Mike S.

Thanks ltc. Interesting...chin stop.

From the above web page...what caught my eye...

"There is a big misconception amongst drivers, officials and others as to what prevents frontal impact head excursion. All tether devices, including FIA specific devices, use the mandible (jaw) to decelerate the head, as ultimately the forward head excursion is stopped by means of a chin strap via the mandible."

gbaker...interesting if fundementally true. Do you and the others in the industry share this opinion/conclusion/finding? This statement appears to want to create a level of fundemental equivilence between the Leatt device and others (e.g. Issac, Hans). Additionally, the statement would also infer that rotation of the head inside the helmet is not just occuring (as I'd suspect/believe), but that it is the key motion that rules the system and needs to be attended to.

Neck Force = [(15 lbm)(10 in)(50G)(1.8)]/(8 in) = 1700 lbf (tension)

Your nos./info + simple pinned connection as you requested...not really the right model for this "system". Potentially a worst case upper bound. Why? Primarily because the head will move inside the helmet due to looseness and foam and chin strap (stiffness and damping), the Leatt device and human body are not rigid (and have both stiffness and damping). and the helmet chin may not be a pure pivot point. This would be a relatively complex system to solve as many of the effects are what engineers would identiy as nonlinear...both geometry and material properties change (too much) as the event occurs.

Thanks,

Mike

bruinbro

Hence the need for experimental data. BTW, the game that Gregg and I are playing is one to see if the neck loads are in the ballpark of believabilty. In this device the head will rotate in the helmet and be restrained primarily by the helmet chinstrap. In the ISAAC device the placement of the helmet attach points puts the load line very close to the cg of the head/helmet combo (if my geometry is correct) thus minimizing internal head rotation and thus causing the forehead pad to provide most of the restraint (Gregg will be along a little later to tell me I have my head firmly planted, and not in my helmet...). I believe the HANS device is the same, but that is just a guess.

Bro

Karl Ebel

Please allow me to introduce myself; I am the Marketing Manager for the Leatt-Brace™ company. I am delighted that the members of this forum have taken the time to look at our fledgling product and are debating it. Our design rationale is simple; create a head and neck system that is effective, safe, user friendly, protects 360 degrees of head and neck movements and is affordable for the average racer as well as the professional. The Leatt-Brace™ has been tested dynamically with sled tests, pendulum tests, drop tests and swing tests during our R&D phase in three countries. When the Automotive Brace goes on sale, it will have SFI accreditation. Neck forces, or rather neck tension, is often cited as the only factor that produces Base of Skull fractures and neck injuries. Although neck tension must be reduced, it is a combination of axial forces, bending moments and shear force at a point in the collision impulse sequence that produces an injury, not to mention head deceleration. The SFI and others use the Nij (neck injury criteria calculations [combining axial force, bending moments and shear in a formula] to calculate the risk of injury. A high Nij at an impact sequence point denotes high injury risk. The Leatt-Brace™ reduces neck tension and bending moments with a resultant dramatic reduction in the Nij. The Leatt-Brace™ reduces neck tension by controlling forward head excursion and helmet trajectory, it can in fact be used with an open faced helmet in Rally events for example and effectively reduces the Nij even if the helmet is removed from a test dummy. What is often forgotten in an impact sequence, is what occurs after the first 140 milliseconds of a sled test - not commonly tested – this is only part of the story and does not show what happens to protective systems after the primary impact, the Leatt-Brace™ controls head and neck movement and forces for the entire impact event. Simulation software is used by our company to optimize design and not to prove effectiveness, due to our constant calibrations it gives results within 10% of dynamic tests. Once we are in production, SFI figures and test results will be available to all, please bare with us as we bring this project to completion. Please feel free to contact me should you have any more questions or comments.



Karl Ebel……….

gbaker

Welcome to the party Karl!

On which sleds did you test?

Geo

Sounds like you're saying the face actually stops the motion in this case if I understand your operating model correctly.

RedlineMan

I find myself exceptionally confused;

My understanding is that the natural crash motion of a harness-restrained occupant will be to move forward, the torso rolling down into a ball, placing the spine more toward the horizonantal (assuming there is nothing in the way to impede forward travel; dash, wheel, etc.), with the head rolling forward and down toward the lap. The upright vertical torso eventually seeks a much more horizontal attitude in keeping with the opposing direction of the force. The head will eventually stop once the spine reaches its limit (one would hope), but the helmet will keep going. The only thing that will keep the helmet on the occupant's head is the chin strap. In this case, it will then be the jaw that catches the helmet strap.

Most of the H&N devices USE the helmet to restrain the head, and reduce neck tension. By pulling back - or resisting extension - on the helmet they would necessarily take the load OFF the helmet strap, and thus the jaw. And yet, Leatt seems to be claiming the opposite is the case. Again, I'm confused.

