gbaker

FBB,

Of all the numbers on that chart, the one in which we have the least confidence is the high HANS number. We heard that someone somewhere, several years ago, tested the HANS with loose tethers and the loads were about doubled--albeit from a low starting value. This is consistent with theory. Some drivers have loosened the tethers so much the thing looks like a kite on a string, so this was intended to remind drivers of the manufacturer's instructions. If anyone has any fresh data, we would be happy to edit the chart.

The Link model is adjustable, so the loads will increase with increased slack. The lower end of the range is from crash testing; the upper end of the range is our estimated load with slack, say an inch or so.

The Isaac (damper model) is not adjustable, although the amount of pre extension of the damper rod affects the mix between tension and compression loads. This is an entirely different issue and can't be expressed on that chart.

From a practical standpoint none of this matters to you guys. It's just salesman's bragging rights and gearhead minutae. Any device having loads under 400# on that sled is good for impacts up to 100Gs, or more. Those are rare, even in the pro ranks. Now, if I expected to put my IRL car into the wall at 220, I'd study that chart closely. If I'm worried about putting my 996 into the trees, I'd use the Link, Isaac or HANS and move on to things like side impact, egress, etc.

RedlineMan

Thank you, Gregg;

Not bad for a dummy, eh? As yet un-crash-tested notwithstanding.

Your detailed addition (whose principles I am aware of) was the basis for my reasoning. I might go further in applying these principles.

The basis for saying that any H&N system is better than nothing is that all of them likely control ultimate head/neck extension within a surviveable range. The difference in the test data comes in how quickly that control is generated.

Since KE is a function of the time interval, it makes perfect sense that stopping head motion as soon as possible would be helpful in reducing the ultimate stress levels on the neck.

The previously vaunted Hutchens device and similar Simpson D-Cel (both made by Safety Solutions) has a fallen out of favor for that reason. It does control neck extention, but it does so rather liesurely. Long straps take up against clothing, that takes up against skin, that takes up against bone, until the head is fully restrained is indeed better than nothing, but not even close to its more recent and sophisticated competition. In case anyone wondered why NASCAR dropped the Hutchens, it was for this, not because a competitor (HANS) offered everyone a case of Bud.

I see that the G-force is substantially less effective than the HANS or Isaac. I might imagine the strap type would be the same, or worse. It would be my guess that the R3 might be slightly better, but not up to HANS/Isaac levels because it too is "waiting" for belts and body parts to run out of elasticity before taking up fully.

The Isaac appears to be King in this catagory, if only slightly more effective than the HANS. I would have guessed the HANS might stop the head quicker, given that it is "actively" held back by the belts where the Isaac is "passively" waiting for the belts to stop stretching to activate fully. Pure guesswork on my part, and subject to the counter-intuition that must be VERY prevalent in this field.

Neat stuff!

fatbillybob

GBaker,

You always lend balanced and well thought out responses to us laypeople. Thanks for taking the time to show this monkey how to open his banana.

gbaker

John,

You've been doing your home work. I can add some G-Force and R3 info, but not this moment.


FBB,

Thanks!

Geo

Would it? I don't know as I accept that. I'm not trying to be argumentative here, but this is my thinking: As long as the head is stopped before any real stress is placed upon the neck, the results would (should) be minor. It's only when you start exceeding some level (don't ask me what that level is, I'm just a monkey here) of extension that you really put any significant strain on the neck.

That said, I imagine there are forces on the head itself, especially within, that could be significantly affected. About 20 years ago there was a big problem in CART with driver's brains sloshing around in their skulls in certain incidents that cause closed head injuries (but not basal skull fracture). I would think this sort of potential injury would be mitigated by the dampers vs. straps.

This was not meant to be part of a HANS vs Isaac argument, rather just a discussion of what is/may be going on.

fatbillybob

Geo,
Was the closed head injury problem ever solved? Dr. H. illuded to a type of closed head injury (skull spins brain stays still) when he talked about how the HANS helps. He illustrated his point with the 30 degree offset crash and it's lateral componant. He showed how the HANS limited head movement.

