2 skydiving questions

[Whammo]

I have two skydiving questions that Unca CeCe doesnt find fitting enough to answer... or... gasp... can't. Even I dont beleive that.

First I saw on tv (dont tune out yet) that in the late 50's or 60's (?) a man in a spacetype suit and an upper athmosphere balloon jumped out and was able to break the sound barrier skydiving. I beleive they said he is still alive today. Would a falling body (literally this time) be able to take the stress? or were early planes that broke up when approaching the barrier of just bad design?

Second.. in a separate show it was said that a skydiver doesnt need to breath when in freefall because his body will absorb enough oxygen through the skin. It was also stated that this is the reason that people dont skydive through clouds as the condensation could cause them to suffocate. Sounds way far-fetched to me.

Any takers? any dopers actually skydive?

------------------
The wisest man I ever knew taught me something I never forgot. And although I never forgot
it, I never quite memorized it either. So what I'm left with is the memory of having learned
something very wise that I can't quite remember. -George Carlin

[Whammo]

wow... shall we count the misspelled words? Lets not.

[Sofa King]

The answers to your questions are:

1) Yes, a falling human can, in fact, exceed the speed of sound without falling apart. This is because humans have much less wing surface area than airplanes.

2) Humans do not need to breathe while falling. This is because as a falling man approaches the speed of sound, time dilation makes the man's fall seem subjectively much shorter than it actually is. Once he is on the ground, however, he will discover his twin brother is now an old man.

It should be noted, however, this has never been tested with feminine pronouns.

[Stephen]

First I saw on tv (dont tune out yet) that in the late 50's or 60's (?) a man in a spacetype suit and an upper athmosphere balloon jumped out and was able to break the sound barrier skydiving. I beleive they said he is still alive today. Would a falling body (literally this time) be able to take the stress? or were early planes that broke up when approaching the barrier of just bad design?

That would have to be quite an aerodynamic suit, to allow a free-falling human to multiply his 'normal' terminal velocity by five.

Second.. in a separate show it was said that a skydiver doesnt need to breath when in freefall because his body will absorb enough oxygen through the skin. It was also stated that this is the reason that people dont skydive through clouds as the condensation could cause them to suffocate. Sounds way far-fetched to me.

I saw that claim on Ushuaia and it's bunk. Cecil and others have debunked the "Goldfinger" myth and this is directly related.

I've jumped through rain clouds and I know others who have done so. We all complain about how painfull it is to be pelted by raindrops at 120 mph and joke about hitting the 'pointy' end, but none of us felt short of breath.

The reason you're not supposed to jump through a cloud, is that you're supposed to have a clear view of the ground below when you jump. It would suck to lose your bearings in a cloud and be forced to land somewhere you could get killed.

Besides, the claim seems to imply jumping naked and discounts the fact that a skydiver naturally continues breathing during the jump. I don't know of anyone stupid enough to think, "Hey, I can breath through my skin, I think I'll hold my breath for the next few minutes!"

I suspect the person who gathered that little factoid spent a good deal of time searching the jump site for a "Hammerfor".

------------------
Stephen
Stephen's Website (http://stephen.fathom.org)
Satellite Hunting 1.1.0 visible satellite pass prediction
shareware available for download at
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[pmh]

question 1:

The show you saw was on TLC. I also saw it. The man was a military jumper testing the limits of HALO (High Altitude Low Opening) jumping. IIRC he jumped from about 60000ft. Thinner air = greater speed.
However, I believe the terminal velocity was somewhat slower.
according to this site: http://www.skyranch.com/faq.htm#howfast
record freefall terminal velocity is 321mph.

Question 2:

Ridiculous.

same site. scroll down.

[Ringo]

I must admit I thought the premise of both questions ridiculous when I read them; and the second most assuredly is. I skydived some many years ago and learned 120 mph as terminal velocity for a human (in the spread eagle free fall position).

Well, anyway... according to my September 1999 issue of National Geographic, on August 16, 1960 U.S. Army Capt. Joe Kittinger jumped from a balloon at a still record altitude of 102,800 feet. According to the magazine he was in freefall for thirteen minutes and reached a speed of "more than 600 miles an hour,..." which, while not breaking the sound barrier, is close enought to say he approached it. The speed of sound in air near the earth's surface is ~680 m.p.h.

