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  #1  
Old 11-02-2007, 03:04 PM
Just Some Guy Just Some Guy is offline
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Best Way to Survive Falling at Terminal Velocity (Need answer fast)

Let's say I fell out of an airplane 20,000 feet up and I don't have a parachute. Obviously the odds are really against me surviving the sudden stop at the end but it has happened from time to time. Let's also say this happened over what looks like rural Ohio; plenty of farmland, not much trees, and little water in sight. Is there a way I could try to hit the ground to maximize my chances to survive?

Any quick suggestions would be appreciated.
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  #2  
Old 11-02-2007, 03:08 PM
flight flight is offline
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In order of priority:

1) Aim for the twenty foot deep snow drift.

2) Cling to the largish section of plane that has a lot of drag to it (and preferable some cushioning).

3) Aim for the hardest surface you can find, because without one of the first two you are going to be dead and it would be best if you didn't have a few moments of excruciating pain while vomiting up your internal organs first.

Last edited by flight; 11-02-2007 at 03:09 PM..
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  #3  
Old 11-02-2007, 03:17 PM
garygnu garygnu is offline
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Best Way to Survive Falling at Terminal Velocity (Need answer fast)

Best. Thread Title. Ever.
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  #4  
Old 11-02-2007, 03:18 PM
UncleRojelio UncleRojelio is online now
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I heard about a parachutist that survived a fall. Apparently, the key to her survivial was the fact that she landed flat on her side. Her foot, ankle, knee, pelvis, elbow, and shoulder all impacted at the same time. She also landed in a recently plowed field. Don't remember if she ever walked again though. Isn't there an Uncle Cecil column on this subject?

Here it is:
http://www.straightdope.com/columns/050311.html

Last edited by UncleRojelio; 11-02-2007 at 03:21 PM..
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  #5  
Old 11-02-2007, 03:22 PM
Hilarity N. Suze Hilarity N. Suze is offline
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Before the 20-foot snowdrift, look for some trees. Grab & break a few branches on the way down.

Do you feel lucky? Well, do you?

Last edited by Hilarity N. Suze; 11-02-2007 at 03:23 PM.. Reason: Yeah, great thread title.
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  #6  
Old 11-02-2007, 03:27 PM
Chronos Chronos is online now
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The other way to survive is to land on a steep slope, preferably one which gradually turns into a shallow slope. This is generally how they do the recovery on those amusement park free-fall rides.

And if there's no snow around, deep mud is nearly as good. I think one of the known cases of a person surviving a high-speed impact was a marsh landing. And if you're falling over farmland, a manure pile will work, too: The stink is much better than the alternative.
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  #7  
Old 11-02-2007, 03:35 PM
Wee Bairn Wee Bairn is offline
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Vesna Vulovic, a stewardess who survived a 30,000 ft fall from a bombed airplane, did so by landing on the steep slope of a snow covered mountain. She was also surrounded by parts of the fuselage IIRC she was in the loo at the time.

A brief bit on her and two others- it seems landing through some pine trees would be good too.

Last edited by Wee Bairn; 11-02-2007 at 03:37 PM..
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  #8  
Old 11-02-2007, 03:40 PM
Terminus Est Terminus Est is offline
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From 20,000 feet up, our unlucky skydiver will take about 2 minutes to reach the ground. The first answer in this thread came 4 minutes after the OP.

Just Some Guy, you alright, buddy?
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  #9  
Old 11-02-2007, 03:41 PM
Bobotheoptimist Bobotheoptimist is offline
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So, in the loo with a stewardess is the best bet?
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  #10  
Old 11-02-2007, 03:42 PM
askeptic askeptic is offline
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Quote:
Originally Posted by Wee Bairn
Vesna Vulovic, a stewardess who survived a 30,000 ft fall from a bombed airplane, did so by landing on the steep slope of a snow covered mountain. IIRC she was also surrounded by parts of the fuselage IIRC she was in the loo at the time.

Aaaaaand.....she never reached terminal velocity because the front of the plane exploded. She was in the tail section which was still attached to the majority of the plane including both wings. The plane went into a flat spin never reaching terminal velocity.

