pchapman

NEW BULLETIN 15 Nov 2010: Australian Parachuting Federation bans using all Arguses in Australia. (And that's one of those mostly AAD-mandatory countries.) Looks like the newer cutter design (Sept 2007+ manufacture) isn't enough, so that the APF is waiting for Aviacom to come up with a demonstratably better cutter. Sorry, don't have the link to the bulletin handy at the moment, but the bulletin is "APF TECHNICAL DIRECTIVE No. APF TD04/2010 Argus AAD".

Skyper wrote: Skyper: True, but these newfangled breath strip things dissolve completely & quickly in the mouth. With nothing in the mouth during the jump, it is far safer than offering a student gum. Skyper: DSE: Looks like you'll have to get all your students to sit on a couch and start telling you about their childhood and relationship with their mother.

I haven't jumped one I'll comment on their stats and promotional material: - The TSO used isn't mentioned, but it must be C-23d, the latest. You'd think that's worth mentioning. (Guessing it is version "d" is based on the relative newness of the reserves, the certification weights used, and having the peak force listing.) - Even their smallest ones are TSO'd to 254 lbs. Neither PD reserves nor r-Max's are certified to the full 254 for their smaller sizes. - Their larger sizes are TSO'd to higher limits (330 lbs) than the PD, Smart, Icarus, or r-Max. - A reserve aspect ratio of 2.3 is a bit higher than for other reserves. (PD about 2.1, Smart 2.0, r-Max 2.2) - They could edit their material better. What they wrote on their web page (and in the .doc's in this thread) is "With its slightly longer chord and wider cells". Um, that combination is just "bigger". They probably meant longer span, referring to the aspect ratio. - No suggested weight limits are given. That's unusually lax. Maybe they mean it'll fly & land OK at any loading up the the FAA limit, sort of like people treat PD reserves in practice, as compared to an early 1980s designed reserve. At least they don't give some ridiculously low limit that has people arguing whether it is an absolute limit or just a suggestion. (E.g., the Smart says max exit weight for the 99 is 131 lbs, which is laughable these days, despite being certified to the latest C-23d.) - You can still pick the color of every cell and rib of the Angelfire reserve. That's a rarity these days. Not a big deal but maybe nice for those who think white is boring or want a "the show must go on" demo jump reserve. - They acknowledge that the reserves pack up a bit bigger. E.g., Angelfire 99 = 286 cu. in. packs up about the same as others' slightly larger canopies: PD 113R = 286 Smart 110 = 275 Smart 120 = 293 Or: Angelfire 150 = 390 versus slightly bigger competitors: PD 160 = 388 Smart 175 = 384

If you are talking about the canopy fliers, that's irrelevant to this thread. The guy at 3:42 in the video was one of the wingsuiters. Looked like he was just having fun flapping his arms, quickly enough that he didn't drop out of the planed out flight. Who knows, maybe it did add drag on average and slow him more quickly than normal. On the other hand, maybe his landing would have been at a slower speed without flapping.

