Supersonic Jumper from 23 miles high

[yabadabapal]

Yep, everyone should try it at least once in their lifetime.

While free falling for five minutes before opening the chute, he is expected to reach subsonic or supersonic speed as a free falling human body exposed to the effects of the speed of sound.

http://www.nytimes.com/2010/03/16/science/16tier.html

[Selden]

I read that story this morning, and thought it was a bit too much of a personal contribution to science. It sounds like they are approaching this in the right fashion (i.e., not a daredevil stunt), but a human body isn't exactly streamlined, and transonic shock waves sound like a very dicey proposition. I wish the guy luck, but I hope he has a big life insurance policy.

[Joe Frickin' Friday]

...and transonic shock waves sound like a very dicey proposition.

 

I wouldn't worry about it much. He's starting his freefall in extremely rarified air, he's not going to get too beat up on the way down. Since atmospheric density increases rather slowly as he descends, his total aero drag will never exceed his weight by a very large margin; I'd bet he'll experience a peak drag-to-weight ratio of less than 1.1, and therefore a peak deceleration of less than 0.1 g. With those kinds of forces, any flutter effects he might encounter can likely be overcome by his muscles pulling his arms/legs up to his core.

 

This is very, very different from being ejected out of a supersonic aircraft at low altitude, in which case you immediately experience huge amounts of aero drag (because of high air density), unevenly distributed over your body. This is when you get broken bones and dislocated joints from your limbs flopping around in the slipstream.

[motoguy128]

"rarified" Now there's a word you don't hear much. Are you sure you didn't make that up? You must have one of them advanced degrees.

 

It's good to know they are using a system to automatically deploy a reserve chute if the jumper passes out.

 

Did anyone think of using a test dummy to see aht happens as an object of similar mass and shape as a human body goes supersonic. Maybe there's no way to control it to prevent spinning and tumbling.

[Joe Frickin' Friday]

"rarified" Now there's a word you don't hear much. Are you sure you didn't make that up? You must have one of them advanced degrees.

 

I've been known to browse the dictionary purely for entertainment. Given that sea level atmospheric pressure is 14.7 psi, and the pressure at 120,000 feet is 0.0678 psi, it's hard to think of a better word than rarified.

 

Did anyone think of using a test dummy to see aht happens as an object of similar mass and shape as a human body goes supersonic. Maybe there's no way to control it to prevent spinning and tumbling.

 

I think they won't be getting their balloon back after the fact - which means a test-dummy jump would be prohibitively expensive. No need, when you've got a willing daredevil.

[flars]

I have no idea why they think he will go transonic. It took years to get an aeroplane thru the barrier, and they had rocket motors. I am thinking drag will keep his speed down to less than 400 mph. Also, I wonder what the effect will be on his suit when he goes from 'rarified' to 'full of humidity' air?

[yabadabapal]

Red Bull, the energy drink is sponsoring this event. I wonder how many Red Bulls he will have to drink before jumping from 23 miles high seems like just another day.

I have never consumed a red bull or any energy drinks.

[Joe Frickin' Friday]

I have no idea why they think he will go transonic. It took years to get an aeroplane thru the barrier, and they had rocket motors. I am thinking drag will keep his speed down to less than 400 mph.

 

Aero drag is proportional to air density (which is proportional to pressure). If you can hit 120 MPH in freefall near sea level (pressure is 14.7 psi), then when you're up at 120K feet (pressure is 0.0678 psi), you'll get to pretty high speed before the aero drag increases to match your weight.

 

Jumping from 102K feet, Joe Kittinger hit 614 MPH before starting to decelerate; with some consideration for aerodynamics (no drogue chute, sleeker pressure suit, etc.), and an extra four miles of freefall (FNG will be falling from 123,000 feet), it should be possible to go transonic.

 

The Bell X-1 had rocket motors because in 1946, jet engines were crap; the technology was brand new, probably not very powerful or durable, and probably not up to the task of operating at high altitude (where thin air would permit high speed runs). The rocket motor on the X-1 didn't have all that much thrust, just 6000 pounds. Contrast this with the F-16 Fighting Falcon, which has a similar wingspan, and an air-breathing jet engine that can deliver 28,500 pounds of thrust (in afterburner); no problem hitting Mach 2 at altitude with that plane.

[Joe Frickin' Friday]

Changing my answer a bit. If what the NY Times article says is accurate - that he was in a sustained 130-MPH "freefall" in a sea-level indoor skydiving facility - then my predictions are a peak velocity of well in excess of the speed of sound, and a peak decel of 0.64 g's. 0.64 isn't too bad; a low-altitude skydiver falling headfirst at 160 MPH might experience this if he rapidly transitions to a flat, arms/legs-out posture.

