Race Car Safety Equipment

[jluetjen]

I was somewhat torn between the Hutchens Device (Price) and the HANS Device (a perceived superior design). Looking at this video has helped to clear up my confusion. It's pretty incredible to see the movement involved given the 5 point seat belts and 35 mph speed. It's also further reinforced my zealousness when it comes to safety equipment. I do suspect that this video was produced by the HANS folks, but I don't know for sure. As they say, a picture does say a thousand words.

BTW; Here's the thread on the SCCA Production Forum related to this video. You'll notice that they're a somewhat more ornary bunch then the Pelicanheads, I suspect from competing against each other all the time. Don't let it put you off, there are some really good thoughts there.

PS: I needed to download an updated version of Quicktime for the video to work.

[addictionMS]

sure glad I have a HANS after that, I have put a lot of effort and money into safety. The next task for me is to go throught the car again and see what will come loose at 50Gs, a lot more than one would expect. Nothing worse than not beaking your neck only to be killed by a flying (insert your worst attached cockpit item here)

Jim

[cstreit]

Not that I doubt the HANS, but this video over-sensationalizes the 35mph crash a tad... For example

You can clearly see the driver in the helmet here..



Here after impact, part of the "head" whiplash movement you are seeing is that the helmet is not properly strapped to the head.




Below it is abundantly clear that much of the movement is the helmet, not the head, and that the helmet is coming OFF the head.




Now by no means am I NOT advocating use of this device... I think is a great idea and plan on investing in one myself before long... But I think this ad is a bit misleading... Maybe on purpose to underline the point.. but still..

[jluetjen]

Let's see, if the average head weighs... 7 lbs * 50G's = 350 lbs of force which is being restrained by the helmet and the flexible neck, and the only thing holding the 350 lbs of head in the "brain pot" is the little 1 inch strap across the chin. I'm guessing that the strap (as well as the tongue between the driver's teeth) will be the weakest link and distort in a situation like that.

One thing I have to say in the Huchens Device's favor (possibly), is that in a crash it appeared to compress the helmet on the same axis as the neck. The good news is that this pulls the helmet down on the head, the bad news is that the whole helmet head thing is still heading towards the steering wheel and flopping around the cabin.

The HANS device on the other hand seems to do a pretty good job restraining the helmet in space. The downside as you noticed is that then the head can try to pull out of the helmet. Definitely two different strategies in restraint.

[Jack Olsen]

Have you thought about the Isaac? It's what I got. It not only (slightly) outperforms the Hans, but also likely provides some lateral protection, which the strap-based systems don't.

Its performance also doesn't depend on the user getting the straps adjusted tight enough. In my opinion, this is a big plus, since it doesn't depend on user diligence, which will surely waver over time.

It's also cheaper than the others.

http://www.isaacdirect.com/

[jluetjen]

Jack;
Without having some sled pictures to review, I'm just imagining that the Isaac might perform like the HANS, but amplify the tendency for the head to try to pull out of the helmet.

[cstreit]

John,

You're spot on... 350# would explain some, I just caught a whiff of exageration in the clip...

I did some comparisons and think I favor the Issac's device also, but would love to see similar sled pictures.

I think I asked this before, but Jack, can you get in and out of the Issac's yourself? How long does it take?

[Jack Olsen]

Well, I'm no kinematics expert (don't even know if that's the right word), but what I liked about the Isaac is that it mounts near the center of the head rather than off on the periphery (like the others). It also allows the point where the shock meets the harness belt to move as the body moves forward, hopefully lining the shock up with the direction of where inertia is pushing the head.



But I agree that it would be helpful to have the same type of video clip for the Isaac.

Chris, it comes off very easily, with two pins. That's another plus: no truss/harness thing to wear around.

[cstreit]

Jack, what about getting the pins IN when you're in the car? Looks like you have to do it blind...

[gbaker]

Hello Jack, how's it going?

Video and photos don't mean much. There is absolutely no head load data on the video. Head loads cause injury, not the position of the head.

Tilt your head over as far as it will go. Are you dead?

Helmets move around on the head, even one with no head and neck restraint.

All the HANS video demonstrates is that it severely limits head mobility, which is drivers' #1 complaint, but HANS salesmen love to show it because some people still think loads and position are related.

[Brant]

bump...

jack, I'd be really interested also in hearing if getting into the Isaac is a one or two person job.

brant

[jluetjen]

gbaker;
Thanks for joining the discussion. I see the chart on your web site where you compare the loadings. BTW, what's the significance of the yellow areas on the chart? It's not explained.

