Richmond times-dispatch. [volume] (Richmond, Va.) 1914-current, 1920-02-22
AUTO LESSONS
EXPERT EXPLAINS WHAT
"H0RSE POWER" MEANS
,Gives SimDie Formula Devised by
Automobile Manufacturers for
C0mparlaon,
DY FREDERICK C. GUERRLICH,
Lesson No. 49,.

S0mpatlnVut
by T,EDERICK C. GUERnLIoH.
Lesson No. lS:.
is constantly S l used lew people pp really
though ali ali know that Il refers t 70 the h;
Mnss is 81 ss and 'i how w. Hei Is ' Ss
termined with regard 70 particular
sizes Of engine:
measure FOR work. and consists of
Of ny. work: t which smaller units arc
One foot-pound is the amount OF
work required to lift one pound tor
an Object is lifted in n Minute, by ITS
weight in pounds gives the number OF
ffs9spafunas or worn dsn9 T. There
Height of ssooS feet %ssEh IN DC mn ,ses
or or II III z sS;oeo,pound weight DO llfted
w3 Th, VII have been done 10 Il.
oure JUST ST oh the hoqse po4er 10 I'LL rs
s,ooo-pound weight Of Fig. one foot.
and to lift the s3o,pound weight Of
Zig. would have to be capable Of
Wife rs ,atp ot Fr but snu ~" eker
run at htsh-speed.
Ascertain Average Pressure.
AS there are $4,000 foot pounds Of
work In ono horse power. Il we can
machine, and also find the distance in
feet, through which this pressure opcr-
two, and then dividing The result BY
hoEse- power OF work Which the ma
Let US see how we can derive a for
ttnu'a far committing this horse power
TOT given engine. We have two cle
IN Ia, ho
soSss Ses the a p9sssu aHe ia a eserseS
n 2 minute.
The pressure Is due to the explosion
Of the gaseous mixture. This viii be
very great at the moment OF explosion
but, will decrease quickly as the piston
Is forced down and the exploded gases
expand. Engineers by means Of an in
s,rument, called ~ indicator. can de-
Easses la for all positions OF the piston
OF an engine. and therefore can quickly
;e'i wnat the i aner rag pressure is With
CURED to exhaust the burned gases to
draw 10 the fresh gases. and to com.
press them. BY subtractins the aver
age OF these preesnres (which repre-
sent consumed work) from the average
pressure during the power stroke. the
Pressure WIN VARY,
sure s vaFy G7 a a:r effective pres
/ u ts effected by the compression OF tie
chanGei by tho mixture; by the en-
an average for automoblie engines IL
VIII DC about eighty pounds per square
inch. In the formuLa We are deduct
nrs i1t Us cali this average effective
.r, rss Indicator slyer the pressure eS-
have ,hers9oss na nSh % e, IN, nna p,sfon
s saoas,y incl, tnis win b. The nresgS!e Pr
area Of the piston head rhs s.'o
head Is Circle. and rom rom seo ne p,st Ss
know that the area Of circle is equal
s!ea y ,ss,S SSd .ims. sass Is su iSe
is s sa@e as sas az w
one,half the bore t,he radiusS sSnare cd
mq,.'piied by 3;ltIs. and the total pres s.
mon nhped h sy p the area P Of p square
Note from this. that tho Ssca,er the
Nore q the engine the greater win be
slze Of the bore Is the element by
s,aiea IN. ene power OF the engine can BE-
iiavinE found the total p,esa,,. -,
erted e. each power stroke. we must
next md tho distance for which this
i pressure Is sxerted in u minute. The
, ssssn o. sns stroke Of the engine.
into tho formula. Tho stroke Of ths
ensin ne. Is the distance through, which
rs s e9n ~ s9a ave during each half
is usually given IN inches and s sa IKE
are Trying TO find tho number Of foot
pounds, tho stroke VIII. therefore. have
70 Pc cHansea TO feet or divided By
stroke l.. TUG
Dt.tsnce in Or" Minute.
Having found the tanee the pres.
sure IS exertcd for each power stroke.
we must next find wha, distance /, is
cxerted In minute. This obv,onsiS
Will be the. stroke times the numher o.
power strokes per minute. and as there
10 one power stroke for each two revo.
multiplied by half the rcvoiution-
minute OF the engine. we will have IN,
distance through which the pressure is
Thus the horse power o. each cr,in.
Ger Of an engine equals plan. or. for
case OF remembering plan, divided by
"S,o00' 70 Which i is the average pres.
sure OF the exploded gases. L eke
the piston (which is equal to half the
bore multiplied by half the bore ,he
result being multiplied by 3.I4i6), and
= the number Of power strokes (which
Is the number or revolutions per min
cte divided By two).
AZ insurance companies and the va
r!ous license bureaus base their rates on
,ne morse power OF the car, and as the
iSnee power formula plan divided by
5000 is cumbersome, automobile en-
comparison. A. /. q. II. or the y. A.
=; G. formula; which is, D squared
lines divided by 2.5. In this D is
number OF cylinders.
IN deciding this FORMULA. Of the
sesulaI formula Is assumed as about
NJ pounds. L a-s five inches and the
Thus. for a six-eylinder VS engine Of
S s:s,id n bore the S. a: T.. horse power
~ouia ce % times 80 times divided