dontbounce 0 #1 February 22, 2006 If I dropped an object from a plane, how long would it take before all lateral motion ceased and the fall was straight down? Say for example, If I wanted to drop a "crash test dummy" from a plane at 2000ft and have it land within a 1000ftx1000ft area. A good spotter could probably tell me... I dont know the math to figure it out... Anybody know? Assuming no wind, minimal drag, etc... Also, it takes 1000 feet and 10 seconds before you reach terminal right? Thanks! Quote Share this post Link to post Share on other sites
CSpenceFLY 1 #2 February 22, 2006 I assume you are talking about forward throw in a no wind situation. . Quote Share this post Link to post Share on other sites
billvon 2,400 #4 February 22, 2006 >If I dropped an object from a plane, how long would it take before >all lateral motion ceased and the fall was straight down? Never. But after about ten seconds, a jumper's horizontal speed becomes so low that it's negligible compared to other forces (like the jumper moving himself around in freefall.) Of course, a down comforter and a bowling ball will act much differently; the comforter will slow down more rapidly and the bowling ball more slowly. Quote Share this post Link to post Share on other sites
dontbounce 0 #5 February 22, 2006 So it would be 100% lateral 0% drop the moment of the drop, 90% lateral, 10% drop after 1 send, and so on? Thanks for the info... Do you know the average speed of say an otter on a drop run (relative to the ground)? Quote Share this post Link to post Share on other sites
gulaz 1 #6 February 22, 2006 In theory, assuming no wind and *no* drag, never. Horizontal will stay constant and vertical will increase due to gravity. The math to actually figure it out is probably gross, and will involve a whole lot of really boring variables to take into account the forces acting upon it laterally (drag). Now to have it land in a specific area, its gonna depend on how heavy your crash test dummy is compared to its surface area. As was said earlier, a bowling ball (lots of weight, small area) is going to behave differently than a down blanket (small weight, large area). A bowling ball would reach a much higher terminal velocity than a person would, and it would probably keep almost the same lateral speed through most of its fall, due to a small surface area and fairly aerodynamic shape. Quote Share this post Link to post Share on other sites
billvon 2,400 #7 February 22, 2006 >So it would be 100% lateral 0% drop the moment of the drop, 90% >lateral, 10% drop after 1 send, and so on? Something like that. The speed approaches zero asymptotically, but never _quite_ gets there (at least in theory.) >Do you know the average speed of say an otter on a drop run . . . About 80kts IAS. If I remember the conversions correctly, that's 92KTAS, 105mph, or 155 feet per second. Quote Share this post Link to post Share on other sites
dontbounce 0 #8 February 22, 2006 OK. So how do the pilots know where to drop you to make you land on the DZ? Wild ass guess? Or does the free fall lateral motion not make nearly as much of a difference? Assuming a 180lb "object", roughly shaped like me going "aaahhhh" falling toward the earth... I have a buddy who is a pilot, and I want to do some experiments on deceleration forces from a terminal impact (and how to mitigate those forces using things like high drag devices, airbags, etc). I dont understand how we can drop an object the size (and weight) of a vw beetle on the surface of mars at almost 100mph and not even scratch the paint on the lander, yet the same technology is not used for divers like us... I know this is a sensitive subject, but it is one I am interested in, and one that should be addressed with the best available technology. Not thinking about it until you have a double mal is NOT a solution. Here is something I have been working on... ------------------------------------ A Diver hitting the ground (going in) could be approximated from the sheer physics involved to a driver slamming their car into a brick wall without wearing a seatbelt. The forces are the same, and are all related to the rapid deceleration of a body in motion. Simply stated: The fall doesn’t hurt you, it is the sudden stop at the end! Anybody in the auto industry will tell you that three main factors determine the