roswell

or:
(2)
ap =
s, •.
t =
D =
Ap = 4 Ss
D
bursting pressure (psi)
maximum allowable tensile stress of fabric
or film (psi) (for safety Sf= 1/2. S J'QOX
where Smax=maximum strees in tension)
thickness of fabric or film (inJ
balloon diameter (in.)
for failure of seams
where:
S s =maximum allowable tensile strength of seams
(lb./in.)
D= balloon diameter (in.)
In general. a balloon should be manufactured so that any failure
should occur first in the fabric or film and thus the tensile
stress of this fabric or film will be the factor in determining bursting
pressure.
Since the non-extensible balloons used in constant-level work by
the N.Y.U. group have been of the open-appendix type. bursting
due to excessive super-pressure has not been a problem. Strength
of the balloon must be considered. however. from the standpoints
of back pressure induced during rise of a full balloon and pressure
distribution of the lifting gas itself in.side of the balloon.
(1) Pressure Distribution of Lifting Gas
It was shown in the previous section that the pressure diff-
erence across any portion of the balloon surface may be equated:
(3) dp
APe-=~~ - (1-8)
de
A plot of' ~P against ~~ would then be .a straight line at
any given altitude. Maximum allowable balloon pressure--
equation (1)--may be plotted as a function of' ~e • rather
than diameter for any given horizontal plane of the balloon
surface. t . U·sing this relationship. cutting any horizontal
plane Z-lacross the balloon (Figure 25). the diameter of the
-48-