The St. Charles herald. [volume] (Hahnville, La.) 1873-1993, 1918-05-25

above the level of the gun there Is
ten-mile wind blowing straight across
the line gun target, the thermometer
is up to So and the barometer has
dropped to %. VIII the projectile hit
the target now7 Not unless you cor
rect the elevation Of the gun for some
Of these conditions and Its laying for
the others. How are you going to
do It?
First. you must find the force with
which your projectile cleaves the dir.
This Is called the ballistic co-etficient,
and Is reduced by simple formula to
a figure. Knowing the weight OF the
proiectile, It's form and Its diameter
the ballistic co-efficient Is easily cal
culated.
| The Air as Check.
You have now taken the first step.
You have the force Of proJectile TO
penetrate the atmosphere under stand
ard conditions. But this force varies
with the atmosphere. On a heavy,
| muggy day the atmosphere is dense,
and you will be surprised the check
ing effect It will have on your projec-
tile. BY means Of elaborate tables one
| can find Just what this effect is, and
we apply II to the original formula.
Also in the atmospheric factor is in
cluded the temperature, for in hot
weather our powder charge when ig-
nited exerts more strength In decom-
posing into gases than It does on a
cold day.
So far 80 good. What about this
troublesome wind that is blowing? II
It blows against the projectile II
checks II; II with It, II helps 1t along
So we have two varying factors
which the ballistician tuggles by utiliz
Ing trigonometry until he gets them In
terms where he can once more change
his ballistic co-efficient, making II
larger or smaller as the wind i'm
pedes or accelerates the projectile.
Not quite so easy as you thought, is
It? But we are not through yet.
We know that under range table
conditions our propelling charge has
force that gives the projectile ar
initial velocity Of so many foot sec
onds, say $3.50. But our powder ha!
been stored in a dugout whose tenn
perature is not normal, so by more fig
uring we find out just what this rea
velocity for the day Is. Now we cal
begin to figure what elevation tn
gun must have to travel that 1O,ooO
ward path to the target.
. Nv dividing our old friend c, as TIL
ballistic co-efficient Is termed, by tn
distance in feet that the projectil
must travel, we get reference mum
Der. This number we take with u
/ and bury our noses in more tables un
, til we find opposite this number in
| column headed by the muzzle velocit
another number. This number, multi
piled by c again, gives,us the sine o
, twice the angle Of departure.
: quick glance into a table Of logaritf
, mic sines gives this to US, and dividin
. by two we have a figure in degrees an
I minutes that represents the angl
9 which the gun must be elevated fror
e the horizontal to send its projectil
1 10000 yards today. Wait a minute
f Our target is 200 feet above the levt
8 of the gun. Also because Of the cur'
J. allure of the earth this 200 feet heigf
has been reduced somewhat. SO ono
e more we delve into mathematics to Co
e rect the curvature Of the earth an
: height Of site of the target. The r.
/ suit we subtract from the angle foun'
o and this time our gun Is ready Il
n business. Is 1t? No; 1t is not so cas-
n The Influence Of abe RifiIng.
e Every rified piece Of ordnance in
parts twist to its projectile, an
It this twist causes the projectile to dey
e, ate from its course. In our service tn
e deviation, called drift, is to the RICH
n and is in ratio with the range. 1t
y constant, therefore, for each range. ar
It we find it very easily, either by mat
e. ematic computation or from drift t
r bles. Also we 60 back to our wiz
It problem and find what effect the VIII