Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Patent
1989-01-12
1990-04-03
Barefoot, Galen
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
244200, 416235, B64C 2306
Patent
active
049133810
DESCRIPTION:
BRIEF SUMMARY
This invention relates to aerodynamic components having leading edge devices for the improvement of performance at subsonic airspeeds.
The term "aerodynamic component" is used herein to encompass structures having an aerofoil section and significant span. This term is intended to include aircraft wings, fins, tailplanes, canards, engine components such as turbine and compressor blades, propeller blades, helicopter rotor blades, and similar items.
Aerodynamic components such as aircraft wings are subject to flow detachment at high angles of attack. Severe flow detachment causes loss of lift and consequent stall. In many aerodynamic components such as the relatively thin wings found on many modern civil and military aircraft the flow detachment originates at the leading edge of the aerofoil section and expands both rearwardly and in a spanwise direction as the angle of attack is increased. This invention is concerned with inhibiting the growth of leading edge flow detachment on such aerodynamic components. The invention will not be effective in aerodynamic components for which flow detachment originates at the trailing edge.
It is known that in aircraft having wings of conventional rearward sweep that flow detachment can originate at the tip of the wing at its leading edge and can progress both inwardly and rearwardly with respect to the wing as the angle of attack is increased. The flow detachment causes undesirable wing movement known as buffeting and severe detachment leads to stall. There are already a number of different wing modifications which have been introduced to either delay the onset of flow detachment or to inhibit the spanwise growth of the area of detached flow to give improved performance at higher angles of attack. Known devices include leading edge saw tooths notches and fences and upper surface vortilons. Such known devices have undesirable side effects, particularly at higher speeds eg supersonic speeds, such as increased buffet excitation and considerable drag penalty.
It is an object of this invention to offer a modified construction for aerodynamic components which enables the growth of flow separation originating from the leading edge to be inhibited with much reduced side effects. The invention is especially directed to improving the subsonic performance of wings designed for supersonic flight.
This invention is an aerodynamic component having an aerofoil section and significant span, comprising on its expansion surface at least one groove having a width at opening in the range 0.05-1.0 percent of that span, extending rearwardly from the leading edge of the aerofoil section, and having a length in the range of 1 to 20 percent of the local chord length of the aerofoil section. The above mentioned width range is given with respect to the span of a single component. For an aircraft this is half the total wing span--ignoring fuselage thickness.
Preferably the aerodynamic component includes an array of at least two of said grooves mutually spaced apart along the span.
The grooves are believed to function as vortex generators, vortices being formed by airflow across the groove. In a swept wing design there may be sufficient naturally occurring spanwise flow to generate the desired cross-flow with grooves extending substantially along the local chord of the wing. In an upswept wing design or a design using forward sweep then the naturally occuring spanwise flow might not be sufficient to create the required vortices. For such designs the grooves may be inclined to the local chord in a toe-in or toe-out configuration as best enhances the vortex formation. Each groove is effective in inhibiting flow detachment in the region within the vortex wake of the groove providing that the groove itself remains in the region of attached flow. Consequently in a swept wing design in which flow detachment normally commences at the wing tip leading edge and extends inboard and rearwardly with increased angle of attack, a groove serves to inhibit growth of the zone of detached flow outboard of that groove u
REFERENCES:
patent: 978677 (1910-12-01), Taylor
patent: 2426334 (1947-08-01), Banning, Jr.
patent: 2800291 (1957-07-01), Stephens
patent: 3463418 (1969-08-01), Miksch
patent: 3578264 (1971-05-01), Kuethe
patent: 3741285 (1973-06-01), Kuethe
patent: 3776363 (1973-12-01), Kuethe
UK Search Report.
Mechanical Engineering, vol. 103, Mar. 1981, (New York, U.S.), "Grooves Reduce Aircraft Drag", p. 71.
Barefoot Galen
The Secretary of State for Defence in her Britannic Majesty's Go
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