roswell

The number of mols in a balloon volume may be readily computed
by dividing the air density, expressed in molar volume. at a given
altitude into the balloon volume. 1he lift of the gas filling the
balloon at any altitude is then equal to the number of mols multiplied
by the buoyancy per mol. For example: To find the lift of the gas in
a completely inflated (hydrogen tilled) balloon of 20-foot diameter,
at an altitude where the pound molar volume is 1000 ft. 3 (This is equivalent
to about 30,000 ft.):
3
Volume of a 20-toot diameter sphere =4190 ft •
Number of mols in sphere at this altitude • 4190 • 4.19 mole
iooo
Buoyancy • 4.19 mols x 26.65 /buoyancy/mol • 111.7 # lift given by
the gas at 30,000 feet.
In one step, this becomes:
Gross Lift/Balloon = (Balloon Volume) x (Difference in molecular weights of
air and lifting gas~
Molar Volume at a given ait~tude
Conversely, the maxtaum altitude to Which a given size balloon will
carry itself and a specified load can be determined, as a molar volume, which
may be evaluated from a graph of altitude versus molar volume. Such graphs,
computed as in Part A of this Section, are given in Figures 19 and 20, at
the left hand edge.
Hydrogen and helium lifts were computed for various molar volumes
for spheres of lifting gas with diameters from 7.5 to 75 feet. Figures 19
and 20 were plotted using the values computed. To use these figures to
determine the maximum altitude of a balloon with a specified pay load, enter
the table with required buoyancy (balloon weight plus payload). Go vertically
to the diagonal line representing the balloon's size, and then read horizontally
on the left hand edge, either the molar volume or the equivalent altitude over
- 17 -