A budy of mine took a drunken fall of a fifth floor balcony and landed on a parked car. He suffered very minor bruising but thats it. Doubt he was able to reach terminal velocity or even close though. Still, try getting drunk and looking for a car to land on.
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  #11  
Old 11-02-2007, 03:44 PM
Chronos Chronos is online now
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This wasn't here when I posted:
Quote:
I heard about a parachutist that survived a fall. Apparently, the key to her survivial was the fact that she landed flat on her side. Her foot, ankle, knee, pelvis, elbow, and shoulder all impacted at the same time.
That's the worst possible way to land. If you absolutely must land on something flat and relatively unyielding, it's best to stretch yourself out as tall and vertical as possible, to give yourself the maximum distance over which to decelerate. You'll break both your legs, but you might, if you're really really lucky, survive.

If you're landing in something deeper than you are tall, like the afore-mentioned 20 foot snow drift, then optimal landing orientation depends on how yielding the material is, and how much of it there is. If the snow is very loose, then landing spread-eagle flat might be good.
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  #12  
Old 11-02-2007, 03:44 PM
flight flight is offline
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Quote:
Originally Posted by UncleRojelio
I heard about a parachutist that survived a fall. Apparently, the key to her survivial was the fact that she landed flat on her side. Her foot, ankle, knee, pelvis, elbow, and shoulder all impacted at the same time. She also landed in a recently plowed field. Don't remember if she ever walked again though. Isn't there an Uncle Cecil column on this subject?

Here it is:
http://www.straightdope.com/columns/050311.html
When you hear someone say, "Their chute didn't open, but they lived," they usually mean, "Their chute was in a big streamer-like mess behind them that, while not acting like a regular parachute, created a huge amount of drag to slow them a great deal so they lived."
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  #13  
Old 11-02-2007, 03:47 PM
Wee Bairn Wee Bairn is offline
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Quote:
Originally Posted by askeptic
Aaaaaand.....she never reached terminal velocity because the front of the plane exploded. She was in the tail section which was still attached to the majority of the plane including both wings. The plane went into a flat spin never reaching terminal velocity.

A budy of mine took a drunken fall of a fifth floor balcony and landed on a parked car. He suffered very minor bruising but thats it. Doubt he was able to reach terminal velocity or even close though. Still, try getting drunk and looking for a car to land on.
I'm no physics guy- why would an explosion prevent terminal velocity? I always assumed if you were high enough you would reach the speed automatically?
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  #14  
Old 11-02-2007, 03:50 PM
askeptic askeptic is offline
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Quote:
Originally Posted by Chronos
This wasn't here when I posted:That's the worst possible way to land. If you absolutely must land on something flat and relatively unyielding, it's best to stretch yourself out as tall and vertical as possible, to give yourself the maximum distance over which to decelerate. You'll break both your legs, but you might, if you're really really lucky, survive.

If you're landing in something deeper than you are tall, like the afore-mentioned 20 foot snow drift, then optimal landing orientation depends on how yielding the material is, and how much of it there is. If the snow is very loose, then landing spread-eagle flat might be good.

Actually the doctors interviewed about this incident specifically said that had she landed feet first should would have certainly died. They explained that feet first landing would have invariably crushed her spine as opposed to spreading the point of impact along the horizontal axis of her body. You mention maximum distance to decelerate, at those speeds you ain't going to decelerate much in the 5 feet between the ground and your head. My guess is the head will impact the ground at the same speed whether you land feet first or head first.

Last edited by askeptic; 11-02-2007 at 03:53 PM..
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  #15  
Old 11-02-2007, 03:52 PM
THespos THespos is offline
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Be a character on Grey's Anatomy.
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  #16  
Old 11-02-2007, 03:52 PM
askeptic askeptic is offline
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Quote:
Originally Posted by Wee Bairn
I'm no physics guy- why would an explosion prevent terminal velocity? I always assumed if you were high enough you would reach the speed automatically?

The explosion did not prevent achieving terminal velocity, the flat spin did.
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  #17  
Old 11-02-2007, 03:53 PM
flight flight is offline
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Quote:
Originally Posted by Wee Bairn
I'm no physics guy- why would an explosion prevent terminal velocity? I always assumed if you were high enough you would reach the speed automatically?
The explosion didn't, the fact that most of the plane was still there did. In fact it did reach terminal velocity, but terminal velocity of a plane with its wings in a flat spin is a hell of a lot lower than that of a person falling on their own.

