Vertical take-off and landing (VTOL) aircraft with cruise rotor positioning control for minimum drag

Abstract

Vertical takeoff and landing (VTOL) aircraft are provided with fixed-position port and starboard wings extending laterally from an elongate fuselage having an empennage at an aft end of the fuselage and a propeller to provide horizontal thrust to the aircraft in a direction of the longitudinal axis thereof. A series of port and starboard rotor units are provided, each of which includes axially opposed rotor blades, and a motor to rotate the rotor blades and provide vertical thrust to the aircraft. A logic control unit (LCU) controllably sets an angular position of the opposed rotor blades along a position axis relative to the longitudinal axis of the aircraft in response to determining an optimal position of the rotor blades during cruise flight operation to thereby minimize airflow disruption over the fixed-position wings.

Claims

1. A vertical takeoff and landing (VTOL) aircraft comprising: an elongate fuselage defining a longitudinal axis of the aircraft; fixed-position port and starboard wings extending laterally from the fuselage; an empennage at an aft end of the fuselage; a propeller to provide horizontal thrust to the aircraft in a direction of the longitudinal axis thereof; a series of port and starboard rotor units each of which includes axially opposed rotor blades, a motor to rotate the rotor blades and provide vertical thrust to the aircraft, and at least one rotor position sensor that senses angular position of the axially opposed rotor blades; and a logic controller operatively coupled to the sensors and to the port and starboard rotor unit motors, the logic controller configured to dynamically allocate positions of the rotor blades of each rotor unit during cruise flight operation based on a current flight state of the vehicle by controllably individually actively aligning the angular positions of the axially opposed rotor blades of each rotor unit along position axes relative to local airflow over the aircraft in response to sensed positions of the axially opposed rotor blades of the rotor unit, to minimize airflow disruption over the fixed-position wings during cruise flight operation.

2. The VTOL aircraft according to claim 1, further comprising port and starboard rotor booms carried by the port and starboard wings and supporting the series of port and starboard rotor units, respectively.

3. The VTOL aircraft according to claim 2, wherein the port and starboard rotor booms are aligned parallel to the longitudinal axis of the fuselage.

4. The VTOL aircraft according to claim 3, wherein the port and starboard rotor booms extend forwardly and aft of the port and starboard wings, respectively.

5. The VTOL aircraft according to claim 4, wherein at least a first one of the port and starboard rotor units is carried by the port and starboard rotor booms forwardly of the port and starboard wings and a second one of the port and starboard rotor units is carried by the port and starboard rotor booms aft of the port and starboard wings, respectively.

6. The VTOL aircraft according to claim 4, wherein a first pair of the port and starboard rotor units is carried by the port and starboard rotor booms forwardly of the port and starboard wings and a second pair of the port and starboard rotor units is carried by the port and starboard rotor booms aft of the port and starboard wings, respectively.

7. The VTOL aircraft according to claim 1, wherein each of the rotor units comprising a said rotor position sensor (RPS) which senses the angular position of the rotor blades of said rotor unit relative to the longitudinal axis of the fuselage and issues a position signal to the logic controller, the logic controller using the position signal to actively align the rotor blades in response to: measurement of local airflow at the rotor unit, or altitude of the aircraft based on linear interpolations over alpha and/or beta values of the aircraft.

8. The VTOL aircraft according to claim 7, wherein each of the rotor units comprises a motor and a motor controller operatively connected to the motor, wherein the logic controller issues a control signal to the motor controller which in turn issues a command signal to the motor to control the rotor blades to assume individual positions based on optimal position of the rotor blades in dependence upon the aircraft's flight phase, that minimize airflow disruption over the fixed-position wings during cruise flight operation.

9. The VTOL aircraft according to claim 1, wherein the propeller is a pusher propeller located at an aft end of the fuselage.

10. The VTOL aircraft according to claim 1, wherein the aircraft comprises two pairs of the port rotor units and two pairs of the starboard rotor units.

11. The VTOL aircraft according to claim 10, wherein a first pair of each of the port and starboard rotor units is carried by the port and starboard rotor booms forwardly of the port and starboard wings and a second pair of each of the port and starboard rotor units is carried by the port and starboard rotor booms aft of the port and starboard wings, respectively.

12. The VTOL aircraft according to claim 11, wherein the port and starboard rotor booms extend forwardly and aft of the port and starboard wings, respectively.

Description

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

(1) The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which:

(2) FIG. 1 is a non-limiting embodiment of a VTOL aircraft in accordance with this invention;

(3) FIG. 2 is a schematic representation of a pair of rotors associated with the VTOL aircraft shown in FIG. 1 shown with the rotors locally aligned with airflow; and

(4) FIGS. 3A-3E are operational control logic diagrams that may be employed for the VTOL aircraft shown in FIG. 1 during various flight phases.

