CA1196816A

CA1196816A - Training ammunition rounds

Info

Publication number: CA1196816A
Application number: CA000400284A
Authority: CA
Inventors: Peter J. Richards
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1981-04-13
Filing date: 1982-03-31
Publication date: 1985-11-19
Also published as: EP0071322A2; EP0071322A3; DE3271108D1; EP0071322B1

Abstract

SPECIFICATION

To All Whom it May Concern Be It Known THAT I, Peter John Richards of have invented certain new and useful improvements in Training Ammunition Rounds and I do declare the following to be a full, clear and exact description of the invention, such as will enable others skilled in the art to which it appertains, to make and use the same.

Abstract of the Disclosure An axisymmetrical projectile having a specified design launch condition has an axisymmetrical cavity therein substantially filled with liquid, the cavity dimensions and liquid characteristics being so tuned that a main natural frequency of the liquid within the cavity approaches a nutation frequency of the projectile to cause resonance after a predetermined duration of flight following a design launch.

Description

IRAINING AMMUNITION ROUNDS
The present invention relates to training ammunition rounds of the axisymmetrical type such as bullets and shells. Such a round will in this specification be referred to as a projectile.
Ammunition rounds, other than for small arms) usually con-tain explosive warheads and their use for training purposes is there-fore inordinately expensive as well as unnecessarily dangerous. It is common, therefore, to produce projectiles specifically for train-ing purposes.
A problem that arises in the use of training projectiles is that the target range is usually much less than the potential maximum projectile range. In realistic battle training, therefore, much greater areas must be used than are called for merely by expected tar-get ranges.
There is, then, a requirement for training projectiles whose ballistic characteristics alter after travelling just beyond the target range so that that range is substantially the maximum range. Projectiles tried have been 1 A composite projectile having a nose which melts due to aerodynamic heating, so allowing the projectile to break up into several smaller pieces, and

2 A spinTIing tubular projectile which at high Mach numbers h,ls "swallowecl" internal Flow but as the Mach number cdecrc-~ases the internal Elow chol~es with a consecluent rise in drag.
Ihese stilL leave problellls in achieving the desired change in ballistic rocluirelllellts whilst consistently maintallling a balllstlc ~.:

8~L6 performance accurately representative of operational projectiles up to the full target range.
.41most all projectiles spin in flight, and with any spinning axisymmetric projectile the axis of symmetry performs angular oscillatory motions with respect to the tangent -to the trajectory.
These oscillatory motions have two natural frequencies, a slower precession frequency and a faster nutation frequency.
According to the present invention an axisymmetrical projectile having a specified design launch condition includes an axisymmetrical cavity substantially filled with liquid, the cavity dimensions and liquid characteristics being so tuned that a main natural frequency of the liquid within the cavity approaches a nutation frequency of the projectile to cause resonance after a predetermined duration of flight following a design launch.
Resonance results in the nutation amplitudes becoming undamped~ giving a rapid increase in yaw angle and hence a sudden increase in drag which will rapidly terminate the projec-tile's flight. The predetermined duration of flight should be such that resonance occurs jus-t after target range has been passed.
Some embcdiments of the invention will now be described, by way of example, with reference to the acccmpanying diagrammatic drawings, of which Figure l is a side elevation, in section, of a spin stabilised projectile.
~i~ure 2 is an end elevation in section along line II-II
of Figure l~ and Figure 3 is a side elevation of a fin stabilised projectile.
.4 projectile lO (Figures l and 2) having an axis of symmetry 1l has within it an axisymmetrical cylindrical oavi-ty l2 of leng~th 2c and diameter 2a. The cavity l2 is subs-tan-tially filled with a liquid. The liquid has a double infinity of natural frequencies of which the frequency of the principal mode of oscillation ~O is well documented as a function of the liquid characteristics, the fineness ratio c/a, and the fraction of cavity 12 volume filled with liquid.
Calibration tables are contained, for example, in the United Sta-tes Arms Material Command Pamphlet 706165 "Liquid Filled Projectile Design".
In use the projectile 10 is launched from a fire-arm (not shown) at a velocity v and having a spin rate a imparted by rifling within the fire-arm. In flight the projectile oscillates with a nutation frequency ~1 which is a furction of spin rate a/velocity v. Both v and a decay due to air resistance during flight, but v decays at a faster rate than a so that ~1 increases during flight.
It can be shown mathematically that resonance occurs between the liquid within cavity 12 and the nutation frequency ~1' if -1 < ? < 1 where s is -the Stewartson parameter. The Stewar-tson parameter is a function of the projectile dimensions and inertia~ the cavity dimensions and the liquid physical properties~ and is defined in the above referenced pamphlet.
If, on projection of the projec-tile, ~1 <~o ~ ~
increases during flight~ until ~ 0 - ~. Any further increase cf ~1 results in resonance, which causes rapid divergence of the projectile yaw angle. The subsequent rapid increase in drag ~1ickly terminates the flight of projec-tile 10.
Modern ballistic theory1 projectile design, and production me-thods are such -that launch velocity and spin rate, and velocity and spin decay ra-tes, are maintained within very small tolerances of a projectile specified launch condition. Liquid within cavity 12 of a projectile 10 can therefore be tuned, by changing the fill fraction, the fineness ratio, or bo-th, to ensure tha-t ~9~

