RedlineMan

Hmmm....

For once I am in agreement with Tim to some degree!

There are different ways of marketing. There are also different ways of reacting to criticism. There are also different levels of truth and understanding that criticism is based on. I know full well that some of those "sled tests" used seats that were nothing like anything you'd ever see is a street car, let alone a track car. The equivalent of sitting the dummy on a milk crate. Who really knows what they are talking about, and how do you react?

Some fight fiercely for their idea, parrying every thrust. Some prefer to remain above the fray, continue working and developing, and let data and history decide. Do you react to every shot and open every attendant can of worms, or simply concentrate on improving your product?

I too am not overly warm and fuzzy about how HANS has handled everything. And yet, Mssrs Downing & Hubbard, along with luminaries such as Hubert Gramling and Karl Schroth have joined in. Richie Hearn DID survive a 130G IRL crash with his HANS. Lots of good people and good data made my decision.

fatbillybob

Sure...I went to a HANS seminar. There was really no talk of other devices just the HANS from its chief engineer. In this venue it is just all about HANS. It would be interesting to have a similar seminar from all the HN designers but they do not have those things for lay people. They ususally do not care bout laypeoples non-scientific opinion. That's why is was such an awesome seminar to hear from Dr. hubbard himself without the marketing guys. They in the industry do have "peer review" of results etc. I think the Society of Automotive engineers is that body. Dr. Hubbard made comment several times of HANS peer rievewed data as he explained the HANS device over several years of development. He did not emphasize it, but "peer rieview" is the gold standard of scientific device/theory acceptance or rejection. Peer review means that their product is looked at by the most important people first which are other scientists. We consumers are the last line or the ultimate determiners of what works...the real life examples. For example you experiment to find a new drug. It appears to work in the lab because you have correctly simulated the human body with rats. You show your results to your like minded scientific peers. They accept/reject/refute. It passes them and FDA you market it. Comsumers eat it and they get well. You have a succesful product. They get sick the FDA recalls you just like Viox.

ltc

FBB,
I find it remarkable/intriguing that a designer would design in, then out, then put back in, a feature, such as 'wings' (and all of the tooling and qualification changes associated with said changes) in an attempt to "make us feel better".
Were those Dr Hubbard's words?

fatbillybob

ITC,

I did not tape record him but yes. For sure his exact words were "... lips no lips...it does not matter..." which was the take home message. "Make us feel better" was said in a flipant funny sort of way. That is just how I remember it as I was listening very carefully for my key concerns which were belt slip, value of full containment, and value of the double shoulder belt 4 belt HANS specfic Scroth Harness. Dr Hubbard just appears to be annoyed by belt slip because he just does not see it as a real life in real time issue. It just seems like an issue that just won't go away just like people can't let go of the idea that the quick realse system of the ISAAC impeads your egress. I have used the ISAAC for over 1 yr and it functions exactly like GBaker says it does from my personal experience I have just never crashed one. While Dr. Hubbard touched on the issues of belt slip, value of full containment, and value of the double shoulder belt 4 belt HANS specfic Scroth Harness during his presentation I specifically asked him about these issues in more depth during our Q&A in front of our entire audience so it was not a one on one private remark. What I have posted in these last three posts is what I took away from him which is basically the same kinds of things Redline Man John has been posting from I guess alternate sources which may or may not be from HANS directly. You need to ask him. As an additional note Geo John and Dr. Hubbard credit much about all this crash safety stuff to Dr. Melvin and Tom Gideon two giants in this industry. Dr. Hubbard specifcially credits Dr. Melvin and Tom Gideon for their work and findings as it relates to HANS. HANS is the microsoft of HN systems. Right or wrong such is life.

ltc

Thanks for taking the time to reply to all these questions.

I am somewhat at a loss as to why a feature would be added, deleted and added again if it made no difference at all. As an engineer, it is completel non-intuitive.

kary993

Here is the text that go with the chart. Notice the last sentence around loose/tight fits. This is what I was refering to about load performance. Am I missing something with this chart?


"Isaac® data is direct from testing conducted at Wayne State University Bioengineering Center. The G-Force data is from company advertising. The other data have been garnered from SAE publications and other sources believed to be reliable. All trademarks are the property of the respective rights holders. (Note: Light colored bands represent a range of head loads assuming certain loose/tight conditions.) "

ltc

I agree.

