The Hammer

For every airplane, there’s a region of the flight envelope into which it dare not fly.

A 1/4-scale F-16 flutter model tested numerous "stores" configurations--bombs, missiles, fuel tanks--in the world's premier flutter testing facility, the Transonic Dynamic Tunnel at NASA's Langley Research Center in Virginia. (NASA Langley)
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Early Saturn flight tests revealed that the bouncing liquids in the tanks was also excited by the random vibrations of the engines.  It launched a vicious cycle: pressures in fuel and oxidant lines began to fluctuate, throttling the engines up and down in time with the bouncing liquids.  This "pogo effect" was cured by placing accumulators in the fuel and oxidant lines to damp out the pressure fluctuations.



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