US3509821A - Apparatus for accelerating rod-like objects - Google Patents

Description

May 5, 1970 s. A. CQLGATE'. 3,509,821

APPARATUS FOR AGGELERATING ROD-LIKE OBJECTS Filed Jan. 6, 1969 lNVENTOR .Sll'r/lhg A. Colgate AGENT United States Patent O 3,509,821 APPARATUS FOR ACCELERATING ROD-LIKE OBJECTS Stirling A. Colgate, 1201 Olive Lane, Socorro, N. Mex. 87801 Continuation-impart of application Ser. No. 620,827, Mar. 6, 1967. This application Jan. 6, 1969, Ser. No. 795,394

Int. Cl. F02k 9/06; F4211 15/26 US. Cl. 10249.3 15 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This application is a continuation-in-part of copending application Ser. No. 620,827, filed Mar. 6, 1967, now abandoned.

This invention relates to the rapid acceleration of rods or rod-like objects, such as for the penetration of a relatively dense medium.

The high explosive sh-aped-charge-jet penetration of ground, rock, concrete, or armor plate is a Well known phenomenon. It was first recognized by Charles Munroe and is known as the Munroe effect. It became renowned by its application to armor piercing shells in World War II. The principle of the hollow cavity shaped charge is that a hollow cone of metal is transformed by a planar shock wave from high explosive into a high velocity jet. The velocity gradient in the jet is large enough that the jet itself behaves almost as a liquid, the residual strength of the metal cone being too small to maintain a structural shape. Nevertheless, the proper hydrodynamic design leads to a tapered rod-like jet that can penetrate materials a distance that is variously estimated to be one to two times the length of the jet times the square root of the ratio of the jet to media density. A typical 4 inch diameter hollow iron cone is transformed into a fast-moving jet and a slower slug where the effective length of the fast-moving jet is approximately 4 inches. In many published experiments, it is demonstrated that the jet will penetrate rock whose density is A of that of the jet, toa depth approximately 2 to 4 times the length of the jet.

SUMMARY OF THE INVENTION The present invention provides apparatus for the accelerating of a rod or rod-like object of arbitrary length to the equivalent velocity of a shaped-charge jet for the purpose of, for example, penetrating or making useful holes in various media such as rock, soil, metal, etc.

One objective of the accelerating mechanism is to achieve the required high velocity uniformly over the length of the rod so that the velocity gradient over the length of the rod is small enough such that the rod integrity is maintained due to its inherent strength. With such a uniform acceleration of a rod, and with the motion in the directon of the axs of the rod, and finally wth the rod velocity high enough to simulate the penetrating characteristics of a high velocity jet, then the rod will penetrate a relatively dense medium the very large distance corresponding to 2 to 4 times its axial length. For example, a 6-foot long steel rod should penetrate rock or ground Patented May 5, 1970 to a depth of 12 to 24 feet and shorter or longer lengths proportionately. It is obvious that if a hole is penetrated to a given depth, then an accelerated rod equal to this depth should penetrate an equivalent fact-or 2 to 4 times further. The possibility of drilling exloratory holes or wells into the ground relatively cheaply is evident.

The mechanism for accelerating a rod or any other object without deforming it is, as is well known, either gun-type or the rocket mechanism of exhausting high velocity gas. The gun mechanism will not accelerate a long object without deforming it. The usual method of creating the high velocity gas for rocket acceleration is the expansion in a nozzle of high temperature gas created either by the oxidation of a fuel in a combustion chamber or the progressive burning of a solid propellant. According to conventional technology, rocket acceleration is limited to to 1,000 times gravity for the most advanced military missiles. Guns, on the other hand, reach 1x10 to 2 1O g.

In accordance with the invention, acceleration of 100,- 000 to 200,000 g. is achieved by means of either special high-pressure gas encapsulated propellants or by a volume ignition and burning of heterogeneous solid propellants. The objective of the high accelerations is to achieve the velocity of the object in an acceleration time and distance that is short enough so that, for example, a penetrating object need not be aimed with extreme accuracy at a target point. In general, this requires a stand-off distance from rest of 2 to 3 meters. The jet penetrating velocity required is roughly 2X 10 to 3 X 10 cm./sec. which gives an impact pressure (iron on iron) of 300,000 to 700,000 atmospheres (3 10 to 7X 10 dynes/cm. This pressure is great enough such that the target material is compressed and flows as a fluid out of the way of further penetrating matter, and the jet penetration becomes proportional to the square root of the intersected mass per unit area. The acceleration required to reach the velocity of 3 10 cm./sec. in a distance of 300 cm. is l.5 10 cm./ sec. or l.5 10 g. during a time 2 10 seconds.

