pchapman

I'm looking for information on how a rig can be set up for AFF style jumps, if it uses a spring loaded pilot chute and an AAD on the main -- and also needs to have a handle for the reserve-side instructor to deploy the main. I heard Perris Valley used to have such a setup until about 2001. The USAF Academy is said to use a similar concept. How are such systems built? If using a ripcord system, an FXC can be set up to pull the pin, but it gets messier to set up a second handle for the reserve side instructor.

Yeah, those cute little trees are pretty scary.

So this thread is getting derailed. We need one for the Twin Otter production line (that although it has gotten the green light, hasn't yet happened), one for the Quantum Leap lawsuit, and one to hurl insults at effing lawyers. From that news article: Good, so I'm sure all money made in the lawsuit will go directly to aviation safety organizations to lobby the FAA for regulatory change, and to Pratt & Whitney Canada, to sponsor research into short engine cycle stresses on PT6's...

Nicely stated Yuri! I hadn't tried to run those numbers. An extreme example of what Yuri's talking about is seen in those videos of tiny non-landed canopies, maybe 21 or 25 square feet ... where the jumper looks like he's face down about 45 degrees off the vertical because of all his body drag, no matter how efficient the wing might be. But Yuri's point is that this sort of thing has a significant and variable effect for "normal" fast canopies too.

A complicating factor is whether one wants to look at 'risk per jump' or 'risk per year'. I'm making up the numbers but it is interesting to think of the issues: The guy with 1000 jumps may believe that a newbie with only 100 jumps has a ten times higher chance of getting killed when he goes on a skydive. But if the newbie is only making it out to the DZ for 25 jumps a year, and the 1000 jump guy is now pounding out 250 jumps per year, they both end up having the same chance of getting killed in the sport per year... [Mathematically the two situations aren't exactly equal, but for small probability events, 1/10th the risk, taken 10 times more, is about equally likely.] Now that's not to say that maintaining equal risks per jumper per year is the right way to go. If one can only jump once per year, one isn't given carte blanche to make it a really dangerous jump.

Too much time on dz.com today already, but I'll bite. Just briefly: My FX88 was flying roughly 46 mph brakes free, and 1750 fpm descent rate (29 fps!). That's at standard temp & pressure conditions, basically sea level. So the actual speed through the air will be higher in summer and higher altitudes. Getting consistent speed data is tougher with the FX, as even a little movement in the harness, or the tiniest harness turn, would increase the speed a couple mph as it tried to dive off to the side. In very deep brakes I was down to 25 mph and 730 fpm. With a Sabre 120 I was getting about 35-36 mph & 1350 fpm. The Stiletto 120 was the same or marginally faster, but descending slightly slower. Under a Manta I was doing 25 mph or just under. Note that these are flight speeds, so the horizontal speeds will be somewhat less. In a previous post in the thread I wrote: Oops, I misspoke. I actually did things the other way around. Since the anemometer is supposed to show true airspeed, therefore if testing up high, the speeds have to be reduced for density altitude effects, so that one can compare all numbers at sea level conditions.

As for the issue of the instrumentation I used, for those wanting the details: THE SHORT ANSWER Electronic vario and anemometer. Decent, but not professional quality. No need to deal with groundspeed vs airspeed issues. THE LONG ANSWER 1) For rate of descent it was an electronic variometer (rate of descent meter) as used by paraglider pilots. 2) For speed, it was a hand held electronic ducted propeller style anemometer, that is supposed to be accurate within a few percent. (Some cheap ones are shown in the manual to be much less accurate.) The anemometer was held out away from myself, risers, etc. to avoid either blockage or venturi effects. It was simply pointed in the direction of the apparent wind, and rotated up or down a bit to see a maximum value. Also, ducted props show insensitivity to errors due to not aligning them perfectly with the airflow. I once calibrated the anemometer in a university wind tunnel to remove what seemed to be small errors at the high end of the speed range. 3) Altitude corrections. The rate of descent changes with altitude, so I had to correct data from different altitudes to a sea level equivalent. I would get a pressure altitude on the ground using the plane's altimeter, and get a rough temperature reading on the ground and at jump altitude, to work out average air mass temps. Formulas are available to do density altitude calculations, or one can plug the numbers into a pilot's old circular slide rule. Initially I did altitude corrections on the speed data but then realized I didn't need them, as the propeller style anemometer reads True Airspeed, rather than Indicated Airspeed as an airplane pitot system would do. This seemed to be confirmed by comparing results for data collected both up high and down low. This made for small corrections in my original glide ratios, bringing them down a bit. Some day I'd like to put all my data together, double check the calculations, and do a clear writeup on it all. The results won't be perfect, but will be better nothing, which is usually what is available! As for a vane and a tilt sensor, sure, that could work, if the difference between the vane and level measurements could easily be recorded. In some ways it could be better because it would be a more direct measurement, rather than relying on calculating descent rate and speed along the flight path, and then doing the trigonometry. For me, I wanted to get speed information as well as glide angle. Paragliding companies use instruments similar to mine, but I have heard that to get really clean speed data with little effort, they use a 'trailing bomb' system with a vane-pointed ducted prop sensor hanging down below the pilot, well away from the interference of the pilot & harness.