Here are excerpts from the HANS manual (70 page version, ref pg 35):
http://www.stand21.fr/tour%20auto/Ow...el%20Hans1.pdf
"Tether Length
The HANS is assembled with an approximately 6 inch (153 mm) tether length that is acceptable to most users and takes into consideration the type of helmet attachment being used. However, the tether length can be adjusted plus or minus ¾ inch (19 mm) for individual preference. The tether length should be long enough to allow motions of the head and helmet that are actually needed, but no more."

The HANS manual on the www.hansdirect.com website is only 15 pages, but on page 9 of 15, it states almost the same thing; they state the tethers can be lengthened +/- 1" but no more"

So, if tether length does not matter, why then state the tethers can be adjusted/lengthened by plus or minus 3/4" to 1", BUT NO MORE?

gbaker

I am in agreement with both Tim and John. (Wow, how'd that happen? ) The most interesting aspect of this thread is Bob's presentation of his product--not that it's changed of late. As John noted, there are several valid approaches to marketing. We don't believe claiming perfection is in the long term best interest of either the company or its customers--especially in light of evidence to the contrary.

I'll just leave it at that. As a wise man once said, when the opposition is in a self-destruct mode, sit down and shut up.

On the technical side, it is important to make a distinction between the belts slipping off the HANS device laterally and the natural tendency of that product to "slip" posteriorly (to the rear) during a crash event. The latter is good in that it, in effect, shortens the tethers and minimizes the amount of kinetic energy in the head relative to the body. Tether length is also a factor because, obviously, if the tethers are, say, 50' long the HLR (head load reduction) is zero. That's why the instructions tell the customer to not screw with the tethers.

The only problem we have with this is that, if the tethers should not be lengthened, why design the device to allow the customers to lengthen them? If 6" is the limit, lock the things down at 6".

With respect to the other slippage, i.e. belts laterally off the HANS device, I'm disappointed to learn that Bob is parsing his words such that Justin Wilson (F1 driver) being airlifted to the hosptial because the belts slipped off his HANS device (causing him to be knocked around the cockpit with such force that he had to retire because of a pinched nerve in his shoulder) does not qualify as "slipping off during a crash" only because he managed to get back to the pits. C'mon, Bob. You make a good product. It's okay to admit to imperfection.

I don't know who is in charge of marketing at HD, but they should be fired while the firm still retains some credibility.

BTW, our product is not perfect. And we admit it.

fatbillybob

Gbaker describes the HANS action in this third paragraph above. Also, I suspect that the 6" is a generic normal like the 75kg man 5'10". Each helmet mounting can be different and perhaps that is the reason for the +/- amount. I'm just guessing.

To GBaker, the tethers are locked down from the factory but as you say need to be replaced at some interval or post crash so the device has removeable anchors so you can reomve/alter the tethers. It is much like the ISAAC piston lenght which is about 6" long and varies about 2" in piston travel. I no longer have the device so I am going by memory. I don't quite understand the ISAAC action but the HANS tether seems to have a similar action to the ISAAC damper which also does not require a specific initial lenght for positive action perhaps this is even similar to the LINK tether. How long is the link tether and how did you come to that calculation? I 'm just curious how that is derived.

Kary993, I don't know. What Dr. H said is not what this chart represents regarding head load vs tether length.. However, if the HANS works the way Dr. H. says then tether length would make no difference unless as GBaker says the obviously ridiculous example of the "50ft tether". Since GBaker is with us here perhaps he can tell us if HANS tether function is or is not similar to ISSAC damper function and if that similarity would translate into no satistical difference in head load with a range of tether lenght. I ask this because if this chart is true then the ISAAC is doing something different than the HANS is how I read the chart. Also if you look at the LINK I do npt understand why the link would have such potentially high head loads. It is basically an ISAAC with a tether. It the LINK tether is no longer than the longest extension of an ISAAC damper how possibly could it generate such high head loads? I have seen charts like this in other sciences. sometimes they are sperious for reasons I don't understand but people who analyse studies and statistics do understand. Therfore Kary993 I too am confused.

kary993

My understanding of the significant difference is the tether must extend fully to restrain while the damper on the Isaac will stop with a quick motion at the position it is currently at in the moment of the sudden stop. Obviously the Isaac will yield a bit but basically stop the head compared to the tether. I think this is what the chart is telling us.

