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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