FrogNog

I've seen theoretical numbers based on mechanical advantage of various 3-ring systems and suspended loads x G forces. There were footnotes about cleaning cutaway cables and flexing the 3-rings

First, as many people will comment, you did good. Kept your head, made some smart decisions, didn't get injured, and _still_ managed to learn from it. :) Second, front riser theory has multiple facets, and they might not have helped you get to the ground with more distance ahead of you before the trees. I won't try and expound on double front riser details like some sort of expert, but I'd say "try it in your regular field a few times in different amounts of wind first" to see what it's like. Third, deep brakes still might have helped, but I think trying anything out for the first time while trying to land off is not the best plan. If you use deep enough brakes, you should be able to get a steeper glide. I would be concerned about the altitude needed to dive and return to full flight (I have had two close calls on this before) and the stall point. Another good thing to play around with up high - how far can you brake the canopy without it collapsing? You mentioned a concern about turbulence in the landing area. Someone in the know should comment on whether a fully braked canopy or a front-risered (and therefore highly pressurized, I would assume) canopy would be more stable in the face of turbulence. -=-=-=-=- Pull.

I find every intentional unstable exit is a blast. They prevent me from worrying about anything, like whether I'll fall off the rail or screw up the count or turn the wrong way while we all have grips... -=-=-=-=- Pull.

Hey, we saved about 50 million dollars on that one. I guess it's sort of like that saying: "If you loan an aquaintance $20 and you never see him again, it was probably worth it." (Only, obviously replace "loan $20" with "offer $xx million contract" and "you never see him again" with "he goes to Texas for $yy million more".) -=-=-=-=- Pull.

Want me to look him up in the phone book and walk on over and ask him? I am continually amazed at what happens in Bothell. Such a little armpit of two counties that neither wants it, and people come here to invent laser retinal-paint displays, work on cancer cures, and study beerology. -=-=-=-=- Pull.

129 square feet planform or projected? -=-=-=-=- Pull.

I think he meant "compressible hard housings". -=-=-=-=- Pull.

Is the cable length shorter on the left side, or is the cable length past the end of the cutaway housing's amp connector shorter on the left side? I imagine the lengths in that doc have something to do with the left cutaway cable being so much longer because it snakes behind the neck, down the left web, and makes a u-turn. This could make the amount of cutaway cable sticking out the amp end of each housing a misleading indicator of which will pull first. The very long, left cutaway cable with two u-turns could have some slack in it that the right, short, direct cutaway cable does not. This could explain why they want the amount of cutaway cable sticking out the end of non-compressible cutaway housings to be equal when we all think we want the RSL-side (left side in their doc) to release second. Compressible cutaway cable housings may exacerbate the slack difference and explain the second drawing, where the left (RSL-side) cable sticks out the housing not even as far. First, I would trust the manufaturer, and call them if I was having any trouble doing that. Second, I would test it on the ground. A diagram on paper may not reveal the nuances that being there in person would. -=-=-=-=- Pull.

Sure, just carefully unpack the canopy. You can basically reverse the packing method without disturbing things, and see where all the lines are hanging out. Or, did you mean a way to check that the lines haven't moved while still moving forward in getting it in the bag and in the container? I know how to do that too, but it's less precise and requires an airplane. I treat packing like cooking: I follow the rules and if I have an accident that makes me think something may no longer be cool (like the cocoon splits in two across my arm while I'm trying to lay it down), I back up as far as necessary and redo it just to be sure*. (The analog in cooking would be if I touched something that had touched raw meat - I would wash my hands again before returning to the current task.) * Unless I'm trying to make the next load. Then I say "it'll probably be fine" and I forget all about it. -=-=-=-=- Pull.

On pulling the slider down, my (74-jump to date) advice would be to try it before you decide you really want it as a feature. I have tried it on 4 canopies and found that on three of them, I was less comfortable once I pulled the collapsed slider down past the toggles, for reasons like visibility, toggle passing risk, and toggle, riser handle, and wrist-mount altimeter visibility. With the chest strap, some people take it all the way off (on the theory, so far fairly well supported, that once under canopy falling out is highly unlikely) and some people just loosen it (I have done this on some rigs, for comfort.) I think the best way to figure out if you really want to do something is to try it. (Don't die, though. ) -=-=-=-=- Pull.

I think more accurately it was "a probably contributing factor in a death...". (Sure, poe-tay-toe, puh-tah-toe.)