DESCRIPTION OF THE DRAWING For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the figures of the accompanying drawing, in which:

FIG. 1 is a longitudinal cross section View of an arbitrary small length of an embodiment using a solid propellant and rocket configurations;

FIG. 2 is a transverse cross section view of another embodiment of the invention taken at lines 6-6 of FIG. 3;

FIG. 3 is a longitudinal cross section view of an arbitrary length of the embodiment of FIG. 2, which embodiment employs a gas-filled hollow tubing propellant; and

FIG. 4 is a longitudinal cross section view of an arbitrary length of another embodiment of the invention which uses a shock ignition of a volume-burning propellant.

DESCRIPTION OF EXEMPLARY EMBODIMENTS In accordance with the invention, a very large accelerating force is imparted uniformly and simultaneously along the length of a long rod so that it attains a very high velocity while advancing no more than several times its own length. As shown in FIG. 1, a rod 1 is surrounded by, and attached to, equally spaced conical rocket casings 2. The preferred axial spacing of the rocket casings 2 is one or two rod diameters. The way of attaching the casings to the rod depends upon the casing material 2, which may be aluminum, fiberglass, plastic, etc., but will usually be by welding for a metal or by gluing for a non-metal. The rod material may be aluminum or steel,

a but a nonmetal (e.g., glass fiber and plastic) may also be used. The spaces between the conical rocket casings 2 are filled with a solid propellant 3, which may be any one of several fastburning propellants, as discussed below. The half angle 4 of the conical rocket casings 2 is preferably 10 to 50 pointing backwards, the particular angle depending upon the propellant burning characteristics. The propellant 3 in all rocket spaces is ignited circumferentially on the outside simultaneously by an electrical system of igniters 5, which may be of any suitable type, many of which are well known to those skilled in the art. The rocket propellant 3 then burns from the outside radially and concentrically inward toward the rod 1. The space between the conical rocket casings serves as the nozzle for the escaping gases. The conical rocket casings 2 should stand a relatively high pressure (say 1,000 to 5,000 p.s.i.) for a short time to second) and may be partially consumed during the burning of propellant 3.

FIGS. 2 and 3 show an embodiment similar to that of FIG. 1, but with a special form of hollow gas-filled tubing 7 as the propellant. This metal tubing is shown in tubeto-tube metal contact for reasons of thermal conduction that will later become apparent. The tubing is shown wound concentrically around the rod 1 in the space between the conical rocket casings 2. A similar simultaneous ignition system 5 applies. The ratio of easing 2 and propellant 7 diameters to rod 1, diameter is determined by the desired velocity, specific impulse of the propellant, nozzle efiiciency, etc., but as will be explained later is roughly 4: 1.

The embodiment of FIG. 4 also comprises a sheet 8 of high explosive buttered by a thin plastic spacer 9 and ignited at one end by an electrical system 5. The ignition system can be at either end of the rod. The spacer 9 weakens the shock wave from the explosive sheet 8 to the degree necessary not to deform badly the conical casings 2, but sufficient to denote the oxidizer (preferably ammonium perchlorate) of the heterogeneous propellant 3. A spacer thickness of roughly A to /2 the thickness of the explosive sheet 8 is considered adequate.

In all embodiments of the invention it is to be understood that the conical rocket casing 2 and conical propellant 3 are to be repeated axially to an arbitrary length of meters to tens of meters even though the rod diameter may be small, e.g., to 3 cm., and that all rockets in the series are to be ignited substantially simultaneously with an ignition time error small compared to the burn time, which is on the order of 2 10 seconds.

The high acceleration and the restriction to stresses below the yield point of the rod material places a restriction on the length of rod that can be accelerated by one given rocket. For a high strength steel rod whose tensile strength is 140,000 p.s.i. the useful periodicity length between rockets should be less than about 8 to 10 cm. The shape of the rocket places an additional restriction in that sufiicient fuel should be contained within the rocket casing concentric with the rod to accelerate the rod to the required velocity.

