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Kevin,
I interpreted the guidance the same way you
did. The installation instructions for several makes of auto
racing harnesses seem to agree, also. One manufacturer specifies that the
shoulder harness can be anchored up to -40 degrees from the shoulder tangent,
but not more than 4" below the shoulder line, however every other manufacturer,
and the SFI Foundation itself (the people who certify safety equipment for
racing cars), recommend -10 degrees or less.
An interesting side point is that the SFI
Foundation no longer certifies Y-type harnesses for it's competition
classes. I wish I still had the article explaining this, but I seem to
remember it had something to do with a pendulum effect, where the length of the
harness between the shoulder and the mounting point will allow the torso to move
from side to side in case of an accident. Ron's installation doesn't seem
to have this problem.
I've tried to figure out some way of attaching a
harness mounting point or a harness bar directly behind the seats, but
everything I could come up with either interferes with the canopy latching
mechanism or cuts off access to the baggage area, or both.
Gary Fitzgerald
LNC2 extra-slow build
~70%
engine: TBD
St. Charles, MO
----- Original Message -----
Sent: Sunday, September 14, 2008 9:55
PM
Subject: [LML] Seat Belts
I was looking on Don Barne’s site
(thanks Don, as many have said, your site is really nice) on the subject of
seat belts. Specifically
http://www.lancairlegacy.com/tips_harness.html
I downloaded and was browsing
through the FAA Advisory Circular (AC) 21-34 concerning seatbelt harnesses,
and it seemed to contradict Ron Brice’s note about seatbelts mounted overhead.
http://rgl.faa.gov/Regulatory_and_Guidance_Library\rgAdvisoryCircular.nsf/0/5214C6FFB14E1383862569B2005E77F9?OpenDocument
(page 26)
It says that “Low attachments create spinal
compression” and high attachments cause additional structural loads and poor
restraint, not the other way around as Rice’s note suggests.
It seems the system Rice put in, unless greater than
-8 degrees tangent with the top of your shoulder would be the dangerous one to
your spine, not the overhead (over +30 degrees
tangent).
Did I miss something? It
seems that the drawback to the overhead isn’t problems with spine crushing;
it’s insuring the structure is strong enough to keep the belts in place?
Is this correct?
Thanks
Kevin
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