You could just pay for the other person's slot and ride the 182 alone. My DZ's 182 is a climbing rocket when it's just me and the pilot. (I wanted to jump BAD and nobody else would go. Some more $ and problem solved.) -=-=-=-=- Pull.

I totally agree that during the hybrid, the force on the chest strap will be low. (It will not be zero, because although the two jumpers will be in velocity stasis once at terminal, their "free" terminal velocities will be unequal, and the difference will be made up as the hanger "pulling" on the wearer.) My concern was really during an unexpected reserve deployment, because I consider that to be the worst-case acceleration one could expect: a canopy that is supposed to open relatively quickly, and a deployment at the highest airspeed expected during the dive. During a brisk opening, it is further true that the duration of the acceleration will be brief (as the pair slow down or, more likely, all or the vast majority of the hanger detaches from the chest strap), and that may allow the hardware to yield without completely failing, or the tension rating of the strap (and stitching) to be exceeded without completely separating. So chances are good that this practice does not comprise a significant increase in risk over the other things we do in skydiving. But without empirical or circumspect theoretical evidence, we are being harness test pilots by doing this. -=-=-=-=- Pull.

Love those colors. Looks like a total "Girly Drink" version. P.S. the color of my suit and canopy in this picture is a matter of "used / borrowed gear", not really color preference. -=-=-=-=- Pull.

I expect to continue wearing gloves in the summer most of the time because of a third reason: 3) Gloves increase strength and durability of the hand in most inclement conditions. I'm thinking if I smack my hand into or scrape it on something, I'd like a glove to be my first line of defense. I've heard weird stuff happens during exit and sometimes in freefall (I assume FF). Also if I ever have to reach, grab, and pull on something with all my strength, fingers coated with performance gloves should be an asset. -=-=-=-=- Pull.

I also use thin scuba diving gloves (that I bought in a bicycle shop - go figure). I haven't tried them with a polypro liner, but without a liner they are COLD AS HELL (the outter circles, obviously) when it's colder than about -10 *C out. I just tell myself "If my hands hurt horribly, I probably don't have frostbite." The great thing is the palms are made from synthetic chamois, so the gloves are all over water-friendly (NOT waterproof) and I can feel handles great at all times. -=-=-=-=- Pull.

