pchapman

I can understand, Captain Stan, if you don't like the terminology "bad luck". But whether you call it bad luck, luck, statistics, act of the gods, fate, a malfunction not otherwise attributable to other categories, or whatever, malfunctions can happen that you can't pin on something the jumper or packer did. (What about off heading openings? For skydivers or B A S E jumpers? Body position is often a factor, sure, but can you find a reason 100% of the time, that one could have done anything about before the jump?) I also understand that you don't want "bad luck" overemphasized, as you stated, so that people don't stop looking for reasons and just shrug their shoulders and say "bad luck". But I figure some of us think you have gone too far the other way, seemingly irrationally denying that there are things that no person can control about canopy deployment. And if you try to pin everything on "human factors", that doesn't help as it doesn't discriminate among different causes -- one doesn't say everything is human factors just because it is humans who design, build, pack, and jump parachutes.

There were clubs in the 1930's too. Little seems to be widely known about them as history got interrupted by the war. As with many "inventions", there are going to be different versions of the "first", depending on how things are defined. A DZ can range from large businesses with multiple turbines, down to clubs owning or renting a single piston Cessna. I can give an example of even humbler origins which happens to be from Canada. It certainly qualifies as a DZ, having some equipment, a fixed base of operations, and catering both to new and experienced jumpers. There must surely have been other examples like it in Canada and the US too. In Canada our official CSPA history always mentions the St. Catharines Parachute Club having been formed in 1948, but no clubs are mentioned before that, only feats by individuals. I knew someone, Cam Warne, who started jumping in Canada in 1938, in a group who called themselves the Canadian Parachute Club, in the Downsview part of Toronto. (Post-war, the St. Catharines club got the publicity because it lasted so long, but there were others too -- Cam was in the Oshawa club east of Toronto for a few years starting in '46.) In 1938 an instructor, George Bennett, was travelling around the country giving parachute courses, I believe with some sponsorship by Irving and the government assisted flying clubs program. (Both the flying and parachute rigging was being encouraged to build up a base of experience in case war came.) After George trained a group of 34 first jump students, some of them plus one other experienced jumper formed the club. They rented an airplane and pilot from a local flying club, such as a 2 seat open cockpit Gypsy Moth biplane. Your very first jump would be a freefall from 2000-2500', with no instructor on the plane. Put your hand on the ripcord, jump, count to 3, and pull! The club owned just one set of gear. It consisted of a standard pilot's emergency seat pack rig, an Irvin with a 24' unsteerable round silk canopy, modified to attach a lap container with another 24' round. When a crowd gathered to watch the jumping, the jumpers would pass the hat to defray expenses. Cam completed the ground school (about 2 nights a week for 4 weeks, focusing on parachute packing), did his first jump, then received his parachutist certificate stating he was qualified to pack, service, and jump all Irving parachutes. After 5 more jumps he could receive his instructor rating. As some have said, it really was creating a sport out of an emergency procedure. Not much of a DZ by modern standards but it was a DZ.

