Message text written by INTERNET:europa-list@matronics.com
<ami@mcfadyean.freeserve.co.uk>
>Why does it have to be "locked" in the vertical position? If it were
>attached to a "mid-point" on the shoulder belt it would be prevent from
>rotating forward by the belt; doesn't matter if its rotates backwards.
>
>Duncan McF.<
>
The bar would have to be at least 12 " above the pivot point and the
seatbelt headrest attachment point is about 6" behind the pivot point. I
think if the belt is used to prevent the bar from rotating forward there
would be levering effect of 2 to 1 thereby doubling the force on the belt
mounting point.
After looking at the actual headrest in the aircraft I find that there is
very little room at the door side of the headrest in which to rotate a 1"
dia tube. I am now beginning to favour the ideal solution that I
mentioned in my original message to the forum, in which a longer tube is
used pivoted at about hip level. This COULD be allowed to pivot forward
with the body during an accident, keeping the top of the bar directly
above the shoulders at all time. The actual pivot points for the bar
could be the fuselage side and tunnel mounting bolts for the lap part of
the seatbelts. There would be no requirement for any further
strengthening of any of the points - - - in actual fact I think that it
would reduce the forces on the fuselage as the compressive force down on
the bar would be taken by the equal upward force exerted by the lower
mounting of the seatbelt through the same bolt. Only the forward force
would be transmitted to the fuselage. There would have to be a lockable
pivot at the top half of the bar to allow it to be rotated back while
sliding in. You could even fix the padded seatback to the bar and have a
shoulder height seatback and even a proper headrest if desired.
Ted
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