When the total quantity of gas needed has been computed,
the lift requirement may be expressed in terms of the
pressure of a number of cylinders of gas. It is not
possible to assume that each tank of gas will give the
same amount of lift, nor is it possible to use a gage
which has not been expertmentally calibrated to relate
lift to pressure. For calibration of a gage it is suffi-
cient 'eb valve gas from an observed equilibrium tempera-
ture and pressure in a cylinder into a rubber balloon
8:ll4 then measure the total lifting capacity o! the gas
from the tank. Check points should be made with tanks
under varying amounts of preseure. Figure 19 shows a
sample gage oalibration worked up for varying temperatures
auUJiling the simple gas law
Lift2 : ..£2._){....!1_ Lift1
pl 1'2
This law applies to w1 thin !1%. Note: Do not use Graph 6
without checking calibration of gage to be used. Ordi-
narily a whole number of full tanks of gas will not
exactly supply the desired lift,which should be figured
with not more than one-tenth tull tank tolerance in ex-
cess (penni t no under inflation). It is thus necessary
to prepare partially full tanks and by combining full and
partially full cylinders get the required total. It is
necessary to allow the cylinders to attain equilibrium
temperature after valving them before taking final pressure
readings.
B. Length of Balloon Bubble
The volume of gas required for a given balloon may be ex-
pressed as the length of an uninflated bubble at the crown
of the balloon. Graph 2 of Appendix II gives the relation-
ship between bubble length and resultant inflated volume,
using gross lift as an expression of volume. It will be
noted that when the elevation of the launching site is
markedly different from sea level, a shift in this curve
is needed to accomodate varying densities of the atmosphere.
The inflation of this bubble, which is pinched off by
launching equipment or shot bags, will serve as a good
check of the final amount of gas in the balloon, thus
warning if the balloon is underinf'la ted.
c. Expected Altitude
To predict the altitude to which a balloon will rise it
is necessary to know the volume of the balloon, the total
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