 

I don't remember much about how to treat supersonic drag, so things might be inaccurate above ~700 MPH (speed of sound). OTOH, the model assumes he's in the same flat, arms/legs-out posture he had in the wind tunnel, so if he goes into a head-first dive, he could end up going a lot faster, too.

 

Will be interested to see the actual results of his jump.

[KDeline]

Do you just carry this stuff in your head? I can't remember what I had for breakfest this morning.

[motoguy128]

Wow, a predicted free fall of over 4 minutes. I'm assuming that is a record as well.

 

So Mitch, what's you theory on the affect on a human body in a pressure suit when a mach cone forms around it??? On early supersonic aircraft, I thought it could cause control surfaes to flutter and stall. Could the legs of the jumper begin to experience server turbulence?

 

 

[Joe Frickin' Friday]

So Mitch, what's you theory on the affect on a human body in a pressure suit when a mach cone forms around it???

 

The troublesome speed is right around the speed of sound, at which point he won't have a fully formed shock wave; that's the period where some areas of his body will be experiencing supersonic flow, and others won't, and strange pressure distributions might result in unexpected behavior.

 

Behind the shock wave, the air is moving at subsonic speeds (but at higher pressure/density/temperature). So once he's travelling well in excess of 700 MPH, he'll have a fully formed shock wave ahead of him, and he shouldn't have any unusual turbulence to deal with at all. He's not terribly aerodynamic though, so if you look at the attached pic at bottom of this post, he'll be more like the blunt body at bottom-right, rather than the pointy-pointy missile at top-left.

 

On early supersonic aircraft, I thought it could cause control surfaes to flutter and stall. Could the legs of the jumper begin to experience server turbulence?

 

Stall isn't really a problem - at those speeds, no way could they reach a high enough AOA to stall a wing - but flutter and buffeting happened on some early transsonic aircraft. The supersonic jumper might get some weird goings-on as he's pushing up (and back down) through the speed of sound. He can probably pull his arms and legs in tight to his body to keep them from really flopping around, but he might end up with crazy ruffling of his pressure suit, depending on how stiff they make it. Ideally I would think they want a relatively inflexible suit to help keep it from ruffling/whipping in the breeze like a flag on a windy day.

[Joe Frickin' Friday]

Two years later, some progress:

 

Skydiver passes halfway point in quest to make highest jump

[Joe Frickin' Friday]

Baumgartner's jump has been rescheduled for 1:30 PM ET today.

 

They're predicting a peak freefall speed of 690 MPH now.

[DaveTheAffable]

Did anyone think of using a test dummy...

Yeah... the guy making the jump! One brave(?) guy.

[MT Wallet]

So what's the plan to decelerate from 690mph? I'd think the chute opening would pose a significant injury potential.

[Glenn Reed]

Live coverage Here.

[Boffin]

So what's the plan to decelerate from 690mph? I'd think the chute opening would pose a significant injury potential.

 

Increasing air density as he falls will increase drag, slowing him gently. He will then go into normal spread-eagle free-fall until he gets to a mere 1500 feet, where he will open his chute. At that time he will be travelling at about normal terminal velocity for a spread human, about 120mph.

 

Andy

[Redbrick]

Baumgartner's jump has been rescheduled for 1:30 PM ET today.

 

They're predicting a peak freefall speed of 690 MPH now.

 

Mitch.....There's something I'm not understanding..A technicality.....He is going to exceed the speed of sound as defined at sea level, 690 mph right?...Does that also mean that he will be "breaking the sound barrier", as the news media has been saying, at 120,000 feet?...I would assume ('cause I can't understand all those technical charts I looked up) that "breaking the sound barrier is significaltly faster at that altitude....

[Mike]

Baumgartner's jump has been rescheduled for 1:30 PM ET today.

 

They're predicting a peak freefall speed of 690 MPH now.

 

Mitch.....There's something I'm not understanding..A technicality.....He is going to exceed the speed of sound as defined at sea level, 690 mph right?...Does that also mean that he will be "breaking the sound barrier", as the news media has been saying, at 120,000 feet?...I would assume ('cause I can't understand all those technical charts I looked up) that "breaking the sound barrier is significaltly faster at that altitude....

 

Explained here.

[Glenn Reed]

So what's the plan to decelerate from 690mph? I'd think the chute opening would pose a significant injury potential.

 

Increasing air density as he falls will increase drag, slowing him gently. He will then go into normal spread-eagle free-fall until he gets to a mere 1500 feet, where he will open his chute. At that time he will be travelling at about normal terminal velocity for a spread human, about 120mph.

 

Andy

 

From the RedBullStratos web site, it says that he will open the chute at 5000 feet, or 1524 meters.

 

Details here.

[Redbrick]

Thanks Mike.........

