This relationship between loss of lift end loss of superheat is
substantiated by analysis of Flight 94. From the rate of descent
the unbalance {~sing the equation of Clerke and Korff, see page 3.3 )
is in the neighborhood of 5 kilograms. Although there 'WJI.S no
temperature measurement on this flight, a previous flight of
this type indicated a superheat of approximately 400C. By equation
{10), with a gross load of 52 kg., the unbalance caused by loss
of all of this superheat would be 9.7 kg. It is believed thet
ventilation past the balloon during a low velocity descent before
operation of the ballast mechanism caused loss of superheat. Since
this loss caused greater descent, and thus more ventilation, super-
heat was lost. An enormous rete of ballast flow would have been
required to check descent.
D. Adiabatic Lapse Rate
One of the causes of temperature difference between the lifting gas
and free air during rise or descent of balloon systems is the
difference in lapse rates of eir end the lifting gas. The adiabatic
lepse rate is that temperature change caused by adiabatic ex-
pansion or compression of a gas during ascent or descent through a
given vertice.l distance. The actual lapse rate of the lifting gas
is the adiabatic lapse rate plus the effects of conduction and
radiation. The adiabatic lapse rate is defined as:
{1)
where:
LR = -¥p
A = 2.39 x 108 col I erg
Cp = specific heat at constant pressure
g = acceleration caused by gravity
In the met-ric system for helium, ( Cp = 1.25 0 ~'~m ) '
LR • 980 X 2.39 X 10-s
-- 1.2! =
or:
The e.diebatic lapse rete for e ir, ( Cp = 0.239 col ) :
OC/gm
LR = 980 • 2.39 • 10·3 _ 9_8 oct km
0.239 =or:
LR = - 2.98oC/IOOO ft
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