Can you share copies of the two SAE papers that you reference. Given that you one of them details the development of your product, I would think that you could (hope?) that you could distribute it without copywrite problems.

[gbaker]

Originally posted by jluetjen
gbaker;
Thanks for joining the discussion. I see the chart on your web site where you compare the loadings. BTW, what's the significance of the yellow areas on the chart? It's not explained.

It represents a range of loads depending on how tight the product is worn. Some people loosen up the tethers on a Hutchens or HANS without realizing that they are defeating the purpose. A Hutchens is inherently adjustable, but the HANS device should use rivets, not screws, to fix the tethers to the composite member.

Can you share copies of the two SAE papers that you reference. Given that you one of them details the development of your product, I would think that you could (hope?) that you could distribute it without copywrite problems.

Not the papers themselves, because the rights have been assigned to the SAE. However, the presentation made at the meeting is ours, so we could send that to you.

[jluetjen]

Thanks for the clarification Gregg. I don't want to be seen as advocating one product over another (I'm not related with any of them by the way), and I've been checking the web to see if anyone has posted copies of the papers in question. Alas, no one has. I'm tempted to cough up the $24 to buy copies from the SAE -- talk about a racket!

Anyhow, just to add more data to the discussion, Here's a link to the Hans Owners Manual. Looking at page 12, there is an interesting chart of the force vectors of Hans versus nothing which I think will help to illuminate somewhat on Chris's earlier pictures and questions. It's good to see that they are also consistent with the 740 lbs thresh hold as shown on the Isaac graph. Like any good marketers, they just have a different way of seeing the number.

It's also interesting to see that a common complaint after using a Hans in an accident is of discomfort on the forehead. As I understand the Isaac view, using dashpots reduces this affect.

Gregg; Apparently Bell (and possibly other helmet manufacturers) have declared their warranty void if a head restraint system is attached to the helmet. What is Isaac's view of this? Admitttedly, it's one of those cases where if the helmet really does fail, who's around to collect? Not to mention all of the usual motorsports waivers etc. get in the way. And if you survive, the helmet's junk anyhow.

[cstreit]

THanks for joining the discussion Gregg.

I have a few questions that I'm hoping you can address...

1. It appears that the "shock abosorbers" attach through the shoulder harness. Is that so?
2. What keeps the harness end of the shock from sliding forward on the shoulder belt as the head is pulled forward on impact?
3. Is the device effective for people using 4 point harnesses? I'm wondering if a car lacked an anti-sub belt, and the driver slid out from underneath his belts (hence the purpose OF the anti-sub belt), what would the Issac's impact be? (Many entry level club races only use 4 pt. harnesses because their seat doesn't have the sub-hole in it)

Thanks!

Chris Streit

[gbaker]

Guys,

I need to make a lunch meeting now, but I'll check back in later today if possible and answer your specific questions.

In the meantime, you may want to read a post I made yesterday to another forum. It's cut and pasted below. It's a bit long an gets a little technical. If you want to avoid the details, just skip to the end to see how an Isaac works.

There were some casual questions going back and forth when one forum member said he liked the idea, but was a mechanical engineer and wanted to know exactly how everything worked.

So...

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Smokey,

Good points all. Whenever I answer questions on a forum I’m never sure who the audience is, so I tend to tone down the technical side. Since you’re a gearhead like me, let’s go over the belt connector, body/head motion and load measurements in more detail. Then I’ll get into how the Isaac system works.

(Hey, it's lunch and I’m bored. If I get a chance I’ll post today.)

Yes, the belt connector ends up pinched between the belt and the shoulder. Both ends of the dampers are equipped with spherical rod ends, so the range of motion is the same whether the driver moves their head relatively slowly or a crash causes rapid motion. The difference, of course, is that any rapid motion invokes a damper reaction.

You raise an interesting point regarding the overall geometry. The dampers are more vertical than horizontal on initial impact, especially if you have an integral headrest with your seat. As the body loads the belts it moves away from the seat—probably 8 to 10 inches in a 45G impact. Due to the inherent friction of the belt connectors, they tend to lag the body motion slightly and adopt a more horizontal orientation, then rapidly “catch up” to the body and lodge at the junction of the shoulder and the belt.

The vertical component of the initial damper reaction causes a slight compression, followed by tension at the end of the event. BTW, all products—and a naked head—will cause both compression and tension, for a variety of reasons. Also, loads listed on our Web site chart are absolute values.

