New H&N restraint design...
07-27-2006, 03:01 PM
#16
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This product was at the PRI show last December but we did not have a chance to speak with any company representatives. We were told by some attendees that test results were not available, or that there were none at that time, I can't remember which.
The more the merrier.
I believe this is the first non-US design.
The more the merrier.
I believe this is the first non-US design.
07-27-2006, 03:35 PM
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Originally Posted by RedlineMan
I do see that it will attempt to hold your chin up, but how does it counter the dynamic forward load that is trying to rotate the head up and over that collar? I don't see that happening. It seems that it relying solely on changing the vactor of that force. So, instead of your head rotating forward and down to such an extereme that your neck is snapped by leverage, it is stretched to an extreme instead.
Bro
07-27-2006, 04:14 PM
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Not to be morbid - but isn't the true benefit to a H&N restraint NOT to keep your head from bobbing forward (i,e, chin to chest) but to keep your head the same distance from your shoulders in the event that your body stays relatively set strapped into the seat and you need a little more than your neck musclues to keep your neck relatively the same length?
Your HANS tethers allow ofr a decent bit of forward flexion. And, since you can touch your chin to your chest normally, doing it fast - shoouldn't kill ya.
It is my understanding from things I have heard / read, that the head continues traveling and "internally disconnects" from the rest of the body - i.e. spinal cord, arteries, etc in an impact - it's note a whiplash movement. Seat belts do a good job at keeping the TORSO close to the seat- but your melon is pretty heavy - and multiply the effect of the g's in an impact and it's like trying to hold onto a bowling ball during a car accident.
While this device might serve to stabilize your head in a low G impact - I believe that it is insufficient for road racing applications.
Your HANS tethers allow ofr a decent bit of forward flexion. And, since you can touch your chin to your chest normally, doing it fast - shoouldn't kill ya.
It is my understanding from things I have heard / read, that the head continues traveling and "internally disconnects" from the rest of the body - i.e. spinal cord, arteries, etc in an impact - it's note a whiplash movement. Seat belts do a good job at keeping the TORSO close to the seat- but your melon is pretty heavy - and multiply the effect of the g's in an impact and it's like trying to hold onto a bowling ball during a car accident.
While this device might serve to stabilize your head in a low G impact - I believe that it is insufficient for road racing applications.
07-27-2006, 04:18 PM
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Originally Posted by RedlineMan
OK...
This is my opinion, and I might be wrong. It is based on intuition. I am not trying to attack you personally DJ, but in my opnion this represents a fundamental MISSUNDERSTANDING of what is going on.
Part of the job of an H&N device is to try and maintain as normal a relationship between the head and the torso as possible. Keeping the head more or less on top of the shoulders and in normal position will reduce neck strain in the geographic, mechanical sense.
However, how do you keep the head in that position if you do not directly hold it in place or restrain it? Obviously, your neck muscles are not strong enough to do it. From my memory of physics - which I failed miserably as a book-learning student - I remember something about equal and opposite forces. To counter a force, you need an equal and opposite force, or in the case of every other H&N device available, a substantial amount of direct restraint. I do not see where this rig will give you that in any possible sense. I do not see how this rig will do anything to lessen the DYNAMIC load on the neck, and I've got to figure that this is at least as important as positional maintenance, if not more so.
I do see that it will attempt to hold your chin up, but how does it counter the dynamic forward load that is trying to rotate the head up and over that collar? I don't see that happening. It seems that it relying solely on changing the vactor of that force. So, instead of your head rotating forward and down to such an extereme that your neck is snapped by leverage, it is stretched to an extreme instead.
Is this safer? Safe enough? I don't see it. I want to see sled test data. Maybe it works. Maybe you survive? Does it reduce the dynamic load or just shift it? Numbers... I want numbers. Computer modeling is next to useless in real terms.
By the way, understanding how the HANS really reacts would reduce some of what I perceive as your dislike for its performance. It is a very well chronicled sequence, and the device performs very well under most circumstances. The Isaac does indeed "outperform" it in total reduction of dyamic load, no doubt at least partially due to the "immediate" take up of the hydraulics. This is a verifiable distinction, but it is a debateable point as to whether you could label it significant. Both are extremely viable products.
This is my opinion, and I might be wrong. It is based on intuition. I am not trying to attack you personally DJ, but in my opnion this represents a fundamental MISSUNDERSTANDING of what is going on.
Part of the job of an H&N device is to try and maintain as normal a relationship between the head and the torso as possible. Keeping the head more or less on top of the shoulders and in normal position will reduce neck strain in the geographic, mechanical sense.
However, how do you keep the head in that position if you do not directly hold it in place or restrain it? Obviously, your neck muscles are not strong enough to do it. From my memory of physics - which I failed miserably as a book-learning student - I remember something about equal and opposite forces. To counter a force, you need an equal and opposite force, or in the case of every other H&N device available, a substantial amount of direct restraint. I do not see where this rig will give you that in any possible sense. I do not see how this rig will do anything to lessen the DYNAMIC load on the neck, and I've got to figure that this is at least as important as positional maintenance, if not more so.