Ya got me. I'm skeptical, but there's always something new out there. I can think of a couple scenarios where the pumping flare is less efficient than a good normal flare, but looks good in comparison to someone's normal not so good flare: 1) If a newbie suggested it, I might think that the pumping just got them to use full brakes, focusing their mind on the arms, rather than making a newbie mistake of not flaring fully because one has shifted focus to one's footwork. 2) Or, someone is a little too spastic on the brakes while planing out, up and down and up and down, but at least they are highly focused on the flare and do better than their usual more lazy big flare with little adjustment part way through. I don't see any advantage in the idea of pumping, which should normally just waste the power of the flare. I don't see that one is adding much energy into the system by flapping the tail or creating vortex lift or creating some dynamic condition that delays trailing edge stall separation or whatever. One can come up with very particular situations where what seems to be ONE brake pump might help, but not multiple ones: 1) An efficient swoop where a sharper rear riser or brake application can plane one out perfectly, where toggles can actually go back up, before finishing the full flare afterwards. 2) There's a fair bit of wind, one over flares and pops up a few feet high, pretty much ending up in a hover 5 ft off the ground. If you just hold brakes, you might run out of flare energy while waiting to slowly start to drop, and then hit the ground harder. Plus your forward speed might still keep dropping, so with the wind you drop backwards and fall on your ass. So instead you let up on the brakes just a little, pitching the canopy a little forward and speeding the descent, without slowing forward speed too much, then hitting the brakes hard to finish the flare again for touchdown. In some similar conditions where one is floating down from a few feet up with zero forward speed in a moderate wind, then one can pump the brakes for fun without causing any problems as one drops down to land. But I don't see this being any better than a proper flare in the first place. But that's a situation with wind, and your experience was in no wind. Edit: The idea in other posts about adding drag is interesting -- Where one already has enough flare to plane out but one wants to make the canopy LESS efficient by adding more drag to slow down faster. The idea is to get the canopy down to a minimum flying speed (and thus minimum touchdown speed) before the canopy starts pitching forward again and dropping after running out of energy to maintain the planed out flare with canopy back. As a thought exercise it is hard to know whether it would work better than a normal good flare, but it is an idea.

+1 Or else we are supposed to believe that all nervous students (or jumpers at any level trying something new) should be grounded. (Great, so now we only have to go up and instruct the cluelessly overconfident students...)

You’re certainly using the static friction off the bearings as a reaction force every time you kick. According to Newton’s 3rd law of motion. But to extend that thought: With line twists, one isn't hanging from a single ideal zero friction point. There is a small amount of untwisting torque at the start of the line twists at the bottom. And in a sense there may be a little aerodynamic friction, keeping someone in a stable sitting back to the wind position, or at least changing the drag up and down at different angles to the wind. So if someone is doing the traditional kicking out of line twists under some student canopy, aren't they doing something like with the office chair? A sharp movement twists half the body in the desired direction, then a slow movement that doesn't overcome the friction allows the other half of the body to catch up without undoing what was done before. Or also, the quick movement is done at a wide radius, and the slower movement is done at a smaller radius so there's less torque being applied, making it easier to 'push off' the friction. In this whole line of thought, what I haven't thought through yet is just what the friction profile is like for the office chair vs. person under line twists. For the self twisting to work, I think one needs some sort of resisting friction or force that doesn't linearly increase with the force applied -- so a small constant friction force at a low applied force works well. While it can come from aerodynamic drag in some positions, I'm not sure how it might exist in the line twists themselves.

The Paradactyl, PZ-81, or Delta II for example are all Rogallo style wings. The Thunderbow is triangular shape but is more just a shaped round canopy. There should be plenty on Mr Rogallo and his wing concept on the web. In general, they were a short lived evolutionary step between round canopies and better performing ram air canopies. The Rogallo concept was also used for early hang gliders (with a rigid frame), and is in use for some paragliding emergency parachutes.

Quite the project. One area of questions though -- what's the source of the holes? CRW burns, mechanical abrasion from churning around on a river bank, UV damage? The rest of the canopy is passing pull tests? I wouldn't want to do all that work just to find that all the other fabric is starting to fall apart.

Just trying to define what exactly Rossy had accomplished. From the initial video I watched, it wasn't clear that he had achieved what the press was saying. I corrected my statement for the record, as soon as I saw in other video that it was a true loop. (And as for loops in regular airplanes, I admit a personal bias -- I assistant judged at a World Aerobatics Championships, so if you can't fly a round loop, you suck.

For the record: The loop wasn't 'around' the balloon but off to the side. And contrary to what I initially saw, the loop wasn't "flopped", although it was still pinched at the top. So he did get it to fly over the top rather than stalling out and recovering. Very nice. That was apparent from a video from a different angle and with different editing than the one I first saw.

Every 100 jumps swap the risers left to right. Rotating the rings: Turning the biggest ring on each riser (and the small one too) with ones fingers some random amount, so that the harness and other rings aren't pulling or pushing on the same spots on the ring all the time. As Rob says, not necessary. Nothing wrong with inspecting the rings occasionally though.