Oh, and I think you are confused about the landing on the side thing. It sounds suspicious like the standard parachutists landing technique, except for that you hit those body parts one at a time, rolling into it in order spread out the impact and slow the rate at which you come to a stop.
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  #18  
Old 11-02-2007, 03:53 PM
Wee Bairn Wee Bairn is offline
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Quote:
Originally Posted by askeptic
The explosion did not prevent achieving terminal velocity, the flat spin did.
You mean the rotation of the section of the plane she was in? If so, it didn't eventually start to fall straight down and gain the needed speed? Physics and I don't get along...

ETA: flight answered this after my post.

Last edited by Wee Bairn; 11-02-2007 at 03:55 PM..
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  #19  
Old 11-02-2007, 03:57 PM
Flander Flander is offline
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Landing flat on you back would spread the impact to a greater area, but it's not going to slow your internal organs much. I imagine the force of your brain hitting your skull at near terminal velocity would suck hard core.
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  #20  
Old 11-02-2007, 04:04 PM
Finagle Finagle is online now
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Quote:
Originally Posted by askeptic
Actually the doctors interviewed about this incident specifically said that had she landed feet first should would have certainly died. They explained that feet first landing would have invariably crushed her spine as opposed to spreading the point of impact along the horizontal axis of her body. You mention maximum distance to decelerate, at those speeds you ain't going to decelerate much in the 5 feet between the ground and your head. My guess is the head will impact the ground at the same speed whether you land feet first or head first.
Apparently what you want to do is to land more or less vertically, but then falling/rolling so you sequentially take the force on your (bent) legs, butt, side, and shoulders -- in other words, spreading out the impact as much as possible.
(Info vaguely remembered from a webpage on survivors of long falls, but more or less duplicated here.)

Shield your head with your arms if possible.
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  #21  
Old 11-02-2007, 04:15 PM
askeptic askeptic is offline
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Quote:
Originally Posted by Finagle
Apparently what you want to do is to land more or less vertically, but then falling/rolling so you sequentially take the force on your (bent) legs, butt, side, and shoulders -- in other words, spreading out the impact as much as possible.
(Info vaguely remembered from a webpage on survivors of long falls, but more or less duplicated here.)

Shield your head with your arms if possible.

What you are describing is a PLF or parachute landing fall. Works great at speed below 20 feet per second.

askeptic- several years in the 82nd Airborne Division where I did countless PLFs...
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  #22  
Old 11-02-2007, 04:16 PM
samclem samclem is offline
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In Cecil's column on this topic, he gave the example of a Marine pilot in 1963, Cliff Judkins, who survived a 15,000 ft. drop into the Pacific, feet first. At least one news story at the time indicated that a "drogue(pilot) chute" possibly slowed his fall.
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  #23  
Old 11-02-2007, 04:23 PM
askeptic askeptic is offline
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It should also be noted that when falling feet first you will impact the ground at a significantly higher velocity than if you are stretched out horizontal maximizing the amount of drag produced.
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  #24  
Old 11-02-2007, 04:32 PM
jimmmy jimmmy is offline
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I asked about falling from a plane some years ago -- so these are some fast thoughts too

garygnu - lol
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  #25  
Old 11-02-2007, 04:35 PM
Valgard Valgard is offline
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Quote:
Originally Posted by askeptic
What you are describing is a PLF or parachute landing fall. Works great at speed below 20 feet per second.

askeptic- several years in the 82nd Airborne Division where I did countless PLFs...
Exactly. Terminal velocity in a flat arch is roughly 180 fps. In a head down no-lift dive (much closer to the standing up posture people are talking about) you're looking at 300+ fps. A 6' person going 180fps who manages to stand up the instant before they hit the dirt will have 1/30 of a second to "roll with the fall".

I have landed a spinning, malfunctioned round reserve in a freshly plowed field (literally, I saw the farmer driving his tractor at the time) and did an extremely good PLF. This was a relatively low-velocity impact and it was both very fast and very uncomfortable - the slap of hitting the ground made me think that some of my internal organs had burst. Net damage was a lot of bruises and sore muscles.