I think something might be wrong in your calculations... according to your table, we might guess that a 1 degree angle would have a force multiplier of around 25... this implies that if you take a piece of chest strap webbing and keep the ends perfectly level and horizontal, it would take less than 20 lbs to break it. I can't believe that... would u mind posting your formula for the force multiplier? I can't figure out what you did from your writing (of course, its probably me... it is 1 AM here) and of course, you have to remember that during a hybrid, the hanger will NOT be putting a force of 1 G on the strap... since the jumpers are both already at 1 G, the "relative G-force" would be 0. and remember, the hanger will only fall faster than the belly flier for maybe a half a second, until the pull on the chest strap brings the belly flier to the new hybrid speed. we'd have to calculate the acceleration the belly flier experencies from the hanger... I would just guess its less than .5 Gs. It does appear you are under the influence of late night. The formula for the multiplier is 1 / ( cosine of angle of applied force). This comes from drawing triangles and figuring out the answer to this question: what force resists the pull on the chest strap? When the hanger pulls down on a chest strap, even standing on the ground, something has to pull up on the chest strap equally to keep the chest strap from accelerating. And we can all agree that at some point, the chest strap is not accelerating - for example, standing on the ground and not moving, if you pull on someone's chest strap and hold onto it, you are exerting force, the chest strap has mass, but it's holding still. So there must be another force acting on the chest strap, counteracting the hanger pulling. And there is, and it's obvious to us all: it's the ends of the chest strap affixed to the MLW. The MLW effectively "pulls" on the ends of the chest strap, and this counteracts the downward pull of the chest strap. (For now we will ignore the force on the MLW, which is connected to the jumper, which is either standing on the ground or falling through the air.) This is where a significant sub-question arises: how can the MLW, which is at the ends of the chest strap, counteract the downward pull of the hanger? This should be confusing because the MLW can only pull directly on the ends of the chest strap, i.e. exert force in a direction parallel to the chest strap, while the hanger pulls down, which is perpendicular to that. And the initial answer is the MLW cannot directly counteract the pull of the hanger, because the MLW can only exert force perpendicular to the hanger force. The secondary answer is that because the MLW cannot directly counteract the pull of the hanger, there is a net downward force on the MLW and it accelerates, which over time means it has velocity, which over time means it changes position. This will happen until equilibrium is restored. But to simplify all this, we can simply say "the chest strap moves downward in the middle where the hanger is holding on." And this matches up with video, so the freefliers may still believe me. Once the chest strap is no longer horizontal, the direction the MLW can exert force along the chest strap - parallel to it - is no longer perpendicular to the force applied by the hanger. This is the chest strap angle I'm talking about. When the chest strap is at an angle, a fraction of the force the MLW applies to the ends of the chest strap can be thought of in the horizontal direction, and another fraction in the vertical direction. But the MLW really exerts its force parallel to the MLW. This is where sinusoidal functions come in: the hypotenuse is the MLW force, and sine and cosine are the vertical and horizontal force components. (I see now looking back at my math that I was using the cosine of 90-degree complement of the chest strap angle. Well, the cosine of a 90-degree complement is the same as the sine, so that was an unnecessary complication.) Anyway, the "force multiplier" comes from the force component issue: if there is a 5 pound downward force on the chest strap, in order to put the chest strap in equilibrium, a 5 pound upward force must be exerted on the chest strap. But only the vertical force component of the MLW's force on the strap ends counts. The vertical force component is sine of the chest strap angle, and we want that to be 5 pounds. The relation of the vertical force component to the overall force exerted by the MLW on the chest strap (which we will call chest strap tension) if the same ratio as sine of the angle. We want to solve for the hypotenuse, given the opposite, so: sine (angle) = opposite / adjacent = 5 / x if sine (angle) = y [a decimal], then we have: y = 5 / x or y / 1 = 5 / x and by cross-multiplying,: 5 = yx. then dividing both sides by y: 5/y = x or 5 * ( 1 / y ) = x Since x is the tension on the strap, and 5 is the force of the hanger (which could just as well have been z), this gives my formula for the "force multiplier" between the hanger pull and the strap tension being the inverse of the sine of the angle the chest strap makes with its MLW-MLW connection axis. For very small angles, i.e. very horizontal chest straps, the MLW would have to exert huge tension on the strap to counteract small hanger pulls. This means if the ends of the chest strap were held so they could not move closer, e.g. the chest strap were attached to a couple of steel beams cemented into the ground, the MLW (or in this case the steel beams) would exert so much force on the strap trying to counteract a small hanger force that the strap hardware would fail. Now, this is clearly not like real life. When someone pulls on a chest strap, the ends are at first relatively free to move toward each other (squishing our armpit flab) as the middle of the chest strap is pulled down. As this happens the angle increases and the MLW does not have to pull as hard to counteract the hanger. This continues until the MLW exerts enough force on the chest strap to hold the hanger. How much force the MLW needs to exert depends on the weight of the hanger and the angle the chest strap forms, and this has to do with how far apart the MLW connection points are, how long the chest strap is compared to that distance, and how flabby the wearer's pectoral area is. The classical experiment is to get a piece of string a couple feet long, hang a weight from its middle, and hold the ends of the string in your hands, then move the hands slowly apart to try to make the string horizontal. The weight does not change the force it exerts, but holding the weight up as the string gets more horizontal requires more and more pull on the string. I guess my advice from this would be: 1. get the strongest chest strap, hardware, and stitching you can. 2. leave your chest strap as loose as safety otherwise permits, so it can form the greatest angle from the MLW-MLW axis. 3. have flabby pects. (This and #2 work together, so you can substitute a bit here or there.) And finally, a 1 degree angle would have a force multiplier of 57.29. Perhaps I should construct a stiff steel frame to which I can attach a chest strap and show its hardware being broken by a 50 pound pull. Of course, it would be a real trick to keep the strap horizontal as the nylon stretched under load and the hardware stretched as it deformed. -=-=-=-=- Pull.

The angles of those chest straps is definitely close to the "safe" end of the angle range. That is good. -=-=-=-=- Pull.

QuoteEugene, I love ya man. Your dedication to science is really admirable. I constantly amazes me that you are more fascinated by skydiving physics than anyone I know of. Keep it up dude. Also you are welcome to hang from my type 17 chest strap whenever you have the skill, it's not that hard but it requires good sit/stand control. Even if I throw and have a slammer while you're hanging on your fingers will tear off before the strap or hardware fails. Assuming it's in good shape which it is. Quote When I get decent at sitting, I may take you up on that offer. See, as long as we're not close friends, I don't too much mind hanging onto your chest strap. Just y'all leave my chest strap alone! I totally admit the theory I'm working with isn't accurate and isn't the whole story and therefore probably nothing will snap. But if the theory is even partially correct (which theories tend to be - partially correct I mean), then it adjusts the numbers people were talking about before: "Nobody can hold on with the 500 pounds of force required to exceed the hardware." And, if I were hanging on and someone threw and slammed, I damn well hope I would fall off! -=-=-=-=- Pull.