This simple difference is why I believe the Isaac actually performs better in all instances over the HANS. I can only provide the information I provided below so if others can provide information to counter my position I would like to hear it.......Beuhler, Beuhler,............Beuhler........

DJF1

I agree with you that the Isaac looks to be working better 100% especially for us club racers. My interpretation of the chart is that Isaac works due to the piston immediately and starts slowing down the head motion therefore by the time it reaches its full extend it has already slowed down the head, therefore the forces at the end are less than the tether which does nothing till fully extended.
I think we are basically say the same thing here. My self I cant imagine driving in a race and having my belts loose and the Hans out of position all of a sudden. I think this can be quite dangerous by itself. What also has come off as of late is the Hans has very specific requirements to work properly. If anyone gets a Hans they better be sure that they go all the way building their cockpit around Hans to ensure that it is going to function 100%^at all times.
I'm thankfull to all for these conversations, at the end of the day we all come off as winners when it comes to safety and doing things right.

RedlineMan

Yes;

Let's all pat ourselves on the back for edifying eachother! Seriously, I've worked out a lot of details in my head during these threads. It really is good stuff.

Getting to the point of why the HANS seems to "beat" the Isaac Link. I would surmize this is because of one of the aspects we have discussed recently: The "HANS Slide."

We have discussed the phenomenon of the HANS remaining "adhered" to the shoulder belts and riding back off of the occupant's shoulders, effectively taking up tether slack early and keeping the head more or less directly in alignment over the torso.

With the Isaac, the device anchors are moving forward with the shoulders. When the belt takes up taught, you get a more or less immediate hydraulic lock-up that achieves similar end results to the "HANS Slide." However, the Isaac Link still has the free length of the tether to be tightened at that point, and therefore more travel of the head yet to go before it is restrained. If you made the tethers shorter to mitigate this, you would lose most of your range of free head motion under normal circumstances.

How am I doing, Gregg?

mamoroso

John I think you "nailed" it. It all makes sense to me. Thanks.

fatbillybob

What I have posted was from Dr. Hubbard directly unless otherwise stated. Since the post of Kary993 chart we are now getting into conjecture to explain the chart and I for one am not trained in biomechanics. John,DJF, Kary I don't think we can draw any conclusions. The only pro biomechanist is GBaker and perhaps if he can explain the variation between the link and the damper ISAAC in this chart we could "guess" about HANS only if the HANS function and ISAAC are similar enough. I would have loved to ask Dr. H about this chart.

gbaker

Agreed. People who prefer different products or design approaches can still learn something by opening up the hood and checking things out.

Well done, John. The only thing one might add is that rather than limiting the position of the head, a good H&N restraint ultimately limits the kinetic energy in the head relative to the body.

In a crash, your body stops but your head keeps going. The net effect is that your head is accelerating away from your body. Because the kinetic energy is a function of the square of the velocity, the KE builds very fast. For the head to come to rest the KE must go to zero, so you want to "catch" the head as early as possible, and hold it as rigidly as possible. Whether this is done with a short tether connected to a rigid anchor holding the head up (HANS), or a damper connected to a rigid anchor controlling the head velocity (Isaac) is just a matter of design philosophy. Either approach done correctly will reduce head loads by 80%+.

Early thinking was that you had to hold the head up in order to hold it on, but we now know that's not true. (Tilt your head as far forward as possible. Are you dead?) The HANS device could do this by getting rid of that vertical portion in the rear and connecting the tethers near the shoulder instead, but its patent requires the tethers be horizontal. Also, you are going to hit the wheel using any device, so no product has a safety advantage in that department.

All dampers react to velocity. Move them slowly and there is little resistance; move them quickly and resistance is high. In the Isaac application, the harder you crash the more aggressively they act to control head velocity. Forget sensors and computer control circuits; a dumb shock will do this automatically.

What happens when you take out the dampers and replace them with webbing, ala the Link? Two things: 1) any slack allows the head to continue accelerating, which will increase loads and, 2) costs drop like a rock. We developed the Link for budget racers. 80% of racers are drag racers or oval racers, and they are always broke--or think they are.

(A more detailed description of the physics is here: http://isaacdirect.com/html/Gearheads.html)

[Edit: spelling]