I do see that it will attempt to hold your chin up, but how does it counter the dynamic forward load that is trying to rotate the head up and over that collar? I don't see that happening. It seems that it relying solely on changing the vactor of that force. So, instead of your head rotating forward and down to such an extereme that your neck is snapped by leverage, it is stretched to an extreme instead.
Is this safer? Safe enough? I don't see it. I want to see sled test data. Maybe it works. Maybe you survive? Does it reduce the dynamic load or just shift it? Numbers... I want numbers. Computer modeling is next to useless in real terms.
By the way, understanding how the HANS really reacts would reduce some of what I perceive as your dislike for its performance. It is a very well chronicled sequence, and the device performs very well under most circumstances. The Isaac does indeed "outperform" it in total reduction of dyamic load, no doubt at least partially due to the "immediate" take up of the hydraulics. This is a verifiable distinction, but it is a debateable point as to whether you could label it significant. Both are extremely viable products.
07-27-2006, 04:19 PM
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Tension limit ~ 4kN.
I think (I'd have to look it up) the M-sub-y limit is in the 75-125 NM range but, as you note Bro, the pivot point is shifting so it gets complicated rather quickly.
Someone should just test it. If it works, great.
I think (I'd have to look it up) the M-sub-y limit is in the 75-125 NM range but, as you note Bro, the pivot point is shifting so it gets complicated rather quickly.
Someone should just test it. If it works, great.
Last edited by gbaker; 07-28-2006 at 09:11 AM.
07-27-2006, 06:47 PM
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This device works only in compression loading, not tension. (please correct me if I'm wrong on this basic point). As such, the forward deceleration of the head/helmet combo can only be resisted by shear restraint at the helmet/device interface and translation into a moment about the chin line. This is because the cg of the head/helmet system is above the chin/device interface. Without an external tensile restrain of some sort the neck has to provide the restraining force associated with the counteracting torque. It is the magintude of the force and it's comparison to the neck's capability that is in question.
Bro
Bro
07-27-2006, 08:56 PM
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Bro,
You had to throw that out there, didn't you?
Okay, I'll play. Let's build a predicting equation.
Assume a 15# head/helmet combo and a 50G sled impact. Given that head Gs are ~1.5-2.0 (say 1.8) greater than crash sled Gs, what neck tension is required for an offsetting moment?
You had to throw that out there, didn't you?
Okay, I'll play. Let's build a predicting equation.Assume a 15# head/helmet combo and a 50G sled impact. Given that head Gs are ~1.5-2.0 (say 1.8) greater than crash sled Gs, what neck tension is required for an offsetting moment?
07-27-2006, 09:16 PM
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Where is the head/helmet cg with relation to the bottom front point of the helmet? Also, what is the distance from the neck axis to the front of the helmet at the chin point?
Bro
Bro
07-27-2006, 09:44 PM
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Whew!
Thanks DJ. I was almost afraid to look at what I might have caused. It sort of sounded like you were dissing HANS and on this new bandwagon full bore. I see now you were just thinking aloud.
It is quite true that we won't know until we see numbers from an industry standard sled test. I still don't see how it reduces the LOAD that the neck sees. I am assuming that this reduction is very important. However, it is possible that this rig will manage the body parts in question in such a way that the load is sustainable. I just don't see how.
I didn't do anything but look at the pictures. Didn't go to the site or look at any clips or anything. Just looked at it. Maybe I'm missing something. I find it hard to believe anyone would actually come out with something that didn't work, but I don't see how it does... really.
Thanks DJ. I was almost afraid to look at what I might have caused. It sort of sounded like you were dissing HANS and on this new bandwagon full bore. I see now you were just thinking aloud.
It is quite true that we won't know until we see numbers from an industry standard sled test. I still don't see how it reduces the LOAD that the neck sees. I am assuming that this reduction is very important. However, it is possible that this rig will manage the body parts in question in such a way that the load is sustainable. I just don't see how.
I didn't do anything but look at the pictures. Didn't go to the site or look at any clips or anything. Just looked at it. Maybe I'm missing something. I find it hard to believe anyone would actually come out with something that didn't work, but I don't see how it does... really.
07-27-2006, 10:05 PM
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Originally Posted by Janni
Not to be morbid - but isn't the true benefit to a H&N restraint NOT to keep your head from bobbing forward (i,e, chin to chest) but to keep your head the same distance from your shoulders in the event that your body stays relatively set strapped into the seat and you need a little more than your neck musclues to keep your neck relatively the same length?
It is entirely normal for the head to project forward with the chin rotating downward. The HANS and Isaac use this to their advantage. Since the head is inside the helmet, and the helmet is directly restrained, the forward rotation of the head presses the forehead and top of the head into the top of the helmet, like a bucket. If the head did not rotate forward and down, your head would project out of the front of the helmet, face first, which obviously would not be good.
