tcliftonr@cc.curtin.edu.au (06/24/91)
In the discussions arising from GRAPH OF OSC'N DUE TO HIGH WINDFORCE Walter@cayman.AMD.COM (Walter Butler) writes: >It is possible that the jumper ( at 750 mph and 1.6 gees of >drag after a 120 000 ft exit) will have stability problems >from the supersonic airflow. Because of the soft impact with the atmosphere there will be an extended period of 30 seconds or so of deceleration, where much more wind force is available to induce "rocking" in a normally utterly stable skydiver. (A non skydiver is likely to go further, into a tumble, and a spin is also likely) >I am no expert, but believe that the shockwaves can cause >very localized areas of high stress and drag. Yes! The sound waves going down cannot escape downwards and so bank up as a flat cone of compressed air around each extremity. This would mean for a normally exposed skydiver that chin, knees etc would take more of the wind force than usual. But how much more? Will it make you sneeze or will it make your eyes water? Will it be enough to sense under all that protective clothing? The total force is still only 16 N/kg or so averaged over the whole body. It doesn't seem that local concentrations of force would be intolerable, but perhaps enough to provide for some rare phenomena to be first experienced by a brave pioneer. Certainly the position and attitude of the chin etc will affect the amount of build up. How long does it take to build up to equilibrium anyway? The compression can't accumulate indefinitely, it must bleed off sideways. If it takes a second to build up, the jumper will experience a tendency to nod in free fall. Hardly a terrifying danger. >A simulation of the jump performed in this manner would >be interesting. It sure would. Perhaps some of your NASA colleagues - the re- entry people - might know enough of the physics. Perhaps they already have a re-entry simulator. As it stands, this (subsonic) simulator is extrapolated out of its proven valid range. In particular, we need to know how the drag coefficient (for us brick-shapes) changes for low supersonic flight. Then we need to know the effect of temperature on the drag coefficient. Certainly the stratospheric cold of -56 degrees affects viscosity and reduces drag. For vibrations and oscillations, we need to know the effect of the compression cones on the extremities and how long they take to build up. >The diver might use a style tuck while supersonic. It would one way to get respite from some irritation due to vibration or suchlike. But it would be more unstable than an arch and the moment of inertia would reduce, so increasing the likelihood of a fast rotation or tumble in the high force wind. >This would also have the added "benefit" of increasing >his top speed. How gung-ho do they have to be? What a story that would make! "First supersonic skydiver in history strains for a morsel more of the unknown..." Let's salute their first exploration of impact. Whatever they find out for us, it is going to be interesting. Roger Clifton Curtin University West Australia. 6:91
jerrys@mobby.umiacs.umd.edu (Jerry Sobieski) (06/24/91)
In article <1991Jun24.135815.8781@cc.curtin.edu.au> tcliftonr@cc.curtin.edu.au writes: >>The diver might use a style tuck while supersonic. >>This would also have the added "benefit" of increasing >>his top speed. > >How gung-ho do they have to be? What a story that would >make! "First supersonic skydiver in history strains for a >morsel more of the unknown..." Geez Louise!!! The fall rate is fast enough! I have problems staying with an eight way with 10lbs of weights and a skin suit! And now supersonic isn't enough?! Do we *really* need that extra competitive 25 mph fall rate... As I strap on my JATO bottles... Jerry -- Domain: jerrys@umiacs.umd.edu Jerry Sobieski UUCP: uunet!mimsy!jerrys UMIACS - Univ. of Maryland Phone: (301)405-6735 College Park, Md 20742
yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) (06/25/91)
In article <1991Jun24.135815.8781@cc.curtin.edu.au> tcliftonr@cc.curtin.edu.au writes: >In the discussions arising from >GRAPH OF OSC'N DUE TO HIGH WINDFORCE > >Walter@cayman.AMD.COM (Walter Butler) writes: > > >>It is possible that the jumper ( at 750 mph and 1.6 gees of >>drag after a 120 000 ft exit) will have stability problems >>from the supersonic airflow. Don't let the term "supersonic" affect you too much. If a skydiver was going supersonic at low altitude, *that* would be something to write about, but going supersonic at high altitude is nothing to scream about. > >Because of the soft impact with the atmosphere there will be >an extended period of 30 seconds or so of deceleration, where >much more wind force is available to induce "rocking" in a >normally utterly stable skydiver. (A non skydiver is likely >to go further, into a tumble, and a spin is also likely) Intuitively, I disagree. > > >>I am no expert, but believe that the shockwaves can cause >>very localized areas of high stress and drag. The skydiver will go fast but the atmosphere will be tenuous, so why shockwaves? Airplanes experience shockwaves but they have *engines*, skydivers don't. > >It sure would. Perhaps some of your NASA colleagues - the re- >entry people - might know enough of the physics. Perhaps they >already have a re-entry simulator. As it stands, this >(subsonic) simulator is extrapolated out of its proven valid >range. Ha! As it stands, what is the range of the simulator? (what is its maximum altitude?) > >In particular, we need to know how the drag coefficient (for >us brick-shapes) changes for low supersonic flight. Then we >need to know the effect of temperature on the drag >coefficient. Certainly the stratospheric cold of -56 degrees >affects viscosity and reduces drag. > >For vibrations and oscillations, we need to know the effect of >the compression cones on the extremities and how long they >take to build up. Vibrations, vibrations? Hey, we are made of soft (living) tissue, not rigid metal. Nor are we hollow, unlike most airplanes. > >Let's salute their first exploration of impact. Whatever >they find out for us, it is going to be interesting. Agreed. -- Philip Yzarn de Louraille Internet: yzarn@chevron.com Research Support Division Unix & Open Systems Chevron Information & Technology Co. Tel: (213) 694-9232 P.O. Box 446, La Habra, CA 90633-0446 Fax: (213) 694-7709
mspurgeo@oucsace.cs.OHIOU.EDU (Mike Spurgeon) (06/25/91)
In article <1991Jun24.135815.8781@cc.curtin.edu.au>, tcliftonr@cc.curtin.edu.au writes: > How gung-ho do they have to be? What a story that would > make! "First supersonic skydiver in history strains for a > morsel more of the unknown..." Are you guys forgetting that it's already been done? If I'm not mistaken, subsequent calculations showed that Col. Kittinger DID go supersonic briefly on his 102,000 foot jump. Mike Spurgeon Internet: mspurgeo@oucsace.cs.ohiou.edu
csa18@seq1.keele.ac.uk (R.J. Husmo) (06/26/91)
In article <996@lhdsy1.chevron.com> yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) writes: >but going supersonic at high altitude is nothing to scream >about. Because, in space, no-one can hear you scream. Sorry about that, honest! Back to the 'Skydiving at supersonic airspeeds' discussion, as it is getting quite interesting. I always wanted to skydive from ORBIT, myself. (No, this time I am being perfectly serious.) I have already had comments like: 'If you fall any faster now, you'll need tiles on your jumpsuit.' Would anybody like to comment on the problems with such an undertaking? Apart from how to get into orbit in the first place, of course. Blue skies, Radar.
