A question about skydiving at high altitude

[Mute5916 0]

I am researching free falling from high altitudes and I read this on the U.S. Air Force official website.

"As new jet aircraft flew higher and faster in the 1950s, the USAF became increasingly concerned with the hazards faced by flight crews ejecting from high-performance aircraft. The emerging space age introduced the problem of how to provide astronauts with a safe method of escape while within the atmosphere. Without proper stabilization, a crewmember ejecting from an aerospace vehicle at high altitudes could enter a life-threatening flat spin of up to 200 rpm.

Project Excelsior was formed in 1958 to study and solve high altitude escape problems as jets became increasingly high performance."

So basically, I'm trying to figure out why a person would enter into a "life-threatening flat spin" in the stratosphere. Is this not a problem at lower altitudes? Any links you can give me that would answer this question, I'd greatly appreciate it. Thanks.

[labrys 0]

I'm looking forward to expert answers but I'd like to take a guess before they chime in. I'd suspect that the concern would be that having an inexperienced person alone in freefall for any length of time would pose the risk of a high speed spin regardless of how high they are.... as long as they have time to develop the spin. I assume that means they would not be able to deploy a parachute at really altitudes either because they may not have sufficient o2 for such a long ride or the air density isn't good for canopy flight.

Ultimately I have no idea but it's a great question.

Oh hey. Colonel Joseph Kittenger, who made that Excelsior jump, has done a couple of interviews with Skydive Radio. The most recent wasn't long ago. Not more than 2 or 3 episodes I think. He seems like a very approachable guy and I'm pretty sure he gave out his email address during the interview.

Check it out and email him. If you do please share his answer.

Owned by Remi #?

[jake95 0]

I would have to say it has more to do with the speed of the aircraft not just the altitude.

[labrys 0]

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I would have to say it has more to do with the speed of the aircraft not just the altitude.

They test from balloons so I don't think airspeed is a high priority

Owned by Remi #?

[mjosparky 3]

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=search_results&search_forum=all&search_string=high%20altitude&sb=score&mh=25

My idea of a fair fight is clubbing baby seals

[JohnRich 4]

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I'm trying to figure out why a person would enter into a "life-threatening flat spin" in the stratosphere. Is this not a problem at lower altitudes?

Possibly because the air is so thin at those altitudes that there is no air pressure with which to control your body's orientation, to stop such a spin.

In freefall from normal altitudes we use the airspeed of 120 mph or more to control our bodies. But if you're just walking down the street at 2 mph, you can wave your arms and legs around all you want and it won't change a thing.

So the lack of high pressure air in the stratosphere might be like waving your arms around while walking - it will have no effect on your body position.

[Airviking 0]

That alone doesn't add up in my book. The reduction in air density is compensated for with an increase in terminal velocity. At terminal, the presuure that the air excerts on your belly is constant regardless of air density.

Also, it's the air that induces the spin as well as provides you the means to control yourself out of it.

I don't know the answer here, but it probably lies at the molecular level. Certainly a control surface in a given air density will behave differently than at half the density and twice the speed. I think I'm gonna walk over and chat with out fluidics PhD.

I believe you have my stapler.

[billvon 2,396]

>In freefall from normal altitudes we use the airspeed of 120 mph or more to
>control our bodies. But if you're just walking down the street at 2 mph, you can >wave your arms and legs around all you want and it won't change a thing.

Ah, but at 30,000 feet you're doing closer to 180mph - and it feels just like regular skydiving at 120mph.

"Life threatening spins" are a possibility with any non-skydiver at any altitude (just watch any level III for what can happen when someone doesn't know how to stop a spin.) The big difference at 40,000 feet is that you can't just pull and stop the spin; you have to freefall to 12,000 feet or risk death from hypoxia.

An additional problem is that above 40,000 feet you need a pressure suit, and an inflated pressure suit is nearly impossible to arch in.

[pchapman 261]

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So basically, I'm trying to figure out why a person would enter into a "life-threatening flat spin" in the stratosphere. Is this not a problem at lower altitudes?

I'll guess it is largely a matter of time. A bail out at 40k' will leave a lot more time to start spinning up than if bailing out at 20k'.

In cases where pressure suits or partial pressure suits are involved, the additional stiffness of them (when inflated for high altitude bailout) might make it easier for a person with no freefall training to spin. Just as a stiff student is more likely to spin than a relaxed one.

Then there's the air density issue. That's a tricky one. When the person gets to terminal velocity, the dynamic pressure felt will be normal (basically pressure = weight), so both the forces leading to spins and the forces available to stop a spin would be like down low, even if the true velocity were a lot more at high altitude.

