Note: Descriptions are shown in the official language in which they were submitted.
The preser1t invention relates -to prac-tice a~nmunition a1~d
more partic~llarly -to short rar1cJe projectiles for artillery
-training .
A signi3cant problem în artillery raininy is limiting
the danyer ~one createcl b~ the projec~ile, including ricochets,
while maintaining a reasonable simulation of act~al artillery
trajectories. Attempt~ -to sol~e ~his problem ha~e lnvo1~ed -the
design o various types oE practice or ~raining rounds that are
intended to follow the trajectory of the simulated round up to a
fixed distance and then relatively abrup~ly to end their ~light.
One type oE training round that has bee}1 designed for this purpose
is the spinnincJ tub1l]ar projectile (STUP~. Pro jecti:Les of this
type are (1escribed ir1 Lav;o1ette Canacl:iar1 ~at~nts 956,17~, lssued
15 Octo~er 197~; I,013,L'~7 iss~1e(l 5 J~1ly 1977 anc1 L, n~ 32
issuecl L6 October 1~379. Of Particu1ar interest is the S'I`11P
deslgnated "C-62s', which is a Eull bore projectile designecl to
simulate a 105 millimeter armour piercing, discarding sabot (APDS)
round. The C-6~ STUP is Eired at a supersonic muæzle velocity.
The flow throucJh the center of the STUP is supersonic and the
trajectory is a close match to that of the simulated round. After
the speed o~ the sTue pro~ectile is reduced below a critical
level, the ELow through tihe hollow core of the projectile is
choked and the projecti]e develops a bow shock wave. rrhis
produces a sharp rise in the dra~ on the projectile and a much
curtailed -trajec-tory, a9 descr:ibed in the patents referred to
above.
lt is now desired to s:imulate an armo~lr piercing, Ein
stabilized, discarding sabot ~APF`SDS~ rour1d ancl otherwise to
improve on so~1e of the characteristics of the known STUE'
~ ~,6~7~
projectile.
One area of potential improvement is a reduction in
cross wind sensitivity. As cross wind sensitivity decreases with
decreasing gyroscopic stability and retardation~ this implies that
the STUP should be subcaliber for low retardation and with just
enough gyroscopic stability for flight. However, with a STUP
designed to these criteria the choking effect alone is not
sufficient to limit the range as desired. The present invention
is concerned with an alternative or additional mechanism that,
combined with the choking effect provides the desired
characteristics in a practice projectile.
According to the present inven-tion a short range
practice projectile comprises a hollow tubular body and spin
damping formations on a surface oE the body.
The spin damping formations cause the STUP to lose spin
in flight and to become unstable at a predetermined range. The
onset of instability from spin decay causes a gradual increase in
the angle of attack until the projectile begins to tumble. In the
presently preferred embodiments, the STUP is designed with an
internal wedge at the leading edge to produce either supersonic or
choked flow through the core, according to the teachings of the
Laviolette Patents previously discussed. An increasing angle of
attack provokes early choking of the flow, so that the high drag
from both the tumbling of the projectile and the choked flow
causes high retardation and a short range. Additionally, the flow
choking effect prevents any return to a low drag flight regime
even if the STUP becomes stable again. This could occur if the
velocity decreased faster than the spin rate in the tumbling phase.
~2667~
,
The spin damping formations are desirably three fins on
the outside of the tubular body adjacent its center of gravity~
~ efore firing, the STUP will preferably be mounted in a
sabot that is discarded when the STUP leaves the muzzle of the
firing gun.
It has also been very desirable to construct the tubular
body of the projectile with a fineness ratio (length of
projectile/diameter of projectile) of approximately 4. Where
desired, the projectile may be equipped with a tracer.
In the accompanying drawings, which illustrate exemplary
embodiments of the present invention:
Figure 1 is a perspec-tive view of a STUP according to
the present invention;
Figure 2 is a cross sectional view of the ':TU~ of Figure
1 mounted in a sabot;
Figures 3, 4 and 5 are plots showing the accuracy of
firings at lOOOm. range of three different projectiles, one of
which is constructed according to the presen-t invention;
Figures 6, 7 and 8 are Figures like Figures 3, 4 and 5
respectively, displaying accuracy of firings at 2500m. range;
Figure 9 is a plot showing the comparison oE maximum
ranges of different projectiles launched at an elevation of 15.
Referring to the accompanying drawings, and particularly
to Figures 1 and 2, there is illustrated a spinning tubular
projectile 10. The projectile has a hollow tubular body 12 with a
leading section 1~ that tapers to a sharp or slightly rounded
leading edge 16. The hollow core 18 of the tubular body is
configured to present an internal wedge 20 adjacent to the leading
edge 16. The area ratio of the projectile, that is the ratio of
the smallest open area in the hollow core to the area of the core
-- 3
~26~67~
~-assage at t'lle ed(-le 16 is selected to provide a supersonic flow on
firillg ancl subs2q-len-t cho~ecl 1OW when the spee(l of the projectile
reduces to a desired critica:L level, or else ~ihen the angle of
attack is larcJe. This characteris~ic is described more ully in
Canadian Patent 1,064,321 -t-ha~ has beel-l reEerred to in ~'ne
foregoing.
