Quote:
Originally Posted by RFSchaller
I humbly suggest that if you get the point of relying on the thickness of your seat cushion for protection you are VSF (Very Severely ---well you can figure out the rest)! 
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I think we can all agree that same statement can be made in most situations where a 'chute pull has become necessary!
The thickness of seat cushion, it's density etc can play a role in absorbing vertical impact forces, however in cases where there isn't sufficient depth available to allow development of a purpose-engineered seat cushion solution, then the underlying structure needs to be design to absorb the vertical energy.
I don't know anything about how one goes about designing for "controlled crumple" of structure, but I have seen the end result of a well-designed energy absorbing seat. A particular helicopter was involved in a high energy crash where the main rotor RPM decayed badly, resulting in quite high vertical speed on impact. The pilot (the only person aboard) didn't walk away, but, because of the seat design, he also didn't suffer crippling spinal column injuries. The seat structure looked well and thoroughly "squished". To my untrained eye it looked as though the structures engineers hit their design goal pretty much right on the money.