dayle 0 #1 March 12, 2002 Hello all, Is there an altitude that you start to experience Ground Rush at or can it happen at any time. The reason I ask is that on one occasion I did experience Ground Rush (you don't need to know the details, suffice to say I f#@$ed up) just after I became self-supervised and have been forever trying to figure out how low I actually was. If anyone knows when Ground Rush starts i'd really like to hear some anwsers. Quote Share this post Link to post Share on other sites
PhreeZone 15 #2 March 12, 2002 I've had ground rush at 5000 feet and then again never had it when I went and took it down to 2200 feet.... its all personal perception imho....Cause I don't wanna come back down from this cloud... ~ Bush Quote Share this post Link to post Share on other sites
ChromeBoy 0 #3 March 12, 2002 Never had ground rush but I had tunnel vision on my second jump. Pretty freaky. Kachink,ChromeBoy-Mirage G3 Unisyn- Quote Share this post Link to post Share on other sites
n2skdvn 0 #4 March 12, 2002 3000 to 4000 ft is when i start experienceing ground rushcool feeling just remember to pull!!!!!!!It's not the fall that kills you, it'ssudden deceleration syndrome. Quote Share this post Link to post Share on other sites
rhino 0 #5 March 12, 2002 1900 feet.. Someone was on top of me and I had to keep tracking. I was in the seat at 1400.. That is the lowest I have gone.. I make it a point never to go below 3k on waveoff. Will never do that again..Blue Skies and Smooth Rides!! http://www.aahit.com Quote Share this post Link to post Share on other sites
billvon 2,402 #6 March 12, 2002 >Hello all, Is there an altitude that you start to experience Ground Rush at or can it happen at any time. It can happen at any time. I've experienced it at 3000 feet when I looked down and realized I was _much_ lower than I thought I was. OTOH I've been in freefall at 800 feet and not noticed it, because I had just exited a bridge and I wasn't falling very fast yet. (Within a few seconds I did experience it.)I think ground rush happens because we all have motion detectors around the edges of our visual field. They're intended to alert us to danger or prey, and their main purpose is to make us look in that direction, bring our fovea (high resolution area of our eye) to bear on the problem. In ground rush, those motion detectors begin to detect the ground rising on all sides, and it feels eerie because there's no one direction to look in - the horizon on all sides is rushing up to meet you. In a way, it's a very good thing we experience that, because it's often our last warning that we're getting very, very low.-bill von Quote Share this post Link to post Share on other sites
SkymonkeyONE 3 #7 March 12, 2002 I generally become cognizant of ground rush at around two grand. My webpage HERE Quote Share this post Link to post Share on other sites
SkyDekker 1,128 #8 March 12, 2002 excuse a complete newbie question, but, what are the dangers of groundrush?SkyDekker"We cannot do great things, only small things with great love" Mother Theresa Quote Share this post Link to post Share on other sites
dayle 0 #9 March 12, 2002 re: excuse a complete newbie question, but, what are the dangers of groundrush?Well, Sky, in case nobody has ever told you no question is unimportant in this sport especially if it can save your life. There is no danger of groundrush, it's what groundrush signifies. It means you are awfully low in most cases. (some people have experienced it fairly high up from what I've read in previous posts) the big danger from groundrush is..... SPLAT!!! Quote Share this post Link to post Share on other sites
dayle 0 #10 March 12, 2002 Thanks alot Bill, I've always guessed that I was at around 1800 to 2000 feet when I deployed but I've never been sure. I can tell you that it scared the living sh@% out of me though. I think I agree with you about the speed part too. I've done hop and pop's at a slightly lower altitude than recomended and never experienced it. On this particular jump I had exited at 14,000 so I was well into full freefall.Dayle Quote Share this post Link to post Share on other sites
quade 3 #11 March 12, 2002 Actually Bill, I think it has to do more with the surface objects registering near the edge of the fovea appearing to move farther outward toward the periphery. Your basic assumption about the motion detectors near the far edges of the field of view is correct, but your statements about the horizon "rising" can't be correct unless you're comparing things from the surface up to altitudes where you can see the curvature of the Earth.Imagine you were 100 miles away from an infinite plane that divided the universe in half. Unless there were surface features on the plane, there would be no way just by looking at it how far away from it you were. The "horizon" would appear exactly the same 100 miles away as it would 10 feet away. I think that at the altitudes we're normally jumping, the Earth is seen as still being pretty much "flat".quadehttp://futurecam.com Quote Share this post Link to post Share on other sites