The dummy measures 33 different variables, including shear. Data is collected at rates ranging from 1,000 to 10,000 samples per second. At the neck-head junction, all six loads of interest are measured, i.e. linear and rotational loads about the X, Y and Z axes. The most important is the linear load along the long axis of the neck, F-sub-Z. Shear and rotational loads for the Isaac system are not at the injury levels. Hubbard/Downing, Inc. has, to our knowledge, never published these values for the HANS device, but I suspect they are similar.

Before I get into the details of how the Isaac system works, it is important to review the physics.

Basilar skull fractures are caused by excessive F-sub-Z loads, which are generated in a two-step process. First, the body stops and the head keeps moving, so the head is accelerating away from the body at an increasing rate (the plot of acceleration vs. time is shaped like an inverted “V”). Then the head must decelerate to a stop, and this is where the problem begins. We know from Newton’s Second Law of Motion the force needed to decelerate a mass: F=ma. With a naked head, the only “F” is F-sub-Z. The mass is fixed, so the force is determined by the peak velocity and how much time/distance is available for deceleration to V=0. Unfortunately, the unprotected driver runs out of time and the head loads spike to about 1,800 pounds in 30-50ms. 900 pounds is lights out, fade to black.

Any head and neck restraint puts another “F” in the equation: its reaction. The F-sub-Z load to the head will be the total load (F=ma) less the restraint reaction, or:

Fz = ma – Fr

Classic, position-based designs attempt to hold the head back, which generates the restraint reaction, so:

Fz = ma – dE

where d = displacement and E = elasticity of the system.

This reaction, however, does not occur until it becomes tight. Until then, the head is gaining velocity at a very rapid rate. A HANS device works better than a webbing product like the Hutchens/Simpson because there is little stretch in it, so the reaction occurs sooner, the velocity is lower, and the head load is lower. If you increase the length of the HANS tethers, head loads will increase.

So how does an Isaac system work? The same basic equation applies (Fz = ma – Fr), but the restraint reaction term is different:

Fz = ma – CV

where C = damping coefficient and V = velocity.

(Given that velocity is the first derivative of position, and that acceleration is the second derivative of position with respect to time, the solution is a second order, first-degree differential equation.)

Two very interesting things happen when you take out the tethers and replace them with dampers: 1) The faster the head moves, the greater the damper reaction and 2) the damper reaction begins the moment the head starts to move. Both of these characteristics work to minimize head velocity and loads, without regard to position.

Forget force for a moment and look at this from the perspective of kinetic energy. In order to stop a moving head one must dissipate its KE. Since KE is a function of the square of velocity (KE = 0.5mv^2), which is increasing at an increasing rate, it is critical to invoke the restraint reaction at the earliest possible moment in order to minimize KE.

Obviously, I’ve simplified some of this and didn’t mean to get so wordy here, but there is no easy way to verbalize a complex crash that is best understood by reviewing load cell data.

So much for theory. What happens in the real world? In sequence, here’s what occurs when a driver using an Isaac system hits something:

1) Car crashes.

2) Seat begins to stop.

3) Body moves forward while decelerating, head keeps going, dampers begin to react and become more horizontal (all at about the same time).

4) Dampers reach maximum extension while rolling forward to the belt-shoulder junction.

5) Isaac system becomes an extremely rigid head restraint.

In other words, the dampers react very early to minimize the KE, and then everything locks up as the dampers reach maximum extension.

We are all going to have to trust the crash dummy on the numbers, but you can try an Isaac system with our rental program. Borrow a HANS and decide which you prefer.

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[Lothar]

Chris,

You asked about 4 point systems and sliding under the belts. I thought that the term anti-submarine belt was something of a misnomer. I read that the true purpose is to control the position of the lap belts to avoid them riding up and causing internal injuries. The difference being that the belts ride up rather than the occupant sliding down.

Can someone confirm?

[cstreit]

Lother,

Could be either way... In the end, it's a good idea for either reason.

[addictionMS]

It is my understainding as well the the fifth belt is to keep the lap belt down over the pelvis, and not allow it to ride up to the Abdomen where is can do a lot of damage. If there is a risk of really submarining, then you need the six point where the legs are in separate loops. Since most sports cars do not have a deep recline in the seat, submarining is not likely.

Jim

[Lothar]

Chris,

I think that Jim expressed the point perhaps more elloquently. What I had heard was that the risk of sliding under the belts in minimal. Jim has indicated that this is due to seat angle.

Does that mean that F1 drivers all use 6 point systems? They are almost flat on their backs in those cars. Ask me how I know.