On Oct 26, 2013, at 4:18 PM, Bob Harrison wrote:
> I have at some time seen an arrangement with a hinged block on top of
the existing seat back which ensures that the potential for any spine
compressive forces is removed. However It would need extensive load
testing and need to be very resilient so I=92ve never done anything
further. It would also need the length of the shoulder straps to be much
longer .
Mark...as Bob mentions the standard build allows for spinal compression
in the event of a hard landing (or worse). I made some hinged block
risers as Bob describes; the hinge serves to allow the top of the seat
back to be used as a transition seat when entering or exiting the
aircraft. By no means did I conduct an "extensive load testing" program;
I did however, simulate a 15G load on the shoulder straps in the
appropriate direction. I claim 15G on the basis of an assumption of 100
# upper body weight which could be imposed on the shoulder straps in the
event that the body were restrained from moving forward. The shoulder
strap mounting point did not change, so whatever stresses such an event
would cause will be handled by the airframe as designed. Suprisingly,
the stock shoulder strap length still serves.
...no guarantees...
Fred
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