US3604352A

US3604352A - Spherical free fall apparatus

Info

Publication number: US3604352A
Application number: US869479A
Authority: US
Inventors: Thomas E Bench
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1969-10-27
Filing date: 1969-10-27
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14

Abstract

A spherical free fall apparatus is disclosed. The free fall apparatus has airfoils thereon to cause spin of the apparatus about an axis of rotation, the spin resulting in the apparatus having a glide path, and one or more flexible means attached at the axis of rotation for the purpose of causing the free fall apparatus to precess in its glide path thereby making it possible to control the flight characteristics and ground impact points of the free fall apparatus.

Description

United States Patent Inventor Thoma E. Bend! Richmond, lnd.

Appl. No. 869 479 Filed Oct. 27, 1969 Patented Sept. 14, l97l Assignee Avco Cor-pardon Richmond. Ind.

SPHERICAL FREE FALL APPARATUS 7 Claims, 5 Driving Figs.

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[56] References Cited UNITED STATES PATENTS 2.526.45l I0/l950 Bensen 244/138 A 2.9l8,235 l2/l959 Abergetal. 244/l38A 3,l 70,398 2/1965 Paulson et al 102/9 X 3,332,348 7/1967 Myersetal. .w l02/7.2X

Primary Examiner- Samuel W. Engle Attorneys-Charles M. Hogan and Eugene C. Goodale ABSTRACT: A spherical free fall apparatus is disclosed. The free fall apparatus has airfoils thereon to cause spin of the ap paratus about an axis of rotation, the spin resulting in the apparatus having a glide path. and one or more flexible means attached at the axis of rotation for the purpose of causing the free fall apparatus to precess in its glide path thereby making it possible to control the flight characteristics and ground impact points of the free fall apparatus PATENTEDSEPMIQH 3.604.352

(J0 MAGNUS LIFT AXIS OF w AXIS OF PRECESSION PRECESSION E g VELQCITY VECTOR WEIGHT E 5 VECTOR DIRECTION DIRECTION OF FLIGHT m OF FLI GHT Lu $1.1. 2L, 3 g 1:51: fifth 4 l ,4 I m II 11 .J, if LATERAL DISPERSION LATERAL DISPERSION INVENTOR.

THOMAS E. BENCH E 4 BYM'hLf/QZZ a ATTORNEYS SPHERICAL FREE FALL APPARATUS BACKGROUND OF THE INVENTION This invention relates to free fall apparatus and more particularly to free fall apparatus having flight controlling means in order to obtain uniform ground impact patterns of the free fall apparatus.

Ground impact patterns for clustered spherical autorotating free fall apparatus, such as bomblets. are often characterized by a large central void, commonly referred to as the doughnut hole ground pattern.

The trajectories of nearly all spherical autorotating bomblets are quasiballistic. Bomblets which have low aspect ratios, small lift to drag ratios, high terminal velocities (high ballistic coefficient), and large axial moments of inertia will result in quasiballistic trajectories. When this type of bomblet begins to spin up and to orient with its spin axis normal to the velocity vector, its angular momentum tends to fix this axis in some random orientation about the velocity vector and to hold it there throughput the trajectory. Therefore, the Magnus lift also tends to act in one direction throughout the trajectory, so that the bomblets in a cluster are forced outward from the means flight path and away from each other. The doughnut hole" can then be explained as a result of this outward expansion due to Magnus lift in a cluster of bomblets.

This nonunifonnity is especially undesirable for dispenser or missile delivered free fall apparatus, such as bomblets, which must hit the target with a single delivery. In addition to the doughnut hole" problem, the overall pattern size of a single cluster of bomblets is often too large, causing the impact densities to be less than optimum for the highest kill probability. While these problems have been partially solved in the past by overlapping the impact patterns of two or more clusters; this solution has not been optimum for all delivery systems. These is a growing need for a method or technique of controlling Magnus rotor flight characteristics in order to control pattern size and also achieve more uniform random densities. With such a technique, bomblet impact patterns could more easily be optimized for a given delivery system and/or target requirement.

It has been found that if Magnus lift does not act in one direction throughout the trajectory, but is caused to rotate or precess, the quasiballistic bomblet would spiral in its flight path. As a result, impact patterns would be reduced in size and the "doughnut hole" would become small or even nonexistent. Precession is defined as the gyroscopic reaction to a couple or moment which is applied normal to the spin axis and in a plane containing the velocity vector and the center of gravity.

Accordingly, it is an object of this invention to provide a free fall apparatus such that the glide path of a plurality of the free fall apparatus may be controlled so as to avoid the doughnut hole ground impact pattern.

Another object of this invention is to provide a means to orient the free fall apparatus to increase the ease of transition from random orientation to the spin or glide orientation.

A further object is to provide a free fall apparatus having means capable of providing precession rates which will reduce ground pattern sizes and eliminate the doughnut hole."