DETAILED DESCRIPTION OF EMBODIMENTS

(5) Accompanying FIG. 1 shows an exemplary VTOL aircraft 10 in accordance with an embodiment of this invention. The aircraft 10 includes an elongate fuselage 12 defining a central elongate axis A.sub.L having a forward passenger compartment 14 and an aft empennage 16, the latter being provided with port and starboard elevators 18a, 18b and rudders 20a, 20b, respectively. A tail-mounted propeller 22 powered by an on-board motor (e.g., an electric motor (not shown)) provides pusher thrust for the aircraft 10.

(6) Port and starboard wings 24a, 24b extend laterally outwardly from the fuselage and carry port and starboard rotor booms 26a, 26b, respectively. In the embodiment depicted, each of the rotor booms 26a, 26b includes port-side rotor units 30 and starboard side rotor units 32, each having an axially opposed pair of rotor blades 30a, 32a (i.e., so-called two-blade rotors) and a dedicated motor 30b, 32b which provides the blades 30a, 30b with sufficient revolutions to allow for lift during takeoff and landing operations as well as to provide controllability to the aircraft 10.

(7) An exemplary pair of the port-side rotor units 30 are depicted in FIG. 2 and are representative of all other pairs of rotor units 30, 32. As such, reference to the other starboard-side rotor units 32 will be noted parenthetically in the following discussion in relation to the air of rotor units 30 depicted in FIG. 2. Each of the rotor units 30(32) is provided with a rotor position sensor (RPS) 40 which senses the axial positioning of the rotor blades 30a(32a) (i.e., along a position axis A.sub.P). The RPS 40 will therefore issue a position signal to a logic control unit (LCU) 42. The LCU 42 will receive the position signal from the RPS 40 and issue a control signal to a motor control unit (MCU) 44 which in turn issues a command signal to the individual motors 30b(32b) to position the rotor blades 30a(32a) along a position axis A.sub.P to form angles α1 and α2 (which may be the same or different) based on the optimal position of the rotor blades 30a(32a) in dependence upon the aircraft's flight phase. The rotor blades 30a(32a) will therefore be actively aligned along individual axes A.sub.P relative to local airflow during cruise flight based on the LCU 42 determination of optimal positioning so as to provide minimal airflow disturbance over the wings 24a, 24b.

(8) The LCU 42 may therefore either actively align each of the rotor blades 30a(32a) along axes A.sub.P either in response to measurement of the local airflow (e.g., by suitable on-board instrumentation), or in response to the aircraft's altitude (i.e., by setting a new optimal rotor position for each of the aircraft's alpha and/or beta angle. The latter is easier to accomplish as compared to the former because alpha and beta angles are available for flight control purposes. The former requires local airflow measure. The optimal rotor position can thus be estimated offline (when set in consideration of aircraft altitude) or online (when set using local airflow measurement). With regard to optimal rotor positioning based on aircraft altitude, a table can simply be stored in the LCU 42 using linear interpolations over alpha and/or beta values.

(9) According to the embodiment depicted, the RPS 40 will determine the axial positioning along axis A.sub.P relative to the longitudinal axis A.sub.L of the aircraft 10 as previously mentioned. The LCU 42 may therefore include control logic having a dedicate resolution algorithm for rotor blades 30a(32a) for each of the rotor units 30(32). To command the rotor blades 30a(32a) to the desired position, the control logic of the LCU 42 will modulate the stator's magnetic field to minimize the error between measured rotor position and optimal position determined by the resolution algorithm.

(10) Typical operational phases of the multi-copter aircraft 10 include takeoff, climb, cruise, descent and landing. The control logic processes for the aircraft 10 for each such phase are depicted in FIGS. 3A-3E, respectively. During takeoff phase (FIG. 3A), after all regular procedures, the motors 30b, 32b start so as to rotate the rotor blades 30a, 32a and generate sufficient lift to assure a required altitude climb rate. In climb (FIG. 3B), the pusher propeller 22 can be engaged and the combination of hover and pusher rotor thrust s allows the aircraft 10 to gain speed and altitude at a controlled rate. At the end of the climb phase, the wings 24a, 24b will generate all lift and hover rotor units 30, 32 are unloaded, at which time the cruise phase begins (FIG. 3C). Using all measured positions and local airflow of the hover rotor units 30, 32 and/or the attitude of the aircraft 10, the LCU 40 via the MCU 44 will command all hover rotor blades 30a, 32a to the optimal position during cruise phase flight. In descent (FIG. 3D), the aircraft's control can employ the hover rotor blades 30a, 32a to control altitude descent rate and the pusher propeller 22 to reduce forward speed. At the end of descent phase, the wings 24a, 24b are aerodynamically unloaded and the hover rotor blades 30a, 32 are fully aerodynamically loaded. During landing (FIG. 3E), the control law uses hover rotor blades 30a, 32a to precisely land the aircraft at which time the rotor units 30, 32 may be turned off.

(11) Therefore, while reference is made to a particular embodiment of the invention, various modifications within the skill of those in the art may be envisioned. Therefore, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.