Aeronautics and astronautics – Missile stabilization or trajectory control – Externally mounted stabilizing appendage
Reexamination Certificate
1997-10-08
2001-10-02
Tudor, Harold J. (Department: 3641)
Aeronautics and astronautics
Missile stabilization or trajectory control
Externally mounted stabilizing appendage
C244S003100, C244S130000, C102S385000, C102S490000
Reexamination Certificate
active
06297486
ABSTRACT:
BACKGROUND OF THE INVENTION
A drag force acts on an object which moves in a fluid environment such as air or water. This drag force includes several specific drag forces wherein the main one is known as a pressure drag force. The pressure drag force is caused by a net pressure force acting on the object. The rear end contribution to the pressure drag is called “base drag”. Flow separation at the base of the moving object creates a vortex system and reduces base pressure thus increasing drag. This problem exists for truncated objects, which have blunt bases, such as a box, a cylinder and the like.
Reference is now made to
FIG. 1A
which is a schematic illustration of a device for reducing drag which is known in the art (Frey, D. “
Guide Vores” Foschung Ing Wessen
, 1933 and Hoemer, S. F. “
Fluid Dynamic Drag
”, 1958 p. 3-27). One of the ways known in the art for reducing the base vortex strength in two-dimensional objects such as high aspect ratio wings, is by utilizing winglets near the base of the wing or behind it. wing
10
includes four winglets
12
,
14
,
16
and
18
, which reduce the base drag by depressing the ascilatory vortex shedding from the base.
The asymmetric, ascilatory vortex shedding which greatly increases the base drag in a 2 dimensional configuration does not exist in three dimensional bodies.
Reference is now made to
FIG. 1B
which is a schematic illustration of a device, known in the art (Maull, D. J. “
Mechanisms of Two and Three Dimensional Base Drag
”, Plenum Press, 1978), which was tested for aerodynamic drag reduction. A three dimensional blunt object
20
, which in the present example is a truck, includes two rear side flow deflectors
22
and
24
and a rear top deflector
26
. This configuration has proved to be inefficient in reducing the base drag and has even shown slight increases in the drag force, as compared to the baseline configuration of a truck without such deflectors.
Another device aiming at base drag reduction on blunt-based trailers is described in U. S. Pat. No. 5,348,366 (Baker and Levitt, 1994). It is shown in
FIG. 3
(of Baker). The amount of drag reduction achieved by deploying the device shown in
FIG. 3
is 15%. The mechanism of drag reduction is similar to that in boattailing a blunt axi-symmetric object and thus increasing its base pressure, as was suggested by Mair (1965).
Other devices for reducing the base drag of airborne axi-symmetric bodies use air bleed through the blunt base (U.S. Pat. No. 4,807,535 by M. Schilling and M. Reuche (1989) and U.S. Pat. No. 4,554,872 by U. Schleicher (1985)). These devices require, however, modification of the internal volume to accommodate the charge used to accommodate the base bleed jet.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide a device for reducing drag in a three dimensional object.
It is a further object of the present invention to provide a novel device for reducing drag in a three dimensional cylindrical object, which can be adapted to variable velocity in real time.
In accordance with the present invention there is thus provided a ringlet shaped device for reducing drag of a cylindrical rear truncated object moving in fluid, to be placed near the rear end of the object. The device includes at least one ring shaped winglet.
According to another aspect of the present invention, a selected one of the ring shaped winglets includes a plurality of partial winglets and winglet connectors, wherein each of the winglet connectors connects a predetermined pair of the partial winglets. Each winglet connector can be adapted to move the predetermined pair of the partial winglets connected thereto either to increase or decrease the distance between the elements.
Furthermore, the device may also include a ring shaped winglet, a plurality of partial winglets connected to the ring shaped winglet by a plurality of hinges, wherein the hinges enable the partial winglets to rotate along an axis tangent to the circumference of the ring which is defined by the hinges.
According to another aspect of the invention, the device further includes a controller for controlling at least one of the ring-shaped winglets according to predetermined parameters and a processor, for determining the values of each of the parameters, according to the speed of the cylindrical rear truncated object and the properties of the fluid, the processor providing the values to the controller. The predetermined parameters are selected from the group consisting of:
distance of the winglet from the cylinder shaped object;
winglet circumference;
the angle between the ring chord and the symmetry axis;
winglet profile; and
winglet chord length.
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patent: 4807535 (1989-02-01), Schilling et al.
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patent: 5295643 (1994-03-01), Ebbert et al.
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“Effectiveness of Passive Devices for Axisymmetric Base Drag Reduction at Mach 2”P.R Viswanath and S.R Patil National Aeronautical Laboratory, Bangalore,India Article :J. Spacecraft vol. 27, No. 3 p.234, Aug. 1989.
“Axisymmetric Bluff-Body Drag Reduction Through Geometrical Modification”. Floyd G. Howard and Wesley L Goodman NASA Langley Research Center, Hampton, Virginia. Article-J. Aircraft vol. 22, No. 6 p. 516, Mar. 1984.
“Passive Devices for Axisymmetric Base Drag Reduction at Transonic Speeds” P.R. Viswanath National Aeronautical Laboratory, Bangalore, India Article-J. Aircraft vol. 25,No. 3 p.258, Apr. 1987.
James A. Kidd, Dennis Wikoff, Charles J. Cottrell “Drag Reduction by Controlling Flow Separation Using Stepped Afterbodies”- Air Force Armament Laboratory, Eglin Air Force Base,Florida. Article - J. Aircraft vol. 27,No. 6 pp.564 Engineering Notes, Nov. 1989.
Maull, D.J. “Mechanisms of Two and Three Dimensional Base Drag”, Plenum Press, 1978.pp. 137-159.
Kapoor K. “Effect of Radial Fins on Base Drag of an Axisymmetric Body at Low Spreeds”, J. Spacecraft vol. 19, No. 1, Jan-Feb., 1982, pp. 89-92.
Mason, W.T. ; Beebe, P.S. “Truck and Bus Drag”, Aerodynamic Drag Mechanisms of Bluff Bodies and Road Vehicles, Plemum Press, 1978 pp. 45-93.
Hoerner, S.F. “Fluid Dynamic Drag”, 1965 pp. 3-27.
Rom Hanan
Weinberg Zvi
Eitan Pearl Latzer & Cohen-Zedek
Rafael - Armament Development Authority Ltd.
Tudor Harold J.
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