A reasonably high specific impulse solid propellant fuel such as KClO and aluminum powder has a specific impulse of I=250 seconds. The rocket equation for the velocity and mass ratio (Mi iti l/Mfm l) is V=Ig exp (M /M Therefore, the mass of propellant required to accelerate a unit mass of load to 3X 10 cm./sec. is roughly 3 times the mass of the load. If the weight of rocket casing is a small fraction (less than 10%) of the fuel weight, then the fuel plus casing-to-rod weight ratio becomes 4:1, and then the mean diameter of the rocket fuel of density 1.5 required to accelerate A of its mass of steel rod to 3x10 cm./sec. is 4.5 times the diameter of the rod. This results in the distribution of rocket cones or casings as shown in FIG. 1 where the spacing of the intersections of cone apices with the rod is no more than 8 to 10 cm. for high strength steel. The mean density of rod, propellant, and easing (e.g., fiber glass and epoxy or aluminum) is roughly =l.8 so that the shear stress per unit area at the surface 7', required to give an acceleration of 2x10 g. is determined by (surface area per unit length) r=(rnass per unit length) (acceleration),

21rrT=1rr pl1 where r is the radius of the rod 1 in cm., or

1-=r 10 dynes/cm. or 1400 r p.s.i.

If the tangent of the cone half angle is tan 0/ 2=u then the effective exhaust pressure required to give the stress becomes p=1-/oc The efficiency of rocket acceleration (fraction of axial thrust) is dependent upon the exhaust gas angle 0/2, being proportional to [cos (ti/2)] so that a small angle is desired, provided the required pressure P is not too large. Choosing a compromise of oc=% gives of the axial thrust and a mean pressure of 300 r atmospheres or 4200 r p.s.i.

The cone casing must support this pressure, which is modest for small r compared to present material strengths. For high strength aluminum (70,000 p.s.i. tensile strength) the Weight fraction in cone casing is approximately the ratio of pressure to tensile strength so that the weight fraction for high strength aluminum cones (70,000 psi. tensile strength) and a 4 inch rod is about and for fiber glass epoxy (300,000 p.s.i.) about A further advantage is gained if the cone casing progressively burns as the propellant is expelled.

PROPELLANTS Presently known solid propellants burn faster than liqquid propellants because of the limitation of pumps. Nevertheless, present technology limits the solid propellant peak burn rate to about 20 cm./sec. For the burn time required for acceleration within a time of 2X10 seconds, this requires that the web thickness of the grains (burning from both sides) be 2 10- cm. Since this thickness must be graded as a function of length, the gas channeling becomes too complex for practical construction.

Consequently, a faster burning propellant is required. It is one purpose of this invention to provide three propellant mechanisms.

ENCAPSULATED GAS PROPELLANTS If one or both components of a reactive propellant are encapsulated as a high-pressure gas (see Gustavson U.S. Pat. No. 3,204,560) in small volume containers, several advantages are achieved. The actual weight penalty for storing oxygen as a gas is small if the inherent strength of the container is high, and if, furthermore, the container is the fuel to be oxidized (e.g., aluminum) then the weight advantage is more favorable yet. The second advantage for the present application is the faster surface burning rate which is achieved because the flame front moves from capsule to capsule in a step-wise fashion where the time delay depends upon the heat penetration of the relatively thin capsule wall so that the high pressure stored gas ruptures the wall and the flame jumps to the next wall. This is only true provided a thermally insulating matrix bonding agent is not used. Instead, the interstices should be filled with a thermal conductor (metal) or gas. The time for the penetration is less than in the usual solid propellant where the heat conduction must carry the flame through solid material.

The highest strength material commonly used is glass in fiber form where the ultimate strength is 600,000 p.s.i.

In fiber wound vessels 300,000 p.s.i. has been achieved. The concept of encapsulation requires that the size of each capsule be small enough such that two conditions are met. These are: (l) the emptying time of the largest size capsule must be less than the mixing time to burn Within the nozzle defining volume; and (2) the smallest size is limited by the maximum burning rate desired.