jerrys@mobby.umiacs.umd.edu (Jerry Sobieski) (06/26/91)
In article <1265@keele.keele.ac.uk> csa18@seq1.kl.ac.uk (R.J. Husmo) writes: >... I always wanted to skydive from ORBIT, myself. >(No, this time I am being perfectly serious.) >I have already had comments like: 'If you fall any faster now, you'll need >tiles on your jumpsuit.' > >Would anybody like to comment on the problems with such an undertaking? >Apart from how to get into orbit in the first place, of course. > You better be able to spot! :-) Jerry -- Domain: jerrys@umiacs.umd.edu Jerry Sobieski UUCP: uunet!mimsy!jerrys UMIACS - Univ. of Maryland Phone: (301)405-6735 College Park, Md 20742
tcliftonr@cc.curtin.edu.au (06/27/91)
In article <3547@oucsace.cs.OHIOU.EDU>, mspurgeo@oucsace.cs.OHIOU.EDU (Mike Spurgeon) writes: > In article <1991Jun24.135815.8781@cc.curtin.edu.au>, tcliftonr@cc.curtin.edu.au writes: >> How gung-ho do they have to be? What a story that would >> make! "First supersonic skydiver in history strains for a >> morsel more of the unknown..." > > Are you guys forgetting that it's already been done? If I'm not > mistaken, subsequent calculations showed that Col. Kittinger DID > go supersonic briefly on his 102,000 foot jump. Well, some authors say that he did go supersonic. But it doesnt check out. Remember the postings last year, when we simulated Kittingers jump? To get a free fall time of 277 seconds, a peak velocity of 460 mph was obtained. Definitely a world record, which still stands, but not supersonic. Even at -50 degrees, the speed of sound is still greater than 500 mph. I'll repost it or email if anyone's interested. Roger Clifton.
tcliftonr@cc.curtin.edu.au (06/28/91)
In article <1265@keele.keele.ac.uk>, csa18@seq1.keele.ac.uk (R.J. Husmo) writes: > I always wanted to skydive from ORBIT, myself. > Would anybody like to comment on the problems with such an undertaking? > > Radar. Why not do a mini shuttle trick? Start with a low circular orbit. Then v2/r = g so v = sqr(g*r) = 8 km/s Now nudge down (with a retro burn of your remaining rocket of course) so that you hit enough atmosphere for one gee of drag. It would be good to design a flight path so that one gee of drag is maintained throughout the descent. Then that 8 000 m/s is reduced at 10 m/s per second over 800 seconds, which shouldn't be too much oxygen to carry! If you have enough flying control, you can nose down for increased drag and nose up for reduced drag. This will be pretty sensitive at the hoigh speeds, so I for one would prefer an automatic control. There is a mean amount of KE to be gotten rid of as heated, eddying air. Power = force*vel = 10 N/kg * 8 km/s = 80 kW/kg at height, decreasing. This would need tiles on your feet and some sort of refractory control surface. Since the compression cones would be tight, arcsin(v/c) = arcsin(250/8000) = sfa it might be wise to keep your nose out of the wind. That requires a shell around your feet-first hurtling body, a mini-shuttle. What slowed-down velocity is cool and smooth enough for skydiving? We might know more when the 120 000 ft experiment is performed - they will reach 0.3 km/s supersonic. We wish you luck, brave traveller.
yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) (06/30/91)
In article <1991Jun27.180343.8816@cc.curtin.edu.au> tcliftonr@cc.curtin.edu.au writes: >To get a free fall time of 277 seconds, a peak velocity of 460 mph >was obtained. Definitely a world record, which still stands, but >not supersonic. Even at -50 degrees, the speed of sound is still >greater than 500 mph. > At -50 degrees and at the altitude where the jump would be made, the speed of sound would be below 500 mph. At sea level and under Standard Condition (atmospheric) does the speed of sound reach 500 mph. But as the altitude increases, the density decreases (the air molecules get further apart per unit volume) so it takes longer for collisions to happen, hence the compressional waves (sound) take longer to cover the same distance. Speed of sound, Mach 1, is the speed of sound at sea level. When an airplane reaches the speed of sound at altitude, it is going faster then the speed of sound for that altitude. -- Philip Yzarn de Louraille Internet: yzarn@chevron.com Research Support Division Unix & Open Systems Chevron Information & Technology Co. Tel: (213) 694-9232 P.O. Box 446, La Habra, CA 90633-0446 Fax: (213) 694-7709