SUMMARY OF THE INVENTION This invention provides an improved free fall apparatus having means attached thereto providing a precession of the apparatus in its glide path. The free fall apparatus has a plurality of airfoil elements disposed about the periphery of its housing to induce spin of the apparatus about a spin axis or axis of rotation. Means are attached to the housing at one end of the axis of rotation to provide an aerodynamic drag which results in the procession of the apparatus.

Other details of this invention will become apparent as the following description of the exemplary embodiment hereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show a present exemplary embodiment of this invention in which:

FIG. 1 is a perspective view illustrating one exemplary embodiment of this invention;

FIG. 2 is a schematic elevation view of a free body diagram;

FIG. 3 is a schematic front view of a free body diagram;

FIG. 4 is a simulated view illustrating an example of the doughnut hole ground impact pattern; and

FIG. 5 is a simulated view illustrating the uniform ground impact pattern of the present invention. 5

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT As seen in the free body diagram of FIG. 2, when a stable free fall body spins or autorotates it generates Magnus lih and glides at an angle 8 from the vertical where 6 arctan Lift/Drag) The trajectory or flight path of an autorotating body or autorotor which is symmetrical, both externally and internally, i.e., the center of gravity coincides with the centroid, will lie in a two-dimensional plane. The simulated view of a doughnut hole" ground impact pattern which results from free falling bodies or bomblets under these conditions is shown in FIG. 4. It can be seen from FIG. 4 that there is a free area of nonimpact in the center of the impact area such that the overall pat tern does resemble a doughnut and doughnut hole.

However, if the autorotor is not symmetrical, it will tend to turn or spiral in its guide path. The spiral-glide mode of flight for an autorotor is often a desirable quality, and may be used to control flight characteristics and ground impact patterns.

Reference is now made to FIG. 1 of the drawings which illustrates an exemplary embodiment of an improved free fall apparatus or bomblet which is designated generally by the reference numeral I0. The free fall apparatus or bomblet 10 has a housing 12 substantially spherical in shape. Disposed about the periphery of the housing 12 are a plurality of substantially Vshaped airfoils, driving vanes or flutes I4 which produce a torque about the center of gravity when the apparatus I0 falls through the air. Because of the airfoils 14, the apparatus 10 has the inherent ability to spin itself and is thus said to autorotate. The apparatus 10 will spin itself about an axis of rotation or spin axis generally designated as 16 in FIG. 3. It may be seen that the points of the V of the airfoils all lie in a common plane about the periphery of the housing perpendicular to the axis of rotation and the center of gravity 18. The airfoils increase the ability of the apparatus 10 to spin itself about the axis of rotation.

To provide the aerodynamic drag necessary to cause the precession of the free fall apparatus I0, a ribbon 20 is mounted to the housing 12 on the axis 16. The ribbon 20 may be any flexible material, either singular or a plurality thereof, which will trail the body and remain parallel to the velocity vector. The ribbon may be fixed to the body or allowed to swivel with respect to the body and is attached at one end of the axis of rotation.

As seen in FIG. 1, any suitable attaching means such as a bolt 22 is mounted to the housing 12 on the axis of rotation 16. The ribbon 20 is swivelly attached thereto by means of a slipring or the like 24.

The ribbon 20 applies an unbalanced aerodynamic drag force to the apparatus 10 which in turn produces a moment about the center of gravity in a plane parallel to the velocity vector. Since the apparatus 10 is spinning, there is a gyroscopic reaction to the applied moment which causes the body to turn or precess in a plane to the velocity vector (see FIGS. 2 and 3). In free flight, the precession causes a spiral-glide trajectory.

The rate of precession, I =30M/1r!,,w where M=dD/2= moment applied by the offset ribbon d= diameter of the body D= drag produced by the ribbon l,,= polar moment of inertia 0; spin rate of the body, rpm.

The precession rate can be changed by simply changing the unbalanced drag force, which is a function of ribbon size, ribbon material, and the number of ribbons. However. there is an upper limit to the amount of drag which any given spherical autorotor can withstand and still maintain dynamic stability.

It has been found that the aerodynamic drag generated by the ribbons 20 provides an additional advantage in the initial stages of free fall. The ribbons 20 tend to trail and stabilize the free fall apparatus end on into the wind, or with the spin axis or axis of rotation 16 aligned with the velocity vector. The apparatus 10 makes the transition from the end on condition to the glide orientation condition with the spin axis perpendicular to the velocity vector very quickly, i.e., on the order of l to 2 seconds. The random falling of apparatus such as 10, without ribbons attached thereto, often take considerably longer to orient and assume the glide condition. Thus, in the case of bomblcts, the attachment of drag means such as ribbons 20 thereto improves the ability of the bomblets to spin arm and would reduce the overall arming time of a cluster of such bomblets. in addition, dud rates would be reduced.

