Crash test researchers have proved that the human body can withstand a 40 g impact with little lasting damage as long as the body is restrained within an area of survivability. The pilot can be properly restrained by a well designed system with three major components: the seat belt, the shoulder harness, and the crotch strap.
The seat belt is the primary component. Even in a negative g situation the seat belt will pull the body down and back into the seat. Ideally, the seat belt should be positioned at a 45 degree angle to the horizontal so that the pilot is held both back and down. If the seat belt is too low, it crosses the legs and loses some of its effectiveness for forward restraint while also interfering with leg movement for brake and rudder control. If it is too high, it will allow the body to distort and possibly slide out from under the belt or contribute to internal injuries.
The shoulder belts form the second component of the restraint system. They keep the upper body from moving forward and reduce the chance of a fatal head injury. The shoulder harness structural attachment should be as near to the shoulder height as possible, preferably no more than 5 degrees below and no more than 30 degrees above. Lower angles increase the risk of spine compression injuries while higher angles diminish the effectiveness of the forward motion restraint.
The crotch strap forms the final element of the 5 point restraint system. The crotch strap keeps the lap belt properly positioned at the correct angle across the pelvic girdle. Without the crotch strap, the shoulder harness may lift the lap belt up during an accident and allow the pilot to slide beneath. The crotch strap is also helpful when experiencing turbulence or negative g conditions.
As shown in the photo, the Hooker Harness seat belt can be equipped with a stainless steel ratchet like those used to tension cargo straps. This enables the pilot to easily apply as much tension as desired and to increase it in flight if necessary. My experience with belts that did not have this feature has been that it is difficult to tighten them due to space limits and mechanical disadvantage, and that once airborne making further adjustments (at least in a Cassutt which has no trim system) is nearly impossible. With the Hooker ratchet, I can tighten the belts until I feel like I'm "one with the airplane" and then easily add a couple of clicks in flight if necessary. I'll never fly with anything else.
There's a lot of excellent information at Hooker. Check it out and upgrade your system to the safety standards professionals demand.
Most recent revision: April 11, 2001