[lbryce]

While there never was a launch failure in Saturn V history there was a very serious design flaw that caused huge oscillations within the rocket known as the pogo effect that NASA, von Braun had to contend with that plagued the Saturn V, finally resolved.

[Southack]

http://en.wikipedia.org/wiki/Pogo_oscillation

[Atlas Sneezed]

While there never was a launch failure in Saturn V history there was a very serious design flaw that caused huge oscillations within the rocket known as the pogo effect that NASA, von Braun had to contend with that plagued the Saturn V, finally resolved.

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In testing, they actually detonated bombs in the nozzle to generate a pulse to trigger the oscillations that occasionally troubled them. When they could bomb the engine and it kept running smoothly, they knew they beat the problem.