Pretty much what I would say. -=-=-=-=- Pull.

On takeoff and initial climb I try and not worry about what could happen. If the plane crashes, tough. I'll let the pilot fly it as far as he/she can and hope I live, I guess. This is a good time to breathe, look at the pretty stuff out the window, and pray to the Deity/ies of your choice. (For the record, I am a noninvasive monotheist.) -=-=-=-=- Pull.

That is SO wrong, but it's funny as hell, too. Yeah, my voice did that before puberty when I got pissed, too. Hmm, and later in life I had friends with paintball guns, too. Reminds me of the time my friend told me to come over one night. I ride up on my Ninja and long story short, he hoses me down with his new semi-auto. Good thing he started before I turned to park. -=-=-=-=- Pull.

Hey, why only the girls get to answer this? (Personally, I am not a fan of other peoples' poles, and I singularly prefer my pole-fans to be female. But I still believe in equal rights to posts.) -=-=-=-=- Pull.

I think you're right. unless someone has a good enough grip that they could do a pullup with a couple 150 lb people holding onto them (500 lbs total), then i think the hangers grip would break before the strap. Trigonometry says a person need not put a 500 pound load on a strap to exert a 500 pound tension. Load to tension is only 1:1 when they are pulling on the strap in-line, i.e. hanging onto one end of it. I believe the tension is equal to the inverse cosine of the angle at which the force is applied to the strap, multiplied by the force. As the strap approaches horizontal (i.e. it is flat across the wearer's theoretical square chest), the angle of the force to the strap approaches 90 degrees, and cosine approaches zero, and the force multiplier approaches infinity. This is what I think is bad. As the strap approaches vertical (i.e. it stretches away from the wearer's chest and down toward the hanger), the angle of force to the strap approaches 0 degrees, and cosine approaches 1, and the force multiplier approaches 1. In between, if the chest strap hangs down 30 degrees away from its anchor points, the force multiplier is 2. Now someone need only weigh 250 pounds and undergo a single gravity of acceleration - the equivalent of merely hanging by his hand or hands - to exert 500 pounds of force. On the side of reducing the likelihood of failure, I find: * most jumpers will weigh less than 250 out the door, but maybe not a whole lot. * the hardware is rated to 500 lbs and will probably have a safety factor before it truly breaks, but maybe not a whole lot. * the angle of the chest strap _will probably_ increase as a load is applied to it. This will reduce the force multiplier. Unfortunately, I don't know how much the chest strap angle will increase. It depends on stretchiness of the strap, harness geometry, and the deformation of the body of the wearer underneath the harness. On the side of increasing the likelihood of failure, I find: * many jumpers can hang their out-the-door weight from one hand (i.e. remain hanging while under one G of acceleration). Some of them may be able to do it under a little more. * the chest strap angle may be less than 30 degrees from horizontal. It doesn't seem likely, but I don't have any proof either way on chest strap angles with hangers. And as Cosine heads from .5 to 0 as the angle (in this case the angle of applied force, the complement to the chest strap angle) goes from 60 degrees to 90, the force multiplier exhibits hyperbolic behavior. That is, the force multiplier goes up increasingly quickly as it trends toward infinity. For various chest strap angles moving toward horizontal in 5 degree increments, the force multipliers are: 30 degrees: 2.00x 25 degrees: 2.36x 20 degrees: 2.92x 15 degrees: 3.86x 10 degrees: 5.75x 5 degrees: 11.47x So a 50 pound pull on a chest strap 5 degrees from horizontal would cause 573 pounds of tension if the strap couldn't stretch or the endpoints couldn't move inward. Realistically, it may well be safe to hang from chest straps. This math has not been adjusted to apply to the bendy nylon webbing, and there are safety factors, and etc.. But I don't like what the theory says here. -=-=-=-=- Pull.

They can figure it out pretty quick regardless. Option 1: "Hmm, that canopy isn't moving very fast relative to me." Option 2: "Hmm, that canopy appears to be moving 40 mph across the ground." Option 2b: "Hey, why is his pilot chute sticking straight out in front of his leading edge?" -=-=-=-=- Pull.