destructive forces on the driver: 1. the speed of the driver right before the event (initial velocity) 2. The mass of the driver 3. The stopping distance (from full speed to complete stop). When we deploy our main, we slow from terminal to about 10mph over a period of 3 or 4 seconds. When we “go in”, the same deceleration occurs, just over a much shorter time frame. This is explained: Force on Driver in Example Car Crash http://hyperphysics.phy-astr.gsu.edu/hbase/carcr2.html#cc2 and CHAPTER 24 AIRCRAFT ACCIDENT SURVIVABILITY http://www.iiimef.usmc.mil/medical/FMF/FMFE/FMFEref/fs_man/CHAPTER%2024.html and Gas Laws Save Lives: The Chemistry Behind Airbags http://www.chemistry.wustl.edu/~edudev/LabTutorials/Airbags/airbags.html and Mars Pathfinder Project Information http://nssdc.gsfc.nasa.gov/planetary/mesur.html Using the calculator from the 1st link, I punched in some test figures and got the following information: A human weighing 180 lbs traveling at 53 meters/sec (120mph) decelerates to zero meters per second in .1 feet (1 ½ inches). (going in, no canopy, minimal drag, hard ground) Force exerted on the body: 867,075 lbs, or 433 tons. A human weighing 180 lbs traveling at 53 meters/sec (120mph) decelerates to zero meters per second in 1 foot. (landing on a mattress for example) Force exerted on the body: 86,707 lbs, or 43.3 tons. Lesson: distributing the deceleration over a 1 foot area lowers the destructive force on the body by 90%!! A human weighing 180 lbs traveling at 53 meters/sec (120mph) decelerates to zero meters per second in 2 feet (landing on two mattresses for example). Force exerted on the body: 43,353.75 lbs, or 21.6 tons. (this is about twice the force of a 60mph car crash while wearing a seatbelt) A human weighing 180 lbs traveling at 26.82 meters/sec (60mph) decelerates to zero meters per second in 2 feet. (landing on two mattresses under partial inflated canopy) Force exerted on the body: 43,353.75 lbs, or 5.41 tons. (the force of a 15mph car crash with no seatbelt) Painful yes, but Survivable… This is less than 1/100 the force of going in at full speed with no cushion. To greatly increase the likelihood of survival, two of these factors must be compensated for. 1. Speed at time of impact 2. deceleration time If you can decelerate the jumper from terminal to 60mph using some sort of "quick deploy" drag device behind them (like an auto airbag with a flat shape and a LOT of surface area, or a "mammoth drogue" powered by a CO2 canister like in BB guns)), and give them 1-2 feet of padding on the head/torso/abdomen/hips (such as an auto airbag, also power by CO2 cannister), they would experience 1/100th the force of impact as going in hard. Additionally, the quick drag device would force them into "belly down" to distribute the force of impact over the largest surface area possible. It is possible to develop some sort of "last chance" system much like an aad that would deploy at say 150-200ft at a speed of >75mph. Since the Cypres shuts off at ~130 feet, this could make the difference between wearing a couple of casts for 5 weeks, and... 1. Develop it cheap 2. Develop it with minimal weight and size. (front airbag could be as small as a pack of cigarettes attached to your chest strap) (drag device could be smaller than a cigar box, directly above the parachute, or one the size of a coke can on each side) 2. design it to be retrofitted onto existing harness systems 3. design it so that it doesnt interfere with the operation of the control systems (or the two canopies) in case of accidental deployment. You could cut the fatality rate by a lot... Maybe like 20%-40%. Take a look at the fatality database. Look for "low pull", hard pull, late reserve activation, double mal, etc. It wouldnt fix some guy loaded at 3:1 doing a hook turn at 90mph 50 feet off the ground, but it would fix a lot of other problems. You could probably build something like this for less than $300.00 if you used readily available technology. Quote Share this post Link to post Share on other sites
dontbounce 0 #9 February 22, 2006 so, (roughly) when you leave the plane, you travel 704 feet in the same direction as the plane before your lateral motion is negligible. So, at 2000 feet, you would have to drop the dummy 800 feet or so before you passed over the drop zone to make sure it landed in the right area and didnt take out a barn or something. Quote Share this post Link to post Share on other sites