My recommendation for a terminal velocity impact would be to aim for something big and soft and relax. Being rigid when you hit will not help.

Back in my skydiving days I was friends with a guy who survived an ~80mph impact from a stunt gone wrong, he hit the roof of a car in a parking lot and lived to tell about it, but he broke an awful lot of stuff and has plenty of metal in him. What I read about most sport skydiving incidents is that victims of high-velocity impacts generally survive the sudden stop but they are severely injured and die before the paramedics can get to them.
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  #26  
Old 11-02-2007, 06:44 PM
cormac262 cormac262 is online now
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Quote:
Originally Posted by Valgard
My recommendation for a terminal velocity impact would be to aim for something big and soft and relax. Being rigid when you hit will not help.
I don't have a cite, but I seem to recall reading/hearing some statistic about survivors of failed-parachute falls. And that one of the keys was that the person was unconscious at the time of impact - they had fainted or passed out during the fall.
So how best to survive a fall: knock yourself unconscious !

(I've thought about this, and have wondered if it would even be possible given the amount of adrenaline that would be pumping through your body at the time).
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  #27  
Old 11-02-2007, 07:16 PM
Chronos Chronos is online now
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You mention maximum distance to decelerate, at those speeds you ain't going to decelerate much in the 5 feet between the ground and your head.
You're absolutely going to decelerate much. If you didn't decelerate, you'd just keep on going straight through the ground. Since it's the deceleration which kills you, the idea is to have as low a deceleration as possible, which means to do it over as great a distance as possible. Five feet probably isn't a large enough distance to matter (most such falls are fatal, after all), but it's a heck of a lot better than the inch or two you'll get if you land flat.
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  #28  
Old 11-02-2007, 07:23 PM
askeptic askeptic is offline
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Quote:
Originally Posted by Chronos
You're absolutely going to decelerate much. If you didn't decelerate, you'd just keep on going straight through the ground. Since it's the deceleration which kills you, the idea is to have as low a deceleration as possible, which means to do it over as great a distance as possible. Five feet probably isn't a large enough distance to matter (most such falls are fatal, after all), but it's a heck of a lot better than the inch or two you'll get if you land flat.
Even if you were right about that, which you are not, how do you get around the fact that falling feet first you will hit the ground at about 300 fps versus 180 fps if spread out horizontal to the ground? Any illusory advantage gained from feet first landing would be negated by the higher impact velocity.
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  #29  
Old 11-02-2007, 07:40 PM
Quartz Quartz is offline
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If you're heading for water, would it help to drop something to break the surface? Say you've got a handy big rock; its terminal velocity is rather higher than yours, so you drop it and follow it in. Or, more likely, there's some lunk in the same situation who's panicked and is dropping faster than you. The surface of the water is now disturbed and should offer less resistance to you? Right or wrong? Or right, but not right enough?
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Old 11-02-2007, 09:54 PM
Sam Stone Sam Stone is offline
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Quote:
Originally Posted by Quartz
If you're heading for water, would it help to drop something to break the surface? Say you've got a handy big rock; its terminal velocity is rather higher than yours, so you drop it and follow it in. Or, more likely, there's some lunk in the same situation who's panicked and is dropping faster than you. The surface of the water is now disturbed and should offer less resistance to you? Right or wrong? Or right, but not right enough?
Wrong. It's not surface tension that causes the water to be hard, it's the inertia of the water itself.

Most deaths from falls come from head trauma or internal organ damage. The heart is suspended by its arteries, and if you stop suddenly the heart will rip itself right out of place (that's how Diana died in the car crash). The spleen will rupture. The brain will slam against the skull and mash itself. Etc. So your best chance of surving would seem to me to be to stay perfectly flat for as long as you can, to lower your terminal velocity, then attempt to rotate to a feet-first position and lock up your joints so that your leg bones and pelvis absorb the impact by shattering, kind of like your very own personal crumple zones.

Then you might increase your chance of surviving from .000000000000000001 to .0000000001 or something. Falls from a height are one of the most reliable ways to die.

