Figures 2 and 3 show the tear-drop cell of the stressed tape design developed by General Mills, Inc. The film is .001 inch polyethylene, butt-welded, with scotch tape laid along the seam to reinforce the seal and to carry and distribute the load. These strips, which converge to the load ring at the bottom, actually support the load.
The overloading of a General Mills 20-foot balloon on Flight 12 at Lakehurst kept the lower end of the balloon open during ascent. The ceiling was greatly reduced by the resulting dilution of the helium with air. On later flights an unsuccessful attempt to minimize this mixing was made, using a 10-foot external appendix passing through the shroud lines. This appendix fouled in the rigging and twisted completely shut, causing the balloon to burst at pressure-altitude. A modification with a 10-foot appendix outside the shroud lines also failed in actual flight. Figure 4 shows this appendix construction on a General Mills balloon which is being inflated. The final style is shown in Figures 5 and 6. It consists of a 2-foot external appendix stiffened with cardboard battens. This is taped on the outside of the load ring. It serves as a one-way valve which excludes air during ascent but allows the extra helium to valve freely when the balloon is full. No external appendix can be used whenever the rate of rise exceeds 600 feet per minute. For optimum balloon performance, it has been determined that: 1) the equipment load for the General Mills 20-foot balloon should be held under 30 pounds; 2) rates of rise should be less than 900 feet per minute; and 3) for maximum altitudes an external appendix is needed; hence the limiting rate of rise is about 600 feet per minute in this case.
Several experimental flights have been made using shrouded Dewey and Almy neoprene balloons, as well as small and large experimental cells in
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