This invention relates to airfoil structures for fixed wing aircraft, and more particularly to a leading edge construction for an airfoil.
Present day state of the art commercial twin-engined aircraft use leading edge slats for controlling airflow over the fixed wings of the aircraft during takeoff, landing and cruise conditions. However, slats are heavy, expensive, cannot use common parts, and must use the high-speed (i.e., cruise) wingfoil shape in the extended, angled positions at takeoff and landing. Current production Variable Camber Kreuger (VCK) devices are two-position devices (cruise and gapped), which have excessive drag for takeoff. The VCK advantage is a more optimum aerodynamic shape. One specific area of leading edge flap design where even further improvement is desired is in the seal between the panel of the leading edge component and the airfoil, and also between the panel and bullnose of the leading edge component. Often it has been difficult to achieve an excellent seal between the panel/wing and panel/bullnose interface without the use of separate seal elements. An excellent seal formed at these areas, directly between the forward and rearward portions of the panel and the airfoil, would even further enhance the aerodynamic efficiency of the variable camber leading edge when the leading edge flap is in its takeoff and landing positions.
Still another area where even further improvement would be desirable is in the manner in which the variable camber leading edge flap is deployed from a retracted (i.e., cruise) position into either a takeoff or a landing position. Some designs of variable camber leading edge constructions, when initially moved out of their retracted positions, tend to xe2x80x9cscoopxe2x80x9d air using the undersurface of the panel forming the variable camber leading edge assembly. It would be desirable to provide a leading edge construction which does not operate to scoop air when it is initially deployed from its retracted (i.e., cruise) position into either a takeoff or a landing position.
The present invention relates to a Variable Camber Kreuger leading edge assembly for an airfoil of an aircraft. The leading edge assembly includes a variable camber panel which is hingedly secured to a bullnose. The panel/bullnose assembly is suspended from a lower surface of the airfoil by a forward suspension link and an aft suspension link operatively associated with a linkage assembly. The linkage assembly includes connections to the panel at three points along the panel. The linkage assembly is also coupled to the bullnose to cause the bullnose to be folded toward the panel when the leading edge assembly is in a cruise position.
In the cruise position the bullnose is folded toward the panel, and the panel forms a generally smooth, continuous lower surface of the airfoil. As the aft suspension link is driven rotationally by a torque shaft of an actuator, the panel rotates outwardly from the lower area of the airfoil such that a leading edge of the panel moves at a greater rate of travel than the trailing edge of the panel. During this portion of movement the bullnose also begins to unfold. The trailing edge of the panel is maintained close to a forwardmost leading edge of the airfoil to thus prevent the leading edge assembly from xe2x80x9cscoopingxe2x80x9d air during this portion of movement.
The forward and aft suspension links, together with the linkage assembly, continue to urge the panel/bullnose rotationally, with the bullnose continuing to unfold, until the panel/bullnose is in a landing position. In this position a gap exists between the trailing edge of the panel and the forwardmost leading edge of the airfoil. The bullnose is also rotated during this portion of movement so that it forms a generally smooth, continuous curvature with the panel when the panel reaches the landing position.
When the aft suspension link is rotated further it causes the linkage assembly to urge the panel/bullnose into a xe2x80x9ctake-offxe2x80x9d position. In the take-off position the trailing edge of the panel abuts the forwardmost leading edge of the airfoil to form a smooth seal therebetween. A forwardmost edge of the panel also rests over a trailing edge of the bullnose to also form a smooth seal at this interface. When in the take-off position, the aft suspension link and linkage assembly form an especially strong truss-type load path to provide a highly rigid arrangement that is not susceptible to deflection in response to the high loads experienced during take-off. The sealing action provided by the leading and trailing edges of the panel eliminate the need for separate seals at the panel/bullnose interface and the panel/airfoil interface, thus also serving to reduce the cost of the leading edge assembly.