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May 29, 2008

Atmospheric freefall

Posted: 09:18 AM ET

As a meteorologist I’ve been fascinated by the French skydiver trying to jump from a balloon at 130,000 feet.  Flying thru the stratosphere at the speed of sound with nothing but a skimpy space suit is just crazy to me.  Michel Vournier dreams of breaking the freefall record were postponed again this week when his balloon flew off without him.  Regardless, the whole story got me wanting to jump.   So up I went with a plane full of other more experienced skydivers at Freefall Adventures in south Jersey.  Going “tandem” with a pro attached to me for safety, we jumped at 15,300 feet (solidly in the troposphere).  That’s about 600 mb of atmospheric pressure (surface is around 1000mb).  So the breathing isn’t easy and I got a little light headed and cold (temperature is less than 40 degrees at that height).  Doesn’t matter cause you’re not there for long, and once you jump the adrenaline erases any chill in the air.  A quick acceleration to a peak speed of 138 mph and you realize Newton was right about this whole gravity thing!  Wow what a ride!!!!  At that altitude the air is thin but oxygen isn’t required… no helmet or space suit either.  Tee shirt, jeans, and instructor Range Luda strapped to my back is all that was needed.  Freefalling for 70 seconds was incredible… spiritual in fact.  I’ve been on top of high mountains, but being that high with NOTHING beneath you is mind blowing.  The view, of course, is phenomenal.  All you hear and feel is the air rushing around you.  You want it to last forever but the ground approaches quickly.  At 5000 feet I pull the chute and Range guides us to a smooth landing.  It’s a rush to say the least.  Admittedly this was my second jump, but the butterflies were swirling just as much as during my first leap 6 years ago.  You say you like roller coasters, a nice view, and being buffeted by the wind?   Well jumping out of a perfectly good airplane may be just the thing for you… just don’t forget to pull the rip cord!!! 

Rob Marciano    CNN Meteorologist


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JAy.   May 29th, 2008 2:48 pm ET

I haven't ever jumped before, but you may be right about it being just the thing for people who want an incredible view. Using your numbers for my basis, you should have experienced 54 seconds of free fall. What a chance to see the world from a point of view that so few will actually see!

Then you still the the last 5000 feet of decent under parachute.

Totally amazing!

Scott   May 30th, 2008 10:16 am ET

I just jumped with the Golden Knights of the US Army Parachute team last week and it was totally amazing!!!! We jumped at 13,100 ft and had about 45-50 seconds of free fall. I have never experienced anything like it. Once the parachute opened up and we started to float in the air (or at least it seemed like it), you get to see the world like never before.

tim   May 30th, 2008 10:18 am ET

so you did a dive....big deal. what a baby!

KnuckleHead   May 30th, 2008 1:14 pm ET

I actually tried to bungee jump once. Couldn't make myself do it. I had to take the walk of shame. After that experience, I can't even imaging jumping out of an airplane. In my mind, I think about it in much the same way as body piercing; I generally try to aviod getting holes poked in my body about as much as I try to avoid falling from high places. Just ain't me, I guess.

Lindsay   May 30th, 2008 4:35 pm ET

Hi Rob, I also jumped tandem at Freefall Adventures in southern New Jersey. But you jumped at 13,500 feet.

FAR Part 91.211 states that no person may operate a civil aircraft at altitudes above 15,000 feet unless each occupant is provided with supplemental oxygen.

The FAR regulations don't make the experience any less amazing or life-changing, though.

Erica   May 30th, 2008 7:46 pm ET

Congratulations on your second skydive! Don't wait so long to make your third. It seems like you loved it, so you should take the next step and learn to go with your own parachute. Taking more ownership of the experience makes it even more amazing.

In the wise words of Leonardo da Vinci,

For once you have tasted flight you will walk the earth with your eyes turned skyward, for there you have been and there you will long to return.

Mark Rejhon   May 30th, 2008 8:36 pm ET

I am a licensed skydiver (Actually, Canada's first licensed deaf skydiver, listed on the website)

I think what he was given was data given by the instructor recorded by a freefall logging device such as a ProTrack, which is about the size of a Zippo lighter or wristwatch. From my knowledge, 70 seconds of freefall from 15,300 feet is normal, and 138 mph is a normal peak speed, though 120 mph is a normal average terminal velocity speed.

However, terminal velocity is not constant (as any of you watching Mythbuster's skydiving episode all knows), based on how streamlined your body position is, you can speed up or slow down your fall. Tandems vary in fall speed, and it takes approximately 10-20 seconds to accelerate to peak freefall speed. So the first 1000 feet could take more than 10 seconds, while the next 1000 feet could take only 6 seconds, for example, because it took time to accelerate to near your terminal velocity.

Aussie Jane   June 1st, 2008 4:15 pm ET

Mark, you're talking about B2E (belly to earth) right? That is true, I think the terminal speed is roughly 120-130 mph. What I wonder is, due to the density layering at various levels, would a terminal velocity be much higher at say 50,000 feet because the air is so sparse up there, and not as much wind drag? I would assume that terminal velocity is faster the higher up in the atmosphere you are falling, then would decrease as the air gets more dense.

Herb   June 3rd, 2008 12:03 pm ET

Aussie Jane, your comment shows you are thinking but...just like atmospheric density, gravitational forces also change as you get further from earth 🙂

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