All,
Hans addressed an important point in his posting yesterday, which has been
on my mind, too, since the earlier discussion on this issue (check out the
thread on Matronics' site). I cannot see that a solution was offered,
however.
FAA's AC21-34 leaves one in no doubt that the existing fixation point for
the shoulder harnesses should not be used. See it at
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular
.nsf/1ab39b4ed563b08985256a35006d56af/5214c6ffb14e1383862569b2005e77f9/$FILE
/AC21-34.pdf
It recommends between -5 and +30 degrees from the seatback perpendicular, at
shoulder height. What one may overlook is that not only is the pressure
acting down the spine from both the front and the back, resulting in twice
the compression load on the spine compared to if the harness were tangential
over the shoulder and then down the chest, but the force on the harness at
the back (which is multiplied by 2) is so much higher because of the sharp
downward angle, given the same restraining force in the aircraft
longitudinal direction.
Assuming that not only Hans and I are interested in exploring this issue, I
called Andy at Europa 2004 today and suggested that they do us all a service
by investigating if a hardpoint could be made to satisfy FAA's
recommedation, and then address it in their next Tech Talk column. Andy was
very understanding of the background for my question, and promised to have
his structural man take a look at it.
I am not aware that 4-point harness is a requirement, one diagonal shoulder
harness should satisfy the rules, I believe (have not checked!) but if a
fourpoint (or more probable, two shoulder harnesses attached to a common
point in the back) can be arranged, then all the better. I hope E2004 can
address this earlier rather than later, and maybe they can make some money
on a mod kit at the same time?
Regards,
Svein
A225 - XS trigear now in Norway
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