Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
1999-09-22
2001-06-05
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S139000
Reexamination Certificate
active
06241195
ABSTRACT:
TECHNICAL FIELD
This invention is related generally to aircraft wing structures, and in particular to a flexible sail that can be selectively extended to enable an aircraft to takeoff and land at reduced air speeds.
BACKGROUND ART
Short takeoff and landing, abbreviated STOL, refers to the ability of an aircraft to clear a 50-foot (15 meter) obstacle within 1500 feet (450 meters) of commencing takeoff, or in landing, to stop within 1500 feet after passing over a 50-foot obstacle. It is desirable under certain conditions for fixed-wing aircraft to be able to perform STOL operations at relatively low air speeds, for example twenty-thirty knots (37-55 kilometers/hr) indicated air speed. This requires either a high ratio of power to aircraft weight or high ratio of wing area to aircraft weight. Slats and flaps are the primary means for increasing the wing area of conventional aircraft. Typically, slats and flaps change the camber as well as increase the effective lift area of the wing. Increased wing area and changes in camber generally yield a greater lifting force on the wing, thereby reducing stall speed.
The benefits of reduced stall speed flight include short takeoff and landing roll. Additionally, reduced stall speed flight can prevent inadvertent stalls and permit high angles of climb, which may be useful at noise sensitive airports or at airports where obstacles encroach the glide path. Landing at slower speeds also decreases the wear and tear on brakes, landing gear assemblies, wing struts and tires.
There are some significant limitations on the use of slats and flaps. Slats and flaps should be retracted during cruising flight to reduce drag. Slats and flaps are complex flight control devices which may substantially increase the weight of an aircraft. Typically, the manufacturing and operating costs of aircraft utilizing slats and flaps are increased by the complexity of developing, manufacturing and maintaining the slat and/or flap assemblies. Also, retrofit installation on aircraft not originally equipped with slats and flaps involves major structural modifications.
Another method used to enable aircraft to takeoff and land at reduced stall speeds is through the development of lift-optimized wing designs. Increasing the camber of the airfoil of a wing can result in increased lift and decreased stall speeds. However, by using too much camber, drag penalties can become excessive for an aircraft operating at cruising speed. The same flight characteristics of the wing are present throughout all phases of flight. Consequently, conventional airfoil designs are optimized for all phases of flight (takeoff, cruise and landing) and must necessarily result in a compromise of various design factors which provide reasonable performance throughout all flight regimes. Conventional methods (installing slats/flaps and changing the airfoil) have been only marginally successful in reducing stall speed.
Instead of increasing the wing surface area, aircraft manufacturers sometimes increase the power available to an aircraft to reduce the takeoff roll. However, there are some limitations on the use of more powerful engines. First, an improved engine can be prohibitively expensive. Installation may not be feasible because of airframe limitations, maintenance can be more extensive, weight and balance factors may be affected and fuel consumption may be drastically increased. Moreover, the increased noise generated by a more powerful engine may not be tolerated at a noise sensitive airport.
Consequently, there is a continuing interest in providing an auxiliary wing structure that can be selectively deployed for enabling fixed wing aircraft to fly without stalling at slower speeds during takeoff and approach to landing, and that can be retracted during other phases of flight. This would permit the aircraft wings to be optimized for high speed cruise, with the auxiliary wing structure being deployed only during takeoff and landing, and retracted during high speed cruising flight.
DISCLOSURE OF THE INVENTION
In accordance with the present invention, a retractable airfoil assembly for augmenting the wing surface area of an aircraft includes a pair of flexible sails coupled to a rotatable boom. Additionally, the retractable airfoil assembly includes means for furling and unfurling the flexible sails on the rotatable boom. The flexible sails are guided in tracks extending along a leading edge or a trailing edge of the main wing during deployment and recovery. The retractable airfoil assembly also includes a guide cable for extending and retracting the sails laterally as the sails are unfurled (extended) and furled (retracted), respectively.
According to one embodiment of the present invention, the retractable airfoil assembly is coupled to the leading edge structure of the main wings of an aircraft. This assembly includes a pair of flexible sails, a furling boom for unwrapping (extending) and wrapping (retracting) the flexible sails and a pair of tracks for guiding the flexible sails along a leading edge structure of the wings during extension and retraction. The retractable airfoil assembly also includes a drive cable attached to the flexible sails for extending and retracting the sails along the leading edge tracks, and for maintaining tension in the sails while they are deployed.
According to another embodiment of the invention, the retractable sail assembly includes trailing edge tracks for guiding the flexible sails along a trailing edge structure of the wings. The flexible sails are extended (unfurled) and retracted (furled) by clockwise and counterclockwise rotation of the furling boom, respectively. A guide cable maintains tension in the sails as the sails are deployed and recovered.
According to yet another aspect of the present invention, the furling boom includes a drum mounted for rotation on a static support tube that is rigidly attached to the aircraft. A pair of flexible sails are attached to the rotatable drum and are unfurled (extended) from the drum or furled (retracted) around the drum as the drum is rotated clockwise or counterclockwise about the static support tube.
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patent: 1 272133 (1968-07-01), None
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Barefoot Galen L.
Griggs Dennis T.
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