There have been several freak occurances of people surviving falls from airplanes. Usually they are slowed down by streaming parachutes or other debris. One person I read about hit the side of a hill and slid to the bottom. Another hit a large tree, with small branches at the top which slowly got larger.

If it were me, I'd aim for some kind of structure and take my chances. If I could see a house or a barn, I'd try to steer myself for the roof. You might hit it at an angle and glance off it. Or you might crash through it and have the breaking wood absorb some of the energy. Failing that, I'd aim for a hill or marshy area. Anything that has a chance of absorbing impact.

But who am I kidding? I'd probably just yammer IMGOINGTODIEIMGOINGTODIEIMGOINGTODIE over and over again until I hit something in whatever random position I happened to be in while my brain jibbered.
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  #31  
Old 11-02-2007, 10:02 PM
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For some extra drag you can unbutton your jacket or shirt and spread the front with your arms, more or less like in this pictures. That should reduce your terminal velocity, how much I don't know.

What's that you say? you´re wearing a polo shirt?, aim for a pigstay.
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  #32  
Old 11-03-2007, 05:06 AM
Themenin Themenin is offline
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Quote:
Originally Posted by Sam Stone
But who am I kidding? I'd probably just yammer IMGOINGTODIEIMGOINGTODIEIMGOINGTODIE over and over again until I hit something in whatever random position I happened to be in while my brain jibbered.
Not quite on point for this thread - but I had a snowboard fall a few years back. It was basically a straight drop of about 10 meters followed by a slope. There wasn't much snow, and it was pretty icy, which is why I fell in the first place. I had recently read the column about falling cats (and the back and forth letters appended to it). As I tumbled off the edge, I actually found myself instantly trying to jockey my body into survival positions, while simultaneously trying to squirm past rocky outcrops - the whole straight dope column flashed before my eyes. As it turns out, I was completely uninjured, but this probably had more to do with the roughly gaussian curve of the slope at the bottom, than my application of the flying cat thesis. So my point - normal distribution is a better explanation for survival than any technical knowledge the fallee may have. Still, that falling cat thing was a great column.

Yes, 10 meters is probably a little less than what we're talking about here.
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  #33  
Old 11-03-2007, 06:01 AM
Chief Pedant Chief Pedant is offline
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Quote:
Originally Posted by Just Some Guy
Let's say I fell out of an airplane 20,000 feet up and I don't have a parachute. Obviously the odds are really against me surviving the sudden stop at the end but it has happened from time to time. Let's also say this happened over what looks like rural Ohio; plenty of farmland, not much trees, and little water in sight. Is there a way I could try to hit the ground to maximize my chances to survive?

Any quick suggestions would be appreciated.
Before artificial crash test dummies were invented, a fella named Lawrence Patrick used to decelerate himself on rocket sleds...while not a vertical fall, the problem of rapid deceleration is really what you are after here. I believe Mr Patrick lived into his 80s. FWIW. Perhaps looking into some of his research might help solve the arguments about the best way to land, etc. I think he eventually wised up and started using cadavers. He also used animals until PETA was invented, IIRC.

While I've seen many suggestions about the best way to position oneself, and which surfaces to aim for, my observation as an emergency physician is that survival in an actual accidental fall depends more on luck than deliberation at the last moment on how to land.

As an aside, I've had some interesting discussions about whether or not a truly great height fall is peaceful. I used to argue that it was--endorphins and all that. As a geezer doing a >700 foot bungee at the Verzasca dam, my own observation was that once I stepped off the platform, fear instantly dissipated. However a coworker of mine found a reference to a worker who fell off the Mackinaw Bridge and "screamed all the way down" so I ended up losing my bet. He did not have the reassurance of a bungee cord, of course.
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  #34  
Old 11-03-2007, 06:23 AM
chowder chowder is offline
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Quote:
Originally Posted by Wee Bairn
Vesna Vulovic, a stewardess who survived a 30,000 ft fall from a bombed airplane, did so by landing on the steep slope of a snow covered mountain. She was also surrounded by parts of the fuselage IIRC she was in the loo at the time.

A brief bit on her and two others- it seems landing through some pine trees would be good too.
I imagine she was shitting herself all the way dooooowwwwnnnn.

