How do I avoid damage to systems during flight.

by Mike Manes, W5VSI

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Sent 01-Jun-03

Regarding things getting ripped up:

Although there can be some pretty nasty wind shear (AKA Clear Air Turbulence - CAT) if you pass right thru the jet stream, EOSS's experience is that "post-burst chaos" (PBC), where the system accelerates downward to speeds upwards of 12,000 fpm, is the biggest source of in-flight dings. In some cases, the parachute can actually fall >>below<< the payload string, as some of our video shows, and 'chutes don't work all that well going sideways. Not real sure exactly what's at work here, but we've gone by the theory that the most stable descending flight string is one which has the fastest- falling payload package on the bottom and the slowest on the top; this should tend to keep the flight string nearly vertical in descent. And since we've applied that theory to our flight string designs, we've not seen very much "PBC" effects. In practice, we put the bomb-shaped APRS module at the bottom, with the ATV module and little wheel farther up. We also make every effort to cut away the balloon shards as soon as possible after burst to unload the 'chute apex. Another "low-drag" example is our cross-band repeater.

Another goody in the trick bag is to make >anything< on the outside of the payload strong. Not so much for PBC survival but to last thru a parachute drag after landing - we've seen horizontal excursions after touchdown as far as a quarter mile! This often means making stuff heavier than it might be, but the extra weight's a worthy price to pay in order to keep antennas operating prior to recovery and to minimize effort to get the package ready for the next flight. RG-142 coax is nearly indestructible and has a life-cycle cost many times less than RG-58 or -174.