So I posed the issue whether there would still be errors if one calculated the horizontal and vertical speeds independently, as long as one took into account the body angle. So there's already some "coupling" (as one poster termed it) because one has to do the horizontal calculations as well as the vertical ones, to figure out the body angle to plug into the vertical drag calculations. But for a given time slice being calculated (once one knows a given body angle), the vertical speed can still be calculated alone, without knowing the horizontal speed. On further reflection I'm thinking that it is theoretically quite incorrect to calculate the vertical speed independently, due to the non linear relationship of drag and speed. So there is more "coupling" involved than I thought about last night. This may or may not make a difference in real life big enough to care about -- one would have to run a simulation to see what the results really are. For the typical freefall tables, with typical aircraft speeds, it probably doesn't make enough of a difference for us to care whether one jumped out of a King Air or a C-182. But when trying to calculate the exact number of seconds to terminal velocity, errors would be introduced. (Of course one only approaches terminal velocity asymptotically, but one can come up with some way to determine what is close enough for our purposes.) Here's the reason as I see it: The calculation of acceleration from the forces on the jumper can accurately be calculated separately vertically and horizontally. Acceleration is force over mass, so acceleration scales linearly with the force. Therefore one can resolve the forces into 2 axes, do the calculations, and have correct results. But this sort of thing isn't true when it comes to calculating the forces in the first place, that result from drag on the jumper. Drag forces vary quite closely with the velocity squared. That non linear term in the standard aeronautical drag equation makes it impossible to treat vertical acceleration separately. Here's a simple look at numbers to make the point: Say a jumper is on the hill, at 100 mph speed along his flight path, at an angle where he's moving forward 2 units for every 1 unit down. That works out to a 26.56 degree descent angle. The horizontal speed component becomes about 89.4 mph, and the vertical about 44.7. Their contribution to the drag equation is based on those speeds squared, or 2000 vertical, 8000 horizontal. Compare that to calculating things in a proper 2-dimensional manner. The actual speed on an angle is 100 mph, so the contribution to the drag equation is 10,000. When that is resolved into horizontal and vertical components, (where again one gets a vertical component 44.7% of the full value, and a horizontal one of 89. 4%), one has 4,470 vertical, and 8,940 horizontal. Big difference. The number in the drag equation is correctly 4,470 when resolving component of the drag in the vertical direction. But when we tried to treat horizontal and vertical separate, we only had 2,000. That's incorrect by over a factor of two in this particular example! Therefore how fast a jumper accelerates downwards (with air to cause drag!) will depend on their forward speed. Not because the jumper might be tracking on the hill or some such thing, but because drag varies with the square of the velocity. A jumper falling from a 727 will lose altitude slower than one falling from a balloon. You could even have the situation where a jumper at a very high speed at a small descending angle may be slowing down vertically for a while - instead of accelerating faster towards the ground. Their vertical speed is nowhere near terminal, but with their very high air speed they are being slowed rapidly by high drag at high speed (hitting a wall of air). So one cannot ignore the jumper's forward speed. Horizontal and forward speed are coupled. Still, that doesn't answer the original time to tandem terminal question.

If one tried to calculate horizontal and vertical drag and acceleration independently, one would have to take body angle relative to the wind into account! For a belly to earth jump from a balloon, one will be using the full belly to the wind area for the jumper to calculate the drag. But if someone is jumping from a moving plane, and is for a moment at a 45 degree angle on the hill, one isn't going to be able to use the full belly to the wind area to calculate drag. One could try using a 45 degree angle to calculate the projected area. The best thing to do would seem to be to do a full 2-D trajectory calculation, instead of trying to calculate the horizontal and vertical separately. But would there be errors if the horizontal and vertical accelerations were calculated independently, if one already takes into account the changing body angle during the transition off the hill? To do that "taking into account" one would have to calculate the area projected by the jumper in the horizontal and the vertical direction. And one would have to run both a horizontal and vertical calculation at the same time, as the area to be used at one microsecond of the calculation will depend on the trajectory (and thus body angle) both horizontally and vertically in the previous microsecond. That's 'coupling' of a sort. But is that body angle issue the only 'coupling' there is, or is there still some other interaction that would cause errors? I'm not seeing any clear reason for there to be any additional error. That's the part I'm not sure about thinking about this late at night. If there's no other error source, treating the axes independently works out accurately (as long as body angle is taken into account). It can be asked whether a source of error would be that the drag coefficient may change somewhat depending on body angle to the wind. (Drag is a function of the area times the drag coefficient.) But the person is essentially belly to the wind all the time, so there wouldn't be any drag coefficient change. One would be using different areas for horizontal and vertical calculations, but keep the same coefficient. (When the jumper is on a 45 degree trajectory, they aren't really at a 45 degree angle to the wind when calculating the vertical acceleration, even if one is using a projected vertical area of sin(45) = 70.7% of the full belly to earth area.)

