(Approximate)
where G • gross load
A chart, Figure 24, has beendrawn up, based on this equation, expressing free
lift as a percentage of gross load, allowing the rate of rise to be approximately
predetennined.
E. Ballast Requirements
The amount of ballast Which must be dropped through the manual
ballast valve to keep the balloon at its ceiling, can be approximately
determined by the following measurements: a balloon of similar size and
construction is inflated and its loss of lift with time is measured with
correction for variation of temperature. This inflation is not complete,
but is of the same magnitude as that of a balloon ready for release,
approximately 14%. of full inflation in the case of a General Mills balloon.
The loss of lift per hour, multiplied by a factor representing the increase
of the surface ~nich results from total inflation, is thus obtained. This
factor is the reciprocal of the fraction of inflation raised to the two-thirds
power for a spherical balloon, and is approximately the same for the tear-drop
shaped General Mills balloons.
Field experience has shown that ballast leak pre-set to slightly exceed
the computed loss of lift is insufficient. A bailast leak of double the
computed loss of lift has usually been adequate. It is believed that increased
liquid viscosity and valve closure caused by the ·colder temperatures of the
high atmosphere are responsible for the need for this higher ballast setting.
An investigation into temperature effects on the ballast release systems has
been started.
1he amount of ballast which must be released ~.t sunset to compensate
for the loss of superheat, may be computed as followu
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