Still she was in the loo
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  #35  
Old 11-03-2007, 08:04 AM
aerodave aerodave is offline
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Quote:
Originally Posted by flight
In fact it did reach terminal velocity, but terminal velocity of a plane with its wings in a flat spin is a hell of a lot lower than that of a person falling on their own.
askeptic, I just wanted to make sure you saw this. flight is absolutely right on this one. A skydiver using a parachute also reaches terminal velocity, a very low one. And good thing too...because not hitting terminal velocity means you never stop accelerating.
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Old 11-03-2007, 08:39 AM
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Originally Posted by aerodave
And good thing too...because not hitting terminal velocity means you never stop accelerating.
Does acceleration have anything to do with it? Is hitting the ground at x kmph while accelerating worse than hitting it at x kmph while at terminal?
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  #37  
Old 11-03-2007, 08:43 AM
John DiFool John DiFool is offline
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I remember a story about a female skydiver whose chute failed, and she plummeted feet first into someone's very soggy front lawn. She survived as her leg structure basically shattered and "telescoped" together.
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  #38  
Old 11-03-2007, 08:45 AM
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Originally Posted by garygnu
Best Way to Survive Falling at Terminal Velocity (Need answer fast)

Best. Thread Title. Ever.
Seconded.
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  #39  
Old 11-03-2007, 01:17 PM
Quartz Quartz is offline
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Quote:
Originally Posted by Sam Stone
Wrong. It's not surface tension that causes the water to be hard, it's the inertia of the water itself.
Ah well, colour ignorance fought. I was hoping for some sort of sliding off the roof type result.
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  #40  
Old 11-03-2007, 01:25 PM
askeptic askeptic is offline
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Originally Posted by aerodave
askeptic, I just wanted to make sure you saw this. flight is absolutely right on this one. A skydiver using a parachute also reaches terminal velocity, a very low one. And good thing too...because not hitting terminal velocity means you never stop accelerating.

Yeah I know. I was answering based on the terminal velocity of a human in free fall which is what the OP asked about. I was pointing out that the stewardess never reached that velocity because she was inside the body of an aircraft in a flat spin.

Furthermore a skydiver under a deployed chute does not reach terminal velocty. Terminal velocity refers to an object in free fall.

Last edited by askeptic; 11-03-2007 at 01:27 PM..
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  #41  
Old 11-03-2007, 01:39 PM
Q.E.D. Q.E.D. is offline
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Quote:
Originally Posted by askeptic
Furthermore a skydiver under a deployed chute does not reach terminal velocty. Terminal velocity refers to an object in free fall.
Yes, she does. Terminal velocity refers to the free-falling (that is, not powered) velocity at which the the force of gravity and the force of air resistance balance out and the object no longer accelerates.

Last edited by Q.E.D.; 11-03-2007 at 01:39 PM..
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  #42  
Old 11-03-2007, 01:47 PM
askeptic askeptic is offline
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Quote:
Originally Posted by Q.E.D.
Yes, she does. Terminal velocity refers to the free-falling (that is, not powered) velocity at which the the force of gravity and the force of air resistance balance out and the object no longer accelerates.
True in a physics class but not at most dropzones.
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  #43  
Old 11-03-2007, 02:42 PM
beowulff beowulff is online now
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You might find this helpful:
http://farm3.static.flickr.com/2274/...82e2061b_o.jpg
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  #44  
Old 11-03-2007, 03:26 PM
LiveOnAPlane LiveOnAPlane is offline
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Quote:
Originally Posted by askeptic
True in a physics class but not at most dropzones.
????
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  #45  
Old 11-03-2007, 03:41 PM
Malacandra Malacandra is online now
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Quote:
Originally Posted by yelimS
Does acceleration have anything to do with it? Is hitting the ground at x kmph while accelerating worse than hitting it at x kmph while at terminal?
No - it's the amount of kinetic energy you have to get rid of that does you in, and that's solely speed-dependent.
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  #46  
Old 11-03-2007, 03:42 PM
askeptic askeptic is offline
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Originally Posted by LiveOnAPlane
????

