Lifting surfaces and associated method

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.