Brain,
Interesting report. One problem you may encounter with rear-anchored crotch
strap(s) is that they do not "pull downwards" on the shoulder belts. I had
a rear-anchored single crotch strap and was never satisfied with the
tightness of my shoulder belts, no matter how tight the other belts were.
Yes, my lap belts are properly installed & positioned, but the shoulder
belts would still tend to pull the cam lock buckle out of position & higher
on my torso than I wanted. Shotening the crotch strap length only served to
elevate the voice pitch.
I moved the crotch strap mounting forward to a point in the floor just
slightly behind my crotch, the strap feeding through a hole in the seat
bottom cushion, so the vector is more aligned with the shoulder belt vector.
Now I can get my shoulder belts really tight without sounding (or feeling)
like a castratus.
Just my 2 cents worth of experience -- thanks for posting your report, it
was one of the most useful & appropriate messages seen on this list. I will
probably re-think a few things, which is a never-ending activity anyway.
Regards,
Mark Palmer, happily restored baritone
>From: Brian Evans <brian@uunet.ca>
>Reply-To: Brian Evans <brian@uunet.ca>
>To: varac@yahoogroups.com, vintage-race@autox.team.net
>Subject: Safety musings.
>Date: Mon, 9 Jul 2001 10:53:50 -0400
>
>I've had race car safety on my mind lately - and it's always been something
>of a hobby-horse for me. I recently was given a video of a seminar lecture
>that discussed various elements of race car safety - in particular the HANS
>device, harness systems, steering wheels, and cockpit side head
>cushions. While I haven't absorbed all of the data yet, and I'm still
>reading the detailed data in the three SAE papers on the HANS device that I
>also received, I do have some initial discoveries that were new to me, at
>least.
>
>In no particular order...
>
>The actual crash speed in Indycar type crashes (car impacts wall at an
>angle) is rarely more than 60 - 70 mph in the vector of the car into the
>wall. There is often a very high speed vector along the wall, since these
>crashes often occur at quite high over-all speed. But the impact vector
>speed is comparatively low. This was pretty obvious, but the data shown
>was collected from 600 odd instrumented and data-logged Indycar crashes.
>
>The reason that Indycar type drivers have comparatively low incidence of
>spinal injury prior to HANS is that the head hits the steering wheel, which
>stops the whipping motion that causes the characteristic injury. Of
>course, hitting the steering wheel which your head creates it's own set of
>problems.
>
>It turns out that rear attached dual crotch straps (Willans style) are 50%
>better at controlling the pelvis and chest motion than forward attached
>dual or single crotch straps. The single strap on five point harnesses is
>the worst. You can use the Willans single seat style, which passes the
>crotch straps through loops on the lap belts, you can get cam style belts
>with click in dual crotch straps, and you can get latch-and-link Simpson
>style crotch straps that are set up with dual straps that can be attached
>at the rear. The key would seem to be that the crotch straps are anchored
>behind the driver, either to the same mounts as the lap belts (if they are
>behind the driver rather than at the sides of the hips), or to mounts
>directly behind the seat. The video clip showing the difference in
>performance between five point and proper six point setups was
>dramatic. This is most true even in fairly upright, sedan type seats - the
>kind that most often have five point belts installed.
>
>It's obvious that in a crash, the driver moves forward quite a long
>way. Only 20% of that motion is related to the belts stretching - the rest
>is body deformation. Mostly, the torso compacts, loosening the shoulder
>belts.
>
>The neck injury that causes the deaths in not related to the actual
>deceleration force as much as it is to the "whipping" motion of the head as
>it reaches it's maximum forward movement. Think rock on a string. The
>HANS device acts less to reduce the decelerative effect than it does to
>eliminate the whipping motion of the head. Apparently, attaching the
>tethers in correct relation to the CG of the head is key. Interestingly,
>the tethers don't have to be very tight, so reduced head freedom isn't
>really much of an issue. One related factor is that without HANS when your
>head hits the steering wheel the helmet is rotated on the head such that
>the eye-port is over the forehead. This puts the rear of the helmet into
>the back of the neck in a big way, adding to the total force.
>
>Side impacts are worse than frontal impacts. The stock car crashes that
>have made the headlines were all side/frontal impact crashes. The cockpit
>surrounds of modern formula cars are there to handle this type of impact,
>but our cars, and stock cars, have/had little or nothing to deal
>effectively with side impacts. Interesting video clip of a dummy in a
>typical NASCAR Butler aluminium seat, equipped with their
>then-state-of-the-art head surrounds. The dummy's head just blew right by
>them, bending them flat like they weren't even there. Now, NASCAR seats
>often have far more substantial head supports, and have right side interior
>nets to further restrain the head during side/front impacts. In watching
>the Busch race at Watkins Glen yesterday (yay Ron Fellows, he ROCKS) I saw
>that many of the cars had new and far more substantial head restrains,
>right side nets, and shoulder bolsters in addition to chest bolsters.
>
>Again with side impacts - it's most important to bolster the body at the
>hips and shoulder, not at the chest. So those Nascar style seats with
>wrap-around chest bolsters aren't necessarily the best deal. Of course,
>they usually aren't strong enough to really work either, but just the same,
>shoulder supports are pretty important.
>
>HANS devices help substantially in not only frontal impacts (as you would
>expect) and in side impacts, but also in rear impacts - for all sorts of
>that I don't fully understand.
>
>The only head restraint cushion material that the gentleman recommended was
>the IRL cockpit surround foam, which is probably available over the counter
>in Indianapolis. Apparently, getting the right mix of deceleration and
>repeatability over a wide range of temperature is quite a trick. This is
>no doubt the same type of material used in CART, F1, etc.
>
>What I'm going to do with this, I don't know. I switched to Willans style
>six point belts this season. I don't have any side impact restraints, but
>I can see a way to add it, both at the shoulders and head. I don't have a
>HANS, but that can be rectified - a larger problem is that I will have to
>substantially modify my roll bar to gain the room for the head restraints
>and the HANS device. I can also install leg side protection, by panelling
>the forward bay of the car and adding a center divider, although I'm not
>sure about that yet.
>
>The SAE papers are:
>
>983060 - Development of the HANS Head and Neck support for Formula
>One. Hubert Gramling, Peter Hodgman, Robert Hubbard.
>2000-01-3541 - Sensitivity Analysis of the HANS head and Neck
>Support. Hubert Gramling, Robert Hubbard.
>2000-01-3543 - Development of an Airbag System for FIA Formula One and
>Comparison to the HANS Head and Neck Support. Hubert Gramling, Robert
>Hubbard.
>
>I don't have the title of the seminar handy - forgot to write it down this
>morning! The Professor was the same guy who has been doing the crash
>analysis for IRL and CART. Thirty years at the University plus time at GM
>safety labs, etc.
>
>Cheers, Brian
>
>Brian Evans
>Director, Canada
>MCI Wholesale Internet Services
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