TRAINING AMMUNITION ROUNDS

MUNITIONS D'EXERCISE

English 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.

Claims

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.
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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.
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Description

1 22762-395
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
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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

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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