velo90 0 #10 February 22, 2006 QuoteA good spotter could probably tell me A good spotter would tell the crash test dummy to learn how to spot and not rely on someone else. Quote Share this post Link to post Share on other sites
kallend 1,625 #11 February 22, 2006 QuoteIf I dropped an object from a plane, how long would it take before all lateral motion ceased and the fall was straight down? Say for example, If I wanted to drop a "crash test dummy" from a plane at 2000ft and have it land within a 1000ftx1000ft area. A good spotter could probably tell me... I dont know the math to figure it out... Anybody know? Assuming no wind, minimal drag, etc... Also, it takes 1000 feet and 10 seconds before you reach terminal right? Thanks! Try my freefall simulator at www.iit.edu/~kallend/skydive/... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
billvon 2,400 #12 February 22, 2006 >You could cut the fatality rate by a lot... It's been done - at least for bikes. http://www.sheldonbrown.com/airbag-helmet.html Quote Share this post Link to post Share on other sites
dontbounce 0 #13 February 22, 2006 Thats great... Balloons... Quote Share this post Link to post Share on other sites
FrogNog 1 #14 February 22, 2006 QuoteI dont understand how we can drop an object the size (and weight) of a vw beetle on the surface of mars at almost 100mph and not even scratch the paint on the lander, yet the same technology is not used for divers like us... If we were wrapped up in big enough canvas balloons and we could survive repeated 20-G bounces, we could skydive without parachutes all we want. It would be hard to fit in the plane with all that on, and we wouldn't be good at freeflying or flying canopies anymore. Regarding drop accuracy, when they drop something onto Mars they're really happy if it lands within a couple of miles of where they meant it to. That kind of spotting accuracy is marginal to most skydivers. Perfect spotting would allow someone falling straight down to burn into the peas. Good spotting would allow someone falling straight down to deploy at an appropriate altitude and at the end of deployment end up within the cone of return. We fly back to the dropzone and we can fly a long way, so the difference of several hundred feet due to forward throw on leaving the plane is not a big deal. The five groups that get out of the fast-moving plane after you, and who are supposed to leave enough horizontal separation between you and them, are a big deal because everyone wants to fall into the cone. (And a lot of people want to fall near the central axis of the cone. And some of them can't open higher [where the cone tends to be wider in most configurations] and some of them don't want to open higher.) -=-=-=-=- Pull. Quote Share this post Link to post Share on other sites
dontbounce 0 #15 February 22, 2006 QuoteQuote It would be hard to fit in the plane with all that on, and we wouldn't be good at freeflying or flying canopies anymore. I disagree. Airbags in cars are actually very small BEFORE they are used... :) You could make them even smaller if you vacume sealed it... Like the infomercials where you vacume the air out of a bag of clothes to save space... bag http://www.lanl.gov/quarterly/q_sum03/images/composite_draft_bag_a.jpg another bag http://www.lemurzone.com/airbag/images/driverairbag.jpg propellant http://www.kaldi.com/graphics/charger_0084.jpg CO2 cartridges http://www.adventureracingconcepts.com/prod/bike/tool/inflation1.html Quote Share this post Link to post Share on other sites
billvon 2,400 #16 February 22, 2006 >Airbags in cars are actually very small BEFORE they are used... :) Right, but they inflate on impact, which is easy to detect - and they do exactly one thing, which is slow your impact with the steering wheel/dash. I have side impact airbags too, and they take up a bit of room around the sill of the door. Again, though, they only cushion against impact from one direction, and are impact activated. Designing an AAD to know when you are freefalling at 50 feet, and not in an airplane, and not under canopy, is something that has not been done even for conventional AAD's yet. Witness the misfires caused by swooping and the non-fires when someone cuts away below 1000 feet. Consider