Time to snicker at turbine babies! Just recently in another thread a new guy wrote about not wanting to "suck it down to 3000 ft" before deploying.

From the videos in the linked page, I only saw one depiction of the actual loop. Based on only that, I would say: It wasn't a clean loop, and wouldn't score in an aerobatic competition. It was more a case of flopping over backwards from a pullup past vertical. But it was a complete rotation done by pitching in the vertical plane, so it counts as a loop. So he doesn't have the energy or g capability (yet) for a clean loop, but it is still a great achievement.

OK, this is some actual, useful information amidst the usual blather about, "dude, don't you know things don't always work perfectly in skydiving". So, to clarify, for you there has been a small percentage of the time where the reserve pilot chute seems to beat the Skyhook RSL in pulling out the freebag. How do you tell? Is it just from looking up and seeing or videoing what is happening? Things happen fast. If the freebag is later found separated from the main, that could just mean they pulled apart after being cut away, so that won't prove the pilot chute beat the Skyhook.

An old canopy will get easier to pack - so porosity or permeability, whatever you want to say, does go up. I don't know what the contribution is from the fabric itself vs. sewn seams, but if the canopy gets easier to stuff in the bag, then something is letting more air through. An old canopy may start to show a bunch of pinholes in high wear areas like the top center panel at the back, or eventually just rip. (e.g, as for a 3200 jump Stiletto a friend used to jump.) Occasionally someone might pull test their canopy, if they'd rather get a rip on the ground than in the air. (Eg, the center aft panel on an old Stiletto ripped at 20 lbs when I tested it. It could have kept flying. How long? Who knows, but probably quite a while longer.) Performance will go down a little with age. Although the drop will be less sudden and smaller than for F-111, one then has to decide whether the missing performance was really needed or if one can get away with a little less. Often a canopy is retired when someone figures they're rather put their money towards a newer canopy, rather than paying for a reline on the old canopy. So you might have a canopy lying around that is basically free to anyone who wants to pay for a reline. Others will have better info on canopy lifetimes. If one is around a bunch of professionals putting 500+ jumps on a canopy a year, they'll learn more about this than when being around fun jumpers putting 100 jumps a year on a canopy.

There can be additional complications and grey areas, even with knowing some of the standard plan B rules. If planning a single formation, then it is easy for people to make the best formation they can, and leave out the guy who goes low. If planning a sequence of formations, then it may make little sense to try to build and change incomplete formations without the low guy, so people are more willing to go to the low guy. If the low guy is 20' down, maybe people will go to him. But if he drops 50' down, people may count him out. (Plus it is harder to close nearly pure vertical distance without some good skills.) If a formation is completely broken up, people are more likely to head for the low guy than if there are some chunks of formation left -- then the tendency is to go for whatever group looks most like the original base, or the largest group of people. I'm not saying what's right, but saying what actually happens. Rules or recommendations are still good to have, but in reality there's a lot of behaviour that is made up on the spot because the rules don't cover all the circumstances involved.

AFF and PFF are the same basic system, the former being the US method, the latter the Canadian method. While instructors can discuss the differences, overall for the student it is the same way of learning to skydive. Grand Bend is quite a small DZ, but they've specialized in PFF training. Unless things have changed, one of the instructors that students always go up with in the beginning is the dropzone owner, Bob Wright, who has somewhere over 10,000 jumps. So it isn't a big "happening" DZ for the experienced skydiver, but it is very good for skilled, personalized attention for students. Other DZ's have PFF programs too, or hybrid tandem-to-PFF programs. (I'm at Skydive Toronto and Parachute School of Toronto, but learned with Bob years back.)

