As said before, centripical force. As the chopper turns it pushes your ass in the in the direction of the center point of the choppers rotation. If the chopper was going slow enough when it turns then yes you can fall out but you go to be going pretty damn slow and at a verted angle which isn't gonna happen. Other then that same Black Hawks do have a rope that can be connected at both ends of the cabin, but its never used though.
I asked the same question to my brother-in-law's brother that works on BlackHawk's and he told me it's basically gravity pulling you in like when you make turns in a car and you feel that pull!
Hey Zenk I remember the first time I saw seats in a black hawk was when I hoped in the Customs Service one. They slid open the door and I was like WTF. Talk about some no flying mofos. We were considering putting an OP on a good-sized hill/mesa but they didn’t want to land because there were tall bushes that might scratch the bottom. They pilot had the nerve to ask us to climb up and cut stuff down because the lading spot was so small. Of course I told him that in the military we would have had 2 blackhawks, a ch-47 and 4 little birds in the same spot. They really took the fun out of flying.
I always thought the key to keeping your ass in the bird was to put as much weight as possible in your kit and rucksack. Always worked for me, kept me glued to the bird and the ground.
The only time I got tosit in the door of a blackhawk was at JOTC at Ft Sherman in Panama. Our Co Cmdr rounded us a couple up. They informed the company Scout Swimmers to get us ready for some helo casting into the lagoon. I made 2 jumps. WHAT A FUCKING BLAST.