Supersonic Skydiver

ohio_eric · 06-02-2010, 01:00 PM

What numbers are you plugging in? I'm not sure how to guesstimate his surface area, drag coefficent are the medium density.

forelander · 06-02-2010, 01:02 PM

If I had to guess, I'd suggest he's breaking mach1 outside of the atmosphere. When he re-enters he'd slow down to terminal velocity, the parachute will be opening in the same conditions a regular parachute opens, won't it?

Soopahmahn · 06-02-2010, 03:46 PM

Without getting silly and actually trying to calculate this, I know there is a shape factor involved in the drag coefficient. We could probably assume he'll present a roughly circular cross-section, but hey, he could be a Canadian with a square body.

Won't the terminal velocity be higher if there isn't as much atmospheric pressure at the higher altitudes? I think we'd have to set up a system of equations to compare the pull of gravity increasing with the inverse square of his distance to the Earth's core vs. the increase of resistance from the atmosphere as he plummets toward sea level pressure. Plus there's water in the air.

But I'm wasting time at work as it is, so why would I try to do that when it's much harder than the work I'm avoiding...?

Soopahmahn · 06-02-2010, 03:54 PM

Quote:

Originally Posted by forelander

If I had to guess, I'd suggest he's breaking mach1 outside of the atmosphere. When he re-enters he'd slow down to terminal velocity, the parachute will be opening in the same conditions a regular parachute opens, won't it?

Terminal velocity is the asymptotic maximum speed in a given set of conditions at which a body will travel - so when falling through the atmosphere, you assume a constant gravitational pull and a constant air medium etc. You wouldn't say he slowed down to terminal. So he will probably reach and maintain terminal velocity at some point, but the terminal velocity will change as he falls. And since I'm going to assume he'll be traveling faster than "ground terminal", he will slow down, but he may be going much faster than usual when he gets there.

Does anyone think returning from supersonic will cause him to get hit from above with the sound of his own passing?

Drew · 06-02-2010, 04:03 PM

Quote:

Originally Posted by Leon

According to Terminal Velocity if the guy is 200lbs and about 2sqft in area, his terminal velocity is 2995 ft/s. I wonder how much force a parachute can handle...

Forget the parachute, what about his body, when it opens?

I almost think you'd have to use a couple parachutes - the dude narrows himself into a pencil shape, breaks the sound barrier, then fans out a little, hits a small 'chute that applies a bit more drag, then follows up with a proper one.

Even then, it's risky as hell, because at the speed of sound he's traveling something like a quarter mile a second - if the world record is a 19.5 mile jump, then if we assume it takes maybe half of the distance to break the sound barrier, that gives him ten miles, at a mile every four seconds, to successfully break his speed to something where he won't get ripped apart by the force of his 'chute opening at almost 800 miles an hour.

ohio_eric · 06-02-2010, 04:16 PM

Here's an interesting read on the guy who holds the record that is trying to be broken.

Speed of a Skydiver (Terminal Velocity)

Quote:

On 16 August 1960, US Air Force Captain Joseph Kittinger entered the record books when he stepped from the gondola of a helium balloon floating at an altitude of 31,330 m (102,800 feet) and took the longest skydive in history. As of the writing of this supplement 39 years later, his record remains unbroken.

The air is so thin at this altitude that it would make for a moderate laboratory vacuum on the surface of the earth. With little atmosphere, the sky is essentially black and the sun's radiation is unusually intense despite polar temperatures.

Sitting in my gondola, which gently twisted with the balloon's slow turnings, I had begun to sweat lightly, though the temperature read 36 degrees below zero Fahrenheit. Sunlight burned in on me under the edge of an aluminized antiglare curtain and through the gondola's open door.

The density of air at 30 km is roughly 1.5 % that at sea level and thus drag is essentially negligible.

No wind whistles or billows my clothing. I have absolutely no sensation of the increasing speed with which I fall. [The clouds] rushed up so chillingly that I had to remind myself they were vapor and not solid.

This is not true for skydivers at ordinary altitudes, which is why they reach terminal velocity and cease to accelerate.

According to Captain Kittinger's 1960 report in National Geographic, he was in free fall from 102,800 to 96,000 feet and then experienced no noticeable change in acceleration for an additional 6,000 feet despite having deployed his stabilization chute. This gave him an unprecedented 3900 m (12,800 feet) over which to accelerate. At such extreme altitudes the acceleration due to gravity is not the standard 9.81 m/s2, but the slightly lower value of 9.72 m/s2. Using these numbers, it is possible to calculate the maximum theoretical velocity experienced during this record-setting jump. The result is amazingly close to the value recorded in National Geographic.

Quote:

As one would expect the actual value is slightly less than the theoretical value. This agrees with the notion of a small, but still non-zero, amount of drag.

At nine-tenths the speed of sound, Captain Kittinger also holds the record for the greatest speed attained by a human without the use of an engine. The standard value of the speed of sound in air at 31,000 m is 300 m/s (670 mph).