Forums: Skydiving: Safety and Training:
Re: [mjosparky] Injury in San Diego

 


alan  (D 17868)

Nov 24, 2003, 9:24 PM
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Re: [mjosparky] Injury in San Diego Can't Post

Quote:
It is just one form of deceleration injury.

You must mean acceleration injury or it can also be expressed as a negative acceleration injury. It was pointed out to me in no uncertain terms a short time ago in a different forum here that deceleration is just a layman's term and that from a Physics perspective they are the same thing, with no real difference. Apparently it has something to do with relative movement. I was fairly well called a fool and/or a common troll for suggesting that one does not accelerate up to a stoplight. Wink

At any rate, I think that if we are going to endorse and promote the use of helmets, we ought to at least encourage the manufactuers to provide some testing data and adhere to some type of standard. Of course that will mean testing, liability issues, etc., and ultimately raise the cost of a helmet. That's OK though because if it means saving a life then it is cheap insurance. You know, like a Cypres. People seem to have no problem with paying $1000 for the benefits they offer.

I also think it is unfair to limit the discussion to collisions with the ground while using a high performance canopy. Collisions occur with aircraft tails, other skydivers in freefall, and even big slow canopies can go fast enough to cuasa a head injury.


bigbearfng  (D 29442)

Nov 24, 2003, 10:11 PM
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Re: [alan] Injury in San Diego [In reply to] Can't Post

In reply to:
Quote:
It is just one form of deceleration injury.

You must mean acceleration injury or it can also be expressed as a negative acceleration injury. It was pointed out to me in no uncertain terms a short time ago in a different forum here that deceleration is just a layman's term and that from a Physics perspective they are the same thing, with no real difference. Apparently it has something to do with relative movement. I was fairly well called a fool and/or a common troll for suggesting that one does not accelerate up to a stoplight. Wink

In reference to head injuries-it's actually called a "contra-coup" type of injury-the brain con't in it's direction of travel as the skull stops-then the brain bounces back.......maybe sudden deceleration would cover it......

Helmet ratings-Snell and Dot....been a lot of controversy over the two ratings-Dot was the original and supposedly absorbed slower impacts better; using the "crush" effect, while Snell will withstand a higher velocity impact, but will transmit more force at the slower speeds that dot does better at....So it doesn't seem as if you can have both....but agreed 100% that A helmet is better than no helmet.
Does anyone know what/if any testing standards there is now for any helmet used in skydiving?
And best wishes sent for a full recovery.


mjosparky  (D 5476)

Nov 25, 2003, 10:51 AM
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Re: [bigbearfng] Injury in San Diego [In reply to] Can't Post

In reply to:
You must mean acceleration injury or it can also be expressed as a negative acceleration injury

We are not talking physics, deceleration injury is a medical term for injuries caused by a sudden stop. I don't think you the fool, I decelerate to a stop sign.
Sparky


freakydiver  (D 26421)

Nov 25, 2003, 11:03 AM
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Re: [bigbearfng] Injury in San Diego [In reply to] Can't Post

I just called Bonehead - they do not currently submit to any. I'd gander they are one of the biggest. Take it from there...


pilotdave  (D License)

Nov 25, 2003, 11:06 AM
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Re: [bigbearfng] Injury in San Diego [In reply to] Can't Post

In October, I spent a couple days at the US Army Aeromedical Research Laboratory and got a tour that included their helmet testing labs. VERY interesting stuff. They mostly do testing on army helicopter pilot helmets, but they have tested all kinds of helmets. The place is full of them. I'd love to see how different skydiving helmets compare to each other. One interesting thing I learned is that modern (or really future) helicopter pilot helmets are made of a material we're familiar with: Spectra.

Also learned a lesson about helmet ratings. DOT ratings mean almost nothing. This lab had maybe a 20-25 foot tall drop tower. They put the helmet over an instrumented metal head, and drop it onto a block of steel. They can then measure the acceleration (or deceleration if you prefer) experienced by the head inside the helmet.

Back in the vietnam era, the idea was to design a helmet that would keep a pilot's skull from fracturing. I think 400 Gs was the max allowable acceleration. Now the idea is to keep the pilot conscious, with a max of about 140 Gs.

But this lab can't test modern, snell approved motorcycle helmets. Their drop tower isn't tall enough to generate those kinds of accelerations when testing those helmets.

Another test they do showed how strong these helmets really are. They mount the helmet under the drop tower and raise up a sharp steel "tooth" which weights about 5 lbs I think. Raise it up 15 feet, and drop it onto the back of the helmet. It hurt just to hold that tooth in my palm. The helmets, even really light spectra helmets, can survive the hit with only a scratch. Amazing stuff.

Dave


kallend  (D 23151)

Nov 25, 2003, 3:30 PM
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Re: [mjosparky] Injury in San Diego [In reply to] Can't Post

In reply to:
In reply to:
You must mean acceleration injury or it can also be expressed as a negative acceleration injury

We are not talking physics, deceleration injury is a medical term for injuries caused by a sudden stop. I don't think you the fool, I decelerate to a stop sign.
Sparky

Physicists speak English too. Anyone who claims not to know the meaning of deceleration is a fool and a knave.

It is convenient when setting up equations to use acceleration for rate of change in velocity regardless of sign, otherwise we'd need two versions of Newton's Law.

We can also handle both "speed" and "velocity".


mjosparky  (D 5476)

Nov 27, 2003, 1:34 AM
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Re: [kallend] Injury in San Diego [In reply to] Can't Post

In reply to:
Physicists speak English too. Anyone who claims not to know the meaning of deceleration is a fool and a knave.

John,
I am glad because I don't speak physics verry well and when I slow down it seems like I am deceleerating.Tongue



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