Ok, ok, I'll try to throw some data in here, although it isn't exactly answering your question in a clear fashion: FX 88 = 2.1 glide ratio brakes free, 2.3 at quarter brakes, 2.8 in deep brakes (Goes way up in deep brakes, unlike old F-111 canopies where the glide ratio would go down.) (All tests at 165-170 lbs suspended) Sabre 135 = 2.1 free Stiletto 120 = 2.4 free (Stilettos were always good at gliding.) a 265 ft sq F-111 7 cell canopy = 2.2 free, 1.7 brakes set an experimental high-glide 11 cell 170 elliptical = 3.2 brakes free, over 4 in quarter brakes (Just to show what can be done largely with different trim.) I haven't confirmed it but figure something like a Manta, although bulky, is a high aspect ratio canopy with a decent glide, so it could be in the 2.75 range. In another earlier thread I wrote about 2.25 to 3.0 glide ratios for skydiving canopies in general, but now I'd revise that down to "2.0 to 2.75". (I've gained a better understanding of the characteristics of my variometer and anemometer instrumentation and thus fixed how I adjusted for density altitude.) Other reminders from an earlier post of mine: ======== Remember that skydiving canopies are often built nose low for speed, rather than trimmed nose up for efficient glide (more like paragliders). So a skydiving canopy's airfoil usually has potential for a higher glide than it actually achieves. Also, for small canopies, the pilot size may not change, so the "payload" gives proportionately more drag. A smaller version of the same canopy, with the same pilot, will therefore glide more steeply. ========== As an example of the above, Paraflite used to publish some detailed flight test results on their canopies. One high aspect ratio zero-p topskin canopy showed a brakes free glide ratio varying between 2.2 for the 154 size, and 2.8 for the 240 size. With all of this, remember that the numbers could easily be off by + or - 0.2. It's hard to get really good data without a lot of test jumps in still air, and well calibrated instruments. So use this as a general guide only.

My friend's Talka does contain a PZ-81, and he has a manual. Unless someone else gets one sooner, I should be able to get it and scan it in, in a few weeks when he'll be at the DZ. As for translating from Russian, that you'll have to figure out separately. Maybe we can get the manual added to parachutemanuals.com too.

Talka. (The "n" is just the Cyrillic "L".) The canopy very occasionally shows up in other threads about rogallo style wings. As for packing, sorry no idea but I'll email a Russian at my DZ who jumps a Talka rig. While it is nice to have TSO standards, it's also nice that here in Canuckistan we can also jump non-TSO rigs.

Anyone got a source of foam for adding to leg straps where the old foam is worn out? Sigma tandems, and I think recent Vector III's have really nice thick padding that retains its springiness a long time. Unlike, say, the padding in old Vector II's that gets compressed to nothing. The Sigma stuff is 1/4" or so of closed cell white foam. I once found something similar, but about 1/8" thick, which worked well for retrofitting. I thought it was something used as a flooring underlay, but can't find anything like it now. Flooring stores either have very thin foams that compress easily, or foams that are too thick -- Like 3/8" to 1/2" for carpet underlay. I've seen people using foam from camping mattress pads, but again that's getting pretty thick. So I'm wondering what type of store or industry might have 1/8" to 1/4" foams, that one can buy in retail quantities.

