Aeronautics and astronautics – Aircraft control – Vertical fins
Reexamination Certificate
2000-12-11
2002-11-26
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Aircraft control
Vertical fins
C244S199100
Reexamination Certificate
active
06484968
ABSTRACT:
TECHNICAL FIELD
This invention relates to winglets adapted to reduce the induced drag created by an aircraft's wings when they create lift. More particularly, it relates to the provision of a winglet that is continuously curved from where it joins the outer end of the wing out to its outer end or tip and the curvature at least closely approximates the curvature of a conical section, viz. has elliptical, parabolic or hyperbolic curvature.
BACKGROUND OF THE INVENTION
Lifting surfaces (wings) create drag when they create lift. This drag-due-to-lift is called “induced drag.” Aerodynamic theory shows that for essentially planar wings (wings that line essentially in the x-y plane), that the induced drag is minimized if the lift on the wing is distributed elliptically along the span of the wing. That is, the lift per unit span as a function of spanwise position should vary elliptically, with the largest lift per unit span at the wing centerline, and with the lift per unit span gradually dropping in an elliptical manner as the tip is approached. This theoretical result is well known, and many aircraft wings have been constructed with elliptical wing planforms to ensure that the lift does, in fact, vary in an elliptical fashion. The British Spitfire is a classic example of an aircraft wing constructed in an elliptical shape to take advantage of this theoretical result.
The purpose and operation of “winglets” is described in “Aerodynamics, Aeronautics and Flight Mechanics”, by Barnes W. McCormick, and published 1979 by John Wiley & Sons, Inc. (pages 215-221). Known winglet constructions in the patent literature are disclosed by U.S. Patents: No. 4,017,041, granted Apr. 12, 1977 to Wilbur C. Nelson; No. 4,190,219, granted Feb. 26, 1980, to James E. Hackett; No. 4,205,810, granted Jun. 3, 1980, to Kichio K. Ishimitsu; No. 4,240,597, granted Dec. 23, 1990, to Roger R. Ellis, W. Martin Gertsen and Norman E. Conley; No. 4,245,804, granted Jan. 20, 1981, to Kichio K. Ishimitsu and Neal R. Van Devender; No. 4,714,215, granted Dec. 22, 1987, to Jeffrey A. Jupp and Peter H. Rees; No. 5,275,358, granted Jan. 4, 1994 to Mark I. Goldhammer and Karela Schippers; No. 5,348,253, granted Sep. 20, 1994 to Lewis B. Gratzer and No. 5,407,153, granted Apr. 18, 1995 to Phillip S. Kirk and Richard Whitcomb.
FIGS. 1-4
of the drawing are identical to FIGS. 1, 2, 4 and 11 in U.S. Pat. No. 5,275,358. Referring to
FIG. 1
, the aircraft (
2
) basically comprises an aircraft body (
4
), left and right wings (
6
), and a tail section (
8
). A winglet (
10
,
110
) is shown at the outer end of each wing (
6
). A coordinate system is defined for the aircraft (
2
) in the following manner. A longitudinal axis (x) is defined to extend through the center of w the aircraft body (
4
) in the fore and aft directions. Further, a vertical axis (z) is defined in the up and down directions, while a transverse axis (y) is defined in the left and right directions. The longitudinal axis (x), vertical axis (z) and transverse axis (y) are orthogonal to each other and meet at an origin located at the foremost plane of the aircraft (
2
).
Referring to
FIGS. 2 and 3
, a winglet (
16
), which is generally trapezoidal in shape, is joined to the wingtip (
12
) so that the winglet (
16
) upwardly extends from the wing (
6
). A strake is indicated by reference character (
16
a
) in FIG.
2
. The wing (
12
) (
FIG. 2
) has upper and lower wing surfaces (
18
) and (
20
), a wing leading edge (
22
), and a wing trailing edge (
24
). Similarly, the winglet (
16
) has upper and lower winglet surfaces (
26
) and (
28
), a winglet leading edge (
30
), a winglet trailing edge (
32
), and a wing/winglet intersection (
14
). Conventionally, the terms “upper” and “lower” used in reference to the winglet (
16
) generally corresponds to the “inner” and “outer” directions, respectively. This convention will be followed herein. The winglet (
16
) is swept back at an angle (&agr;) from the vertical z-axis at least equal to the sweep angle of the leading edges of the wings at the wing tip (
14
) relative to the transverse y-axis (FIG.
