Abstract: Methods are provided for operating an air vehicle, the air vehicle including fixed wings configured to provide mild stall characteristics including a post-stall regime, and a propulsion system capable of generating a controllable thrust, the thrust being variable at least between an idle thrust and a maximum thrust. During a landing maneuver, the air vehicle is caused to attain an angle of attack corresponding to said post-stall regime, and during the landing maneuver, there is concurrently generated a thrust level of said thrust greater than said idle thrust to provide a thrust vector having a thrust lift force component at landing. Corresponding control systems are also provided, and air vehicles including such control systems are also provided.

Abstract: Methods are provided for operating an air vehicle having fixed wings. Such methods include the step of providing an operating map of angle of attack associated with the fixed wings with Reynolds number, including conditions of separated flow over the fixed wings and conditions of attached flow over the fixed wings. Such methods also include the step of using the operating map for guidance, causing the air vehicle to operate at least within a low Reynolds numbers range corresponding to the operating map, such as to avoid or minimize risk of causing the air vehicle to operate at conditions of separated flow over the fixed wings.

Abstract: Two element aerofoils are provided, having an aerofoil chord, a primary element having a first leading edge and a first trailing edge, a secondary element having a second leading edge and a second trailing edge, a gap between the primary element and the secondary element, and an axial overlap between the first trailing edge and the second leading edge. The secondary element is deflectable with respect to the primary element about a fixed hinge point by a flap deflection angle. The secondary element is configured to operate in airbrake mode when deflected by a respective the flap deflection angle corresponding to a design airbrake deflection angle wherein to generate an airbrake drag. In at least some examples, the axial overlap is numerically greater than ?0.5% of the aerofoil chord, at least for the design airbrake deflection angle. Also disclosed are methods for operating air vehicles, and methods for designing two-element aerofoils.

Abstract: Aerofoil accessories are provided, configured for selective attachment to a wing element, the wing element having an outer facing aerofoil surface and being based on at least one datum aerofoil section. Each accessory provides a modified geometric profile to a datum profile of the at least one aerofoil section when attached to the wing element. The accessories are each configured for having a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element is airborne with the respective accessory attached to the wing element. The modified geometric profile is such as to provide said wing element with the accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent the accessory. A kit is also provided for enhancing performance of a wing element in off-design conditions. A method is also provided for enhancing performance of a wing element in adverse conditions.

Abstract: A method for providing a controllable side force to an air vehicle having a vertical stabilizer arrangement includes (a) selectively causing the vertical stabilizer arrangement to generate a first side force in a first side direction to provide the controllable side force, the first side force inducing a corresponding first yaw moment in a first yaw direction; and (b) selectively providing to the air vehicle a second yaw moment in a second yaw direction, the second yaw moment being induced by a force component of an auxiliary force applied to the air vehicle, the force component being in a force direction that is non-parallel with respect to the first side direction and the force component being spaced from a center of gravity of the air vehicle; wherein the second yaw direction is opposed to the first yaw direction. Also disclosed is a corresponding auxiliary yaw generating system.

Abstract: Methods are provided for operating an air vehicle having fixed wings. Such methods include the step of providing an operating map of angle of attack associated with the fixed wings with Reynolds number, including conditions of separated flow over the fixed wings and conditions of attached flow over the fixed wings. Such methods also include the step of using the operating map for guidance, causing the air vehicle to operate at least within a low Reynolds numbers range corresponding to the operating map, such as to avoid or minimize risk of causing the air vehicle to operate at conditions of separated flow over the fixed wings.

Abstract: Methods are provided for operating an air vehicle, the air vehicle including fixed wings configured to provide mild stall characteristics including a post-stall regime, and a propulsion system capable of generating a controllable thrust, the thrust being variable at least between an idle thrust and a maximum thrust. During a landing maneuver, the air vehicle is caused to attain an angle of attack corresponding to said post-stall regime, and during the landing maneuver, there is concurrently generated a thrust level of said thrust greater than said idle thrust to provide a thrust vector having a thrust lift force component at landing. Corresponding control systems are also provided, and air vehicles including such control systems are also provided.

Abstract: Two element aerofoils are provided, having an aerofoil chord, a primary element having a first leading edge and a first trailing edge, a secondary element having a second leading edge and a second trailing edge, a gap between the primary element and the secondary element, and an axial overlap between the first trailing edge and the second leading edge. The secondary element is deflectable with respect to the primary element about a fixed hinge point by a flap deflection angle. The secondary element is configured to operate in airbrake mode when deflected by a respective the flap deflection angle corresponding to a design airbrake deflection angle wherein to generate an airbrake drag. In at least some examples, the axial overlap is numerically greater than ?0.5% of the aerofoil chord, at least for the design airbrake deflection angle. Also disclosed are methods for operating air vehicles, and methods for designing two-element aerofoils.

Abstract: A two element aerofoil, and wing element based thereon, is provided, including a primary aerofoil element including a leading edge of the aerofoil and a secondary aerofoil element including a trailing edge of the aerofoil. A gap is provided between the primary aerofoil element and the secondary aerofoil element. The primary aerofoil element has at least one of a profile, orientation and location with respect to a respective at least one of a profile, orientation and location of the secondary aerofoil element that is configured for minimizing or avoiding accretion of contaminant on the secondary aerofoil element when subjected to an airflow that includes the contaminant, at least at one design set of conditions. A method for designing a two element aerofoil is also provided.