Oh yeah, that's one thing I was afraid of. I gave the caveat that buying the 'compressible foam' helmet isn't necessary the best strategy, and it is helmets with better certifications that have EPS style foams. Compressible foam helmets are often lower profile than the EPS style ones, which is convenient for skydiving, despite the increased risks. One can also buy sets of low rebound 'memory foam' pads for ProTecs, which are known as the Pararescue liner. (Not built by ProTec.) That should help, if the foam densities were properly chosen. But at $85+ they are pricy for adding to a cheap helmet. So thanks for expanding on the foam info.

On the topic of finding ways for swoopers and non-swoopers to coexist: What about the idea of trying to separate a landing area into left and right parts, with 270 degree swoop turns "to the outside of the pattern"? That is, the non-swoopers do a standard left pattern for their landing. The swoopers extend their base leg until they're over the far side of the landing area, then can do a 270 right to land. (See attachment.) Why doesn't this get suggested more often? It seems to be a simple but useful modification of what in practice happens at some places already -- the swoopers follow the pattern through the base leg, then crank their 270 the opposite way. While that at least produces standardized procedures, the danger being pointed out lately exists where swoopers dive onto final approach and have to mix with the slower non-swoopers. Non-swoopers can't well watch above and behind them to avoid collisions, and swoopers can get too focused on their approach to see potential conflicts. For the separated landing method, left or right patterns can of course be chosen depending on DZ buildings, prevailing winds, and who should have to walk in further to the packing area! Sure it doesn't achieve the ideal of a private landing field for each person. But it does allow two fundamentally different approaches to exist, with an attempt at keeping fast and slow apart during the critical part of the swooper's approach. It still demands some discipline, but stops short of banning swooping. At busy DZ's, some limitations on swooping may be necessary for it to coexist with other types of jumping. The same applies for other forms of skydiving, like CRW, wingsuits, freefly vs. RW -- or the limitations that one has to accept for the benefits of a big airplane in the first place. I myself only owned an accuracy canopy for 11 years, but now I want to enjoy my swoops too... One counter argument I won't accept, which I sometimes see in these discussions, is that swoopers wouldn't be following a "proper pattern", as if there is only one god-given definition of a pattern. Our skydiving patterns can be whatever we choose and agree them to be, to suit our sport. They don't have to be the same as a pattern as learned by a student airplane pilot.

And a camera too. How's he going to put a camera on that? Pro-Tec still makes the "Classic Full Cut Water", the usual style used for skydiving, with protection over the ears. The style of foam used on the inside has changed a few times over the last 15 years though. Lately they've added some sort of simple rubber strap at the back of the head. Not sure if it really helps to hold the helmet better in position or just gets in the way. The pic in the original post was of the Classic Skate -- i.e. their skateboarding helmet. It also traditionally uses the 'compressible' foam (that rebounds fully) like the Full Cut Water, rather than an EPS style 'hard foam' / 'one time use' foam found in snowboard or bike helmets. That's what I found when I recently bought one for multi sport use including CRW, that appears to have been built late in '06. Yet Pro-Tec's site seems to indicate that this year's production of the Classic Skate uses the EPS foam?! Their other Skate helmets I believe used EPS but are now moving to what they call SXP, which is similar in feel but is supposed to have some multi impact protection. For skydiving I prefer the compressible foam more for comfort and general feeling that it will cushion better than the very stiff EPS. That is not necessarily the best strategy. The compressible stuff is understood to be better only for minor accidents, but worse for major ones where it can bottom out. That's where the EPS and similar foams win out, and are found more in helmets that have higher certification levels. Oh, and the phone number on the new helmet is 562 565-8267, for Pro-Tec in Santa Fe Springs, California.

Interesting. And the bubbles etc, make it much more difficult to determine what is an actual crack -- everything looks fractured.

To go to silly extremes, if we really wanted to throw the PC a lot further we'd need better pilot chute deployment staging. Put the PC in its own little cylindrical bag or diaper with a lock at the mouth, to keep it's drag low, while it is being propelled outward by the momentum of a deliberately heavy hackey. Sort of like what's done for a mortar-deployed ultralight recovery parachute, or some staging chutes on ejection seat systems. Or if you don't like the heavy hackey idea, we need an even smaller pilot chute to extract our pilot chute, ad infinitum... (Ignoring scale and viscosity effects...)

