Lifting surfaces and associated method

Abstract

An arrangement of lifting surfaces including a primary lifting surface having a flexural axis extending in the spanwise direction of the lifting surface, a root, and a tip. A first tip device is attached to the tip and has a first lifting surface. A second tip device is attached to the tip and has a second lifting surface. A control system is coupled to the first and second tip devices for moving the first and second lifting surfaces relative to the tip and/or for actively controlling circulation of the first and second lifting surfaces. The control system is operable to change a value of torque effective at the primary lifting surface about the flexural axis. Also, a method of controlling an arrangement of lifting surfaces.

The invention is: 
     
         1 . An aircraft having an arrangement of lifting surfaces comprising:
 a primary lifting surface having a flexural axis extending in a spanwise direction of the primary lifting surface, a root, and a tip;   a first tip device attached to the tip and having a first lifting surface;   a second tip device attached to the tip and having a second lifting surface; and   a flight control system coupled to the first and second tip devices and configured to move the first and second lifting surfaces relative to the tip by moving at least one of the first and second tip devices relative to the primary lifting surface and/or to actively control circulation of the first and second lifting surfaces;   wherein the control system is operable in a first mode of operation in which the first and second lifting surfaces are actively controlled to change a value of torque effective at the primary lifting surface about the flexural axis whilst maintaining a value of lift generated by the first and second tip devices substantially constant, and   wherein the flight control system is operable in a second mode of operation in which the first and second lifting surfaces are actively controlled to change a value of lift generated by the first and second tip devices whilst maintaining a value of torque effective at the primary lifting surface about the flexural axis substantially constant.   
     
     
         2 . The aircraft according to  claim 1 , wherein the first lifting surface is moved mechanically independently of the second lifting surface. 
     
     
         3 . The aircraft according to  claim 1 , wherein the first lifting surface is moved relative to the primary lifting surface in a first direction, and the second lifting surface is moved relative to the primary lifting surface in a second direction opposite the first direction. 
     
     
         4 . The aircraft according to  claim 3 , wherein movement of the first lifting surface is mechanically linked to movement of the second lifting surface. 
     
     
         5 . The aircraft according to  claim 1 , wherein the first tip device has a leading edge and a trailing edge, and the first lifting surface extends full chord between the leading edge and the trailing edge of the first tip device. 
     
     
         6 . The aircraft according to  claim 5 , wherein the arrangement further comprises an actuator for rotating the first lifting surface relative to the tip. 
     
     
         7 . The aircraft according to  claim 5 , wherein the arrangement further comprises an actuator for morphing the first lifting surface. 
     
     
         8 . The aircraft according to  claim 1 , wherein the first tip device has a leading edge and a trailing edge, the first lifting surface extends only part chord between the leading and trailing edges, and the first tip device has a third lifting surface fixed with respect to the primary lifting surface. 
     
     
         9 . The aircraft according to  claim 8 , wherein the first lifting surface is hinged with respect to the third lifting surface and the movement of the first lifting surface includes rotating the first lifting surface about the hinge. 
     
     
         10 . The aircraft according to  claim 1 , wherein the second tip device has a leading edge and a trailing edge, and the second lifting surface extends full chord between the leading and trailing edges of the second tip device. 
     
     
         11 . The aircraft according to  claim 10 , wherein the arrangement further comprises an actuator for rotating the second lifting surface relative to the tip. 
     
     
         12 . The aircraft according to  claim 10 , wherein the arrangement further comprises an actuator for morphing the second lifting surface. 
     
     
         13 . The aircraft according to  claim 1 , wherein the second tip device has a leading edge and a trailing edge, the second lifting surface extends only part chord between the leading and trailing edges, and the second tip device has a fourth lifting surface fixed with respect to the primary lifting surface. 
     
     
         14 . The aircraft according to  claim 13 , wherein the second lifting surface is hinged with respect to the fourth lifting surface and the movement of the second lifting surface includes rotating the second lifting surface about the hinge. 
     
