I was assigned to the US Army Safety Center my last 2 years in the Army. I assisted in several aviation accident investigations. Many factors come into play during a crash sequence. Angle of impact,speed,aircraft weight etc etc. I can assure you that if you are not wearing a seat belt during a crash sequence, you will become a human projectile. Conduct your own experiment,put something(about 5lbs)on the back window shelf of your car and drive down the street really fast. Slam the brakes on and watch what happens. Be sure to wear a helmet. Wearing your seat belt in addition to leaning over and wrapping your arms under your legs will help prevent flailing injuries. The crash will probably be not what kills you, getting out of the acft will be your biggest problem. Just a note, the Army will soon start installing airbags into helicopter cockpits. The BS part of the deal is that the crewchiefs will still be the most unprotected.