resonance occurs, after a specified launch, af-ter a predetermined flight duration, and hence at a predetermined range, within very fine limits.
Another type of axisymmetrical projectile 13 (Figure 3) is stabilised by fins 14 which set up a slow spin-rate (relative to the spin rate of a spin stabilised projectile) t ~ue to the effects of the fins 14 the velocity and spin rate decay at the same rates, so that the nutation frequency ~1 remains substan tially constant t In this type of projectile a cavity (no-t shown, but similar to that described above and illustrated in Figures 1 and 2) contains liquid whioh, relatively slowly, takes up the spin rate of the projectile 13. The liquid and cavity are tuned so that the liquid resonates with the equilibrium nu-tation frequency~rherLthe liquid has- the same spin rate as the projectile 13, and so that the liquid reaches the spin rate of the projectile 13 after a predetermined flight duration.
It will be appreciated by those skilled in the art that variations in the above described projectiles are possible within the scope of the inven-tion. For example the oavity 12 may be of axisymmetric spheroidal shape. When completely filled with liquid, the liquid has a single natural frequency of oscillation in such a cavity. Construction of a projectile with this shape of cavity is, however, oomplicated. t

Claims

What I claim is:-

1. An axisymmetrical projectile comprising structure;

at least part of said structure defining a cavity;

said cavity being substantially filled with liquid;

said structure having dimensions, and said liquid having characteristics such that a main natural frequency of said liquid within said cavity approaches a nutation frequency of said projectile after a predetermined duration of flight following a launch of said projectile at a specified design launch condition.

2. An axisymmetrical projectile having a specified design launch condition of velocity ? and spin rate .alpha., and comprising structure; at least part of said structure defining a cavity having a length of 2c and a diameter of 2a;
said cavity being substantially filled with liquid to an extent such that it has a principal mode of oscillation .gamma.o;
said principal mode of oscillation .gamma.o being such that after launch of said projectile at said specified design launch condition a nutation frequency of oscillation .gamma., of said projectile, which is a function of spin rate a divided by velocity V and which increases during flight due to a faster decay rate of V than of .alpha. during flight, becomes equal to .gamma.o - .gamma.s, where S is a parameter known as the Stewartson parameter, after a predetermined duration of flight.

3. An axisymmetrical projectile comprising structure and stabilising fins:
at least part of said structure defining a cavity;

said cavity being substantially filled with liquid;
said liquid having characteristics such that when said liquid and said projectile have the same spin rate said liquid resonates at a nutation frequency of said projectile;
and said cavity having dimensions and said liquid having characteristics such that said liquid and said projectile achieve the same spin rate after a predetermined duration of flight following a launch of said projectile at a specified design launch condition.