brent@terra.Eng.Sun.COM (Brent Callaghan) (05/16/91)
A friend of mine is keen to drop me out of his 172. The airplane is STC'ed for door removal, and he has access to an emergency rig. NOTAM and property owner's permission are no problem. The only uncertainty is the landing. The DZ will be in the Rockies at 9,500 MSL. How much harder will the landing be than at sea level ? I'd be grateful to hear from anyone who's done a high altitude landing - say 5,000 and above. Is there anything special to watch out for in landing technique ? What's the increase in rate of descent and ground speed ? My stats are: 950 jumps, 175 lbs, Fury main (220 sq ft, 7 cell). Thanks -- Made in New Zealand --> Brent Callaghan @ Sun Microsystems Email: brent@Eng.Sun.COM phone: (415) 336 1051
bleck@ai.mit.edu (Olaf Bleck) (05/16/91)
In article <13377@exodus.Eng.Sun.COM>, brent@terra.Eng.Sun.COM (Brent Callaghan) writes: |> The only uncertainty is the landing. The DZ will |> be in the Rockies at 9,500 MSL. How much harder |> will the landing be than at sea level ? |> |> What's the increase in rate |> of descent and ground speed ? First order calculation: Assume steady state fall rate under canopy, so weight equal to force on canopy: W=Pressure*Area=0.5*density*velocity^2(squared)*area of canopy Weight is constant at both sea level and 9,500ft, as is area, so density1*velocity1^2 = density2*velocity2^2 => velocity2 = velocity1 * Square Root (density1/density2) Using standard atmosphere, density of air at sea level = 1.19 kg/m^3 density of air at 3000meters = 0.885kg/m^3 so, velocity(3000m) = 1.16*velocity(sea level) Not too bad. This is assuming I didn't miss some key point in my calculation by sleeping through class as an undergrad! Of course this is a much hairier aerodynamic problem than this calcualtion, but I suspect this will get you kind of close, and I'm not current enough to figure it out. Believe it or don't, -Olaf A-12241
jerrys@mobby.umiacs.umd.edu (Jerry Sobieski) (05/16/91)
In article <15939@life.ai.mit.edu> bleck@ai.mit.edu (Olaf Bleck) writes: >In article <13377@exodus.Eng.Sun.COM>, brent@terra.Eng.Sun.COM (Brent Callaghan) writes: > >|> The only uncertainty is the landing. The DZ will >|> be in the Rockies at 9,500 MSL. How much harder >|> will the landing be than at sea level ? >|> >|> What's the increase in rate >|> of descent and ground speed ? > >First order calculation: > >Assume steady state fall rate under canopy, so weight equal to >force on canopy: > >W=Pressure*Area=0.5*density*velocity^2(squared)*area of canopy [much technical stuff deleted] >Believe it or don't, > >-Olaf >A-12241 (Just what you'd expect from an MIT response:-) But seriously folks, I think the equation Olaf used is not necessarily going to be applicable to airfoils' flight characteristics and/or descent rates. Empiricly speaking... I jumped in Casper, WY - 5700' MSL and was quite impressed at the difference in landing speed. I weighed ~145 lbs under a StratoCloud (as I recall). The landing was not HARD, as much as it was FAST. I did make it into the peas which probably was a Good Thing, but the ground speed was considerable. The para-skiers land around 7-8000' I believe (Does anyone out there have para-ski experience?). But they have the benefit of cooler air (i.e. denser), probably higher winds (i.e. lower actual ground speed), and a couple feet of soft snow (i.e. fewer landing injuries). I would be prepared to PLF or "slide" in, so a big grassy LZ would be primo. Heavy suit/shoes to protect against ground rash, etc. The more wind I think the better as long as it isn't too turbulent from hills, treelines, buildings, etc. Don't expect your normal flare. I probably wouldn't try doing accuracy until you have some experience with the landing characteristics at that altitude. I am surprised a 172 could get to 12000' or better (but then I am not a pilot). Are you going to do a clear and pull or are you trying to get some FF? Good luck and let us know how it goes. Jerry -- Domain: jerrys@umiacs.umd.edu Jerry Sobieski UUCP: uunet!mimsy!jerrys UMIACS - Univ. of Maryland Phone: (301)405-6735 College Park, Md 20742
