roswell

This effect adds to the stabilit.y of stratospheric balloon flights.
If a system in equilibrium in the stratosphere were to lose lift
and descend. the compression of the gas would cause an increase
of the lifting gas temperature relative to the air temperature.
causing a decrease in 'Imbalance.
Similarly. an initial 1.mbalance causing rise of the system would
cause relative cooling of the lifting gas and thus again decrease
the unbalance. Hence. the rate of rise or descent in the strato-
sphere will be limited by the rate of heat exchange due to con-
duction and radiation. which will counteract this effect of
adiabatic heating or cooling.
Empirical evidence indicates that there is a great deal more
stability in a stratospheric balloon system than in a similar
system floating in the troposphere. This "adiabatic stability" is
a principal reason for better performance of stratosphere tlighte.
E. Diffusion and Leakage of Lifting Gas
The lifting gas of a balloon can be lost by:
leakage through small holes in the fabric or film;
solution, migration and evaporation th~ugh fabric or film;
true molecular diffusion through openings. such as the
appendix opening.
(1) Leakage
Volumetric flow, Q, of a gas through any given opening in the
balloon surface may be evaluated as a function of the area of
the opening. A; the pressure head causing the flow, Is and a co-
efficient of leakage,Cd•
(1) where g is the acceleration
due to gravity
It would be difficult to evaluate the amount and area of holes
in the be.lloon surface. Let us, then, compare the rate of
leakage at any given altitude with leakage at sea level. rather
than attempting to evaluate the leakage at a given altitude.
Firs-t; we shall compare the rate of leakage of a full balloon
at any given altitude with leakage of a full balloon at sea
level. Let us assume that the area of any opening in the sur-
face of the balloon does not vary with altitude and that the
coefficient of leakage is constant. Thus:
(2)
-40-
where h is pressure head in
feet of lifting gas