This year and last I've been running a canopy flight skills seminar at a local DZ or two in Ontario. The target audience seems to be from 'A' license on up to 500 jumps or so. The idea is to provide an alternative somewhere in between the well known professional courses, and nothing at all. The professional courses can have high minimum number of participants and be quite costly. I get the impression there's a lack of courses "in between". I only do classroom work, not jumping, to keep time and cost down. People are welcome to bring in their own landing videos, but that doesn't often happen. So I use some pics and videos from off the web and shot around the DZ in general, for use in critiquing landings. As background reading material I put together a bunch of 30+ written documents for anyone at the DZs to read over at: Education for Canopy Flight Skills The docs all in one big zip file, but there's also a separate summary document that gives a brief overview of all the other documents -- you might find that useful to get ideas. Most docs are collected from all over the web, plus a couple things I wrote. I annotated a few of the documents to note some information that is getting older or which is more disputed. (Even for educational things there is the issue of the author's rights -- at least I encourage people to go back to the original web sites if people like what they read and want to learn more. That's also why there's one big inconvenient zip file, rather than replicating others' web pages. There's everything in there from the classic Brian G. wing loading chart to the BPA canopy flight documents to the USPA SIM -- hence the bulky file size.) The idea was to collect a lot of the good stuff out there in one place, rather than just telling jumpers that "it's all out there on the web".

I agree that the vertical acceleration is not entirely independent of what is going on horizontally. Acceleration downward is the same in terms of what gravity is trying to do, but different in the end due to drag. The drag (and its horizontal and vertical components) will depend on the body angle and the direction of the relative wind at any given moment. Properly, one has to calculate everything in two dimensional space as the jumper transitions through "the hill". It's not quite the same as assuming the jumper is belly to earth and falling straight down. But at a first approximation the vertical-only method is probably OK. How much of a difference there is, that's an open question.

Hey, that would completely change dropzone.com! I don't disagree with the points in your post. Sometimes though, one doesn't have the time to coddle every person and gradually try to alter their perceptions through a course of well thought out instructional and motivational practices and content. Much quicker just to slam people. A warning about dangers can still be a starting point, although adding some positive aspect may help a lot (e.g., adding reasons for the danger, or how to learn to avoid the danger). Even depersonalizing the warning can help reduce the defensive attitude that is likely to occur -- "you could kill yourself" rather than "you'll kill yourself".

http://en.wikipedia.org/wiki/Coffman_starter

Actually the CSPA got more liberal in recent years: At some point they changed the requirement to only a B certificate, which needs only 50 jumps. But that's only a minimum -- they say the jumper should be competent in the freefall discipline they are practicing, and should seek advice from competent videographers. An audible altimeter must be used and an AAD "should" be used (which is not mandatory). While I'm personally all in favour of avoiding hard rules like 200 jumps, I wouldn't mind it if they suggested 200 were still advisable in typical cases.

Some days it is like April 1st here all year long. Let's see that profile filled out too. To be sarcastic but truthful, everyone knows you can get gear cheaper if it is used gear. For example, it took me only $200 to put together a rig last year with a Paracommander and a belly mounted round reserve. (But a little rigging knowledge was needed too.) However serious the original post, the point about prices is interesting. Prices listed for the BaserR are: $1100 rig w. normal accessories $425 belly container ~$1400 new BaseX main (price varies by size) $1190 new Strong 26' LoPo That adds up to $4115, with the whole rig and harness $1525 of it. The rig is cheaper than a regular rig, although one gets into the question of what to what degree discounts off list price exist for other rigs. The main is comparable in price to other F-111 canopies out there (eg, from Flight Concepts), although a lot cheaper than most zero p designs. Jeez, what's happened to the price of round reserves? It's getting right up there. A PD square reserve is only $1280 list. Compare that to ParaGear in 1993/4 where a Strong Lopo was $695 and typical PD reserves $912, a whole 30% premium for a square. To defend F-111 style canopies, F-111 won't pound you in especially if it is new and generously sized. Also, a decently designed BASE canopy tends to flare very nicely in my limited experience. Anyway, I won't get into the various reasons why the BaseR system isn't all that handy for day to day skydiving, even if it keeps you alive.

Great. Doubled the area. If the drag coefficient doesn't change, instead of 120 mph, he'll hit at 1/(2^.5) times the speed, or 85 mph. If the inflated suit provides a sort of cylinder around the jumper, doubled the area means twice the width. Say a person is 45 cm wide. Twice the area gives a cylinder of 45 cm radius. Lets say that's how much cushion space is available infront of the jumper, and that the suit keeps the jumper somehow stable, belly to earth. (There would be less inflated space to the sides of the jumper otherwise the drag area would be more). Ok, so he's hitting at 85 mph with a crush distance of 45 cm. Unless I mucked up the calculations, that gives something like 155 g deceleration at a very minimum if it crushes in an ideal manner. Splat. I think we need someone like Franz Reichelt to test the idea. (The guy who jumped his big overcoat from the Eiffel tower to his death.) I have neglected the buoyancy of the helium that'll only be about a cubic metre, displacing about 3 pounds of air at the maximum. The inventor should have been able to run the same high school physics calculations to see the issues. Perhaps he could further develop his idea into a larger air inflated structure, that uses the surrounding air to inflate it rather than a helium bottle... and call it a parachute.