[Joe Frickin' Friday]

Mitch.....There's something I'm not understanding..A technicality.....He is going to exceed the speed of sound as defined at sea level, 690 mph right?...Does that also mean that he will be "breaking the sound barrier", as the news media has been saying, at 120,000 feet?...I would assume ('cause I can't understand all those technical charts I looked up) that "breaking the sound barrier is significaltly faster at that altitude....

 

Explained here.

 

Speed of sound at room temperature is about 765 MPH, and varies with the square root of temperature (measured relative to absolute zero, so room temperature = 293K or 529R). At high altitude, temps are much lower, well below zero F, so the speed of sound ends up being quite a bit lower. 690MPH corresponds to an air temperature of about -30F, which is roughly what's expected at the altitudes where he'll be hitting peak speed (around 100,000 feet).

 

Looks like they've called off today's attempt altogether; no word currently on when they'll try again.

[pbharvey]

690MPH corresponds to an air temperature of about -30F, which is roughly what's expected at the altitudes where he'll be hitting peak speed (around 100,000 feet).

 

 

That's a wind chill index of -121 F! I hope he wears a hat.

[Redbrick]

Appreciate the response Mitch.....

[Jake]

The part I like most is that Col. Kittinger will be talking Felix all the way up during the ascent. Pretty cool for the record holder and the one guy who knows what you will be going through to be in your head.

 

[George S.]

690MPH corresponds to an air temperature of about -30F, which is roughly what's expected at the altitudes where he'll be hitting peak speed (around 100,000 feet).

 

 

That's a wind chill index of -121 F! I hope he wears a hat.

 

There is no wind chill because his skin is not exposed.

[Dave McReynolds]

There is no wind chill because his skin is not exposed.

 

I wonder at what velocity wind chill starts becomming wind heat? Is there a velocity where you could be falling through the air just fast enough that the resistance of the air would create a balmy 68 degrees F temperature on the outside of your suit, even though the ambient temperature was -30, so that you would neither fry nor freeze?

[mbelectric]

For those of you who want to follow:

 

http://www.redbullstratos.com/

 

And a link here for a live feed:

 

http://www.youtube.com/watch?v=vkJ5ItzEq3M

 

MB>

[Danny caddyshack Noonan]

I wonder at what velocity wind chill starts becomming wind heat? Is there a velocity where you could be falling through the air just fast enough that the resistance of the air would create a balmy 68 degrees F t

 

There is. It is a function of both velocity and air density. You start with aeroheating due to highly compressed flow, below mach, but not a whole lot below IIRC.

If you were constantly accelerating, going almost straight up, you would progressively get hotter and hotter where impinged upon. Then as you find you can no longer breathe, you'd get cooler.

[George S.]

I know I mis-stated that wind-chill comment. I'm fighting the flu and am very tired.

Sorry.

[pbharvey]

I know I mis-stated that wind-chill comment. I'm fighting the flu and am very tired.

Sorry.

 

Hope you feel better George.

[Joe Frickin' Friday]

I wonder at what velocity wind chill starts becomming wind heat? Is there a velocity where you could be falling through the air just fast enough that the resistance of the air would create a balmy 68 degrees F t

 

There is. It is a function of both velocity and air density. You start with aeroheating due to highly compressed flow, below mach, but not a whole lot below IIRC.

 

I'll repost my speed/acceleration and altitude plots from earlier, and add a third plot showing temperature profiles:

 

 

 

The blue line shows the local temperature (in Celsius - sorry, America ) in the still, undisturbed air just ahead of his shock wave; this is taken from known atmospheric temperature profiles. The red line shows the air temperature that he will experience due to compressive heating of the air as he moves through it. If ambient temps were higher, he would experience much higher peak temperatures, but under the circumstances, it looks like the highest temps he should experience (on the outside of his suit) will be just barely above freezing (0 degrees C = 32 degrees F). At that point, the air starts getting thicker, and he starts decelerating, which reduces the compression heating of the air. Eventually he's going slow enough that the temperature rise is only minor (just a few degrees) - which is a good thing, because around t=125s, the ambient temps start going up.

 

I'm probably overestimating peak tempsa little bit; my simulation came up with a peak velocity of about 800 MPH, and they've recently predicted just 690MPH.

[Danny caddyshack Noonan]

Joe,

did you adjust g for the effect of 100,000 ft altitude? Not that I ever have to deal with minutae

[Jerry Johnston]

I'm getting a headache !

[Joe Frickin' Friday]

Joe,

did you adjust g for the effect of 100,000 ft altitude? Not that I ever have to deal with minutae

 

Cute. Once a spreadsheet is all laid out, it's easy to try silly little things like this. Gravitational acceleration is actually reduced by just over a percent when he's that high; the peak freefall velocity I calculated for him gets reduced by about half a percent.

 

Looking forward to next Sunday (his next scheduled attempt)...