pchapman

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.

Brand, loading, etc? Which incident? The database of major reserve failures is relatively small.

As for comparing helmets, I just checked the chin strap on my camera helmet -- It happens to look reasonably good, for the spring is recessed into a groove on the ratchet. The chin cup assembly is from Sky Systems. It is starting to look like the spring design is similar on various ratchet mechanisms, but there are differences in how exposed they are. It is still a ridiculously small snag hazard compared to other things...

I didn't get a photo of the actual helmet involved. But online I found the attached Rawa pic. This is of a more recent version with a tab to quick release the chin cup. But one can still see the metal hook at the bottom of the adjuster. Seems that it might have been slightly longer on the one in the incident. P.S. - yet the metal is very small, and hard to see even on the closeup of the chin cup area

Someone at the DZ had an odd little snag issue yesterday. It's not about a big snag point, but is an example of how little things (including design issues) can cause problems in unexpected ways -- Murphy's Law type stuff. So Kyle was climbing out 2nd from the 182 for an RW jump. He presumably tilted his head to the left as he ducked out the door. He gets out on the step, and finds that he can't straighten his head up; his head is somehow stuck to his rig at the shoulder. Shannon behind him sees what's happening and decides to pull Kyle back inside to sort things out, while the outside hang jumper decides to drop off. Shannon and Kyle get back inside OK, sort things out, and jump after a go around. I didn't look closely at the helmet but at the Rawa's left side chin strap ratcheting attachment buckle, there's a bit of stiff steel wire that sticks out just a few millimetres on the bottom of the ratchet mechanism, forming a small hook facing I think towards the jumper's chin. There's nothing to protect the end of the wire. I think it is strong spring steel, part of the spring loaded function of the ratchet mechanism. (I don't know the age of the helmet, or if anything is different on older or newer ones.) As the jumper climbed out, that wire at the bottom of the ratchet hooked right into the fabric of the riser cover. The steel wire being quite stiff wasn't about to let go easily if the jumper tried to pull his head away from his shoulder straps, which would be anyone's natural inclination. The incident could also have happened at some other time, in freefall or under canopy. Granted, some head shaking in different directions, despite not knowing what the hell was going on, would likely have found the right direction to unhook the wire. Still, the RW group could well have jumped, with one guy not too happy about having his head pinned sideways to his rig! It's a small snag point on the helmet but it's still a snag point.