I don't know the big picture here, but it sounds like the guy did get somewhat screwed over by PdF. So we tell him he was an idiot for letting it get so far. But whether or not he's a bit of a jerk about it, I can understand he'd like to fight back at PdF. Plenty of big companies have had unhappy customers set up web sites about the companies' problems -- including web sites with names similar to the companies themselves. PdF doesn't have to publicly apologize, but it sounds like they screwed up pretty big for a lot of people, so it wouldn't be out of place to apologize. As for the gear dealer, well sure it reflects on her, if she's a dealer for a company that sucks. I don't know the details, but she probably didn't contribute to the problem and is just stuck in the middle. I can see that other dealers might distrust the guy a bit, but I'd cut him some slack. It's sort of like nobody wanting to hire a whistleblower -- who probably isn't actually out to screw over every company he works for. It's funny to tell someone that they should have listened to what others whisptered about PdF's order fulfillment, and so they were stupid to order from PdF. But then when things go wrong people want to muzzle him and cover up the issues. So I'll roll my eyes at some of his posts, and wish he'd not crosspost, but I am kind of enjoying it to let him rant and see what he does to lower the reputation of a big, unresponsive company.

OK, I'll accept reporting bias as the reason one always hears of people spinning on their backs. Like I had said, I'd like to see better evidence whether or not people actually end up on their backs at a rate that's more than random.

Other way around.

Hmm, nice idea. Mass distribution that accounts for the behaviour at all airspeeds rather than just aerodynamics which matter more at higher airspeed. But I'm not convinced; I see a problem with that analysis. (I wish I had more empirical evidence as to what happens out there in both lower and higher speed spirals.) So you have a jumper in effect spun around at the end of a rope. The canopy lines are not vertical, but somewhat on an angle, maybe even nearly horizontal. Let's say the situation is as you suggested: There's a 'couple' (in engineering terms), with the mass of the jumper centered behind/above the line formed by the attachment point and spun-up parachute lines. Why is that difference not eliminated by a change in the pitch of the jumper? The center of gravity (C of G) can line up with the line of support from the risers by the jumper swinging butt forward. There's no need for a 180 degree rotation to eliminate that difference. I think we're both agreeing that the C of G should line up with the direction the lines are pulling -- otherwise they would change angle, as they are flexible lines and not a solid beam. The lines end up at whatever angle all the forces on the canopy and jumper pull them to. The angle of the lines depends on the centrifugal apparent force (inwards towards the parachute), gravity (downwards), and some drag on the jumper. If the C of G has to line up with the parachute lines, then with twisted lines that offer almost no resistance to twisting, it comes back to aerodynamic drag to determine which way the jumper faces. See my sketches, which may help anyone trying to understand our words dealing with angles and directions: Sketch # 1. The idealistic case where a jumper hangs straight below the riser attachment. 2. It is suggested that the center of gravity really tends to be towards the back. (But then the jumper should just swing butt forward so the C of G lines up with the attachment point.) 3. Representing the jumper by just a block with an aft C of G 4. Now showing the jumper in a spiral. 5. And the same, using a block instead of the jumper, showing how the center of gravity is postulated to end up above the line of support (or centre of pressure in your choice of words) 6. My suggestion that the jumper would just swing forward rather than roll 180.

Collapse from braking too much or collapse due to turbulence? Both are valid issues but causes tend to differ. Edit: Also search for "dust devil" on skydivingmovies.com.