Regards

[Nickrz]

From my 1973 Guiness Book of World Records:

Parachute, longest delayed drop
--------------------------------
The longest delayed drop and the greatest altitude for any parachute descent was achieved by U.S. Air Force Captain Joseph Kittinger over Tularosa, New Mexico, on August 16, 1960. He stepped out of a balloon at 102,200 feet for a free fall of 84,700 feet (16.04 miles) lasting 4 minutes 38 seconds, during which he reached a speed of 614 mph, despite a stabilizing drogue.
---------------------------------

I'm not sure what the speed of sound is at that temperature (-94 F.) and atmospheric pressure (very little, I imagine).

[Nickrz]

Dangit, beatle! Scooped by 8 minutes.
At least I have a nit to pick; the National Geographic didn't quote that speed for sound, did they? Mach 1 is 760 mph at sea level at 1 atmosphere.

[Stephen]

There seems to be quite a bit of confusion concerning Kittinger's record. An excerpt from TIME quotes him as saying "Within 9/10ths of the speed of sound for my altitude." (which seems to agree with Guiness). While a bio claims he was the first man to break the sound barrier without an aircraft at 714 mph. The NG article mentioned 13 minutes freefall, while others mention ~4.5 minutes.

------------------
Stephen
Stephen's Website (http://stephen.fathom.org)
Satellite Hunting 1.1.0 visible satellite pass prediction
shareware available for download at
Satellite Hunting (http://stephen.fathom.org/sathunt.html)

[Ringo]

Nickrz

No, NG didn't give that number, and I knew it was going to be a little wrong. In my daily life we use 1000'/s for sound in air, while it's actually closer to 1086'/s. I just multiplied it out. I have a physics reference here that gives it 3.31*10^4 m/s at 1 atmosphere and 0º C, which works out to 740 m.p.h.

[Ringo]

13 minutes has got to be wrong; if you just took a near earth terminal velocity of 120 m.p.h., or 176'/s and the near surface gravitational acceleration of 32'/s a 13 minute freefall (assuming that, although the atmospheric pressure up there is significantly lower allowing a much higher than near surface terminal velocity, the gravitational attraction between man and earth would be just barely less than near surface conditions) would consume 5.5 seconds to reach terminal velocity and would have the man travel 25.8 miles. Impossible! The earth would induce significant drag about 6 miles before the end of that journey.

Even using the 4'30" freefall and assuming a terminal velocity of 600 mph is too long w/a linear calculation. But the atmospheric pressure is constantly increasing around this fellow, so he would, I guess, possibly start to slow down before he (or the altimeter/timer) opened the 'chute. I'm not going any deeper tonight, but will say the Guiness number sounds more credible.

Not really knowing, then, how fast he was going when the 'chute opened, I still hope they put some thought into that harness.

Regards

[NanoByte]

So is the speed of sound higher or lower at less air pressure? Of course, I should know, but I don't; though I guess it would always be slower in a less dense material.

Ray

[Ringo]

lower

[Omniscient]

Well since no one has done any actual research heres a thourough link about Capt Kittenger's jump.
http://www2.tsixroads.com/Corinth_MLSANDY/jk004.html

It did really happen. He rode up in a customized Weather balloon, and wore a very heavy pressurized suit and life support system.

He jumped from 102,800 feet. (19.47 miles)
He opened his chute at 17500 feet (3.314 miles)
He free fell for 4 minutes 38 seconds
Landed after 13 minutes 45 seconds
He reached a top speed of 614 mph (9/10ths the speed of sound at atlitude) at 90,000 feet (17 miles).

at 90,000 ft the speed of sound is ~300 m/s (671 mph)

If anyone wants to do the math to fix the silly mistakes above here are your important numbers from the CRC. g(102800ft)=9.7117m/s*s g(90000ft)=9.7208m/s*s Temp(o-f)=227K-224.5K. a(o-f)=302.37-300.4 m/s

The second premise is too silly to comment on.

I read somewhere online that a Russian Cosmonaut has surpassed these records for altitude and speed, I'll look on line and get back to you.

[Coach]

About the speed of sound and the aerodynamics about it...

It is very possible to reach the speed of sound (in air) as a human projectile and it is all owed to the aerodynamics of a swept-back wing design. Although most sky divers cannot attain this speed at normal dive altitudes, it is possible and it is a principle that helped to design the World's fastest planes.

Sweeping back the wing (for those of you who know nothing about aerodynamics, but I guess I probably shouldn't have mentioned this on here :-)) helps reduce drag enabling the plane to engage higher speeds. (Take a look at an F-14 and its design. It has a lever to sweep back the wing for super-sonic flight). Anyway... back to the show.

