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Math wizards please calculate for me...
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John_Scher

Oct 20, 2018, 12:54 AM
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Can any of you math wizards please calculate for me the transmitted force in kN's for a mass of say 70kGs (me) striking a cliff (head on crash, no angle) at 25MPH (canopy forward speed, no wind).

I know there are a zillion variables and I may not be asking a perfectly framed question but I think you know where I'm coming from and what I'm trying to understand/achieve

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EN 1621-1:1997 - Level 1 protectors
The maximum transmitted force must be below 18 kN, and no single value shall exceed 24 kN


EN 1621-2:2003 - Level 2 protectors
The maximum transmitted force must be below 9 kN, and no single value shall exceed 12 kN.

(This post was edited by John_Scher on Oct 20, 2018, 2:38 AM)

BodeyM

Oct 20, 2018, 1:58 AM
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https://www.engineeringtoolbox.com/...ct-force-d_1780.html

I'm not a math wizard at 2AM but there are the formulas. Should be able to plug your values right in.

John_Scher

Oct 22, 2018, 6:06 AM
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Thanks BodeyM,

I have corrected for stupidity and used a forward speed of 5MPH ie toggles still stowed and an accurate mass of 80kgs.

This seems to yield 0.4 kN which seems a tiny amount of force and doesn't correlate with the massive impacts that I've seen in videos of cliff and building strikes.

What am I doing wrong?

(This post was edited by John_Scher on Oct 22, 2018, 6:07 AM)

TomAiello

Oct 22, 2018, 7:11 AM
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I came up with something around 8KN (a bit less than 2000 pounds of force) for impact under a canopy in full flight.

I'll try to revisit the math this morning.

Can you explain the ratings you cited for the armor?

Is that a maximum transmitted force--meaning the amount of force that can be passed through to the wearer and still have the armor qualify for that specific rating?

John_Scher

Oct 22, 2018, 7:30 AM
Post #5 of 20 (2251 views)
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Tom,

I agree that for a canopy in full flight 8kN to 9kN is around the right numbers and is also what I came up with however object strike probably takes place prior to releasing the toggles (you know better than me as you've done it) therefore 5MPH forward speed (as per "the Sky-Diving Handbook") is probaly more appropriate to this scenario.

Can you explain the ratings you cited for the armor?

These are CE Levels for protective armour.
The ratings I mentioned above have actually now been supersceded as per:

Two levels of energy absorption providing two options for riders: slim, light and fairly safe or thicker, heavier and very safe. Beginning in 2014, the same tiered system will come to limb protectors, along with revised test methodology.

In the CE tests, body armour’s ability to absorb energy is measured by propelling an 11lbs weight with a 1.5 x 1.0-inch striking face into the armour with 37lb/ft (50J) of energy. The amount of energy transmitted through the armour is then measured and expressed in Kilonewtons.

The new set of standards, dubbed "EN 1621-1" now includes testing ambient, wet, cold (-10 degrees Celsius) and hot (40 degrees C) conditions. CE 1 armour needs to transmit 35kN or less mean and still allows a onetime spike of up to 50kN, but not in "Zone A," the centre area of the protector. CE 2 armour drops those numbers to 25kN mean and 35kN single.

In layman's terms, CE 1 is enough to prevent broken bones in most crashes at street speeds. CE 2 will absorb 71 percent more energy, making it substantially safer.

(This post was edited by John_Scher on Oct 22, 2018, 7:32 AM)

TomAiello

Oct 22, 2018, 7:37 AM
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Any idea how fast they propel the weight in the tests?

It sounds like basically they are throwing lead weights into the armor and measuring the amount of energy transmitted to the wearer?

TomAiello

Oct 22, 2018, 7:40 AM
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One of the issues is that object strikes are highly dynamic. No two are the same.

The majority of the critical injuries I've seen in object strikes have been on secondary strike (impact with the ground, usually, under a non-functioning or partially functioning canopy).

Most of the critical injuries I've seen on primary strike have been the result of focused impact (a relatively small point or bar transmitting the entire impact force into a small area), or head impact causing lack of consciousness (and usually therefore contributing to secondary strike injuries).