The first limitation is equivalent to a flow pattern restriction of Reynolds number where the jet mixing Reynolds number is 4 to 5 and for complete burn 5 to 10. This means that the capsule size must be less than the nozzle throat dimension. The burning rate is determined by the heat penetration of the walls of the capsule. Assuming that the time for gas release after rupture of the capsule wall by heat is small compared to the heat diifusion time into the wall, then the rate of burn x becomes for cylindrical (hollow glass fibers or metal tubes) or spherical (metal, glass, or plastic) capsules where r is the mean chord or mean lineal spacing of the capsule and To is the heat dilfusion time through the Walls. This time to raise the wall temperature to /2 the flame temperature (approximate rupture point) is To (4c/ k) (Ar) 2 seconds where p is the wall density, is the specific heat per unit mass, k is the thermal conductivity and Ar is the Wall thickness (the heat must penetrate two walls).

vTo support a given gas pressure, P, in a capsule (cylindrical or spherical) at a constant wall stress r below the yield point of the material, then r/Ar=7' cyl1ndrlcel or z'rs/pspherical so that substituting into the burn velocity equation gives a burn velocity of x=K1 4pcP r In other words the velocity increases inversely as the capsule size, r. As an example of the preferred embodiment of this invention, consider the cone rockets of FIG. 2 formed of hollow aluminum tubing wound around the rod either not bonded at all or bonded to each other making a homogeneous matrix of tubing similar to the way wire is wound in electrical coils. The hollow tubes are filled with oxygen gas at 7,000 p.s.i.density 0.4 g./cc., and Wall stress 70,000 p.s.i. corresponding to tempered high strength aluminum alloy. The wall thickness, Ar, is then the tubing radius r. For a tube radius, r=0.025 cm. (0.020 inch diameter) the velocity of burn is 4 10 cm./sec. This is the burn velocity needed for accelerating a 4 inch steel rod in less than two meters. The same criteria apply to hollow glass fibers or spheres.

VOLUME BURNING PROPELLANTS The second method of achieving rapid propellant burn in this invention consists of igniting a heterogeneous propellant throughout its volume so that it is burning simultaneously but at dififerent rates in different regions depending upon the grain size of the heterogeneous components. A preferred embodiment is a solid oxidizer, such as KClO or NH ClO and either hydrocarbon or aluminum fuel. The particle size and material determine the burn time, once burning is initiated in the solid state, but roughly the turn time is the time for suflicient heat to penetrate the particle to vaporize it. This time is approximately To (K/pc)d where K is the thermal conductivity, p the density c the specific heat per unit mass, and d the particle size. For 10 micron aluminum this time is roughtly 1 microsecond so that .03 cm. particles should take about 1 millisecond to burn. By grading the particle size from exhaust end to front of the rocket, the fastest burning material will be expelled first and subsequent layers will burn to completion and a progressive mass ejection takes place as in any rocket.

IGNITION There are two methods of establishing volume burning. NH ClO and KClO both decompose when shocked to a pressure of approximately 14 kilobars (200,000 p.s.i.) so that a weak shock wave will decompose the oxidizer providing free oxygen which initiates burning. FIG. 3 shows the rocket-s and rod surrounded by a thin layer of explosive that can be initiated at one end in any suitable manner. The explosive is thin enough (1 mm.) that it does not destroy the rocket casings, but still sends a shock wave into the propellant sufficiently strong to initiate burning. The strength of the shock wave is almost the limit of the strength of the materials, but if the deformation and flow are small, then the structure should remain intact.

An alternate method of initiating the volume burning is with particles of piezoelectric material, such as barium titanate, or lead zirconate, etc., that generate a voltage when shocked. If these particles are surrounded with very fine aluminum powder, 1-5 micron size, with stoichiometric mixture of oxidizer (KClO then when the voltage breaks down from one aluminum grain to the adjacent one, the current is sufficient to initiate buming. It has been found that 50 to ergs is suflicient to initiate reaction so that .05 mm. piezoelectric particles of barium titanate will give this energy at 1 kilobar pressure, which is a significant reduction of shock strength and well below the yield point of the rocket materials. A structure like the embodiment of FIG. 3 is used except less explosive is used, and possibly a thin layer of soft material, e.g. plastic, is provided to act as a butler. The propellant contains about 5% of piezoelectric particles coated with powdered aluminum and KClO Ignition of the explosive layer may be effected by any appropriate expedient.

TAYLOR UNSTABLE BURNING When a heavy fluid is accelerated by a light fluid, an instability takes place at the interface whereby the light fluid interpenetrates the heavy fluid with fingers of penetration (i.e., try to support water by air). If the density difference is large, the depth of penetration is a fraction of (e.g. V3) the distance the whole mass moves during acceleration. In the usual rocket the hot (light) exhaust gases push on the high density propellant. The only reason these two systems do not mix by Taylor instability is that the heavy material, the propellant, is semirigid and does not flow like a fluid.