that a misfire in an airplane could kill everyone in the plane, if the jumper is next to the pilot. Also consider that if you are trying to drop your canopy into a tiny clearing near powerlines, and the thing misfires, it just might kill you instead of save you. Finally, it would have to be huge. You're talking about protecting a 6 foot tall human, which means an array of 4-8 impenetrable airbags 3-6 feet in diameter. (Won't do you much good if they are easily popped by a cactus or agave or something.) Which is dozens if not hundreds of pounds of airbags, gas generators and harnessing. You'd also need a drouge to slow you enough that an airbag landing is survivable. And if you hypothesize a 10 foot diameter drouge that would fire in an ultra-reliable manner at 100 feet or something, why not just make it a 26 foot diameter drouge? That will land you safely with no airbags, with the same harness you normally jump with. Quote Share this post Link to post Share on other sites
dontbounce 0 #17 February 22, 2006 The voice of experience... Damn I hate it when people talk sense into me. Quote Share this post Link to post Share on other sites
packerboy 3 #18 February 23, 2006 My first cutaway, the freebag landed in the bowl about 10 ft from center.. that's good spotting! -------------------------------------------------- In matters of style, swim with the current; in matters of principle, stand like a rock. ~ Thomas Jefferson Quote Share this post Link to post Share on other sites
ZigZagMarquis 8 #19 February 23, 2006 * bangs head against wall * DOESN'T ANYONE TAKE PHYSICS IN HIGH-SCHOOL ANYMORE!!!!????! Quote Share this post Link to post Share on other sites
kelpdiver 2 #20 February 23, 2006 Quote* bangs head against wall * DOESN'T ANYONE TAKE PHYSICS IN HIGH-SCHOOL ANYMORE!!!!????! high school physics, even at the AP level, is a world of frictionless planes and vacuums. It won't answer the question. Quote Share this post Link to post Share on other sites
ZigZagMarquis 8 #21 February 23, 2006 QuoteQuote* bangs head against wall * DOESN'T ANYONE TAKE PHYSICS IN HIGH-SCHOOL ANYMORE!!!!????! high school physics, even at the AP level, is a world of frictionless planes and vacuums. It won't answer the question. DOESN'T ANYONE TAKE COMPUTATIONAL FLUID DYNAMICS ANYMORE!!!!!????! Quote Share this post Link to post Share on other sites
kallend 1,625 #22 February 23, 2006 QuoteQuote* bangs head against wall * DOESN'T ANYONE TAKE PHYSICS IN HIGH-SCHOOL ANYMORE!!!!????! high school physics, even at the AP level, is a world of frictionless planes and vacuums. . That is not correct. Friction and air resistance are both covered in the AP curriculum.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
kelpdiver 2 #23 February 23, 2006 since when? Could be my failed memory, but I don't recall much of it in 1990. Got the 5, too, so I wasn't totally sleeping in class. Quote Share this post Link to post Share on other sites
jumperconway 0 #24 February 23, 2006 Never. But after about ten seconds, a jumper's horizontal speed becomes so low that it's negligible compared to other forces (like the jumper moving himself around in freefall.) --------------------- This is assuming no wind. A couple of weeks back we were exiting 1/2 mile from the dz and opening rt over main landing area. Uppers were close to 100mph Quote Share this post Link to post Share on other sites
sarge 0 #25 February 24, 2006 Quote A human weighing 180 lbs traveling at 26.82 meters/sec (60mph) decelerates to zero meters per second in 2 feet. (landing on two mattresses under partial inflated canopy) Force exerted on the body: 43,353.75 lbs, or 5.41 tons. (the force of a 15mph car crash with no seatbelt) Painful yes, but Survivable… This is less than 1/100 the force of going in at full speed with no cushion. Is it possible to relate that to what happens when someone falls off a ladder from twenty feet? ie: If someone is cleaning their gutters on their raised ranch, and falls on their head into not one but two mattresses, is he much less more likely to walk away than the guy that had no mattress to fall onto? I wonder if the design of the object is significant? what are the control factors? . edited to correct more from less...-- I'm done with the personally meaningful and philosophical sigs!! Quote Share this post Link to post Share on other sites