John_Scher

Oct 22, 2018, 7:51 AM
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Tom,

I appreciate your replies as not that many others are chipping in to this discussion but your comments are actually making me laugh (in a good way)

It sounds like basically they are throwing lead weights into the armor and measuring the amount of energy transmitted to the wearer?

I know you don't mean it the way you've made it sound but you are oversimplifying the complexity of energy absorption/transmission science and testing

I don't know the actual velocities of the hard things or their shape or size but yes they are chucking hard things (metaphorically speaking), at various materials and configurations and then averaging and using various other formulas and algorithms to calculate the energy transmission and absorption.

I'm not as clever as you guys especially with math that’s why I've requested help.

(This post was edited by John_Scher on Oct 22, 2018, 7:51 AM)

John_Scher

Oct 22, 2018, 12:02 PM
Post #9 of 20 (2179 views)
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The majority of the critical injuries I've seen in object strikes have been on secondary strike (impact with the ground, usually, under a non-functioning or partially functioning canopy).

I sort of guessed this was probably the case and was going to move onto this after having discussed the initial impact and related energy management. I guess there never can be enough impact protection (armour) for such a catastrophic event.


Most of the critical injuries I've seen on primary strike have been the result of focused impact (a relatively small point or bar transmitting the entire impact force into a small area), or head impact causing lack of consciousness (and usually therefore contributing to secondary strike injuries).

When you mention "focused impact" I believe you are referring to objects which are more penetrative as opposed to blunt slamming type impacts (i.e. blunt force trauma). Such impacts might best be managed by hard shell armour as opposed to molecular soft armour i.e. D3O.

TomAiello

Oct 22, 2018, 1:49 PM
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John_Scher wrote:
When you mention "focused impact" I believe you are referring to objects which are more penetrative as opposed to blunt slamming type impacts.

Yes. Especially with armor, a person curled into a ball and striking a flat surface can take quite a lot of impact. It's the pieces that stick out (arms and legs) or the pieces that stick "in" (penetrative trauma) that are most damaged/damaging.

kleggo

Oct 24, 2018, 9:49 AM
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John_Scher wrote:
Tom,

I appreciate your replies as not that many others are chipping in to this discussion but your comments are actually making me laugh (in a good way)

It sounds like basically they are throwing lead weights into the armor and measuring the amount of energy transmitted to the wearer?

I know you don't mean it the way you've made it sound but you are oversimplifying the complexity of energy absorption/transmission science and testing

I don't know the actual velocities of the hard things or their shape or size but yes they are chucking hard things (metaphorically speaking), at various materials and configurations and then averaging and using various other formulas and algorithms to calculate the energy transmission and absorption.

I'm not as clever as you guys especially with math that’s why I've requested help.
.

Interesting discussion, but don't rag on Tom too much.
You have heard the anecdotes about a fighter plane canopy designer continually failing bird strike impact testing because they were using FROZEN chickens.........................?

Colm

Oct 24, 2018, 7:52 PM
Post #12 of 20 (1931 views)
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kleggo wrote:
Interesting discussion, but don't rag on Tom too much.
You have heard the anecdotes about a fighter plane canopy designer continually failing bird strike impact testing because they were using FROZEN chickens.........................?

Fake news. USAF contractors are perfectly capable of misusing tax dollars without resorting to such technical incompetence.

Snopes heard about this story too: https://www.snopes.com/fact-check/catapoultry/



(and don't get me started on the mythbusters episode)
Attachments: fakenews.gif (500 KB)

John_Scher

Oct 25, 2018, 1:56 AM
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Re: [Colm] Math wizards please calculate for me... [In reply to] Can't Post

Ahh that’s nice, a double act, 2-fer-1, Waldorf & Statler.
One pipes up and then the other; a team effort.

Good old meaningless, off topic humour never goes amiss, lightens things up.
Don't want to be too serious now do we.

I have a question for you both…
Are you in anyway related, brothers perhaps, live together?

