RedlineMan

And another techincal point about the tethers...

The length seems to be an issue, but there are other factors involved in how the HANS works that decrease the tether length issue.

When the body travels forward, and as the belts are stretching, the HANS device is held in its same relative position by the friction material on its top surface. Instead of the HANS collar travelling with the body, it stays trapped rearward under the belts - essentially "shortening" the tethers - and keeps the neck from extending. The crash test photos clearly show this phenominon.

This might be a large mitigating factor in the tether length -vs- shock absorbtion properties between the two products.

ColorChange

Nice ltc. You definitely engineer.

I laughed Jack.

George, for simplisity sake, if you eliminate the dashpots for straps, the ISAAC and HANS are the same. The key difference, is that while your head is moving at full speed untill the teathers snap taught, the dashpot in the ISAAC is already dramatically slowing your head before it bottoms out and goes taught, just like the HANS tethers.

John, as long as people keep their tethers short, I agree with you. But, for convenience sake, I often see people with really loose tethers, and this is way bad. With the ISAAC, you get nearly full slow motion range as the dashpots give way, but if you try to move quickly (like in a crash), they are very firm. It's kind of like getting your cake and eating it too.

Now, the ISAAC has gotcha's too, but they're much more obvious. You have to make sure the rollers are on the front part of your shoulders in order to get the shock dampening benefit. If you leave the units extended behind your shoulder, you basically have a HANS with no ISAAC benefit as the shocks are already fully extended. When I get in, I clip in, and then position and compress the shocks to make sure I am retianing as much dampening as possible.

Geo

My question remains the same. What data do you have to support your position that the dampers do a better job? Webbing stretches and will decelerate the head. Dampers are speed sensitve and we (all of us, but especially you and I) don't have a shock dyno plot of the dampers in the Isaac. As I said before, intuitively one would suspect the dampers would do a bit better job, but life is not always intuitive and also, at difference velocities, the Isaac will not be as effective.

I'm not dissing the Isaac. It was the only one I considered along with the HANS. I've also met Gregg Baker and think highly of him. He takes great care of his drivers too. I've seen that first-hand.

Let's just be careful how we state facts and speculation. Fair enough?

Have you discussed this with Gregg Baker? I've NEVER seen a photo of the Isaac in front of your shoulder. In fact, I would speculate it would render the Isaac totally ineffective since it would not likely limit your head motion before you head separated from your shoulders.

Geo

It seems to me all of your explanations of how the BSF can occur still revolve around displacement between the head and the shoulders. This was my point. The displacement occurs because of the force placed upon the head, but if you eliminate the displacement the force won't cause BSF, right?

Exactly. That is my guess as well. I have an event a month from now, so I'm not sure if I'm going to send it out before or after, but off it will defnitely go.

Larry Herman

John, do you have a link to those pictures? If that is true, are you (in an accident) sliding forward under the Hans shoulder bars? Even withh all the questions, I would probably buy the Hans right away if it weren't for instructing. I think that I probably have a greater chance of getting in an accident as a passenger in someone else's car than in mine.** I want something that will move with me from car to car, and that is looking more and more like the R3.




**Stop laughing John, you know I'm right here.

38D

I thought the HANS attached to the driver? (or are you concerned about the students car not having the proper harnesses?)