Instead, it has been found that there is a more rapid burning of solid propellant when no binder is used in the usual solid propellant mixture so that the mixture of, say, KClO and Al is fluidized by the reacting gases and fingers of flame penetrate into the propellant. This has the result of causing a very much faster overall burn of the fuel. The object will then move 10 to 20 times the original thickness of the propellant during the time of burn. If an additional small viscosity is added to the fluidized propellant, e.g., larger grains, then the Taylor mixing can be slowed down to any desired level. The resulting rapid burn rate will also accelerate the rod in the desired short distance.

Thus, the invention provides for rapid acceleration of objects using ultra-fast-burning propellants. The objects need not necessarily be rods, but axial acceleration of rods is the preferred embodiment for penetrating any and all media. The propellant mechanisms described are, briefly:

1) Encapsulation of a gaseous oxidizer in hollow spherical or tubular shapes and bonded by metal to form ragid propellant systems. The preferred embodiment is ill 7 a coil of tubular aluminum filled with oxygen, the tubeing itself serving as the fuel.

(2) The volume ignition of heterogeneous propellants utilizing a fairly strong shock wave from a layer of explosive or by a weaker shock wave in a propellant containing powdered aluminum-coated piezoelectric grains.

(3) The Taylor unstable mixing of a fluidized propellant mixture.

I claim:

1. Apparatus for accelerating a rod-like object to a uniform high velocity without substantially deforming it comprising a multiplicity of annular rockets surrounding and joined to the object and distributed along its length in adjacent relation, each rocket including means defining a generally conical casing containing a fast-burning propellant.

2, Apparatus according to claim 1 wherein the casings are defined by spaced generally conical elements joined to the member, each element constituting a common wall for two adjacent rockets.

3. Apparatus according to claim 1 wherein the apex angle of the casing is between about 20 and about 100.

4. Apparatus according to claim 1 further comprising means for igniting all of the rockets substantially simultaneously.

5. Apparatus according to claim 1 wherein the propellant is a granular solid mixture of a fuel and an oxidizer and further comprising means for igniting substantially the entire volume of propellant substantially simultaneously.

6. Apparatus according to claim 5 wherein the means for igniting the propellant includes means for generating and conducting a shock wave through the propellant.

7. Apparatus according to claim 6 wherein the means for generating a shock wave includes a thin layer of an explosive surrounding the propellant of the rockets.

8. Apparatus according to claim 5 wherein the means for igniting the propellant further includes a stoichiometric mixture of a finely divided solid fuel and a finely for selectively electrically energizing the piezoelectric material.

9. Apparatus according to claim 8 wherein the means for igniting the propellant further includes a stoichiometric mixture of a finely divided solid fuel and a finely divided oxidizer for the fuel.

10. Apparatus according to claim 9 wherein the fuel 5 and oxidizer constitute a coating surrounding the piezoelectric material.

11. Apparatus according to claim 1 wherein the propellant includes small volume containers containing a gaseous propellant substance under pressure.

12. Apparatus according to claim 11 wherein the containers are made of a material serving as a propellant fuel and contain an oxidizer for the fuels.

13. Apparatus according to claim 11 wherein the containers are bonded to each other by a thermally conductive material.

14. Apparatus according to claim 11 wherein the containers are elongated tubes wound into a coil surrounding the rod-like objects to be accelerated.

15. Apparatus according to claim 1 wherein the pro- 20 pellant comprises a mixture of a particulate solid fuel and a particulate solid oxidizer for the fuel, the mixture being fiuidizable upon burning by the mechanism of Taylor unstable mixing.

References Cited UNITED STATES PATENTS 3,088,273 5/1963 Adelman et al 60253 3,137,126 6/1964 Madison 602l9 3,142,959 8/1964 Klein 60-250 3,167,016 1/1965 Czerwinski 10249.4 3,204,560 9/1965 Gustavson 60-255 X 3,218,798 11/1965 MacPherson 60252 3,293,855 12/1966 Cuttill et al 60-229 VERLIN R. PENDEGRASS, Primary Examiner U.S. Cl. X.R.

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