2
). The winglet (
16
) is also canted at a cant angle from a plane parallel to the (x) and (y) axis (FIG.
3
). Two methods of defining the curvature of the aft portions of the air foils of the wing (
12
) and winglet (
16
) are set forth in U.S. Pat. No. 5,275,358, commencing in column 4, at line 7, and continuing into column 5.
FIG. 4
in the drawing is identical to FIG. 11 in U.S. Pat. No. 5,275,358. It is prior art to the present invention and constitutes the invention of Pat. No. 5,275,358. Referring to
FIG. 4
, the tip of the wing (
6
) is designated (
112
). Point (
114
) is where the wing reference plane (
148
) intersects the winglet reference plane (
150
). The winglet (
116
) is generally trapezoidal in shape. It extends upwardly from the wing tip (
112
) and the inner section (
114
). The wing tip (
112
) has upper and lower wing surfaces (
118
and
120
), a wing leading edge (
122
) and a wing trailing edge. The winglet (
116
) has upper and lower winglet surfaces (
126
and
128
), a winglet leading edge (
130
), a winglet trailing edge and a winglet root. Generally, the wing/winglet configuration (
110
) of U.S. Pat. No. 5,275,358 (
FIG. 4
) has three primary features. Firstly, the aft portion of the upper wing and winglet surfaces (
118
and
129
) are flattened to prevent flow separation at the wing/winglet intersection (
114
). Secondly, the wing and winglet leading edges (
122
and
130
) are drooped downwardly to prevent premature shockwave development. Thirdly, the winglet (
116
) is not canted outwardly, so the wing bending moments are not substantially increased by the addition of the winglet (
116
). These primary features and certain secondary features are described in detail in U.S. Pat. No. 5,275,358.
FIG. 5
of the drawing is identical to FIG. 1B of U.S. Pat. No. 5,348,253. Referring to
FIG. 5
, what is referred to as “a blended winglet” is shown connected to a typical wing end portion (
1
). The winglet chord equals the wing tip chord at the attachment line (
3
). A transition section (
2
) is bounded by the transition line (
3
) and a chordwise line (
4
) designating the transition end of the winglet (
9
). The nearly planar outer portion of the winglet (
9
) is generally straight from the transition end (
4
) to the tip (
5
). A first feature of the
FIG. 5
wing/winglet arrangement is a continuous monotonic chord variation bounded by a leading edge curve and a trailing edge curve (
8
). These curves are tangent to the wing leading edge and trailing edge respectively at the winglet attachment line (
3
) and are also tangent to the leading edge and trailing edges respectively of the straight section (
9
) at line (
4
). The leading edge curve (
7
) is selected to provide a smooth gradual chord variation in the transition and also, to limit the leading edge sweep angle to less than about 65°. This is necessary to avoid vortex shedding from the leading edge which would comprise the surface loading and thereby increase drag. The shape of the trailing edge curve (
8
) is generally not critical but is selected to correspond to the airfoil chord and twist required to achieve optimum loading. This restriction will usually allow the wing and winglet trailing edges to lie in the same plane which is desirable functionally and esthetically.
The second feature is a continuous monotonic variation of cant angle. It is stated that the rate of curvature R must be large enough to accommodate the chord variation in the transition section and allow the practical achievement of optimum aerodynamic loading and minimum interference between wing and winglet. The radius and curvature criteria is given below in terms of a parameter, K
r
having fairly narrow limits:
R
h
=
K
R
cos
(
φ
4
2
+
π
4
)
/
cos
φ
4
;
35
<
K
R
<
.50
where,
h=winglet height measured along a normal to the wing chord plane
&phgr;
4
=cant angle of the planar
Barnard Delbert J.
Dinh T.
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