Balloons and Accessories

Abstract

We employed polyethylene balloons manufactured by Raven Industries with a volume of 80.000 cu ft. The balloons were filled with hydrogen. The net weight of such a balloon varies from about 17 to about 19 kg. The pay-load consisting of a TESIO, a parachute, lines, and a squib for line cutting amounted to 8.1 kg at each flight. These data determine a summit altitude reached by the balloon of about 32 to 33 kms corresponding to pressure levels of 7 to 8 mb respectively. In order that the balloon ascends with a velocity of about 300 m/min which proved to be a reasonable value, a free lift of about 20% of the gross load has to be provided. This is obtained by filling the balloon on ground with about 36 m³ of hydrogen. The accurate conditions were checked before each flight and then the lift of the balloon weighed out appropriately. Since the balloons were filled at open air one has also to account for the dynamical lift when winds are blowing. In the first place one has to keep the balloon so stout that it remains always spherically. This has the advantage that on the one hand the side wind pressure does not increase to a troublesome extent even at velocities up to 10 m/s and on the other hand the dynamical lift can be estimated and compensated rather accurately for this simple shape if the wind velocities are measured.