It appears to me that the Leatt Brace will impede the natural forward travel of the head toward the horizontal, holding it much more upright. However, it seems to me that the helmet pushing down on the brace will create an equal and opposite force pushing up on the helmet, trying to push it off of the head. It seems to me that the only thing holding it on the head will be the chin strap, which will be resisted by... the occupant's jaw.



The Leatt claims of the biomechanics of this seem to be exactly opposite of what I understand. What am I missing here?

Mike S.

Hey John,

Hope the summer has been fun for you.


As bruinbro pointed out, with tethers located close to the head's cg, rotation will be minimized and I envision the helmet foam, especially on the forehead, to be the primary means to decellerate the head moving forward. I see the chin strap potentially involved at some point, but not to the extent indicated by the statement I lifted from the Leatt web site. I'm hoping gbaker responds.

I think you have described the basic physics well. As I said previously though, there are more effects to consider/include to get a proper understanding and not potentially overstate the neck tensile force.

Mike

RedlineMan

The pic I posted is a still showing the Isaac during a sled test using SFI 38.1 Spec. protocol. The HANS also places the body in a similar position at full extension. This does not reflect a lessening of rotation as Bro offered. THIS is the classic position of the body regardless of whether an H&N device (other than the Leatt) is used or not.

Since the helmet can't be going two directions at once, relative to the head, the head cannot be pressing into the top of the helmet, and the chin strap pressing into the jaw at the same time. What happens during recoil is another matter.

The summer is going good. Got my next project car yet?

Mike S.

John,

Very informative pic...I'm with you re general "ball" position whether H&N or none...just sooner head/helmet rotation and ultimately more travel w/o H&N.

Who says the helmet can't be going in 2 directions at once...translation + rototion Sorry, but my mechanics prof would be proud I answered this way! Seriously, the head can be rotating within the helmet and my sense is that this is why the Leatt website quote said:

"There is a big misconception amongst drivers, officials and others as to what prevents frontal impact head excursion. All tether devices, including FIA specific devices, use the mandible (jaw) to decelerate the head, as ultimately the forward head excursion is stopped by means of a chin strap via the mandible."

I'm leaving the door open for others (e.g. gbaker, Karl) more intimate with the motion of the head relative to the helmet to respond. It's not the conclusion I would have reached without being prompted, by this statement, to consider it. If it's true, it make me think both differently about the chin strap

This is what may be happening...consider this food for thought and discussion. Due to elasticity (flexability) in a tethered H&N system (tethers, support system, and even the body), both translation and rotation of the head and helmet starts at a similar rate. As the event unfolds, the tethered H&N system becomes increasingly more influential on decellerating the helmet and head subsystem. While the helmet proper decellerates both translationally and rotationally, the head does not an the same rate due to the foam elasticity. And I wouldn't be surprised to also hear that looseness of the skin to the skull is a meaningful contributor to the rotation of the head in this forward crash situation as well. So the head is driven forward and rotating downward relative to the helmet. Something like the forehead is not purely compressing the foam, but rotating down and shearing it as well. The jaw is now loading up the chinstrap due to the head rotation.

Re the location of the tethers as bruinbro mentions, a unfortunate amount of this benefit might be lost because the helmet and head have begun to rotate as well translate. All due to system (H&N, harness, seat, etc) flexability.

The good news for you is that I haven't done anything re getting the next P-car. The new news is that I'm thinking hard about a 911 as well as sliding from a heavy track config to more of a street/track balance. I'm getting in some drives in 911's to see if they're my cup of tea and specifically which version is the one for me. If I'm not infatuated with what I find, I'll head back to the 944, which is a know entity. If so, you're right at the top of my list for the items above my amateur skills and head.

Mike

DanS911

Can some of you smart guys chew on this for us?

gbaker

Based on Karl's comments regarding Nij, I suspect the chart is a plot of the front/rear bending torque (M-sub-y moment). The baseline plot is not familiar.

Carrera GT

Seeing what happens at shifter-cart events, I would have thought BSF would be a big issue but it seems relatively infrequent, perhaps it's a product of the track and safety design.

Karl Ebel

Hi All
Leatt-Brace will publish all data shortly. This will appear on our website so be sure visit and keep up to date. Please bare with us through the iterum period as we finalize our ramp up to production. Thank you greatly for all of your interest.
If you have any questions please contact me at karl@leatt-brace.com

ltc

My comment was based on the fact that it is assumed that the driver will come out of the kart/seat in a classic "BSF style front impact", thus reducing the likelyhood of the scenario that belted drivers face.
Cracked/broken ribs (and sternums) seems to be the most likely injuries.

Carrera GT

Good luck with the new product -- I hope you have high profile rider endorsements. Travis Pastrana comes to mind for obvious reasons.

Once parents start seeing these things at competition events being used by the pro riders, it has the potential to become part of the gear they buy for their kids.

Convincing your average rider will be a tougher sell. We're all riding around in a sort of suspended denial of just how badly things can go.

(ps. I was riding dirt bikes at Hollister yesterday, sure enough, along came the ambulance ... thinking about it now, you sort of assume a leg or an arm ... hopefully not a neck!)