Reguar skydivers who drop form 12K or so ft. can push the 200 mph envelope with special suits and techniques. Source: just browse.... you can't miss it.

[E1skeptic]

Note: the speed of sound in air varies with temperature. Temperature diminishes with altitude.

Omni, help!

[Danny]

I believe that sweeping the wings back is needed to alter the center of force relative to the center of mass, so that the plane can continue to produce lift with the appropriate center of force as the air flow characteristics alter drastically going supersonic creating significant bow waves.

Or some such! No expert here.

[Strainger]

The speed of sound, a, as it relates to temperature is a = (gamma*R*T)^0.5 where:

gamma = 1.4 (for air)
R = a constant that I have to look up
T = Temperature in Rankine or Kelvin, depending on R

I'll get back to y'all on R. Been a while since my aerodynamics classes.

[Strainger]

OK. From Introduction to Flight by John D. Anderson, Jr., we have:

R (the specific gas constant) = 287 J/(kg-K) = 1716 ft-lb/(slug-R) for air.

By the way, gamma (written as a lower case Greek gamma), is the ratio of specific heats, Cp/Cv.

[Strainger]

BTW, my last 2 posts were in response to E1skeptic's post, even though he didn't think of me ::sniff::

[Omniscient]

E1, I gave you the speed of sound at the two altitudes so you don't need to calculate it with the temps. FYI at the altitude we're concerned with here it gets warmer as you get higher. If you want it here they are: T(o-f)=228.5K-224.5K (o=initial alt, f=final alt of free fall)

[E1skeptic]

Thanks Strainger, I was too lazy to go grab my Aerodynamics book.

Hey, Omni, I was oversimplifying, ok? I know that the temperature at the tropopause is a (supposedly) constant of -56.4°C, remaining there until up to about 12 miles, and then increasing slowly (all this within the stratosphere) before reaching half way into the mesosphere where it begins to decrease again, and... shall I continue?

[E1skeptic]

But thanks to both of you anyway.

:)

[Whammo]

swept wings are needed because you have to keep them within the "cone" of the air wave that comes off of the nose of the plane and spreads out around it. OR. you need short stubby wings kept in the cone, hence, the first sound barrier breakers.

------------------
The wisest man I ever knew taught me something I never forgot. And although I never forgot it, I never quite memorized it either. So what I'm left with is the memory of having learned
something very wise that I can't quite remember. -George Carlin

[Lumpy]

The wisest man I ever knew taught me something I never forgot. And although I never forgot it, I never quite memorized it either. So what I'm left with is the memory of having learned something very wise that I can't quite remember. -George Carlin Dang, that actually makes sense!

[Sam Stone]

B-12: Exactly. And that's why the F-104 doesn't have swept wings.

[Sam Stone]

A swept wing is not required for supersonic flight. The X-1 did not have swept wings. Swept wings certainly help a lot, as does a fuselage shape like a coke bottle.

[dkgreath]

I personally am amazed at how many people skydive (or bungie jump). My rule regarding such activities:

2 things fall out of the sky...Bird shit and fools.

[Sam Stone]

Do you have any statistics to back up your assertion that skydiving is foolish? Is it more dangerous than car racing? How about playing football? Mountain climbing? Going on a cross country holiday drive? Just where does it fit in?

And if you don't know, why do you feel compelled to judge people?

[Nickrz]

So, to sum up.. We know people don't breathe through their skin, water clouds don't suffocate us, and a few of us have jumped out of perfectly good airplanes.. but we're still not sure if anyone has broken the sound barrier while in freefall.

[Omniscient]

I wish I could find this link that I read a while back (looking up this same topic) that discussed the Russian Cosmonaut who supposedly broke the sound barrier and jumped from a higher altitude than Kittenger. I searched on a handful of engines and can't find the link I found last time, IIRC he jumped from slightly higher, but reached speeds in excess of 700 mph. Granted Russian records around this time are dubious at best so I imagine Guiness needs more reliable data (or maybe not).

[zuma]

Hrm... apparently a skydiver, in a pressurized suit, is planning to jump from 130,000 feet, breaking kittinger's 40-year old record. One odd quote from the article:

"He appears undaunted by warnings from scientists that the descent through near-space could be so fast that his head will explode."

His head might explode? That sounds rather silly to me.

http://www.sunday-times.co.uk/news/pages/sti/2001/10/21/stifgnaus01001.html

[postcards]

That sounds perfectly reasonable to me. His head just might explode. I was starting to think what might happen to your unprotected eardrums at the speed of sound when I came to this post.