I have been talking about the terminal velocity of a human. When at a dropzone we don't look up and see a person under fully deployed chute and say or think "Wow they are at terminal velocity". While it may be true that for the deployed chute person "system" it has acheived its functional terminal velocity but it is not the TV for the person alone. That person under the chute is falling much slower than it woulod without the chute. The chute person "system" itself would fall faster if the chute collapsed. Hence my asertion that a fully deployed functional parachute does not fall at its terminal velocity because if the parachute deforms it will fall faster. This is all semantics to determine TV of a chute should we through a fully packed undeployd chute out and calculate that or do we calculate the speed of a properly deployed chute. Keep in mind that modern ram air chutes are more like wings in that they not only function by creating drag to offset gravity but they also generate a certain amount of lift.

When I read the question posed by the OP it was clear that he was talking about the TV of a person without a chute. Now can we stop with the symanticism?
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  #47  
Old 11-03-2007, 05:31 PM
KP KP is offline
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However you may choose to use the term colloquially, terminal velocity has a very specific meaning: you are no longer accelerating. The how or why is incidental. In every measured setting I am aware of, from model rocketry to the scientific literature, the orientation/configuration is noted in the results.

Given enough time, an unconscious body is likely to end up either a) straight vertical head down, b) flexed at the hips, supine; or c) a spinning tumbling. (Though "feet down, straight" may seem a plausible "minimum resistance" position, the force on the feet/legs would flex the knees, and the added resistance of flxed legs would pull them up into position B or (more likely?) C

[20,000 ft wouldn't always be enough free-fall for to cancel out the tumble of an unconscious body, based on what I have seen, but A and B are two relatively stable positions that don't freely interconvert, depending on one's limb/torso proportions and weight distribution.]

Face down, limbs deliberately spread, is almost certainly not the best position at impact, but it is possibly the best position to decrease downward velocity, as evidenced by its widespread use by parachutists to maximize air time. More importantly, it offers a limited steerable glide for a larger radius of potential landing zones, and is a good position to observe the ground to select your landing site -- in the second of clear vision you'll get with ungoggled eyes facing into super-hurricane level "wind". (I don't know anyone who jumps without goggles)

Recreational vertical wind tunnels are springing up everywhere. We have one near me, and I've heard rumors of a second. Most have airspeed gauges, and could be valuable empirical resource for this class of perennial question, even allowing our 'divers' to assess terminal velocity and stable positions in street clothes.

Minimizing terminal velocity by body configuration seems to be the best initial step, and possibly the only one with a significant and consistent effect. Changing position before impact (e.g. to land in water "feet first" or as I was taught, legs flexed against the torso to land "soles and butt first") seems likely to be useful, but would be hard to test definitively, and probably couldn't have nearly the same magnitude of effect. On the plus side, you wouldn't need superhuman reflexes -- changing position a second or two before impact would be almost as good.

The OP did specifically ask how best to "hit the ground", but that may be too late to do very much to maximize your survival, compared to the glide position.
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  #48  
Old 11-03-2007, 06:34 PM
Sage Rat Sage Rat is offline
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A person falling with a deployed and perfectly operating parachute is falling at terminal velocity at the time he ceases accelerating, as is a person who is falling without a parachute at all.*

"Average human terminal velocity" does not equal "terminal velocity." Terminal velocity is a value that varies depending on not only the object in question, but even the direction it is facing in mid-air.

* Ignoring wind factors that might provide extra lift.

Last edited by Sage Rat; 11-03-2007 at 06:36 PM..
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  #49  
Old 11-03-2007, 08:11 PM
Darth Nader Darth Nader is online now
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I was nearby when a window-jumper failed to kill himself. He was saved by the same thing John DiFool mentioned-- his legs crunched (telescoped) and absorbed the impact. The hospital this happened at wasn't equipped to deal with said trauma, and doofus was sent to another hospital to have his lower self rebuilt.

The thing is, that only works if your pelvis is strong enough. Otherwise you get femur popping out the top of your shoulder, and, well, game over. Sorry, Chronos.

Last edited by Darth Nader; 11-03-2007 at 08:14 PM..
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  #50  
Old 11-03-2007, 08:28 PM
Key Lime Guy Key Lime Guy is offline
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What height is required for terminal velocity?

I've heard the statistical curve flattens at about three-stories; i.e. you're (essentially) just as likely to die falling from a three-story building as you are from any higher point.

But this might be a myth.
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