I believe the toggles should move up to a point where the canopy would normally be completely unstalled, flying slow, but not wobbling around on the edge of the stall. That'll allow the canopy to fly again with as little forward surge as possible. That surge can both be dangerous at low altitudes and, if not perfectly straight, have the canopy dive off to one side with lines that are unloading and result in the jumper falling into line twists. It has also been argued that the brake position could be as high as the brakes set position -- you'd have to look at that ahead of time and see at what hand position the brake eyes are at the guide rings. The manufacturer has already determined that the canopy opens well at that brake position -- although some amount of forward surge may be accepted. Also, that brake setting is appropriate for a more orderly, slider up deployment, so it isn't tailored to stall recovery. I'm not sure exactly where those two brake points might be best, but I'd put emphasis on the slightly-above-the-stall-point answer. That also tends to match what is done in the paragliding world with very surge prone canopies. In any case keeping ones hands right next to one's body and keeping the arm muscles tight will be useful to avoid having the toggles yanked up on one or both sides by the sometimes sharp and unsteady forces during the stall or recovery.

Yeah just a friction lock. I haven't thought about it in detail. One would have to get the geometry right. But fundamentally I don't think the friction concept is really any different than for a chest strap adapter or especially a Parachutes de France style leg strap adapter.

Here's a pic from an MT-1 military rig I saw. I don't know these things well, but I figure the routing of the webbing through the grommets is the 'standard' way it was done. The trim tabs I have on a canopy are sheathed in cordura so you don't see the inner workings.

Doing a jump run angled across the wind line doesn't give any more space in terms of dropping area where jumpers can get back to the DZ. The shape of the area from which jumpers can get back to the DZ tends to be an elongated oval, with the axis along the wind line. Any drop points off that axis will result in a shorter usable jump run in terms of distance. One would have to curve the jump run to use more of that usable area. The messy details if I have to try to prove my assertion: This is actually handy for clarifying one's thinking about the area from which a jumper can get back to the landing area. Some skydiving instruction mentions the 'wind cone' but isn't really clear on the shapes involved, what exactly the usable area is in which the jumper can deploy and make it back. Technically the "shorter available jump run off axis" is because the local curvature of the circular arcs that make up the ends of the oval area are necessarily less than the curvature achieved by drawing an arc from the center of the elongated oval area. Why is the shape a sort of oval? Let's first look at the simple case where any given parachute has one forward speed and one descent rate. Then a parachute can get back to the DZ from a circular area. I'll call this the usable area. (Freefall drift can be considered separately, doesn't invalidate the concept, and need not be dealt with here.) If there is no wind, the circular area is centered on the DZ. The point at the center of the circle is the only drop point for an unmodified round canopy that has no forward speed at all. (Fig 1a). For example, if a canopy flies 30 mph horizontally, is open at 2000', and has a 1000 fpm descent rate, the canopy will have 2 minutes in which to fly, and can travel 1 mile. (60 mph = a mile a minute). These numbers are picked to make the math easy to comprehend. The same circle will also apply to a canopy that has half the speed but half the descent rate, so that the doubled time in the air makes up for the halved speed. If the canopy has half the speed, the radius of the circle is halved. So that's all simple enough. Fig 1b: When wind is added, the circle shifts upwind by the amount the canopy would drift in the time available until landing. Say the wind is 30 mph. (We're only looking at constant wind here.) Then the 30 mph canopy can be dropped over the DZ and hold into wind all the way down, or be dropped 2 mi upwind and run with the wind all the way. It can also drop 1 mi off to the sides, but has to be exactly 1 mile upwind if it is to make it back. If crabs and drifts confuse the issue, think if it this way: The 30 mph canopy has 2 minutes to landing. Where ever it drops, it has to fly to the guy who was dropped with the round canopy in the ideal spot, and reach him by the time he touches down. The guy with the 15 mph canopy has the same ideal drop point, but has a circle of half the diameter in which he can drop and still make it back to the DZ. Fig 1c: Now let's be more realistic about canopies, as each has more than one forward and downward speed. For each speed and descent rate combination we can draw a circle for the usable area when flying at that particular speed combination. The circle location upwind depends on the drift time available, and the size of the circle depends on the distance the canopy can travel, a function of its speed and the time available based on its descent rate. In reality a canopy will have a continuous variation in speeds and descent rates depending on brake, rear riser, and front riser positions. For simplicity say the canopy can fly at any of these three speed combinations: 35 mph, 1500 fpm descent rate front risering (if it can actually be held the whole flight…) 30 mph, 1000 fpm normally 20 mph, 600 fpm in brakes These give circles that are of the following sizes and locations: distance upwind (miles), diameter (miles) .67 , .78 1.0 , 1.0 1.67 , 1.11 Fig 1c shows these all superimposed. If there is a continuous variation between all of these different flight modes, we can fair the different circles together -- as in 1d, where we end up with a sort of elongated oval. The radii of the circles at the top and bottom end will just depend on the tradeoffs between speed and descent rate. For example, the circle at the top (upwind) applies to where the jumper is trying to float the canopy in brakes. The circle may be small if the canopy is slowed down a lot while floating, but in this example the radius is relatively large because the canopy floats well without losing a lot of speed. (Lost 33% of its speed but has 67% more time in the air.) Getting back to the issue of jump run, the longest dimension within the oval shape of the usable area is along the main axis, along the wind line. If the jump plane started doing curved jump runs, or upwind and downwind runs, or multiple upwind runs, of course one would be able to make more use of the usable area, spreading opening points more, at the cost of increased complexity and fuel use. When different canopies are on the load, one of course ends up with a mix of usable areas. The usable areas will also vary depending on the opening altitude, so that it makes sense that tandems that open high drop near the end up the jump run well upwind.