If a large ground pattern is required such as the one shown in FIG. 4, but with a uniform random distribution, it would be necessary to fill in the doughnut hole" area with bomblets which are made to spiral. Therefore, the payload would be mixed, having some bomblets with and some without ribbons. However, the bomblets with ribbons have slightly higher drag and would fall short as illustrated by a comparison of ranges in FIGS. 4 and 5. In this case, only about half of the "doughnut hole" is filled. This could be greatly improved if the bomblets were released at high dive angles. The complete resolution of this problem involves the ability to ballistically match the different bomblets of two different ground patterns so that one pattern exactly fills the doughnut hole of the other. It is thus necessary to use two different aerodynamic configurations, such that the configuration without ribbons would have slightly more drag than the configuration that used ribbons. Then with ribbons added, the second configuration could be made to ballistically match the first and effectively fill in the void or doughnut hole" to provide a maximum ground pattern with a uniform random distribution.

Thus, it is seen that a free fall body such as a spherical autorotor will spiral or precess in its glide path if a ribbon or the like is attached at either end of the axis of rotation so as to produce an aerodynamic drag thereto. More than one ribbon may be used, the ribbons may be different sizes, and they may be made of any flexible material which will trail the body and remain parallel to the velocity vector Comparable precession rates have been achieved with the ribbons either fixed firmly to the body or allowed to swivel with respect to the body. By use of the aerodynamic drag imposed by the attachment of the flexible ribbon to the free fall apparatus, the flight characteristics and ground impact points of the self-dispersing apparatus are more easily controlled.

While a present exemplary embodiment of this invention has been illustrated and described it will be recognized that this invention may be otherwise variously embodied and practiced by those skilled in the art.

What is claimed is:

1. An autorotor having a spiral guide path comprising:

an autorotor having a substantially spherical shape;

a plurality of airfoils disposed about the periphery of said autorotor which produce torque about the center of gravity of said autorotor when said autorotor falls through the air causing said autorotor to spin itself about an axis of rotation;

means attachable to said autorotor at the axis of rotation to provide an unbalanced aerodynamic drag force to said autorotor wherein said autorotor will spiral in its glide path.

2. An autorotor as set forth in claim 1 in which said means comprises a flexible material which trail the autorotor.

3. An autorotor as set forth in claim 2 in which said flexible material is attached directly to the outer surface of said au torotor on the axis of rotation.

4. An autorotor as set forth in claim 2 further comprising attachment means secured to said autorotor at the axis of rotation and extending axially outward therefrom;

rotatable means mounted on said attachment means; and

said flexible material secured to said rotatable means wherein said rotatable means will spin about the attachment means on the rotation.

5. An autorotor as set forth in claim 2 in which said flexible material further comprises a plurality of flexible ribbons.

6. An autorotor as set forth in claim 1 in which said airfoil further comprises substantially V-shaped vanes in which the V point of said vane lies in a plane perpendicular to the axis of rotation thereby enhancing the ability of the autorotor to spin itself about the axis of rotation.

7. In a free fall apparatus adapted for release from a cluster assembly of a plurality of such apparatus after dispersal from an apparatus container, the improvement comprising:

a housing having a spherical outer surface symmetrical about the center of gravity and the center of gravity coinciding with the axis of rotation of the apparatus;

a plurality of airfoil elements disposed about the periphery of said housing and disposed substantially parallel to the axis of rotation to produce a torque about the center of gravity of the housing when falling through the air causing the housing to spin itself wherein Magnus lift is generated causing said housing to glide in a velocity vector at an angle from the vertical; and

means attached to said housing at the axis of rotation to provide an unbalanced aerodynamic drag force to the housing during free fall to produce a minimum about the center of gravity in a plane parallel to the velocity vector thereby causing said apparatus to precess in a plane n0rmal to the velocity vector.

Claims

1. An autorotor having a spiral guide path comprising: an autorotor having a substantially spherical shape; a plurality of airfoils disposed about the periphery of said autorotor which produce torque about the center of gravity of said autorotor when said autorotor falls through the air causing said autorotor to spin itself about an axis of rotation; means attachable to said autorotor at the axis of rotation to provide an unbalanced aerodynamic drag force to said autorotor wherein said autorotor will spiral in its glide path.

3. An autorotor as set forth in claim 2 in which said flexible material is attached directly to the outer surface of said autorotor on the axis of rotation.

4. An autorotor as set forth in claim 2 further comprising attachment means secured to said autorotor at the axis of rotation and extending axially outward therefrom; rotatable means mounted on said attachment means; and said flexible material secured to said rotatable means wherein said rotatable means will spin about the attachment means on the rotation.

7. In a free fall apparatus adapted for release from a cluster assembly of a plurality of such apparatus after dispersal from an apparatus container, the improvement comprising: a housing having a spherical outer surface symmetrical about the center of gravity and the center of gravity coinciding with the axis of rotation of the apparatus; a plurality of airfoil elements disposed about the periphery of said housing and disposed substantially parallel to the axis of rotation to produce a torque about the center of gravity of the housing when falling through the air causing the housing to spin itself wherein Magnus lift is generated causing said housing to glide in a velocity vector at an angle from the vertical; and means attached to said housing at the axis of rotation to provide an unbalanced aerodynamic drag force to the housing during free fall to produce a minimum about the center of gravity in a plane parallel to the velocity vector thereby causing said apparatus to precess in a plane normal to the velocity vector.