     
         15 . The aircraft according to  claim 1 , wherein the first and second lifting surfaces each include at least one aperture, and the control system is configured to control movement of fluid through the at least one aperture of the first and second lifting surfaces to provide active circulation control. 
     
     
         16 . The aircraft according to  claim 1 , wherein the first tip device is swept forwards and the second tip device is swept backwards. 
     
     
         17 . The aircraft according to  claim 1 , wherein the first tip device is swept backwards and the second tip device is swept backwards. 
     
     
         18 . The aircraft according to  claim 1 , wherein the first tip device is swept forwards and the second tip device is swept forwards. 
     
     
         19 . The aircraft according to  claim 1 , wherein the primary lifting surface is swept backwards. 
     
     
         20 . The aircraft according to  claim 1 , wherein the primary lifting surface is swept forwards. 
     
     
         21 . The aircraft according to  claim 1 , wherein the primary lifting surface is unswept. 
     
     
         22 . The aircraft according to  claim 1 , wherein the first tip device is located forward of the flexural axis and the second tip device is located aft of the flexural axis. 
     
     
         23 . The aircraft according to  claim 1 , wherein the primary lifting surface defines a wing plane, and the first and second tip devices are substantially co-planar with the wing plane. 
     
     
         24 . The aircraft according to  claim 1 , wherein the first and second tip devices are located in different planes. 
     
     
         25 . The aircraft according to  claim 24 , wherein the first and second tip devices are located in intersecting planes. 
     
     
         26 . The aircraft according to  claim 24 , wherein the primary lifting surface, the first tip device and the second tip device are each located in different parallel planes. 
     
     
         27 . The aircraft according to  claim 26 , wherein the first tip device is mounted on a first pylon extending from the tip of the primary lifting surface, and the second tip device is mounted on a second pylon extending from the tip of the primary lifting surface. 
     
     
         28 . A method of controlling an arrangement of lifting surfaces on an aircraft, the arrangement comprising a primary lifting surface having a flexural axis extending in a spanwise direction of the primary lifting surface, a root, and a tip; a first tip device attached to the tip and having a first lifting surface; and a second tip device attached to the tip and having a second lifting surface, and a flight control system coupled to the first and second tip devices; the method comprising:
 using the flight control system in:   i) a first mode of operation in which the first and second lifting surfaces are actively controlled to change a value of torque effective at the primary lifting surface about the flexural axis whilst maintaining a value of lift generated by the first and second tip devices substantially constant, and   ii) a second mode of operation in which the first and second lifting surfaces are actively controlled to change a value of lift generated by the first and second tip devices whilst maintaining a value of torque effective at the primary lifting surface about the flexural axis substantially constant by performing at least one of:
 a) moving the first and second lifting surfaces relative to the tip, and 
 b) actively controlling circulation of the first and second lifting surfaces. 
   
     
     
         29 . The method according to  claim 28 , further comprising moving the first lifting surface mechanically independently of the second lifting surface. 
     
     
         30 . The method according to  claim 28 , further comprising moving the first lifting surface relative to the primary lifting surface in a first direction, and moving the second lifting surface relative to the primary lifting surface in a second direction opposite the first direction. 
     
     
         31 . The method according to  claim 30 , wherein the movement of the first lifting surface is mechanically linked to movement of the second lifting surface. 
     
     
         32 . The method according to  claim 28 , further comprising rotating the first lifting surface relative to the tip. 
     
     
         33 . The method according to  claim 28 , further comprising rotating the second lifting surface relative to the tip. 
     
     
         34 . The method according to  claim 28 , further comprising controlling movement of fluid through at least one aperture in each of the first and second lifting surfaces to provide active circulation control. 
     
     
         35 . The method according to  claim 28 , wherein the arrangement of lifting surfaces is provided at each of a port side and a starboard side of the aircraft, and the method comprises changing a value of torque effective at the respective port and starboard primary lifting surfaces about their flexural axes to effect one or more of:
 i) roll control of the aircraft;   ii) yaw control of the aircraft;   iii) pitch control of the aircraft;   iv) tip vortex control; and   v) drag control.