As a single data point, showing how easily cutter damage can occur: I came across a cracked Vigil cutter insert in February 2007, on a rig which had the Vigil in it for just one pack job. It was a Vector II, on which one doesn't expect problems as much as on a Mirage, due to the cutter location. The rig was also not an extremely small one (as it held a Raven 1 reserve). However, I did note that it was quite a tight pack job when it came to closing the rig. It had been packed by a well known, quite experienced rigger in my region. The cracking and chipping of the cutter insert was minor and on the outside of the barrel only, so AAD/Vigil OK'd packing the rig up again, a decision echoed by the information in their bulletin #3 that coincidentally appeared a day or two later. I wasn't impressed. We may just have to wait one more pack job until the barrel is sufficiently cracked to endanger the closing loop, and get Vigil to send a replacement cutter. It still mystifies my how anyone could have designed the cutter that way and not have a rigger realize within seconds that the insert was going to get crushed given current skydiver expectations and rigging techniques.

Thank you! So it isn't an unheard of situation. I couldn't subsequently find the bulletin anywhere on the web, and haven't heard back from TSE. The matter was briefly mentioned in a report from the BPA riggers' committee (www.bpa.org.uk/forms/council/Riggers%2011th%20April%202002.doc). The report mentions a bulletin coming first from TSE.

And the pilot chute doesn't stay quite as nicely rolled and folded up at 120 mph as on the ground, which clearly adds to the drag too.

To me it doesn't look like something that could happen in a repack cycle, especially to stiff looking dacron line. But I'm not that experienced and can only speculate. In comparison, something like soft non-resin-treated PD Spectra line, now that I've seen all chewed up from a jumper leaving brake lines and velcro unstowed in a gearbag after having a mal. But even then there were few strands torn, just a lot of bunches of strands pulled out from the weave. In your pic, are the strands actually torn or just heavily 'fluffed up'? The location you showed would be hidden if a rigger didn't open up the velcro flaps that are used on some reserve risers to hold the excess brake line. Or if the inspection were too casual, it might even be hidden beneath all the folded line, with the flaps open. Curious indeed.

I figure the most important reason why it is easier to stall on rears than on brakes is because using brakes, the maximum angle of attack before the wing stalls is higher. It isn't really about the speed at which some angle of attack is changed. With brakes, the curvature at the back of the wing is like putting flaps down on an aircraft, which allows the wing to keep generating more and more lift by going to higher angles of attack where the wing would otherwise stall. (Of course brakes don't physically affect the whole span of the wing.) With rear risers, the back of the wing is pulled downwards, distorting the wing in an odd way. This does increase lift, adds some drag (though not as much as for brakes), but who knows how the angle of attack at which it would stall will change. In any case, it won't increase greatly as when brakes are used. So during a landing, one can get a lot slower for touchdown with brakes, than with rear risers. The original post mentioned how Germain's book said that the angle of attack changed quickly when using rear risers, and slowly when using brakes (as brakes took time to drag the canopy back and swing the jumper forward). I don't think he uses a "proper" definition of angle of attack. In aerospace engineering terms, the reference line is from the nose to the tail of the original, undistorted airfoil. (Leaving aside some details). This reference line is not changed when flaps or brakes are moved downwards, even though this changes where the tail of the airfoil is. So using the aerospace engineering definition, distorting the airfoil suddenly, whether by rear risers or brakes, technically doesn't immediately change the angle of attack at all. But, as the shape of the airfoil changes, the lift produced by it will change -- and as I described earlier, the stall point may also change. Germain said that the angle of attack changed quickly with rear risers, perhaps because I think he uses a different definition of angle of attack, a layman's definition where it is defined as the line between nose and tail, wherever the tail may happen to move. So pulling rear risers clearly moves the back end of the wing downwards, including the tail, so according to this definition, the angle of attack has increased -- it's almost like trying to rotate the whole wing suddenly. Call this definition the 'visual angle of attack' for want of a better term. But that definition still causes problems. Pulling the tail down with brakes by say 18" is deflecting the tail down a lot more than when pulling the rear risers down 6", and thus brakes would change the visual angle of attack a lot more. The words in the book just don't make logical sense to me. I find Germain's explanations generally to be a bit mixed up when it comes to understanding detailed aerodynamics, or explaining aerodynamics clearly. But that being said, he does have a very good feel for what is actually happening to the parachute. So I'd generally trust his conclusions, even if the aerodynamic background isn't always clear. And his book still puts a lot of good stuff together in one place, something nobody else has done. In the end, when it comes to rears vs. brakes for reaching the stall, I think the main reason brakes don't stall you as easily is that one can pull brakes a lot further without causing a stall, as brakes deform the wing in a way that is quite efficient adding lift yet avoiding a stall, compared to pulling down on rear risers. Rear risers may not be able to add as much lift as brakes can, but they can add a moderate amount of extra lift more efficiently (with less added drag) than can brakes. (Among prior answers, I like what quade and mr2mk1g wrote. They are using the visual angle of attack definition I think. That's fine, as long as we can all sort out what definition each person is using.) Phew, how's that?

