Evening star. [volume] (Washington, D.C.) 1854-1972, 1906-03-18
terror Of the balloon. the envelope is made
Method of Computing.

NAoutCHodt. 10 .l4G
Total. Observation-Disclosures. sos 1854
Method of Computing.
In one of the plans printed herewith will
be found an exposition of the method of
computing the surfaces, volumes and pres
sures. The body of the balloon is divided
into zones lettered from "a" to 'p'' inclu-
sIve, and the surfaces, volumes and pres
sure are calculated mathematically for each
zone. For the purpose of adjusting the
weight and tensile strength of the envelope
to the work put upon it by the pressure of
the gas within the balloon, five larger zones
are employed, indicated by the heavy
row-pointed lines. Thus, in the central
zone. A, embracing the ''maitre couple or
greatest diameter, the pressure of the gas
rises to 1855 kilos per square meter, equal 10
about 30 pounds per square foot 1t is upon
this central zone the envelope is applied as
outlined above-one strong silk and two
thtcknesses OF cotton, with three coats of
rubber. These three thfcknesses of mate
rial, consolidated into one, give a total ten
sile strength of $500 kilos per square meter,
or about 90 pounds per square foot. Hence
we have this result: Maximum strain, 95
pounds per square foot; tensile strength,
90 pounds per square foot; coefficient of
safety, to 1.
In sections B the pressure ranges from
80 to $50 klos per square meter. With a
maximum of $50 kilos to provide for, II
lighter silk is used i'll these zones, reducing
per square meter but retaining 2,400 kilos
of tensile strength, which means coeffi-
Client of more than to /.
In the sections the maximum pressure is
800 ktlos, and here the envelope is composed
of two thicknesses of cotton with three
coatings of rubber emitting the silk. and
again saving in weight, but securing 1.S0U
kilos of strength per square meter-agaln
with a coetflctent of safety of more than
five to one.
In the Lebaudy airshlp the coefiicient of
safety was three and one-half to one. we
have coefflcient of more than five to one
throughout.
Not Guesswork.
The tensile strength of the fabrics is not a
matter of guesswork. Samples of each con
slgnment from the manufacture are sub
mitted to the Paris Chamber Of Commerce,
tested by dynamometer and officially
stamped. These tests are under the reguIa-
lions Of the chamber of commerce and the
certificates are made the bases of contracts
and their fulfllment.
In computing the work of the gas upon
the fabric of the balloon NJ. GODDARD and
his engineers have assumed that the lnte-
rior pressure IS equivalent to thirty MILL
meters of water or about six pounds per
square foot This pressure IS maintained
by means of the ventilator or blower which
Initiates with air the balloonet interior
balloon, and which IS operated by an indie
pendent motor of fve-horse-power in the
engine room. The use of the pressure is TO
maintain the rigidity of form of the great
balloon, as there are no interior frames or
other stiffening devices. The integrity OF
form Is maintained solely by interior pres
sure. and this pressure Is usually at twenty
to twenty-four millimeters. In taking thir
ty millimeters and adding 1t to the upward
thrust or lifting force of the gas itself
somewhat more than one ounce per cubic
FOOT, NJ. GODDARD has shown the conserva-
tism which characteriZeS all his calcula
lions and work. Though 1t is unlikely the
interior pressure within our balloon will
ever exceed twenty-five millimeters, the
fabric of the envelope has strength suffi-
Client TO give a factor of safety of five to
one at thirty millimeters.
Every Seam Reinforced
In addition to the tensile strength of the
envelope, every seam, whether clrcumfer-
entail or longitudinal. is reinforced. The
material is Tapped about twenty-five milli-
meters Zone inch) and doubly sewn. mas
much as there is danger that the hydrogen
may escape through the little holes made
by the needle. all the sewing lines are COW
cred with bands of fabric comented to the
envelope-hrst band covering the seam,
and over that still another and wider one.
The primay purpose of these Interior bands
is to MAKE the envelope as nearly pos
sibie gastight. but they also add greatly to
the tensile strength of the skin.
The outer surface of the balloon Is quite
smooth There Is no netting Of cordage or
OF wires to hold moisture, snow or frost
Besides the outer surface is a coating Of
rubber, which will serve to shed the rain
and snow and prevent moisture entering the
fabric In effect the double reinforcing
bands which cover the seams circurnferen-
TALLY and longitudinally, act as an interior
netting, consolidated with the enyeIope
and Increasing materially its powers of re-
sistance to all stresses. This added tensile
strength is not computed in the coefficient
Of . 10 /.
No means has as yet been found of max
ing, with fabrics, an absolutely gas-tight
reservoir. In vanished silk balloons. even
when of two or three thicknesses OF ma
terial. the loss ranges from Ia TO 3 per cent
daily. With fabrics coated with caoutchouc
these losses are materially reduced; and
with our three-foid material and three coat
ings of rubber we shall, according to the
experts. approximate very closely to gas
tightness. NJ. Godards contract calls for
an envelope from which the loss by leakage
shall not exceed Ia per cent In twenty -four
hours, and he Is convinced the loss will
not be more than one-half of his maximum
allowance. A loss OF even per cent per
day would not be great enough to inter-
fere with the plans of the expedition.
The Weight of the Balloons.
The weights OF the various materials en-
tering into the construction OF the huge bal
looms will be approximately as follows:
Pounds
fabric OF the envelope and rubber coatings.. 1900
Etrayes and relingues (for suspension OF
carr ..................A. 49,. 100
rive valves .'.-.. =: .............. lie
Balioonet OF light vanished silk. .........s 225
Total .,........................ 2.se0
Allowing for the three thicknesses, for
the laps and for wastage In cutting. ap-
proximately 1900 square yards of fabric
will be required. The cost of material Is
about 81 80 per yard as it comes from the
| factory.
| 1t is the judgment of all the aeronautie
engineers whom ] consulted in Paris that