HANS tethers allow ofr a decent bit of forward flexion. And, since you can touch your chin to your chest normally, doing it fast - shoouldn't kill ya.
It is my understanding from things I have heard / read, that the head continues traveling and "internally disconnects" from the rest of the body - i.e. spinal cord, arteries, etc in an impact - it's note a whiplash movement.
Gregg, if I've flubbed anything, please clean it up, eh?
07-28-2006, 02:44 AM
#26
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I really, really want to try one, because I don't like the lack of motion with my R3, but I have the same concern John, and others, are expressing. I went so far as to order one, but Leatt ran into some design changes at the same time, so I let it go for now.
What they told me is that it is the combination of the chin hitting the chest and then acting as a pivot point that launches the head off the body (BSF to be technical), hence the HANS, R3 et al work by holding everything in check whereas the Leatt is supposed to do it by preventing the sudden torque. OK, I understand what they are saying, but I'm not sure what the neck muscles will do as my head and helmet are trying to fly off my body in a straight extension. And I'm a little worried about that, so I really want to see test data.
They have quite a few racers using them now, particularly rally guys, but it doesn't mean a thing without some real data.
What they told me is that it is the combination of the chin hitting the chest and then acting as a pivot point that launches the head off the body (BSF to be technical), hence the HANS, R3 et al work by holding everything in check whereas the Leatt is supposed to do it by preventing the sudden torque. OK, I understand what they are saying, but I'm not sure what the neck muscles will do as my head and helmet are trying to fly off my body in a straight extension. And I'm a little worried about that, so I really want to see test data.
They have quite a few racers using them now, particularly rally guys, but it doesn't mean a thing without some real data.
07-28-2006, 08:14 AM
#27
NEED MORE INFO
I would not be so quick to toss this out.
Remember how understanding and evolution are suppose to work? Do we really believe that the "original" idea is the best we will ever come up with?
Read all the stuff, they just might be on to something.
I would not be so quick to toss this out.
Remember how understanding and evolution are suppose to work? Do we really believe that the "original" idea is the best we will ever come up with?
Read all the stuff, they just might be on to something.
07-28-2006, 10:57 AM
#28
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The thing that scares me a bit is that it appears they have only done computer simulations. Computer sims are great for design studys and trades, but impact loads are not well described in computers so without a series of tests as basis of understanding I don't really trust anaylsis alone. I know for one that Gregg Baker and ISAAC have done so much sled testing that they can probably predict to great certainty what will happend when they make changes to the ISAAC. Same for HANS. However my feeling is that they learned quite a bit in the first few seld tests. Things that greatly improved their knowledge of the dynmaic forces in such a crash. It does not appear clear that these new folks have that hard testing in their background. If that thing has never been sled tested it scares me.
07-28-2006, 01:26 PM
#29
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Originally Posted by DanS911
NEED MORE INFO
I would not be so quick to toss this out.
Remember how understanding and evolution are suppose to work? Do we really believe that the "original" idea is the best we will ever come up with?
Read all the stuff, they just might be on to something.
I would not be so quick to toss this out.
Remember how understanding and evolution are suppose to work? Do we really believe that the "original" idea is the best we will ever come up with?
Read all the stuff, they just might be on to something.
(Bro: had to put the helmet on the skeleton; numbers available soon.)
Computer sims can be accurate if they are sufficiently detailed. In the case of Isaac, we had some internal models that got us close, but after the first crash test we contracted with WSU for tuning. This is very sophisticated technology, and it still missed the sled numbers.
Slightly OT, but Dan's post reminded me of something I just read about John Barrow, a physicist whose theories caused quite a stir. Quoting from author Joao Megueijo,
"John Burrow once remarked that any new idea goes through three stages in the eyes of the scientfic community.
Stage 1: It's a pile of **** and we don't want to hear about it.
Stage 2: It's not wrong but it certainly has no relevance whatsoever.
Stage 3: It's the greatest discovery ever made and we found it first."
Stage 1: It's a pile of **** and we don't want to hear about it.
Stage 2: It's not wrong but it certainly has no relevance whatsoever.
Stage 3: It's the greatest discovery ever made and we found it first."
07-28-2006, 02:05 PM
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Originally Posted by bruinbro
Where is the head/helmet cg with relation to the bottom front point of the helmet? Also, what is the distance from the neck axis to the front of the helmet at the chin point?
Bro
Bro
Keeping it simple, let's assume the line passing between the cg and the bottom front point of the helmet is 45 deg off horizontal and is about 10" long. Similarly, let's assume the axis of the neck is also 45 deg off horizontal, passes through the cg and is, say, 8" long. Everything rotates easily, so pinned connections would apply. I'm keeping it real simple with static geometry. (Hey, it's Friday afternoon, gimme a break.)