Perfect, thank you!! That's the point I was thinking of making for phoenixlpr. Try running a static line first jump class and advertising, "Our main parachutes malfunction at least one third of the time!" :) Edit to add: Actually I do deal with line twists and end cell closures in the course section dealing with "issues", but I still don't call them "malfunctions". AFFI just mentioned the case of a student landing with line twists. Valid point there. Presumably that wasn't on the first static line jumps? It does sometimes get tricky to teach students who are are past the first jump, added subtleties about parachute problems, that one doesn't address fully in the first jump course. And even in the first jump course, students need to realize that if they can't properly control the parachute, and are still up high, they need to use emergency procedures -- even if they can't quite match their problem to something specific they remember from the course.

Yeah I figure it is an artefact of changing body position. When tracking for separateion at the end of a bellyfly jump, I fairly consistently get a big, wide spike to 140+ mph. While the body position and airflow changes aren't that big, the gadget is clearly getting fooled. As I've said in some other ProTrack thread, if you want to dig more, export the track to a text file, import into Excel, and do your own averaging. The JumpTrack graph bases its numbers on averaging the previous 6 seconds of flight -- so there's a lag as well as data smoothing going on. That confuses the issue when it comes to comparing a particular speed at a particular altitude. I prefer a centered 3 second average to avoid the lag, but still provide some smoothing. (So each point on the graph is the average of all the quarter second data points from -1.5 to +1.5 seconds). I believe the ParaLog program on the market allows a similar averaging.

So are you saying your buddy the DZO is wrong? That Fred should only pay if he packed a mal BECAUSE he had his head up his ass? That is, if someone can prove he was sloppy or omitted some step, he'd pay, but if the mal "just happened" with no apparent cause, he shouldn't? Yes, the DZO makes the rules. But one can always check what is normal in the industry and argue one's case. Everything he has written has been pretty respectful. He simply questioned how the policies at his DZ differ from other DZs, as he personally is not convinced all of them are fair. I believe the "shit storm", to use your own words, is yours alone. As for the actual issue of students and renters paying for repacks (or even a lost main), I think that is an issue that is very poorly presented at DZ's. I'm not sure that very many students and renters are told what the DZ policy is, before they make the choice to rent gear. Before getting into what policy is "right", the renter at least needs to know what it is. I'm not even sure what the policy is at the DZ I'm at. There is a sign warning renters that the previous person who packed the rig -- often another student or renter -- isn't guaranteed to have done it right! But that's more about hard openings or mals, and not about who takes financial responsibility.

I'm trying to summarize some of the types of accidents being discussed: One category is accidents that actually kill skydivers on flights where they planned to jump. I guess that's what the USPA tends to report on. That category is part of a larger category, which are all accidents (fatal to skydivers or not) involving flights where skydivers planned to jump from the aircraft. These are actual jump operation accidents. Then there's the category of accidents involving skydiving industry airplanes and pilots in any other way -- such as ferry flights. These may not usually kill skydivers, but skydiving operators still care if their planes crash. Jumpers aren't going to be as directly worried about such accidents, but they still are indirectly affected by the loss of pilots and airframes and insurance losses. And they should be concerned if the flight was brought down by maintenance or piloting issues that could well have happened on a jump flight instead. With different types and levels of skydiving related aircraft accidents, we may simply need to define different categories of such accidents. So we won't all agree on what should be included in one big aircraft accident category simply called "skydiving accidents". === On a different subtopic, another example of a jump plane flying into a mountain was the case of the small Cessna in British Columbia a few years back. On the descent after dropping jumpers, in an area of unsettled weather & cumulogranite, the plane disappeared. The crash site wasn't found for many months. While it was "not my problem" for the jumpers who had already jumped, I can't imagine the situation was much fun for anyone at the small DZ where it happened.