billvon 2,402 #12 March 12, 2002 >Actually Bill, I think it has to do more with the surface objects registering near the edge of the fovea >appearing to move farther outward toward the periphery. Your basic assumption about the motion detectors near >the far edges of the field of view is correct, but your statements about the horizon "rising" can't be correct >unless you're comparing things from the surface up to altitudes where you can see the curvature of the Earth.You're not seeing the horizon actually rise, you're just perceiving that because of how quickly objects near your visual horizon are "spreading out" in your periphery. (Note that since you don't normally have a 180 degree field of vision you can't actually see the edges of the true horizon while looking down.) Try the following. Stand 10 feet from a wall with something on it. Walk slowly towards it and stare at the wall. At some point, you will notice a dramatic increase in how fast everything is "spreading out" from the center, even though you're not walking any faster. This will be most dramatic on the edges of your vision, and it is this effect, I think, that causes ground rush. (Also the effect that causes students to flare too high, but that's a different discussion.)>Imagine you were 100 miles away from an infinite plane that divided the universe in half. Unless there were >surface features on the plane, there would be no way just by looking at it how far away from it you were.I agree, and if you were jumping over a huge flat lake (or over, say, Antarctica) you wouldn't get the same sort of ground rush. In fact, this is a big issue when landing seaplanes - you simply can't judge distances or speeds over a featureless surface. Since most drop zones have features that seem to move once you get close, you can get ground rush there.-bill von Quote Share this post Link to post Share on other sites
ltdiver 3 #13 March 12, 2002 Quotethe big danger from groundrush is..... SPLAT!!!Then you get the team name "Flat People"! They -come- from the planet "Splat"!Actually, there was a team with this name back in the early '90's! __________________________________________http://www.discover.net/~ltdiver Quote Share this post Link to post Share on other sites
Hooknswoop 19 #14 March 12, 2002 Funny that someone would bring up groundrush. Because just the other night I had the most incredible groundrush I have ever experienced. I exited off an antennea from 1200ft ish, in a cloud. Couldn't see the ground at exit. The ground slowly came into view in a haze, then it completely cleared up. Crystal clear and VERY, VERY close. I pitched immediately, wondering if I had waited a bit too long. Obvisiouly it opened in time (250-300ft -ish). Until it cleared up, the ground seemed so far away because of the water vapor in the air, then it was rushing to meet me at an absolutely incredible speed. It looked like a movie special effect.Hook Quote Share this post Link to post Share on other sites
billvon 2,402 #15 March 12, 2002 >Because just the other night I had the most incredible groundrush I have ever experienced. I won't say this was groundrush, but the oddest change in perception I ever had was on a morning in similar conditions. I had a brand new BASE rig, and of course I had to try it, and there was this 250 foot crane nearby that I figured would be ideal - long end over a sandy pit, no one nearby. (In retrospect, doing it before first light on a foggy night by myself wasn't the best idea, but dammit I had a new rig!)Anyway, I got to the top, fussed over the exit point for about 10 minutes, looked down for another 5, then launched with my 50" PC in my hand. For about half a second the scene remained the same - I was 250 feet above a sand pit, which was plenty high to set up and land. Then a switch in my brain flipped, and I went from climbing-awareness to freefall-awareness, and in my perception I lost about 200 feet in a tenth of a second. I'm sure I was open in less than 50 feet, but it seemed to take at least 200. I turned once, landed, fell down, and then started in with "well that was just about the _stupidest_ thing you've ever done. . . " A workman looked at me oddly as I walked out, but no problems. Live and learn.-bill von Quote Share this post Link to post Share on other sites
bill2 0 #16 March 13, 2002 a question for you Bill: you said:Try the following. Stand 10 feet from a wall with something on it. Walk slowly towards it and stare at the wall. At some point, you will notice a dramatic increase in how fast everything is "spreading out" from the center, even though you're not walking any faster. This will be most dramatic on the edges of your vision, and it is this effect, I think, that causes ground rush. (Also the effect that causes students to flare too high, but that's a different discussion.)____________________________I always thought ground rush was something you experienced as you were about to flare, as you mentioned. but from these comments in this thread, I get the impression it's something you feel high up. Or is it both? I'm asking because I just bought a Spectre 230, after graduating AFF and always jumping the student rigs at 266 sq feet I believe. with the spectre now I'm coming in faster, and while I've flared and landed correctly with a head wind, in no wind I'm coming in faster and the last couple of times I've flared too high (25 - 30 feet). I felt at the time that I was flaring about 10' off of the ground. Is this because ground rush is accelerated with a different rig? Quote Share this post Link to post Share on other sites