Yeah it is stalled, in one sense. Like the original question, it is a matter of definition, and neither "flying" nor "stalled" has a single precise definition that fits all aerial vehicles. For a normal airplane, anything above lets say 18 degrees angle of attack from the zero lift angle of attack is probably getting into stall territory, depending on the wing etc. But for a very low aspect ratio wing, like a delta or a wingsuit, there isn't an easily identifiable stall point, and lift vs angle curve isn't going to show a sharp stall break, where lift suddenly drops off and drag keeps increasing, as angle of attack goes up. The changes in lift and drag are more gradual for a low aspect ratio wing. Vortex related lift becomes an important factor. So you can say wingsuits are stalled -- especially when countering people who think they are flying fully in the "normal airplane wing" sense. They aren't in that magical region where a normal wing is making a massively high amount of lift relative to its drag, the thing that distinguishes a wing from a barn door. The angle of attack is too high to be in that range, even if they were using a normal aircraft wing. (I haven't followed any recent discussions on best glide angles, so I can't say much about exact angles of attack by the best pilots in the best suits.) But you can also say wingsuits are flying, as that's the way low aspect ratio things fly. For the original question in this thread, there is also flexibility. Aerobatic aircraft are still flying when stalled or spinning, and we consider skydivers to be flying even when then are going almost straight down -- especially when maneuvering relative to each other in a controlled way. Who cares if the angle of attack relative to the body axis is 80 degrees or whatever. Yet at the same time it is normal to say that a plane "stopped flying" when it pitched down at a stall. So it isn't "flying" in the normal sense. So we do need to distinguish between flying that is any motion in general through a viscous gas where aerodynamic forces are being applied, and flying that is "flying like a normal airplane (in normal flight at smaller angles of attack, outside of a regime of significant amounts of wing stall)."

I'm not sure it's all that special, but who cares who else has done it. Bring everything you have, jump it all, and end up with a pile of nylon to pack come the evening... (But if we were getting all competitive, a year ago August I had a day where I jumped a Paradactyl -- backwards accidentally -- two different Para-Commanders, a Thunderbow, and my regular FX88.)

But didn't you calculate 12.5% of the area? 6.75 sq ft is like a diameter of 3 ft, rather than a radius of 3 ft, which would be 25% of 12 ft gore length. But it's late and I'm tired so I might have misinterpreted something. But let's for convenience stay with the final value of the 6 ft^2 at the top taking the shock load of a max allowed 5000lb, giving 6 lbs/in^2. What I want to emphasize is that we would also have to look at gore width -- and that's where the stresses on the fabric end up looking a lot worse, and more difficult to pin down. Just making up numbers, say that away from the apex, at the bottom of the area taking the load, the radial seams are 6" apart. So if thinking about little one inch squares, there are 6 in a row from seam to seam. So thats 6*6 lbs = 36 lbs, supported at the seam on either side. That brings the stress to the fabric to a total of 18 lbs per inch. But that's an ideal case since the fabric won't be in a U-shape but pulled somewhat more taut, increasing the stress on the fabric. If one tried to pull the fabric absolutely straight, the sideways loads would go to infinity trying to react the outward force. In practice the canopy gores will bulge, so the actual force on the fabric will be between 18 lbs and infinity. In the end I'm wondering if we end up with too many approximations here to guess at the actual fabric stresses. On the one hand even high opening shock forces end up as a pretty small pressure on any particular square inch, but the forces add up across the width of every gore, and without knowing the final bulged shape of every gore, one can't tell exactly what the fabric stresses will be.

Is that a requirement in Canada? Not so in the U.S. - (Yeah, that is a big US / Canada difference. With an 'A' up here, it isn't anything goes for RW. If not with instructors or coaches, formation jumping is limited to one other person only, who has a B, 100+ jumps, and approval from a Coach 2. Now of course in practice it doesn't always work that way, but basically it means you don't get newbies getting together for a 4 way or joining on a 10 way.)

... which was of equal value earlier this month and is at 98 cents US at the moment

I know this is a bit off topic, but I presume this has to do with some German rules on gear life? Not just rules on reserve canopies for example, but on harnesses too?!

I don't know the military and haven't watched the vid in a while, but I thought the idea was to get him off the plane. Then hanging under the round, the jumper would deploy his reserve. While there's still some danger if the static line releases at 100', he won't freefall into the ground. "Dude, I can't land with you on the plane like that." - Truman Sparks (from memory)