Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2000-04-05
2001-07-17
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S199100, C244S039000, C244S123800, C244S017110
Reexamination Certificate
active
06260809
ABSTRACT:
TECHNICAL FIELD
This invention relates to wings, and more particularly to rotary-wing blade tips for aircraft. More particularly still, the invention relates to an improved rotary-wing blade tip for noise reduction.
BACKGROUND ART
It is well known that the vortex formed at the tip of aircraft wings and blades moving relatively through the air may give rise to some undesirable resulting effects. One such effect is the resultant increase in drag on the wing caused by the tip vortex. Particular attention has been paid to this effect with respect to the wing surfaces of fixed-wing aircraft, and numerous wing tip designs have been proposed or used to minimize that vortex-induced drag penalty in such aircraft. One such design is described in U.S. Pat. No. 5,102,068 (hereinafter '068) to Gratzer for Spiroid-Tipped Wing.
In that '068 patent, a spiroidal tip device of particular geometry and orientation, depicted in Prior Art
FIGS. 1A-1C
, is used principally to reduce induced drag. A typical wing end portion
1
has a spiroid
2
attached thereto. The spiroid
2
joins the wing at a sweep angle &Dgr;, measured relative to the wing tip chord line
4
and included angle &phgr;, measured relative to the projected wing plane
3
. The subscripts F and A are used to designate the forward and aft ends respectively. The spiroid surface cross sections are typical airfoil sections
5
, shown inset in FIG.
1
A. The spiroid chord, which is a function of distance along a spiroidal generator
6
, decreases approximately linearly from slightly more than half the wing tip chord at its forward end to about 0.3 of the wing tip chord at the spiroid midpoint; thereafter it increases approximately linearly to about half the wing tip chord at its aft end.
Another undesirable effect of such tip vortices is the noise, typically audible, created when the vortex interacts with an object, such as another trailing blade or the body and empennage structures of an aircraft. This phenomenon is known as blade vortex interaction, or simply, “BVI”. The resulting noise may be particularly objectionable with respect to the operation of rotorcraft, such as helicopters, tilt-rotors, and other rotary-wing aircraft, especially during low speed descent to landing and maneuvers. It is this latter effect (i.e.,BVI) that is to be addressed by the present invention.
While the aforementioned '068 Patent also suggests applicability of its spiroid-tipped wing to reduce noise and that it may be used with helicopters, its geometry and orientation are relatively complex and not well suited for use under the high centrifugal loadings imposed by rotary-wing aircraft. Indeed, the spiroid-tipped wing of that patent discloses only an arrangement that is highly asymmetrical to the loadings normally occasioned at the tip of a rotary-wing blade, as noted by the placement of spiroid
2
entirely above the extended plane
3
of wing
1
. Moreover, its geometry is sufficiently varied over the extent of the spiroid as to make it difficult to manufacture.
It is thus an object of the present invention to provide an improved rotary-wing blade tip that reduces blade-tip vortex energy intensity to thereby reduce noise resulting from subsequent vortex interactions. It is a further object of the invention to provide such an improved rotary-wing blade tip in a manner that minimizes additional loading and stresses on the rotary-wing blade during operation.
DISCLOSURE OF INVENTION
The present invention is for an improved aircraft rotor having a plurality of rotary-wing blades for rotation in a direction about a common rotor axis. Each of the rotary-wing blades includes a tip portion radially outward from the rotor axis, which tip portion is improved by the inclusion of an ovate loop tip at its radially outer end. Each ovate loop tip has an ovate geometry transverse to the direction of blade rotation and is substantially symmetric with respect to a plane defined substantially by the chord of the tip portion of the rotary-wing blade. The ovate loop tip structure reduces substantially the intensity of blade tip vortices, thereby also reducing the noise otherwise produced by blade vortex interference. Moreover, the geometry and positioning of the ovate loop tip minimize additional loading of the respective rotary-wing blades.
The loop forming the ovate loop tip comprises upper and lower halves that are substantially coextensive and coincident with each other in the direction of rotor rotation. Each of the loop halves has a root portion, and the respective root portions of the upper and lower halves are attached to the rotary-wing tip portion. The upper and lower halves of the ovate loop diverge at an angle &agr; from their attachment at their respective roots with the rotary-wing tip portion, that angle &agr; being less than 90°, typically in the range of 35° to 65°.
The leading edge of each ovate loop tip is substantially a linear continuum of the leading edge of the rotary-wing tip portion adjacent thereto, both of which may be rearwardly swept relative to the direction of rotor rotation. The ovate loop tip has a geometry in the form of airfoil sections, with fore to aft thickness in the chordal direction. In the illustrated embodiment, the thickness is substantially constant over the entire upper and lower halves of the ovate loop tip, however variations may occur as required to satisfy the objects of the invention. The ovate loop tip also is provided with twist, which may be constant or may vary around the loop commensurate with good design practice.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings.
REFERENCES:
patent: 994968 (1911-06-01), Barbaudy
patent: 2576981 (1951-12-01), Vogt
patent: 2805830 (1957-09-01), von Zborowski
patent: 3270988 (1966-09-01), Cone, Jr.
patent: 3974986 (1976-08-01), Johnstone
patent: 4108403 (1978-08-01), Finch
patent: 4975022 (1990-12-01), Perry
patent: 5102068 (1992-04-01), Gratzer
patent: 5137427 (1992-08-01), Shenoy
patent: 5297764 (1994-03-01), Haney
patent: 5785282 (1998-07-01), Wake et al.
patent: 6171056 (2001-01-01), Lorber
patent: 418656 (1910-12-01), None
patent: 726674 (1932-06-01), None
J. Schneider, “Can You Name It?” photograph, VERTIFLITE, vol. 44, No. 2, Spring 1998, p. 51.
P. J. Fardink, response to “Can You Name It?” photograph query, VERTIFLITE, vol. 44, No. 3, Summer 1998, p. 6.
Egolf T. Alan
Wake Brian E.
Eldred J. Woodrow
United Technologies Corporation
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