I'm not really experienced in this but: It seems common enough for someone with spiralling line twists to be 'spiralling on their back'. Once a jumper gets under canopy he may adopt a normal after-opening 'sitting' position in the harness. Sitting in the harness is fine under a normal canopy, but when lines are twisted (providing almost zero resistance to further twisting), and someone is spiralling down at a higher airspeed, the sitting position is in effect a huge unstable de-arch. So the relative wind turns them to a stable position, back to the wind!

If one is in favour of the metal reserve handle, the counter argument is always that for almost all jumpers, the cutaway handle is still a soft handle. Valid point, but a PARTIAL counter argument is: - If I think a soft handle is harder to grab and pull, then I'd rather have just 1 not 2 of them to deal with. - Then I'd also rather deal with finding and pulling a soft handle while spiralling at 50mph downwards speed, than deal with one in freefall when accelerating from 50 towards 120. (But harness distortion should be less after the cutaway. But that didn't help in the Rick Horn case.)

To update the list and add one more excuse: Seriously? I've heard lots of reasons: 1) I will be REALLY CAREFUL until I'm more experienced. 2) You've never seen me land, so your opinion isn't worth shit. 3) I have a natural ability because I (ride motorcycles/fly airplanes/have a fast car.) 4) I asked around the DZ and this really really amazingly talented guy (a lot more talented than you) said I'd be fine. 5) Dave Splat jumped one with even fewer jumps and was mostly fine. 6) I've put 37 jumps on it and never once seriously injured myself. 7) I only jump it in good conditions. 8) I have Mad Skillz™. 9) I had to downsize. My old canopy wouldn't land right; this new one cuts through the air better and has more flare. (#9 may be valid to a reasonable degree for a huge underloaded boat of a student canopy vs. a small canopy, but is usually just an excuse for a single size downsize)

Like Riggerlee said. There are special approved markers, eg "MIL-I-6903C, Type IV Parachute Ink" as mentioned in the PIA's TS-108 on pull testing orphaned round reserves. I've never seen one. Mind you, National's round canopy pull test document just mentioned using a "suitable" ink pen. In a dz.com discussion some years back there was the concern expressed that, who knows, there could be some acidity in markers that could damage bridles or line attachments or whatever one is marking. But I don't recall anyone having proof either way -- just that there's no guarantee that ink in general is safe. I've seen old reserve bridles with something like 3 different owners' names on them. Customers don't ask for it much these days around here. So I almost never see anything on say a Wings bridle, but plenty on old Vector II's. I sometimes put distance marks on a bridle, as a packing aid, when a manual spells out at what point to do something different with the bridle (e.g., 5-6' is mentioned for non Skyhook Vectors, 36 - 45" for Wings).

Actually I can't find any similar statement in newer or older Cypres 2 manuals. The Vigil II, however, does have a warning about travelling in closed vehicles - although it states that this is because it is the most accurate AAD and arms itself after a change of only 150 ft. Some will say that's 'too sensitive', other will say it is 'better sensitivity'... The other points you made look fine.