news@solitary.Stanford.EDU (System test) (05/16/91)
Someone asked the question of how landing a parachute at 9500 MSL differs from the behavior at sea level. It's already been mentioned that the only real difference is that all the speeds (descent rate under canopy, forward speed and speed to flare) increase by the square root of the the ratio of air densities - or about 20% at 10,000 ft. While I've not landed a parachute under such circumstances (only paragliders at or near sea level), I have landed hang gliders at high altitude and think the experience is similar enough to be germane here. Specifically, while 20% doesn't sound like much it can really affect your flare timing significantly. I tend to flare by the "feel" of the wing (i.e. its readiness to stall) but nevertheless I sometimes inadvertently use ground speed as a secondary cue. This is a bad thing and can make one flare way too late if it's not recognized. Landing at high altitude when done properly is just as "soft" as on the sand at the beach, but requires an earlier more aggressive flare at a ground speed that always looks "too fast". Be aware of this factor and you should do fine. I guess the best comparison I can make is to note that a high altitude landing is a lot like a dead wind landing on a hot runway at low altitude. If that experience seems straightforward to skydivers then a landing at 10K ft ought to be as well. Later, Fred Vachss (one of those guys who only wears a parachute but never uses it)
lmlee@PacBell.COM (Lloyd Lee) (05/17/91)
Reference the high level calculations from our friend from the MIT Artificial Intelligent LAB-- just do it, the landing won't be as hard as anything you would have from a "double L" canopy. -- Lloyd Lee "Schwinn Continental Forever"
brent@terra.Eng.Sun.COM (Brent Callaghan) (05/18/91)
Thanks to all who replied with advice about high altitude landings. I'm confident I can handle the extra 20% of airspeed. It really shouldn't be any worse than a botched no-winder at sea-level. The DZ is the airport at Leadville, Colorado. At 9,500 feet it's the highest in the U.S. I'll have plenty of room to flare - and nothing to fear in ground obstructions except grass stains... Fred Vachss mentions the visual effect of judging flare altitude. This is also a problem for pilots landing at the airport. The advice I get is to consciously start the flare higher than normal and give the canopy more time to stop. >Jerry Sobieski writes: >I am surprised a 172 could get to 12000' or better (but then I am >not a pilot). Are you going to do a clear and pull or are you >trying to get some FF? It's a 180hp 172 that's based at the airport. The airport is Leadville, Co. At 9,500 the highest in the U.S. With a small fuel load and 2 POB it should be no problem making it up to 13,000. I'm not planning on a long delay - I figure that the air time is better spent on playing with the canopy and showing off to the folks in Leadville - they don't get to see much skydiving up their way. >Good luck and let us know how it goes. Thanks. I will. -- Made in New Zealand --> Brent Callaghan @ Sun Microsystems Email: brent@Eng.Sun.COM phone: (415) 336 1051
brent@terra.Eng.Sun.COM (Brent Callaghan) (05/21/91)
In article <6138@ptsfa.PacBell.COM>, lmlee@PacBell.COM (Lloyd Lee) writes: > Reference the high level calculations from our friend from the > MIT Artificial Intelligent LAB-- just do it, the landing won't > be as hard as anything you would have from a "double L" canopy. Ah that takes me back! I did my first 50 jumps on C9's with various mods - usually double L's though sometimes I was lucky enough to get something "hot" like a 7TU or even "Derry slots". It was mucho macho to do a standup landing and not limp away. The DZ was usually windy enough that you had to make your approach to the target looking backwards over your shoulder. I laid down my life savings and bought a PC. That's when a PC was a ParaCommander (not a Personal Computer). -- Made in New Zealand --> Brent Callaghan @ Sun Microsystems Email: brent@Eng.Sun.COM phone: (415) 336 1051
