I'd like to start a discussion on GA Crashworthiness. Although there is plenty of information out there on how to protect the occupants of a vehicle, particularly automobiles, I see less application in airplanes. Of particular interest to me right now is how protecting my back against a high vertical G crash. I have seen a military heilocopter seat that had a cushion that was about 9" deep. I thought that might do the trick. The upholstery foam would have to have just the right spring rate to hold firm at 1 G, yet be able to have sufficient compression all the way up to 9 Gs or so to protect the spine. Does anyone know what type of foam fits this requirement? My tandem seat/pilot in front design has the pilots rear 4.5" above the spar. That's more than a lot of designs out there, but I'd like more compression distance. I'm thinking that I could mount my seat on a swing arm that would cause the seat pan to travel in an arc that is forward and downward, ahead of the spar, allowing my rear a greater stopping distance in a high vertical G crash. The top of the seat would travel a vertical path. The seat belts will be 5-Point so that I don't "torpedo", or is it "submarine"?