for integrating said vertical rate of change command signal to provide a desired altitude command signal;
• first means of computing a first difference value between the value of said desired altitude command signal and the value of said helicopter's actual altitude signal, and for providing an altitude error signal indicative of said first difference value;
• second means for computing a second difference value between the value of said vertical rate of change command signal and the value of said helicopter's actual altitude rate of change signal, and for providing an altitude rate of change error signal indicative of said second difference value;
• inverse model means for providing for each value of said vertical rate of change command signal, a feedforward collective set point signal indicative of the collective pitch required for the helicopter to aerodynamically respond along its vertical axis at a rate set by the value of said vertical rate of change command signal;
• means for summing said altitude error signal, said altitude rate of change error signal, and said feedforward collective set point signal, and for providing as a summation thereof a modifying collective pitch command signal;
• means for summing said collective command signal with said modifying collective pitch command signal to provide, as the sum thereof, said desired collective pitch set point signal;
• and
• output means for providing said desired collective pitch set point signal value to the helicopter's main rotor, such that by commanding the collective pitch of helicopter's main rotor blades in response to said desired collective pitch set point signal, the helicopter will aerodynamically respond along its vertical axis in a manner to cause the values of said altitude error signal and said altitude rate error signal to approach zero.

A helicopter flight control system which receives signals indicative of:

• the helicopter's actual altitude and actual altitude rate of change, a vertical lift command signal indicative of desired vertical lift along the helicopter's vertical axis, and a collective command signal indicative of main rotor collective pitch;
• the flight control system controls vertical lift of the helicopter by providing to the helicopter's main rotor a set point signal indicative of the desired collective pitch of the helicopter's main rotor blades, the flight control system comprising:
• means for providing, for each value of said vertical lift command signal presented thereto, a corresponding desired vertical rate of change command signal;
• means for integrating said desired vertical rate of change command signal to provide a desired altitude command signal;
• first means, for computing a first difference value between the value of said desired altitude command signal and the value of said helicopter's actual altitude signal, and for providing an altitude error signal indicative of said first difference value;
• second means for computing a second difference value between the value of said desired vertical rate of change command signal and the value of said helicopter's actual altitude rate of change signal, and for providing an altitude rate of change error signal indicative of said second difference value;
• inverse model means for providing for each value of said desired vertical rate of change command signal, a feedforward collective set point signal indicative of the collective pitch required for the helicopter to aerodynamically respond along its vertical axis in a manner set by the value of said desired vertical rate of change command signal;
• means for summing said altitude error signal, said altitude rate of change error signal, and said feedforward collective set point signal, and for providing as a summation thereof a modifying collective pitch command signal;
• means for summing said collective command signal with said modifying collective pitch command signal to provide as the sum thereof said desired collective pitch set point signal;
• and
• output means, for presenting said desired collective pitch set point signal to the helicopter's main rotor to set the collective pitch of helicopter's main rotor blades in response to the value of said desired collective pitch set point signal so the helicopter aerodynamically responds along its vertical axis in a manner to cause the values of said altitude error signal and said altitude rate error signal to approach zero.