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weight of equipment and balloon, the distribution of
density in the atmosphere and the buoyancy of the lifting
gas. Assuming that the lifting gas is helium, Graph 3
in Appendix II summarizes the relationship between gross
load and floating level for balloons of several diameters.
To use this graph t·o .find the floating level of a balloon
of given size and load, enter with the required buoyancy
(equal to the gross load). Go vertically to the diagonal
line corresponding to the balloon size and then horizontally
to the extreme left-hand edge and read the altitude. The
volume of the balloon is related to density by the use
of the molar volume in this chart. Assuming observed
pressure and temperature distributions over selected
stations and theN. A. C. A. standard atmosphere, the
molar volume is given as well as the altitudes. Table 1
of Appendixii gives theN. A. c. A. Standard Atmosphere
relating pressure with altitude, and Table 2 gives the
variation of temperature with altitude. For local condi-
tions more exact measurements may be made using the
temperature ana pressure distribution indicated by a
sounding rather than the standard. To do this, it is
necessary to compute the molar volume from this relationship
molar volumez= 359 ft. 3 x ~ x 1013.3 mb
2730C Pz
Example: Find the molar volume at 30,000 feet MSL where
the reported temperature is -30°C, and the reported
pressure is 300 mb.
molar volume30 , 000 = 359 ft.3 X (273-30fc X 1013 mb, - 1080 ft. 3
2730C 300mb.
This is the volume of a pound mol of any gas at those condi-
tions.
By plotting several points of this curve of molar volume.
versus altitude, it is possible to locate very exactly the
altitude which corresponds to the molar volume to which
the balloon will go (found from Graph 3 or as follows),
This density or molar volume to which a balloon will rise
is given by the following formula:
Molar volume •Balloon volume Gas Lift/mol
Gro•• load
Gas lift/mol= 11.1 kg/mol(using Helium)
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