But what they could have been thinking, is that if a tumble of any kind gets going soon ejection, if the speed is well below terminal velocity, and it takes more time to get to that higher speed, then inertial forces are relatively strong compared to aerodynamic ones. That is, it is harder for any natural stability (or crewman's actions) to stop any motion because of the reduced dynamic pressure and control forces available.

On the other hand, a lot of ejections from high flying aircraft would be at high speed, whether viewed in terms of true airspeed (eg 500 kts) or indicated airspeed (dynamic pressure, taking into account the lower air density) (eg 220 kts IAS). Either way, the ejection is above the typical terminal velocity for a crewman with a rig on.

So in those common cases I'm not sure that the low air density is any issue at all.

There can be subtleties that I'm missing though. For example, aircraft wing flutter is affected more by true airspeed than indicated airspeed.

Overall I still guess the main issue is the distance fallen by high altitude ejectees, possibly aggravated by stiff inflated pressure suits. When at high altitude, the crewman doesn't just have the option of pulling if starting to spin uncomfortably, due to issues of oxygen, temperature, and large increases in opening shock at low air densities.

(In those days they would be talking about ejection seats where the crew wear rigs, and separate from the seat before canopy deployment, rather than having a canopy in the head box. And the seats wouldn't necessarily be drogue stabilized. Some seats might have an automated seat/man separation, some might allow manual seat/man separation. But I don't know exactly what features were on what plane in what year.
The key point is, the crewman might be falling much of the way in an unstabilized seat, or with a rig on his back without the seat. Two slightly different scenarios.
EDIT: I don't know what body position the military recommended either. I could see that just falling in a relaxed position on one's back would make some sense for those who are not freefall trained. That's particularly true if in a stiff pressure suit)

[PiLFy 0]

OK, a number of guesses here. I'll toss in mine, too. Kittinger's first jump was from around 72K'. At first, he thought he was just floating there, & would die. He managed to look behind himself, & saw the balloon "Shoot away @1,000MPH." Then, he knew he was falling. The atmospheric density @those altitudes is almost non-existent. The partial pressure suits Kittinger wore were very restrictive. Pilots forced to bail out might be hurt or wounded.

My guess? The tendency to go into a flat spin is due to 99% of the atmosphere being below you. Kittinger fell @Mach .9 w/no rippling of the suit material or noise. Your arms & legs are different lengths. There's just enough atmosphere to get a purchase on you, & induce a spin. But, there isn't enough for you to get enough traction on, & stop the spin. It's easier to start a spin, than to stop it. Especially once it gets going. The drogue chute slowed him enough to make it manageable.

I found a book on this I enjoyed. It tells all about Joey's jumps. Although it doesn't answer your question. It's titled "The Pre-Astronauts." (Naval Institute Press)

[Bertt 0]

Billvon's answer is the correct one here. A person who's not a trained skydiver will most likely roll over on their back and spin after a few seconds of freefall. When they try to correct the spin using techniques familiar to them (twisting their shoulders, turning their head, etc.), they'll just make things worse. Why is that life-threatening? Because they'll either open the parachute upside down in a spin, or worse yet, spend the rest of their life trying to get stable.
Your profile doesn't say where you are, but if there's a wind tunnel near you, that would be the place to continue your research. Wind tunnels are fun.

You don't have to outrun the bear.

[jsaxton 0]

You might also want to read "Come up and Get Me"
ISBN 978-0-8263-4803-6

That's Joe's Autobiography
I have a signed copy

[labrys 0]

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I think I'm gonna walk over and chat with out fluidics PhD

Did ya?

Owned by Remi #?

[Mute5916 0]

Thank you all for your feedback, especially labry for pointing me to skydive radio. I downloaded the episode where Joe Kittinger comes on the show. I didn't notice him list his email in that. However, he did explain why they needed this parachute in the episode. Apparently pilots were not trained back then on how to sky dive. So they were totally inexperienced. That may also be true for today. So the chute was designed for a person who has little or no experience in how to free fall and to help stabilize and prevent them from entering into a flat spin before the chute opens fully. I'm going to order Joe Kittinger's book as well.

Felix Baumgartner, a man being sponsored by Red Bull, is being helped by Joe Kittinger and others in order to break Kittinger's record of longest free fall. He plans to free fall without the help of this parachute and use his training as a skydiver to help glide him down. However, he still does have a chute similar to it in case something goes wrong or he goes into a flat spin. He does not intend to actually use it unless an emergency happens though. Joe goes into more detail about this in the skydive radio episode. Thanks again for all of your feed back.