And just where the heck has Coach been for the last two years?

[micco]

Here's another team working on a high altitude jump.
http://www.stratoquest.com/default.cfm

Their goal is actually to set the high-altitude record, and freefalling faster than Mach 1 may nor may not be a side effect of that. Their FAQ says:

Q: Will Cheryl break the sound barrier?
A: There is currently no information on this subject and no human has ever broke the barrier without an external vehicle. The speed that Cheryl will be traveling (1.3 mach ) infers that she will break the barrier, although we are not sure that she will have the mass to actually make this happen.

[Popup]

Originally posted by dhanson
Do you have any statistics to back up your assertion that skydiving is foolish? Is it more dangerous than car racing? How about playing football? Mountain climbing? Going on a cross country holiday drive? Just where does it fit in?
Not that I agree with dkgreath (I would love to take up skydiving again, but there are other constraints), but skydiving is dangerous. This list came from a post here a long time ago, and I found it so interesting that I kept it locally:
code:Activity # Fatalities per 1,000,000 exposure hours

--------------------------------------------------------
Skydiving 128.71
General Aviation 15.58
On-road Motorcycling 8.80
Scuba Diving 1.98
Living (all causes of death) 1.53
Swimming 1.07
Snowmobiling .88
Passenger cars .47
Water skiing .28
Bicycling .26
Flying (scheduled domestic airlines) .15
Hunting .08
Cosmic Radiation from transcontinental flights .035
Home Living (active) .027
Traveling in a School Bus .022
Passenger Car Post-collision fire .017
Home Living, active & passive (sleeping) .014
Residential Fire .003
This is taken from the Bicycle Helmet Statistics page,
which quotes it from "Failure Analysis Associates, Inc." whatever that is.

[Edited by UncleBeer on 10-22-2001 at 12:52 PM]

[RM Mentock]

Originally posted by tc
Not that I agree with dkgreath (I would love to take up skydiving again, but there are other constraints), but skydiving is dangerous. This list came from a post here a long time ago, and I found it so interesting that I kept it locally:

Very interesting. Do you mean it was posted to the SDMB? I searched on it, and it seems to have come from this thread:

http://boards.straightdope.com/sdmb/showthread.php?threadid=58139

scr4 said it came from the Bicycle Helmet Statistics page (http://www.bhsi.org/webdocs/stats.htm).

It seems to support my Safety thesis (http://www.teemings.com/issue07/safety.html)--although I wondered about the General Aviation category. In that other thread, Dr. Lao pointed out that General Aviation does not include regularly scheduled commercial flights, so it is odd that the list includes Passenger Cars, but not Commercial Airline Flights.

[audient]

fascinating data on the dangers of ordinary life.

Originally posted by tc
code:Activity # Fatalities per 1,000,000 exposure hours

--------------------------------------------------------
Home Living, active & passive (sleeping) .014
Residential Fire .003

this is intriguing. I'll have to find a full explanation of these entries. It looks to me like I'm safer with my house on fire, then when I'm asleep. I guess I'll have to torch the old place before I knock off tonight. But then, what'll I do to keep safe *tomorrow* night??

[gazpacho]

I assume the fires are somewhat safe because people actively flee a burning house and are usually able to get out.

[Sam Stone]

tc: Those statistics are misleading. They count the risk 'per hour of activity'. But is that a reasonable measure? Not really, because you are comparing a very concentrated activity to one that is more diffuse.

A more reasonable number would be event-based. Like, "What are the odds that I'll be killed in a single skydiving jump" as compared to, say, "What are the odds that I'll be killed driving to the airport?"

If it takes 2 hours to drive to the airport, but the actual skydive jump only takes 3 minutes, then the odds of dying in the car are about 1 in a million, and the odds of dying in the jump itself are about 6.4 in a million. So there's a six-times greater chance that you'll be killed in the skydiving jump than in the 2-hour drive to get to the airport.

But then, if you drive your motorcyle to the airport, the odds of being killed on the way to the jump to 17.6 in a million.

So, if we use your numbers, then if you take a two-hour trip to the airport on your motorcyle to go skydiving, you are almost three times more likely to be killed on the trip to the airport than in the actual jump.

That looks a little different than the way you stated it, doesn't it?

