roswell

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 teet 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 bal-
loon 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 1mb., 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'/o 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 ~is recommended. ln 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 indiv~
dual pieces of line and equipment are rigged with harness
snaps at each end. This permits unit replacements or re-
moval at the last minute with a:t minimum of delay. For
extremely light-weight rigging, wooden toggles and loops
in the nylon may be used instead of the heavier metal
snaps.
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