Abstract: A method for providing a controllable side force to an air vehicle having a vertical stabilizer arrangement includes (a) selectively causing the vertical stabilizer arrangement to generate a first side force in a first side direction to provide the controllable side force, the first side force inducing a corresponding first yaw moment in a first yaw direction; and (b) selectively providing to the air vehicle a second yaw moment in a second yaw direction, the second yaw moment being induced by a force component of an auxiliary force applied to the air vehicle, the force component being in a force direction that is non-parallel with respect to the first side direction and the force component being spaced from a center of gravity of the air vehicle; wherein the second yaw direction is opposed to the first yaw direction. Also disclosed is a corresponding auxiliary yaw generating system.

Abstract: A hybrid transonic-subsonic airfoil is provided that combines subsonic and transonic features for achieving simultaneously acceptable aerodynamic characteristics at low subsonic and high transonic Mach numbers.

Abstract: An aircraft arrangement for Mini or Micro UAV comprising a fore wing (14) and an aft wing (12) in tandem closed-coupled arrangement. The aft wing (12) has side panels (18) and control surfaces (19), and tapered planform with positive sweep, while the fore wing (14) has non-positive trailing edge sweep. The fore wing (14) and the aft wing (12) are disposed at different height, and the aircraft arrangement has no other wings or tail arrangements.

Abstract: The invention relates to an aircraft, and a method for operating an aircraft, the aircraft having a longitudinally unstable configuration and swept wings, the swept wings being based on aerofoils having a leading edge and configured for preventing attachment line transition in conditions of laminar flow over the swept wing for at least a predetermined first range of lift coefficients at a second range of Reynolds numbers. The invention also relates to an aerofoil, and to a method for providing an aerofoil, the airfoil being configured for a thick-sectioned subsonic/transonic swept wing, having a curved leading edge, a trailing edge, a thickness dimension and a chord dimension, wherein the leading edge comprises a leading edge curvature associated with a leading edge radius that is configured for preventing attachment line transition in conditions of laminar flow over the swept wing.

Abstract: A slotted aerofoil configuration is provided in which the leading element thereof is contoured to provide mild stall characteristics. A wing based partially or fully on such an aerofoil, an air vehicle including such wings, and a method for designing an aerofoil are also disclosed.

Abstract: A wing for an aircraft is provided, including at least a first wing portion configured for providing high-lift mild stall characteristics at least at Reynolds numbers in the range between about 0.3*106 and about 2.0*106, and at least a second wing portion comprising a substantially permanently slotted aerofoil arrangement. Also provided are an air vehicle including such wings, a method for operating an aircraft, and a method for designing an aircraft wing.

Abstract: A two element aerofoil, and wing element based thereon, is provided, including a primary aerofoil element including a leading edge of the aerofoil and a secondary aerofoil element including a trailing edge of the aerofoil. A gap is provided between the primary aerofoil element and the secondary aerofoil element. The primary aerofoil element has at least one of a profile, orientation and location with respect to a respective at least one of a profile, orientation and location of the secondary aerofoil element that is configured for minimizing or avoiding accretion of contaminant on the secondary aerofoil element when subjected to an airflow that includes the contaminant, at least at one design set of conditions. A method for designing a two element aerofoil is also provided.

Abstract: Aerofoil accessories are provided, configured for selective attachment to a wing element, the wing element having an outer facing aerofoil surface and being based on at least one datum aerofoil section. Each accessory provides a modified geometric profile to a datum profile of the at least one aerofoil section when attached to the wing element. The accessories are each configured for having a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element is airborne with the respective accessory attached to the wing element. The modified geometric profile is such as to provide said wing element with the accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent the accessory. A kit is also provided for enhancing performance of a wing element in off-design conditions. A method is also provided for enhancing performance of a wing element in adverse conditions.

Abstract: The invention relates to an aircraft, and a method for operating an aircraft, the aircraft having a longitudinally unstable configuration and swept wings, the swept wings being based on aerofoils having a leading edge and configured for preventing attachment line transition in conditions of laminar flow over the swept wing for at least a predetermined first range of lift coefficients at a second range of Reynolds numbers. The invention also relates to an aerofoil, and to a method for providing an aerofoil, the airfoil being configured for a thick-sectioned subsonic/transonic swept wing, having a curved leading edge, a trailing edge, a thickness dimension and a chord dimension, wherein the leading edge comprises a leading edge curvature associated with a leading edge radius that is configured for preventing attachment line transition in conditions of laminar flow over the swept wing.

Abstract: A wing for an aircraft is provided, including at least a first wing portion configured for providing high-lift mild stall characteristics at least at Reynolds numbers in the range between about 0.3*106 and about 2.0*106, and at least a second wing portion comprising a substantially permanently slotted aerofoil arrangement. Also provided are an air vehicle including such wings, a method for operating an aircraft, and a method for designing an aircraft wing.

Abstract: A slotted aerofoil configuration is provided in which the leading element thereof is contoured to provide mild stall characteristics.