Adaptable automatic nacelle conversion for tilt rotor aircraft
Systems and methods for displaying to a tilt rotor aircraft pilot an optimum nacelle position and/or automatically controlling movement of the nacelles for the pilot. An automatic nacelle conversion function employs an active flight director speed mode to provide a current desired speed and a final speed. When the automatic nacelle conversion function is in a passive (uncoupled) mode of operation, the pilot follows visual cues, manually achieving the commanded nacelle position by rotating a thumbwheel. When in an active (coupled) mode of operation, the automatic nacelle conversion function provides a fully automatic nacelle controller requiring no pilot input. This automatic nacelle controller provides a variable nacelle rate along with several angle versus speed schedules tailored for different guidance speed modes and a wide range of aircraft configurations. The automatic nacelle conversion function is improved though the inclusion of altitude, rate of climb, and deceleration rate commands.
1. A method for controlling a nacelle angle of a tilt rotor assembly of a tilt rotor aircraft, comprising the following operations:
converting a commanded groundspeed into a commanded airspeed by taking into account a pressure altitude of a tilt rotor aircraft and ambient air temperature;
inputting said commanded airspeed to a speed versus nacelle angle schedule to obtain a nacelle angle that produces a favorable pitch attitude at a given airspeed in un-accelerated level flight of the tilt rotor aircraft;
receiving or locally inferring, if not available, an inertial descent rate command from a flight management system or pre-planned maneuver for commanding an inertial descent rate of the tilt rotor aircraft;
computing an adjusted nacelle angle command as a function of said inertial descent rate command; and
controlling a conversion actuator of the tilt rotor aircraft in accordance with said adjusted nacelle angle command.
2. The method as recited in claim 1 , wherein said adjusted nacelle angle command is also a function of a deceleration rate command.
3. The method as recited in claim 2 , wherein said computing an adjusted nacelle angle command comprises:
inputting said commanded airspeed to a speed versus descent gain schedule which outputs a descent gain;
forming a first product by multiplying said descent gain and said inertial descent rate command;
inputting said commanded airspeed to a speed versus deceleration gain schedule which outputs a deceleration gain;
forming a second product by multiplying said deceleration gain and said deceleration rate command;
summing said first and second products to form an adjustment angle; and
summing said nacelle angle and said adjustment angle.
4. The method as recited in claim 1 , wherein said operation of converting a commanded groundspeed into a commanded airspeed comprises:
computing a component of wind velocity along a flight path of the tilt rotor aircraft;
filtering said component of wind velocity; and
summing said filtered component of wind velocity and said commanded groundspeed to form a commanded true airspeed.
5. The method as recited in claim 4 , wherein said operation of converting a commanded groundspeed into a commanded airspeed further comprises:
computing a commanded calibrated airspeed using said commanded true airspeed, said pressure altitude, and said associated ambient air temperature; and
computing a commanded airspeed through a weighted average of said commanded true airspeed and said commanded calibrated airspeed using weighting factors which are a function of a nacelle angle.
6. The method as recited in claim 1 , wherein said operation of locally inferring an inertial descent rate command comprises:
summing an inertial rate of climb and a rate of climb error to obtain a commanded inertial vertical velocity;
filtering said commanded inertial vertical velocity; and
limiting said filtered commanded inertial vertical velocity to a range.
7. The method as recited in claim 1 , further comprising displaying said nacelle angle command on a cockpit display for a pilot.
8. A system for generating a nacelle angle command onboard a tilt rotor aircraft, comprising a conversion actuator, a tiltable nacelle, and a computer system programmed to perform the following operations:
converting a commanded groundspeed into a commanded airspeed by taking into account a pressure altitude of the tilt rotor aircraft and ambient air temperature;
inputting said commanded airspeed to a speed versus nacelle angle schedule to obtain a nacelle angle that produces a favorable pitch attitude at a given airspeed in un-accelerated level flight of the tilt rotor aircraft;
receiving or locally inferring, if not available, an inertial descent rate command from a flight management system or pre-planned maneuver for commanding an inertial descent rate of the tilt rotor aircraft;
computing an adjusted nacelle angle command as a function of at least said inertial descent rate command; and
controlling said conversion actuator to tilt said nacelle in accordance with said adjusted nacelle angle command.
9. The system as recited in claim 8 , wherein said adjusted nacelle angle command is also a function of a deceleration rate command.
10. The system as recited in claim 9 , wherein said operation of computing an adjusted nacelle angle command comprises:
inputting said commanded airspeed to a speed versus descent gain schedule which outputs a descent gain;
forming a first product by multiplying said descent gain and said inertial descent rate command;
inputting said commanded airspeed to a speed versus deceleration gain schedule which outputs a deceleration gain;
forming a second product by multiplying said deceleration gain and said deceleration rate command;
summing said first and second products to form an adjustment angle; and
summing said nacelle angle and said adjustment angle.
11. The system as recited in claim 8 , wherein said operation of converting a commanded groundspeed into a commanded airspeed comprises:
computing a component of wind velocity along a flight path of the tilt rotor aircraft;
filtering said component of wind velocity; and
summing said filtered component of wind velocity and said commanded groundspeed to form a commanded true airspeed.
12. The system as recited in claim 11 , wherein said operation of converting a commanded groundspeed into a commanded airspeed further comprises:
computing a commanded calibrated airspeed using said commanded true airspeed, said pressure altitude, and said associated ambient air temperature; and
computing a commanded airspeed through a weighted average of said commanded true airspeed and said commanded calibrated airspeed using weighting factors which are a function of a nacelle angle.
13. The system as recited in claim 8 , wherein said operation of locally inferring an inertial descent rate command comprises:
summing an inertial rate of climb and a rate of climb error to obtain a commanded inertial vertical velocity;
filtering said commanded inertial vertical velocity; and
limiting said filtered commanded inertial vertical velocity to a range.
14. The system as recited in claim 8 , further comprising a cockpit display for a pilot, wherein said computer system is further programmed to display said nacelle angle command on said cockpit display.
15. A tilt rotor aircraft comprising: a fuselage; at least one wing member coupled to the fuselage; a tilt rotor assembly pivotally coupled to the at least one wing member for tilting over a range of nacelle angles; a nacelle conversion actuator for actuating pivoting of said tilt rotor assembly; and a computer system programmed to perform the following operations:
converting a commanded groundspeed into a commanded airspeed by taking into account a pressure altitude of the tilt rotor aircraft and ambient air temperature;
inputting said commanded airspeed to a speed versus nacelle angle schedule to obtain a nacelle angle that produces a favorable pitch attitude at a given airspeed in un-accelerated level flight of the tilt rotor aircraft;
computing an inertial descent rate command for commanding an inertial descent rate of the tilt rotor aircraft;
computing an adjusted nacelle angle command as a function of said inertial descent rate command and a deceleration rate command; and
controlling said conversion actuator to tilt said tilt rotor assembly in accordance with said adjusted nacelle angle command.
16. The tilt rotor aircraft as recited in claim 15 , wherein said operation of computing an adjusted nacelle angle command comprises:
inputting said commanded airspeed to a speed versus descent gain schedule which outputs a descent gain;
forming a first product by multiplying said descent gain and said inertial descent rate command;
inputting said commanded airspeed to a speed versus deceleration gain schedule which outputs a deceleration gain;
forming a second product by multiplying said deceleration gain and said deceleration rate command;
summing said first and second products to form an adjustment angle; and
summing said nacelle angle and said adjustment angle.