[labrys 0]

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I downloaded the episode where Joe Kittinger comes on the show. I didn't notice him list his email in that.

I listened to it again also... no email address. Either I'm making it up or he gave his email address in the first interview they did. That was show #105 from a few years ago.

Owned by Remi #?

[Mute5916 0]

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I downloaded the episode where Joe Kittinger comes on the show. I didn't notice him list his email in that.

I listened to it again also... no email address. Either I'm making it up or he gave his email address in the first interview they did. That was show #105 from a few years ago.

I'll go download that right now. If I am actually able to email Joe Kittinger, I would be eternally grateful. It would be such an honor to talk to a man like him. Few people that have done something so great are as humble as he is. That makes him admirable.

[labrys 0]

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If I am actually able to email Joe Kittinger, I would be eternally grateful.

Hey again. I just listened to the older interview and realize that he gives his snail mail address, not his email address.... so send him a letter.

Owned by Remi #?

[bofh 0]

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If I am actually able to email Joe Kittinger, I would be eternally grateful.

Hey again. I just listened to the older interview and realize that he gives his snail mail address, not his email address.... so send him a letter.

Or mail skydive radio and ask them to forward the mail.

[PiLFy 0]

"...a man being sponsored by Red Bull, is being helped by Joe Kittinger..."

That's surprising. Joey has stated he is often reached out to for help in replicating his famous dive, but he never responds. He stated he doesn't want to be involved if someone else dies (again) trying to do the jump. Something must have changed his mind.

[Airviking 0]

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I think I'm gonna walk over and chat with out fluidics PhD

Did ya?

Yeah, so my expert on all things fluid had this take. All else being equal, it doesn't matter that it takes 60s (or whatever) to reach terminal rather that the usual 10-12. If there's air to put you in a spin, you should be able to use it to counter.

He says that, even though the air pressure against your belly is the same at terminal at any altitude, ("terminal" will obviously be higher at lower pressures) the shape of the pressure wave you push in front of you and around around you is going to be very different at different pressures. At regular skydiving altitudes, we push a pretty steep pressure gradient in front of us. That gives us a nice rigid pressure front to work with. Like lying on a firm bed. But at lower pressures, that gradient flattens, the pressure front gets thicker, and feels softer, so your controls get vague. Like lying on a waterbed. Both beds will support you, but one is easy to move around on, and one is difficult.

So, both scenarios have the same potential to force you into a spin, but you have less control to counter the spin at lower pressures.

I'll see if I can get him to run a FlowWorks simulation for us.

I believe you have my stapler.

[robinheid 0]

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"...a man being sponsored by Red Bull, is being helped by Joe Kittinger..."

That's surprising. Joey has stated he is often reached out to for help in replicating his famous dive, but he never responds. He stated he doesn't want to be involved if someone else dies (again) trying to do the jump. Something must have changed his mind.

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SCR-6933 / SCS-3463 / D-5533 / BASE 44 / CCS-37 / 82d Airborne (Ret.)

"The beginning of wisdom is to first call things by their right names."

[NWFlyer 2]

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I'll go download that right now. If I am actually able to email Joe Kittinger, I would be eternally grateful. It would be such an honor to talk to a man like him. Few people that have done something so great are as humble as he is. That makes him admirable.

Sometimes it just takes being in the right place at the right time.

"There is only one basic human right, the right to do as you damn well please. And with it comes the only basic human duty, the duty to take the consequences." -P.J. O'Rourke

[labrys 0]

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I'll see if I can get him to run a FlowWorks simulation for us.

That would be great.

Owned by Remi #?

[PiLFy 0]

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"...a man being sponsored by Red Bull, is being helped by Joe Kittinger..."

That's surprising. Joey has stated he is often reached out to for help in replicating his famous dive, but he never responds. He stated he doesn't want to be involved if someone else dies (again) trying to do the jump. Something must have changed his mind.

$$$$

I don't think so. He's retired, pensioned, & well-entrenched in his belief system. My guess would be because Red Bull was bringing so much to the table on this one. W/RB's substantial resources, this was going to be a first class effort. He probably felt that w/the increased safety of today's equipment. Along w/the technical & financial resources being brought to bear on this. It was the right time & project to come on board with. Twas a pity the plug got pulled on it. Sadly, I'll never get the chance to do it myself. The video quality this time around would've been awesome!!

[Airviking 0]

Meet: JOEY! This is the model I'm gonna run some flow analysis on tomorrow.

(I can't fuckin' help it...I'm a nerd, and I carry it around wherever I go.)

I believe you have my stapler.