fatbillybob

Do you guys have problems with the HANS fitment to your seat back? If you follow the HANS rule and leave 1.5" for HANS space you have to add an extra cushion in many seats. This causes you to sit more forward out of the seat and less protected by the seat shoulder wings. So you get some fore/aft protection but you loose in the lateral protection of the seat. Remember it is a safety system. If you go with Isaac, it is very user friendly with other stuff out there. HANS is quite frankly IMO a pain. It is more restrictive, can hang on ingress/egress in windownets etc. crunched my shoulders and did not fit well in my seat...OMP carbon seat. John...how does the HANS fit in the Ultra shields with full containment head wings? I have only seen one HANS specific seat and it is the racetech for the doge viper. There may be others. Also, is this HANS going to slip off my 3" belts. I'm not crashing yet and I can pull the straps off the HANS even with LIPS which are really only on the back neck area of the new HANS. It seams like the chest area of the harness is quite at risk but sternum straps are a no-no! I know some of my post is not about safety but hey real life thats how it feels when I tried HANS. My Isaac is connected to my belts and not going anywhere. Also, GBaker adressed some of the concerns another poster had. even if the dampners failed you would be left with a position dependant device like a tether and the device rolls and locks on your belts when pinched with your shoulder when you crash. So belt stretch is taken into account in the Isaac equation.

Larry Herman

Colin, the Hans sits under the shoulder harness belts. If the belts are anchored too far apart or if the do not ride snugly over your shoulders, the effectiveness of the Hans device will be compromised. Additionally, it is only tethered to your helmet, so it may not come right with you if you climb from car to car. And it will not work at all with the 3 point belts, what you find in most green and blue student's cars.

ColorChange

Sorry George, I did not write correctly, the unit is not actually in front of the shoulder, just near the top of the shoulder. When you have an accident, it will roll forward, but I compress the dashpots with my hands and maintain/retain more of the shock absorption.

What I was trying to say was do not leave the unit fully extended in your normal position. This leaves much of the benefit off the table.

Now, the valving of the shocks is quite obvious in its damping of faster accelerations. You can simulate this with your hand and feel the increase in resistance. This is fairly obvious and I think you know it. If you really need it, I can ask Greg for the curves but I don't think that's necessary. I'm not sure what you are gettting at.

Geo

Here's my point. You are stating your opinion as fact. I don't think you have accelerated the dampers at 50 gs or even 10 gs. I don't doubt the folks as Isaac have done considerable work with the dampers. But since dampers are speed sensitive, they will work better at some speeds than others. And do you have data regarding the stretch of the webbing on the HANS straps and how they contribute to deceleration?

The fact is, you're speculating and that's fine. Just say so, because you don't know these things and as I said life is not always intuitive. Perhaps it is in this situation, and perhaps it's not.

Both are well engineered pieces of safety equipment. It's really sad that discussion of them so often comes down to something of a holy war. I made my decision for my own reasons as all of you should. I've had very satisfactory dealings with Hubbard-Downing, and I've never heard anyone say anything the least big bad about Gregg Baker. He's a good guy and stands behind his product and his drivers. I would be absolutely surprised if the Isaac doesn't end up 38.1 certified at some point, but of course it's a risk at the moment for those who may be required to have a 38.1 certified device.

garrett376

Do you guys who have the Isaac system have the "bonded" or screwed-in type of mounting plates? Any reasons you have seen or heard to go with one or the other?

FormulaOne10

Maybe this has already been mentioned but I can't find it...

When ColorChange mentions brainslap *I think* he is referring to frontal lobe injuries with the brain actually contacting the cranium as it continues movement while the cranium is slowed.

Also, being an mechanical engineer, I see a huge advantage in the ISSAC system. No matter how much webbing may slow deceleration (or head acceleration), dampers tuned properly to the application will beat it. Additonally, I continually see the pointless reassertion of the fact that dampers change their applied force with the speed of movement(F=K(dx/dt) for any physics people out there). Who the hell cares? If you are designing the damper, you make sure that they are effective at higher velocities which cause bio-damage and you don't worry about the lower velocites that don't cause damage in the first place. Of course things like travel and varying mass (helmet and head) could factor in...but these can all be integrated into a design without a great deal of fuss. If the folks at ISSAC did their homework (and it looks like they have, I would need more data to be sure), I think the answer for which system is better is obvious.

I will also note that the HANS probably gets the job done in most cases, since I seem to remember you need quite a bit of deceleration for frontal lobe damage.