larry@hpfelg.HP.COM (Larry Chapman X3117) (05/22/91)
Leadville, eh? I've done a demo at 8,500' (Allenspark, CO.) into a packed dirt parking lot. I wore heavy hiking boots and still broke a small bone in my foot. My advice: If it's a no-wind day -- don't do it! From personal experience, I don't believe the 20% numbers you've been getting. The difference between a sea level landing and a landing at 9,500' is very significant. Be careful and write a post-jump report! Oh yea, here are the stats from that jump: Canopy: X-210 (210 sq ft) My weight: 150 lbs Jumps: 500 -- LSC
tcliftonr@cc.curtin.edu.au (05/24/91)
In article <6138@ptsfa.PacBell.COM>, lmlee@PacBell.COM (Lloyd Lee) writes: > Reference the high level calculations from our friend from the > MIT Artificial Intelligent LAB-- just do it, the landing won't > be as hard as anything you would have from a "double L" canopy. Hey, let's not dismiss those careful calculations - they do help the daredevils to assess the risks being taken. Notice how much the base jumpers check their facts before a leap. The calculations are quite correct, too. For those with a distaste for school-stuff, the rule-of-thumb of 2% per grand increase in terminal velocity may be welcome and sufficiently accurate. 1.7% if you have a calculator. Cheers- Roger Clifton ---- Kalgoorlie West Australia.
yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) (05/28/91)
Yes, the calculations shown by the MIT guy seemed correct but an increase of only 25% in landing speed at 9000' is wrong. It is not enough and plenty of people have experienced it. Maybe the velocity square law does not apply and the velocity law in a linear fashion applies, in this case, the predicted landing speed is about 50-60% faster (at 9000') than at sea level. This seems more like it. -- 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
nraoaoc@nmt.edu (Daniel Briggs) (05/29/91)
In article <918@lhdsy1.chevron.com> yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) writes: >Yes, the calculations shown by the MIT guy seemed correct but an >increase of only 25% in landing speed at 9000' is wrong. It is not >enough and plenty of people have experienced it. Maybe the velocity >square law does not apply and the velocity law in a linear fashion >applies, in this case, the predicted landing speed is about 50-60% >faster (at 9000') than at sea level. This seems more like it. Geez, this seems to be getting into the realm where some real data would help. You know, we all go through a good ten grand altitude differential or more, nearly every time we jump. Why doesn't someone borrow a couple of hang glider instruments and take along a recording walkman. Hop and pop at ten grand, and read off the altitude, sink rate, and temperature all the way down. Thermals and wind will be a problem, I grant you, but maybe on a calm day at a flat drop zone we can tell the difference between 25% and 50% increase in sink rates. Anyone got any good ideas on how best to minimize the contaminants? Carry a wind speed sensor, and only compare comparable points? Ignore it, and model fit to the whole data set? Whatever, I think something useful might come out of it. Just a thought, -- This is a shared guest account, please send replies to dbriggs@nrao.edu (Internet) (505) 835-2974 Dan Briggs / NRAO / P.O. Box O / Socorro, NM / 87801 (U.S. Snail)
tcliftonr@cc.curtin.edu.au (05/30/91)
In article <2020017@hpfelg.HP.COM>, larry@hpfelg.HP.COM (Larry Chapman X3117) writes: > > From personal experience, I don't believe the 20% numbers you've been > getting. The difference between a sea level landing and a landing at > 9,500' is very significant. > Well, 20% is 20% more momentum and 44% more kinetic energy. Pretty significant. But yes there may be other factors. For one, there is the effect of viscosity, which decreases strongly with decreasing temperature. In the cold, that should increase the circulation around the airfoil so that lift increases, but should worsen the wingtip vortexes (ices?) so increasing drag there. Is anyone familiar with the theory of airfoils vs viscosity? Roger Clifton.