(This post was edited by John_Scher on Oct 25, 2018, 6:28 AM)

TomAiello

Oct 25, 2018, 6:19 AM
Post #14 of 20 (1869 views)
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John, on the topic of ground impact injuries, have you looked into the airbag systems that some paraglider pilots have mounted under their seats?

bluhdow

Oct 25, 2018, 9:45 AM
Post #15 of 20 (1845 views)
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My wife is an equestrian professional and her sport mandates air vests in certain disciplines. Basically she's tethered to the saddle and when the tether is pulled a certain distance (i.e. the rider falls off) the air vest inflates.

It's been hugely valuable in saving lives/injuries in her sport and I've thought about it a lot for BASE. I'm just not sure how to make it practical. Maybe a manual tether for when you're really in the shit but there's often better things to do with your hands than drop your control(s) and pull an air vest tether.

There are also unintended consequences. For example in her sport sometimes riders will get hurt when they forget to de-tether and then dismount...which scares the shit out of the horse.

base283

Oct 26, 2018, 3:50 AM
Post #16 of 20 (1773 views)
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Sorry to all for remaining on topic Wink
But is crashing vertically expending the same amount of force as horizontally for the same velocity?
Think about that Cool
take care,
space

John_Scher

Oct 26, 2018, 8:21 AM
Post #17 of 20 (1745 views)
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Sorry to all for remaining on topic Wink
But is crashing vertically expending the same amount of force as horizontally for the same velocity?
Think about that Cool
take care,
space


A scientifically true model would have to account for numerous factors ie acceleration, gravity, angular strikes, added kinetic energy due to pendulum, sticking your feet out in front, applying rear risers, turning the body sideways, wind, temperature and so on. This is way beyond me and best handled by Yuri.

My start point or perhaps should I say motivator in initiating this thread was to try to gain an insight into the viability of commecially produced energy absorbtion systems ie hard and soft (molecular) armour so as to ascertain if the predicted forces during our types of impacts could even be managed by such systems and it very much appears the answer is yes.

Even when I've doubled impact velocities but for simplicity sake excluded all other variables, the commercailly made armour still seems to have the capacity to absorb the predicted impact energies.

We all know that the best armour is that which you actually wear so I then tried to determine if the thinner, lighter, cooler and highly wearable L1 category of impact systems would suffice or if it was neccessary to utilise the thicker less wearable higher energy rated L2 systems and this produced a conundrum. The energies transmitted during ground impact either as a result of canopy collapse during object strike or a line over seem to be far less predicatable and of a far greater magnitude than do those encountered during object strike. It is these potentially extreme impacts where the jumper would definitely benefit from wearing thicker, heavier, hotter L2 protection systems which might, in real life situations be at home in the cupboard or in the boot of the car.

Personally I'm going for the trade-off ie L1 spine & shoulder protection which I know I will wear. I'm also going to have some nice thick padded hip protection but thats because I have a new hip.

(This post was edited by John_Scher on Oct 27, 2018, 2:12 AM)

TomAiello

Oct 26, 2018, 9:06 AM
Post #18 of 20 (1732 views)
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Another good strategy is switching armor depending on the jump. Low impact risk jumps might let you go with less armor, and higher risk (slider down cliffs, for example) might call for more armor.

John_Scher

Oct 26, 2018, 9:21 AM
Post #19 of 20 (1730 views)
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Another good strategy is switching armor depending on the jump. Low impact risk jumps might let you go with less armor, and higher risk (slider down cliffs, for example) might call for more armor.

This logic most certainly has its merits and might actually prove to work in real life situations as perhaps more of us might wear the stuff.
Needles to say it doesn't accomodate the (rare) line over or finding oneself committed to an unintended sketchy landing area or even stupidity as was my case ie opening low on a 4 way with Douggs and then turning low (duh) and if that wasn't enough then trying to avoid some trees on what should have been the easiest LZ on the planet. (bring on the crutches)

(This post was edited by John_Scher on Oct 26, 2018, 1:49 PM)

TomAiello

Oct 26, 2018, 12:04 PM
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I was more thinking that it could help convince people to "armor up" for the sketchier jumps.

For example, if you conclude that smaller and lighter armor is generally better because you are more likely to wear it, you could also buy a heavier set of armor for use when the situation looks more serious.


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