After seeing that seminar, it became very apparent that the crotch straps
are not there to keep the shoulder belts tight (which I had always thought
was a significant part of their purpose) but to keep the pelvis in place,
to restrain the tendency of the torso to "slump". This does more to
improve the efficacy of the shoulder belts that keeping them ultra-tight
pre-crash using non-rearward facing crotch straps. In fact, one of the SAE
articles noted that having the shoulder belts slightly loose did not impair
their efficiency to a marked degree, from a HANS point of view. So this is
one of the big things that I took away from this - that some of my old,
pre-conceptions have been wrong all along. In fact, the torso has so much
tendency to collapse that the tightest shoulder belts become so loose in
the crash that the body can move far enough forward to allow the head to
hit the steering wheel. Most amazing when it's pointed out that this is
NOT the belts stretching but the body flexing that allows this.
Brian
At 04:56 PM 7/9/01 -0400, Mark Palmer wrote:
>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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Brian Evans
Director, Canada
MCI Wholesale Internet Services
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