Personally, I think the ISAAC/ HANS debate would disappear into a taste great/less filling argument if only we could get the major sanctioning bodies to allow the device as an alternative to HANS. The likes of F1/CART/IRL/NASCAR see HANS as mandatory. Do they know something we layment just don't or is the HANS marketing really that strong?

M758

Greg... any word one SFI and ISAAC?

.... At this time it looks very much like I will be going for a HANS. They are similar in performanace to the ISAAC, but have the major advantage of "Approved" (SFI Cert and Racing Org Rules and such) thus my $1000 or so investment will be better protected.

I have said it before and I will say it again buying a $300 or $1000 H&N Device only to find it is not "Approved" for my racing org is not a something I want to do. (even if the reason it is not approved is stupid). I feel 100% certain that I can use a HANS for many years, but not so sure about the ISAAC.

Geo

To my knowledge it was not really, but it stopped happening. There was a spate of them about 20 years ago. Some were really bad. IIRC, this is the injury that took Roberto Guerraro (sp?) from a regular front runner (I saw him win at Mid-O a week before his injury) to simply good enough. It was a hot topic of conversation in racing for about a year and then I never really heard of it again.

Now that I think about it, Champ Cars have had the high sides around the head for a number of years now. Perhaps this is what effectively solved the problem? Gregg, do you have any knowledge of this sub-topic?

gbaker

The R3 has not been tested (to my knowledge) on the Wayne State 50G sled, which is the source of the chart data. However the G-Force, R3 and HANS have been hit on the 70G sled at Delphi. For the 30 degree offset protocol the numbers were:

G-Force, 4010 Newtons (source is G-Force publications)
R3, 3000 Newtons
HANS, 1700 Newtons

The latter two are from a HANS press release. I have no problem with these numbers, BTW. They are consistent with what one would expect.

Yes, some of it is counterintuitive.

I don't believe the Isaac is that much better than the HANS I believe so much has been learned that a team of designers can tune either product to achieve a desired test result. I was chatting with John Melvin at the Delphi lab a couple of months ago and he told me that they were able to get tension numbers under 1,000N on that 70G sled by using the 4-belt Schroth system with the HANS. That's a kick butt number. Of course, if the lower portion of the HANS yoke meets the section where the belts merge, the compression/shear load spikes up. Classic example of tuning for one measure.

This is interesting stuff but we've gone beyond the practical. Both products work so well the arguments/debates are whether the head load values are safe at 180+Gs. Who cares? Somewhere around 150Gs your heart will tear away from your aorta, so it doesn't matter. Actually, there is recent evidence that people may be able to survive higher loads, so the magic number for H&N designers may become 200Gs.

gbaker

Agreed.

gbaker

Joe,

We hear ya.

We'll have an SFI certified product in the near future, even though we don't like the SFI design. In fact, we've already tested it and it works well. We just need to go through the "process." Current designs can be retrofitted.

The SFI thing has little to do with head load reduction. SFI demands a design we consider dangerous. In time, I believe the lawyers will be over this like white on rice.

gbaker

Not specifically, but there has been some recent research that has danced around the general subject of brain rattle and it looks promising. One of the WSU researchers (don't recall her name off hand) presented at the SAE meeting in December a very sophisticated computer model of the entire human head, and validated the data from crashes with MRI scans. Shear load was a big factor. Hubert Gramling (FIA) presented a paper which included rotational head loads in Rally car drivers, and at the same meeting two years ago Paul Begeman (WSU) presented a paper on the dangers of rotational head loads. It appears that rotational loads, while rare, can be extremely dangerous.

Now that H&N restraints have kept drivers alive by keeping their heads on, we are left the results of drivers' helmets hitting something in the cockpit. A lot of bells are getting rung, regardless of the product used. There is no agreement on a solution.

rockitman

So are there any belt slippage reports of the belts coming off a Hans with Recaro GT3 seats and 3" schroth shoulder belts ?

Geo

Only on fourth Thursdays under a waning gibbous moon.

rockitman

Just want to make sure I am not buying the wrong setup...schroth and hans for my GT3 seats...