Push 0 #1 February 17, 2003 There is a thread in the Incidents forum that got me thinking. Lets say you are falling at terminal in the neutral (arch) position. You go to pull, and you do some bad mojo, so that you tilt head downwards quickly. As the thread in Incidents describes it, you extend your left hand too far and bend your knees. My question is, in this scenario, what would be your new terminal? And how quickly would you accelerate to it? I have absolutely no experience freeflying if you don't count the stupid stuff I did before I learned to arch properly -- Toggle Whippin' Yahoo Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you. Quote Share this post Link to post Share on other sites
Craig 0 #2 February 17, 2003 I havent read the thread in incidents yet but here is a graph to give a general idea of acceleration vs. time. Hunted through the logbook and JumpTrack and came up with the following dive. I do not keep really detailed descriptions of jumps anymore so some of this is just a guess as to the dive. This was listed as a head down dive...mind you I wouldn't really say I have any real head down skills at the moment and the dive was pretty much getting out, pointing the head to the Earth, get legs spread and arms out a little and trying to feel the relative wind equally on my front and back. From the looks of the graph I exited on my belly and made the transition at about 10.5 seconds in [128MPH] (change of red line about that time). Accelerated, [[email protected] sec.] did somthing after maxing out to slow a little (hang the arms or legs out a little more?) and peeled out slowly into a track onto the belly to slow before opening. You can take it for what it is worth and the numbers may be skewed around a little bit but it still gives a visual representation. Quote Share this post Link to post Share on other sites
Staso 0 #3 February 17, 2003 i calculated my weight during acceleration and deceleration parts of one of my speed dives once. i don't remember the exact numbers, but it was something like 80 lbs and 380 lbs respectively :) stan. -- it's not about defying gravity; it's how hard you can abuse it. speed skydiving it is ... Speed Skydiving Forum Quote Share this post Link to post Share on other sites
kallend 1,679 #4 February 17, 2003 Quotei calculated my weight during acceleration and deceleration parts of one of my speed dives once. i don't remember the exact numbers, but it was something like 80 lbs and 380 lbs respectively :) stan. I don't understand what you mean by this.... 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
SkydiveMonkey 0 #5 February 17, 2003 Your weight changes with accelaration - 1G = normal body weight, 2g = twice body weight etc etc...____________________ Say no to subliminal messages Quote Share this post Link to post Share on other sites
Staso 0 #6 February 17, 2003 QuoteI don't understand what you mean by this. when you accelerate towards the earthe your acceleration will be substracted from G and when you descelerate it will be added. so you will weight less when you accelerate and more when you slow down. stan. -- it's not about defying gravity; it's how hard you can abuse it. speed skydiving it is ... Speed Skydiving Forum Quote Share this post Link to post Share on other sites
Push 0 #7 February 17, 2003 I believe he means the drag force of the air on him, in pounds. Roughly equivalent to the normal force when standing on the ground. -- Toggle Whippin' Yahoo Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you. Quote Share this post Link to post Share on other sites
winsor 189 #8 February 17, 2003 QuoteQuoteI don't understand what you mean by this. when you accelerate towards the earthe your acceleration will be substracted from G and when you descelerate it will be added. so you will weight less when you accelerate and more when you slow down. stan. Okay, from an F=ma standpoint I think I know what you mean, but I'm not sure what is the point of the exercise. If you are referring to the acceleration due to drag you experience in different flight regimes, you could rephrase it in normalized terms. For instance, you could say that stable freefall is one G, that your drag dropped to say 1/2 G when transitioning to a standup (and you accelerated downward at 1/2 G), or that the net lift component your drag and flight went to 3.5 Gs in the flare (so you accelerated upward at 2.5 Gs). Again, I'm not sure what is the particular significance of any of this, but it is only useful if the data relate to some coherent basis. Blue skies, Winsor Quote Share this post Link to post Share on other sites
Staso 0 #9 February 17, 2003 QuoteQuoteQuoteI don't understand what you mean by this. when you accelerate towards the earthe your acceleration will be substracted from G and when you descelerate it will be added. so you will weight less when you accelerate and more when you slow down. stan. Okay, from an F=ma standpoint I think I know what you mean, but I'm not sure what is the point of the exercise. no exersise. we just express our thougths on different topics in skydiving forum. that's it. no very deep or hidden meanings :) stan, -- it's not about defying gravity; it's how hard you can abuse it. speed skydiving it is ... Speed Skydiving Forum Quote Share this post Link to post Share on other sites
Push 0 #10 February 17, 2003 Since he put a smiley at the end of his post, the exercise was probably meant as an interesting but fairly meaningless set of numbers. It's a simple calculation, so why not? EDITED TO ADD: What is your weight on the ground, stan? -- Toggle Whippin' Yahoo Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you. Quote Share this post Link to post Share on other sites
billvon 2,471 #11 February 17, 2003 >My question is, in this scenario, what would be your new terminal? >And how quickly would you accelerate to it? Well, you can come up with limits at least. Under no circumstances will you accelerate faster than 32 fps^2; that's 20mph per second. So if you go head-down for half a second after pulling you have increased your speed by less than 10mph (and likely less than 5mph, since you're not in a very 'good' head down.) Quote Share this post Link to post Share on other sites
Push 0 #12 February 17, 2003 So, to relate this back to the incident, it is unlikely that this problem has anything to do with the hard opening? In fact, it seems unlikely to contribute to hard openings. Of course, you have a high chance of entanglement, especially with a spring loaded pilot chute packed a little off center. -- Toggle Whippin' Yahoo Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you. Quote Share this post Link to post Share on other sites
billvon 2,471 #13 February 18, 2003 >it is unlikely that this problem has anything to do with the hard opening? I think it still might have something to do with it. In a car accident, for example, some things are caused by sheer deceleration (like aortic arch damage) but some things are caused by rotations, or parts of you decelerating at different rates than other parts (like whiplash.) If she went head-down at pull time, her rig is going to rotate her 180 degrees very rapidly, and that by itself could cause injury - her head isn't going to want to rotate as fast as her body. Some old-time skydivers do the opposite to reduce opening shock; they pull and then sit up. That way their bodies are rotated less by the force of the opening canopy, and they are less likely to get 'rotational' injuries (like the classic sore neck.) Quote Share this post Link to post Share on other sites
skr 1 #14 February 18, 2003 >Some old-time skydivers do the opposite to reduce >opening shock; they pull and then sit up. That way >their bodies are rotated less by the force of the opening >canopy, and they are less likely to get 'rotational' injuries >(like the classic sore neck.) :-) You're way too logical. I always understood that form of sitting up as a way to eliminate pilot chute hesitations. I would, in one motion, come out of my track, put left hand high, right hand to ripcord, pull knees in and drop them forwards, twist into the wind so I was sort of side sliding to the right, pull, watch pilot chute go up over my left shoulder, watch the sleeve go, twist back square into the wind while the lines unstowed, put both hands high because that helped me hold my neck straight in case of a hard opening, look at the ground while the canopy inflated to see whether I needed to start thinking about my reserve. I made about 2,500 jumps that way before switching to a hand deploy. I think most people from those days were doing something similar. Skr Quote Share this post Link to post Share on other sites