The STUP constructecl according to the present invention
has three small ~ins 22 spaced equally about the tubular body 12
of the projectile adjacent to the center of gravity of the
projectile. The fins serve to clamp the sPin oE the projectile in
Eligh-t. They are located adjacen-t to the center of gravity of the
projectile so as not to contribute excessive]~r-to ei~he-r the
cJtab~ .a-t:ic>n or destabili~,cltion o~ t'he projectile other than b~
~pin darnphlq~
E`icJIlre 2 ol tlle accompanylncJ drawirl~Js illnstrates the
finned STUP moun-ted in a full bore sabot 24~ The sabot has a base
26 to which -the STUP ls securecl by pins 28 iCit-ted into aligned
'bores in the base and the trailing end of the STUP~ The trailing
end of the STUP also has a bore 30 filled with a tracer material
32 for providing a visual indica-tion of the trajectory on f:iring.
The sabot has a main body 34 connec-ted to the base 26 that
extends forwardly over t'he STUP~ A leading section 36 of the
.sabot body has a series of radlal t'hroug'h slo-ts 38 tha-t end
adjacent external and internal circumferential ~rooves 40 and 42
respectively. rrhe radial slots and the circumferential grooves
perlnit the break-up of t;he sabot body due to the aerodynamic
forces exerted on i-t on launch of the projectile. The base 26 of
-the ~abot carries an obturator 44 for c:losing the bore of the
~un d~ring ~lring o~-the projec-~ile. ~ driving band 46 ls fitted
.~ 67~i
'o the main body of the sabot just ahead of the obturator and a
centering band 48 surrounds the leading end of the main body.
On launch of the projectile-sabot combination as
illustrated in Figure 2, the sabot breaks up releasing the STUP so
that the STUP carries on alone. This arrangement is known and
will not be described further.
The illustrated STUP has a fineness ratio of 4 to
mlnimize drag and retardation. It is desired to minimize
retardation as this is a factor in reducing cross wind
sensitivity. Another factor affecting the cross wind sensitivity
is the gyroscopic stability, the sensitivity increasing with the
increasing gyroscopic stability. It is therefore desired to
reduce the gyroscopic stability by reducing the spin rate of the
STUP. The combined effects of the low re-tardation and low
gyroscopic stability is a delay in the onset Oe chokin~ ancl thus
an extension of the range of the projectile beyond its desired
iimited range.
To re-establish the desired short range, the fins 22 are
applied to the STUP to damp the spinning of the STUP and bring
about the onset of unstable flight.
Figures 3 through 5 i]lustrate the accuracy of firings
at a 1000m range of a training projectile with a discarding
sabot (TPDS) (Figure 3), a STUP identified as "Model 59" without
spin damping fins (Figure 4), and the same STUP "Model 59" with
spin damping fins (Figure 5). The circle at the center of each
chart indicates the aim poin-t, the small cross indicates the mean
point of intersection of the projectiles with the measuring plane
and the other markings, circles, squares or triangles, show the
points of intersection of the individual projectiles. Figures 6,
7 and 8 are like Figures 3, 4 and 5, but illustrate the accuracy
-- 5
~6i~
.It: 25()0 meierC; r.n(;e. As wil:L be sp,p,lrent t}le s'ruP Model. 59 wikh
fins is rnore accurate thati-l:he 59 ~ thollt fin~ and roughly
comparable :in accuracy tO the con~entiollal train:irlg projectile.
I~igure 9 illustra~:es, the cornparat..ive maxiTIlurn ra~ger~3 o
various trajectiles ~ en fire~l u~lder the r;ame conditiorls. Curv~ A
represen~s the l~ro~ectory c~E t11e armour ple.Lc.irlg fin stabil:ized,
discarding sabot ~APFSDS) roun(l -that .is -io ~e simulated. Curve l3
represents the tra]ectory o the traininq pro-jectile, dir;cardiricJ
sabot C-74fTPDS C-74) tnat is referred in E'igu~eF~ 3 and 6. Cur~e
C designates the trajectorv oE a STUP C6~ which is a ul:L bore and
unEinned. Curve D :is the t~ajectory of STU~ Model 5~ wi.-th fins.
~; will be appcii-ent from 1:he clraw.irl~3, t'he trajcc-tory of the 'l'PDS
and of e.lc'l~ S'L'IJl? is a qood Ina~ h to th? t.raject-ol-y o:l the
si.lnul~teci ~PISI)S .~or tt1(? j.~l i.t.i.C~ ?drt: o th~ :roj?c~ ].i.yllt.
The f.inned STUl~.however~ COmeS (10~rl at abOilt 7 .2 k1 LOTI~terC; rathe.r
-t'han 30 k:iloTIieters for the ac-tual round, l4.~l k:i.lometers for the
TP~S and 7.7 kilorneters fc)r the 5TVP C-62.
While orle embodimellt of the inven-t:ion has been described
in the foregoing, it 15 t0 be understood that other embodiments
are possible. F~or exarnpl.e, surface ~ormations on the srruP other
than f.ins, may be :Evund to d~inE) the spi.n o: the projectlle
adequately. The formations m-)s-t orlly interact with the air làyer
around t'he projectlle suf~icierltly to dalllp t.~-le spin at -the desi:red
rate. Some tests have indi.cate~ that grooves in the sur:Eace of a
STUP do not produce enough skin Ericti.on to d~1mP the spin in an
efec-tive way and thus are not spin dampi.ny formcltionc; for the '
purpo~es of the present inventiorlO
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