The Roswell Report: Fact vs. Fiction in the New Mexico Desert

Since the back pressure forcing the helium out of a full balloon when it is rising is 4 times as great at 1000 feet per minute as at 500 feet per minute, the rate of rise is critical when an appendix is used. It has been found necessary to limit the rate of rise to 700 feet per minute to prevent bursting at ceiling when using General Mills 20-foot balloons with standard appendix. It is believed, from laboratory tests, that use of the spring bow stiffeners on the new appendix will permit rates of rise up to 1000 feet per minute. Flutter in the balloon fabric while rising is apt to cause failure due to ripping at speeds of more than 1000 feet per minute. A 20-foot General Mills balloon will burst with an internal pressure of 0.014 psi., which is about 1 mb., equivalent to a 200-foot rise at ceiling with a closed appendix.

## III. EQUIPMENT TRAIN

## A. Lines and Rigging

Following rigging failures early in the testing program, careful study was given to the lines and rigging methods used to attach flight instruments to the balloon. For safety in launching, a factor of 10 to 1 is used on all loads. Thus, if a 40-pound load is to be lifted, it is not safe to use less than a 400-pound tested line. The line strength should be determined independently if possible, since the actual breaking point of lines runs between 50 and 70% of the manufacturer's rated strength.

Braided or woven nylon is recommended for all rigging. A stranded or laid line is subject to untwisting in flight, twirling the suspended instruments and reducing line strength. The nylon material is weather resistant to a high degree and tends to stretch under shock rather than to snap. For some purposes it may be desirable to use a line of constant length, in which case the nylon may be pre-stretched. Only a few of the common knots are useful in tying nylon. Bowlines and square knots have been found to slip and are hard to untie. The carrick bend, shown in Figure 5, is recommended. In addition to this, a safety knot is made in the loose end, and the entire tie secured by a final taping. For convenience in assembly, the individual pieces of line and equipment are rigged with harness snaps at each end. This permits unit replacements or removal at the last minute with a minimum of delay. For extremely light-weight rigging, wooden toggles and loops in the nylon may be used instead of the heavier metal snaps.