JackOlsen

I bought the glue, but then attached it with the bolts. I didn't have a strong reason, at the time, other than that the glue looked like it might get a little messy.

RJay

Hans doesn't just snap taught, it allows stretch, just as your seat belts stretch. They are designed to do so. The arguement that some form of mechanical damping may more effective than a weave may or not be true, but I don't believe that taken as a thought experiment this is obviously so.

I'm no expert, so feel free to shoot at belief system, here is how I understand the problem. So consider the following text in John's red:

Lets remember the point of any of these devices is not to primarily to stop or even slow your head from moving. The point is to prevent the head, neck and shoulders from exceeding a certain angles and distances with respect to eachother. Obviously, in a frontal crash, initially all three are traveling at the same rate of speed toward the front of the car. Not a problem. As the harness stretches and absorbs the forward motion of the upper torso, without a H&N restraint, the forward motion of the head is checked only by the neck. The shoulders because of the harnesses take up begin to slow. The neck and teathers begin to load compensating for the speed differential between the restrained upper body and the relatively unrestrained head. Then there is a critical moment when the belts have done there work and the body recoils and starts to move backward toward the seat, but the head is still moving forwards. Without a HNR, the neck must absorb all the stress of them moving in opposite directions. As it hasn't be designed to do so, it fails and you die. With a Hans, the teathers save your life as they keep the SNH relationship within acceptable limits and distribute the load via the helmet to the top of your skull, rather than having all the force solely dealt with where the neck meets the skull. The shoulders lag behind the pelvis on the returned trip, impeeded by the head thanks to the teathers.

Point here? My understanding is that it's not really about deceling the head, it is about attempting to maintain a relationship between the head and shoulders that doesn't exceed the necks ability to cope.

Fire away

ColorChange

No no no (I’m pretty sure)! It is about decelerating the head. You have missed the critical point we are talking about. You are correct in the overall progression of things, but need to expand the critical zone we are talking about.

1. Bang – the car has stopped. Your head neck and torso continue moving forward at lets say 100 mph.
2. The belts begin to tension and your torso slows down. Your head and neck continue, largely unimpeded.
3. Your torso is now stopped, your neck is being stretched, and your head is still hauling ***. Uh oh! (Hopefully, your torso didn’t stop so quickly that your arteries are ripped apart ala Diana)
4. The mass of your head and helmet continue at 100 mph until your spine finally stretches and Pop, your head flies off. OK, this is BSF.

Now, what happens with the HANS:
1. Same
2. Same
3a. Most of this continues until the tethers finally pull tight and begin to decel your head. Your head is still doing about 100 mph before the decal starts.
3b. The tethers are now pulling hard, trying to decal your head and this load is transferred across your shoulders.
4. The HANS was able to decal your head enough so that the final g force was 40 g’s and you live, but your brain is a little wanked (think loopy, it’s a medical term)

With the ISAAC:
1. Same
2a. The ISAAC starts to roll up the belts and begins to slow your head a little, almost immediately.
2b. After your torso begins to slow, your head begins to slow as the dashpots feel the speed differential between your belts and your helmet. Your head is moving maybe 85 mph.
3a. Your torso is now stopped and the dashpots are now really fighting to slow your noggin. Your head is moving maybe 60 mph.
3b. Finally, your dashpots bottom out and this is roughly equivalent to the HANS tethers pulling tight. BUT, your head is only going 60 mph while your HANS head was doing 100 mph.
4. The ISAAC was able to transfer the load to your belts the final g force was maybe 20 g’s and you get out clean your shorts, but your cabeza is feeling quite fine.

Now, if you are diligent about keeping your HANS tethers tight, my total guess is that the safety of the two systems is comparable. But this is precisely the ISAAC benefit. I can move my head slowly in the pits, but gain the extra protection in a crash. With the HANS, you have to choose between hitting someone in the pits, or playing the brain slap game if you biff.

OK, an over exaggeration maybe but I hope I have made the point.

And I glued mine.