Here's another one: Let's say you become a skydiving fanatic, and get 1,000 jumps under your belt over your lifetime. Let's assume that each jump takes 3 minutes. So you'll spend a grand total of 50 hours skydiving over your life, and your chance of being killed in a skydiving accident in your lifetime is about 6435 in a million, or about .64%

Now, let's assume that you can do two jumps in a full day, so you spend 500 full days in your life engaged in your skydiving hobby. Your neighbor Bob thinks you are a risky idiot, and prides himself in engaging in 'safer' hobbies. So every time you go skydiving, he takes his motorcyle out and goes for a Sunday drive for 4 hours. So he'll spend 2000 hours driving around during the time that you are skydiving. His odds of being killed engaged in his hobby is about 17,600 in a million, or about 1.76%.

Your prudent neighbor just made a choice that will result in it being almost three times more likely that he'll be killed engaging in his hobby than you will be engaging in yours.

And of course, the REALLY safe guy who never ventures out of his house, and therefore doesn't get as much exercise and stimulation as the two of you is making the riskiest choice of all. Because while those other activities have risks that hover around the 1% mark for lifetime engagement, the odds of dying from heart disease are about 1 in 3 - THIRTY times higher.

Just focusing on raw statistical numbers can cause one to lose perspective.

[audient]

my earlier dry humor aside, I still say those fire figures look fishy. Of course the number is low "because people run out of fires". One would guess that the amount of time actually spent exposed to any one fire is measured in seconds, or a few minutes at most.

but we're looking at "Fatalities per million exposure hours". The data implies that someone divided the number of deaths due to residential fires by an estimated amount of time americans spent actually in fires. (adding up all those 10 second dashes, etc).

At .003, that means that for each fire death, there were -
333 million hours spent in burning houses! WHOA DUDE.

But actually, fire deaths number in the thousands, anually, which makes the exposure hours ... um, something really big. Now I haven't spent any time in a burning residence, perhaps everyone else is, to keep the average up, OR... some statistician is counting all hours spent in residences.

[douglips]

Originally posted by RM Mentock
In that other thread, Dr. Lao pointed out that General Aviation does not include regularly scheduled commercial flights, so it is odd that the list includes Passenger Cars, but not Commercial Airline Flights.

Oh but it does.
Flying (scheduled domestic airlines) .15

[Popup]

RM, audient and Sam: I agree that the data look(s) a bit fishy, but it was my only reference that mentioned skydiving. I generally prefer to refer to NSC Odds of dying (http://www.nsc.org/lrs/statinfo/odds.htm), as they seem a lot more reliable. (At least they tell where they get the data from.)
It lists the number of fatalities in US in 1998 according to the WHO "International Classification of Diseases", which (as far as I can tell) ignores skydiving. (unless it comes under category E888 "Other and unspecified fall").

Have a look, and find such fascinating facts as that 740 persons suffered fatal injuries from slipping or falling on the same level. 420 people froze to death, whereas 375 unlucky souls passed away due to excessive heat. I especially pity the 13 pour souls who died "Due to lack of air (in refrigerator, other enclosed space)"

[RM Mentock]

Originally posted by douglips
Oh but it does.

I don't know how I missed it. (Sure I do. I was zombified.)

The flying stat is three times lower than the passenger car stat, which is a little low, from what I've seen. I'll have to look into this further.

Originally posted by Sam Stone
Those statistics are misleading. They count the risk 'per hour of activity'. But is that a reasonable measure?

For some things, it is a very reasonable measure. Of course, I would think that since it is the basis for my Safety thesis (http://www.teemings.com/issue07/safety.html). Comparing passenger car stats and airline flyings stats on that basis makes them more equivalent--as you'd probably expect.

[Sam Stone]

Sure, sometimes that's the reasonable measure. But is it in this case? Not really.

[RM Mentock]

Which cases, though? There are a lot of cases. Some are appropriate, and some aren't.

[Sofa King]

Here's a blurb from this month's Scientific American (http://www.sciam.com/2001/1101issue/1101scicit6.html) on the two skydivers who plan to attempt this type of jump.

Some statistics offered in that article:

Plunge time:
6 minutes

Maximum velocity:
about 900 mph

Terminal velocity:
120 mph

Speed of sound above 36,000 feet:
660 mph

The article also mentions in passing that Kittinger did not think he broke the sound barrier on his own jump.

And I'd like to apologize, two years after the fact, for being a smart ass. I think that might have been the first post I ever made here on the SDMB, and all I can say is that I hope I have made better contributions since then.

[Mangetout]

Originally posted by Whammo
Second.. in a separate show it was said that a skydiver doesnt need to breath when in freefall because his body will absorb enough oxygen through the skinEven if this was true, wouldn't you have to skydive naked for it to work?