The St. Charles herald. [volume] (Hahnville, La.) 1873-1993, 1918-06-01

above the level Of the gun there Is a
ten-mile wind blowing straight across
the line gun target, the thermometer
IS up to 50 and the barometer has
dropped to %. VIII the projectile hit
the target now? Not unless you cor
rect the elevation Of the gun for some
OF these conditions and It's laying for
the others. How are you going to
do It?
First. you must find the force with
| which your projectile cleaves the air.
This Is called the ballistic cO-efficient,
and is reduced by simple formula to
figure. Knowing the weight Of the
projectile. its 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 1t will have on your protec-
tile. BY means Of elaborate tables one
can find Just what this effect is. and
we apply 1t 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 go good What about this
troublesome wind that Is blowing? II
It blows against the protectile II
checks II; II with 1t, 1t helps 1t along.
So we have two varying factors.
which the ballistician juggles by utiliz-
ing tngonometry until he gets them in
terms where he can once more change
his ballistic co-efficient, making It
larger or smaller as the wind i'm
pedes or accelerates the projectile.
Not quite so easy as you thought, IS
1t? But we are not through yet.
We know that under range table |
conditions our propelling charge has |
n force that gives the projectile an
Initial velocity Of so many foot sec
onds, say $3.50. But our powder has
been stored In dugOut whose tenn
perature is not normal, so by more fig
uring we find out just what this real
velocity for the day is. Now we can
begin to figure what elevation the
gun must have to travel that 10000
Yard D0fh t0 tho tarpot
BY dividing our old friend c, as the
oallistic co-eficient is termed. by the
distance in feet that the proiectile
must travel, we get a reference num-
Der. This number we take with us
md bury our noses in more tables I'M
II we find opposite this number in a
column headed by the muzzle velocity
mother number. This number, multi
'lied by c again, gives us the sine OF
vice the angle Of departure. A
Iuick glance into a table Of logarith-
mic sines gives this to us, and dividing
y two we have figure in degrees and
ninutes that represents the angle
1hich the gun must be elevated from ,
he horizontal to send its projectile :
0,000 yards today. Wait a minute.
'ur target is 200 feet above the level s
{ the gun. Also because Of the curv- !
ture of the earth this 200 feet height ,
as been reduced somewhat. So once f
lore we delve into mathematics to cor +
ect the curvature of the earth and c
eight Of site Of the target. The re- +
llt we subtract from the angle found.
nd this time our gun is ready for ,
usiness. Is it? No; 1t is not so easy. :
The Influence Of ahe Rffiino. +
Every riaed piece Of ordnance i'm q
arts a twist to it's projectile, and q
lis twist causes the proJectile to devil d
,e from its course. In our service this :,
,viation. called drift, is to the right, h
Id is in ratio with the range. 1t is h
instant, therefore, for each range, and n
e find 1t very easily, either by math- d
nat1c computation or from drift ia +,
es. Also we 60 back to our wind Il
oblem and find what effect the wind Il