lazerq3 0 #17 March 13, 2002 I guess I've never had it!!! Lowest pull was at 2700ft.......and didnt have any problems.......possibly cuase I was too busy watching for people in the 12way we attempted!! Thats OK though...if I havent experianced it then I must not be going too low for abilities!!jason Quote Share this post Link to post Share on other sites
SkymonkeyONE 3 #18 March 13, 2002 Fascinating. Having caught myself quite low on a number of occasions, I felt time slow down. Anyone else?ChuckMy webpage HERE Quote Share this post Link to post Share on other sites
PhreeZone 15 #19 March 13, 2002 The stupidest thing I've done yet I felt time slow down.... I went a little lower then planned and opening into a spinning main, it went diving and I got the biggest case of ground rush I've ever had. Long story short... lost track of altitude kicking out and got good canopy at 1500. The feeling of looking down at that 2000 feet in a spinning line twist mal made me feel REALLY low, but time was moving really slowly durning the entire time, I could count the line twists and make out structures on the ground as I was spun towards it.... Weird huh?Cause I don't wanna come back down from this cloud... ~ Bush Quote Share this post Link to post Share on other sites
Hooknswoop 19 #20 March 13, 2002 Time slows down and everything feels very peaceful. Details are very sharp and clear, every litle noise stands out, every sensation is felt, and images are forever burned into memory.Now where did I put my BASE rig..........Hook Quote Share this post Link to post Share on other sites
skymedic 0 #21 March 13, 2002 I was thinkin that same thing the other night.....as I left from just over 800 feet.....ahhh....life is good....marcBSBD Quote Share this post Link to post Share on other sites
billvon 2,402 #22 March 13, 2002 >I always thought ground rush was something you experienced as you were about to flare, as you mentioned. >but from these comments in this thread, I get the impression it's something you feel high up. Or is it both?Both, although I think the mechanism is a little different.> in no wind I'm coming in faster and the last couple of times I've flared too high (25 - 30 feet). I felt at the time that >I was flaring about 10' off of the ground. Is this because ground rush is accelerated with a different rig?I think that you're seeing the result of the higher speed. One of the ways we judge distance is by relative speed - if we see things moving faster we assume we're closer. On a lot of students first few jumps, they spend 3-4 minutes at altitudes where the ground just crawls by. Then, at 50 feet or so, they get close enough so they really see the relative speed. Their perception is that they are suddenly very close to the ground, and they flare.Eventually we get over this, but we can still get fooled by faster canopies (or by a downwind landing.) We see more motion at the same altitude, and we mistake the greater speed for a lower altitude. It takes some time to be able to ignore those sorts of false cues.-bill von Quote Share this post Link to post Share on other sites
Cornholio 0 #23 March 13, 2002 This actually brings up a question that I never thought I would ask... but this thread sounds about right for it.... Does anyone know of a video of something or someone hitting the earth at terminal velocity ( such as a watermelon dropped from a plane with a camera attached to the side, or perhaps a person... ) It would be an interesting test to see when the ground rush really starts to happen without you actually having to experience it. - Matt Quote Share this post Link to post Share on other sites
lazerq3 0 #24 March 13, 2002 I dont know if you would really be able to experiance it like that...I watch people on TV BASE jump with cameras on there heads and it doesnt phase me one bit....but put me there on the edge of the cliff and I'll be shitting bricks!!!!! I think its just one of those things you just have totruely experiance for yourself!!!!jason Quote Share this post Link to post Share on other sites
Michele 1 #25 March 13, 2002 QuoteStand 10 feet from a wall with something on it. Walk slowly towards it and stare at the wall. At some point, you will notice a dramatic increase in how fast everything is "spreading out" from the center, even though you're not walking any faster. Do not to do that after a martini or two, and then a Royale Kir (I do love those - champagne and cassis).....you don't get ground rush, you just get dizzy, everything moves in weird directions and then you trip over the cat!! Ciels and Pinks-MicheleIf you really want to, you can seize the day; if you really want to, you can fly away...~enya~ Quote Share this post Link to post Share on other sites
