Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Patent
1984-01-16
1987-04-07
Blix, Trygve M.
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
B64C 314
Patent
active
046554122
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an airfoil and more particularly, to the leading edge of an airfoil having high lift capability.
BACKGROUND ART
In the design of an airfoil forming an aircraft wing, particularly, the leading edge thereof on a fixed wing or in the form of a leading edge comprising a movable slat on a fixed wing, within a required parameter or envelope, it is attempted to improve the lift capability, reduce the pitch-up, reduce the cruise drag, and improve the buffet in comparison with the prior art. Typically, aircraft wings have been shaped to provide a required lift with least possible cruise drag. The shape of the wing is generally comprised between the aerodynamic shape that is most efficient for aircraft cruising speed and the aerodynamic shape required for low air speeds such as encountered during takeoff and landing. It is also known that reduction in pitch-up generally penalizes cruise drag performance.
A search of the patent literature discloses the following patents, International Application, and article, which are of general interest: 81/02557, International Pub. Date Sept. 17, 1981 Aeronautical Journal, March 1979
DISCLOSURE OF THE INVENTION
The present invention provides for improved low-speed handling and high-speed performance in slats or in a fixed leading edge airfoil on airplane wings or in stabilizers, for example.
According to the present invention, an airfoil was developed to increase lift capability, particularly at Mach numbers from 0.72 to 0.84, and improve the load balance of the wing at high angles of attack.
The unique geometric configuration, according to the invention, also was found to substantially reduce pitch-up without penalizing cruise drag performance.
Generally, the airfoil may be described as having multiple local curvature minima on the upper or negative pressure surface. The airfoil according to the invention when used as a stabilizer would generally have the geometric configuration on the lower surface, an exception being the case of an uncambered stabilizer for which both upper and lower surfaces would be identical.
The airfoil has curves including camber divided into first, second, and third curve portions or three regions, I, II, and III. Region I has a starting point aft and adjacent the leading edge and encompasses the airfoil stagnation point. It has a high curvature around the leading edge and the curvature decreases aft measured along the chord from the leading edge on an upper or negative pressure side of the airfoil to a first local minimum value of less than 3 for K times C at the end of region I, where C is the length of chord and K is the reciprocal of the local radius of curvature. Region I is within 10% of the chord length and region II starts at the aft end of region I within 10% of the chord length. The curvature in region II first increases from the first minimum and then decreases to a second local minimum within 40% of the chord length.
The starting point of region I is below the chord, lower than the ordinate value of the leading edge, and is aft of the leading edge by not more than 3% of chord length measured along the chord. The high curvature at the leading edge has a value for K times C equal to or greater than 35 but less than or equal to 120. In region II the maximum value for K times C is greater than 1 but less than 6.
The second local minimum is at the end of region II and the value of K times C initially increases from the second local minimum and after the increase, may remain constant to the trailing end of the airfoil or may have one or more greater points relative to the first and second minimums.
Within the required parameter the airfoil, according to the invention, is considered to be the first to provide pitch-up improvement without penalizing cruise drag performance. It provides a substantially greater lift and improved buffet to permit the aircraft to carry substantially higher weights.
Further advantages of the invention may be brought in the following part of the specification wherein small de
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Blix Trygve M.
Corl Rodney
Heberer Eugene O.
The Boeing Company
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