Flight 17, using a fifteen-foot balloon of .004 Polyethylene is worthy of special consideration. The thickness of this type of cell eliminates much of the problem of appendix design since more internal pressure can be withstood. Despite this factor, and the low permeability of the fabric, balloons of this type are too heavy and costly to be used for high altitude flights.
The trajectory and time-altitude curve of this flight are shown in figure 56 and 57. This controlled-altitude flight demonstrates that the automatic ballast valve combined with a fixed leak, will successfully maintain constant altitude through a sunset. The balloon floated at 29,000 feet + 500 feet for at least three hours, after which the excessive range prevented further radio reception. Here again the necessity of a barograph was demonstrated as the balloon was recovered from Pratt, Kansas, 530 miles away. Two flights, 23 and 38, were made using the shrouded Dewey and Almy J-2000 Neoprene balloon. Both of these flights were failures. Flight 23 (see figure 48) attained a maximum altitude at 50,700 feet and began to descend immediately. Flight 38 (see figure 55) was observed from a B-25, and the balloon was seen to burst within the shroud.
Section 6. Current Objectives
In order to meet the requirements for future flights, improvement must be made in three phases:
1. Performance data for too many flights have been either uncertain or of too short duration. Before more flights are undertaken, altitude-measuring instruments must be improved and increased. To this end, four specific improvements are being undertaken:
A. To supplement the pressure data received by radio, a lightweight barograph will be added to those flight trains in the future when flights of more than a few hours' duration are attempted.