pchapman

There are a number of tales on dz.com (and ones I've heard in person), about women and their tales of bruises, some visible to other people, and some discovered only when one showers. Guys get bruises too from hard openings or poor padding or rigs that don't fit well, but it tends to be the girls who have to convince friends, colleagues, or their gynac that no they aren't being abused. No need to call the cops or social workers! The female jumpers have to convince people that they are in a consensual and usually (but not always) loving relationship with their parachute ... even if playtime with it does get a little rough at times.

And there are a couple old threads on the Woomera, with a few photos in one. (Also, an instructor of mine built a super-light weight rig in the '80s with a throw out PC at the top of the left shoulder. Perhaps a throwout reserve PC is better than a pull-out reserve PC, but this is all off the original topic.)

Looks autocorrected from Yanta Escape System, YES!

Fair enough, I guess openings can be snappy, but at least we don't have to jump them all day long or take them to terminal! A snippet I have translated from a manual does say "categorically forbidden for the parachutist to turn his head (up) at the moment of inflation, in order to prevent trauma". Okay... I don't have a translated packing manual, but I can offer the rough notes I took when I learned to pack my UT-15 rig. I had forgotten that I had specific UT-15 notes that I could share! ... although they do include a few "I think??..." statements, so there are no guarantees. I would be interested in getting a copy of your Russian manual, councilman, if you have or get it all scanned or photographed. AI had found a few drawings from the manual online, but even a full set of them might add a little to understanding it more.

It's interesting how people react to the pluses and minuses of the two candidates. Everyone has them. (Just using your post as a starting point.) Some right wing people say the left wing people just didn't understand the desire for change in the Washington power structure. That's why Trump won, they say. But It's not that some of us aren't aware of problems in that regard. The negatives of Trump so totally disqualify him to be president in our minds. Sure, Hillary may be a sleazy power hungry Washington politician, and more so than most, but at least she's a reasonable politician and able to act like a rational human being. (There may be some personality issues involved too -- Some on the left may not like people who act like big loudmouthed egotistical macho jerks. But what if someone like that is an effective leader at the same time? Ok, some on the left might think, maybe it's ok for a drill sergeant or a mafia don or Hells Angels leader, but not for a normal leader in society.) So if Trump is just an unfit human being for the job, it doesn't matter whether there might be some interesting ideas he has, some things that whether good or bad are within the range to be debated or discussed rationally. (While I might be identified as being on the left, there are plenty of times I might have thoughts that aren't politically correct and want to be able to discuss them rationally and not be shot down for voicing them. It is easy to both be concerned about the right and the far left at the same time.) I'm not sure that the worst things said about Hillary really are true, and maybe I'm uneducated on the matter. But what Trump says still disqualifies him -- whether it is the things he says of people, or the endless ignoring of facts. (And we're not talking about just the occasional oversimplified misstep, as nobody can be entirely correct about everything all the time. Ah, one can long for the innocent era of Dubya Bush's verbal goofs!) To exaggerate as a mental test case: Even if one gives the right wingers the benefit of the doubt by thinking the worst of both candidates, Trump still doesn't seem like the right choice. If one did believe Hillary to be really evil, then it's almost like you had two candidates who are suspected murderers in their spare time. One keeps quiet about it and otherwise tries to act normal, while the other brags about it and flaunts it. Do you pick the person who at least goes about their workday normally, or the one who flaunts it too? It will be interesting to see how much of Trump's words are things he really will try to follow up on, versus being the words of a snake oil salesman for a hooked crowd. And how much he really can push through Washington.

There is a manual on the other site that has rigging manuals, uk-slydiver.co.uk: http://www.uk-skydiver.co.uk/cms/files/file/1458-swift-cirrus-orion-manualpdf/ That shows an archaic flat pack folding method that one can ignore, but does show the rather unusual Swift brake line system, which is important. (I once saw one with the brakes assembled wrong and missed by 5 subsequent riggers. Good thing the jumper hung onto his toggles after deployment -- they were fly-away like with slider-off BASE.)

While you've made some reasonable points I'll also note that Dokeman (early in the thread) reported bungees wearing out and fraying Spectra ripcords. I'm not sure where he saw it, but I have seen it start where the pin cover flap pushes down on the ripcord's loop.

Jeez, it doesn't seem all that complicated. It's not like you are looking at jumping something with a massively increased performance. You have plenty of jumps on the 168, and are taking a long winter off, that's all. So you do a few jumps on the 190 and go back to the 168. If you're not comfortable after a few jumps on the 190, do a few more, and make sure that includes low wind conditions too. While rental fees can add up, it's still probably easier than buying a whole new canopy just for that. Unless you really want to put the time into searching and negotiating, or you just happen to see a really great deal come up. There here can be a lot of time spent getting a canopy and getting it into service. On the other hand, if you find a decent deal it is possible you might sell the 190 for the same price you got it, after putting only a few jumps on it.

I guess that's fair, and takes us back to the start of the thread: In general (that is without any sudden wind shear), the canopy will recover the same either direction, but our perception of it could change due to the different ground speeds.

Aw, come on, that typical length ripcord cable weighs slightly more that half an ounce. (3/32" 7*7 stainless = 1.6 lbs per 100 ft) The Spectra and bungee can't be nearly as much. So a jumper is going to be maybe 1/4 to 1/2 ounce lighter, clearly a big improvement!

Blue Skies to Pat. Not that it was easy understanding his unique style of writing, like some oracle, in recent years! But 8200 jumps and 55 years in the sport isn't bad.

For the record, the pull force issue did come up before, in 2015, and wasn't really resolved: http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=4733570; Gowlerk, mxk, and myself were all in on that discussion.

Slack harness: oh the horror, oh the humanity! Nobody here is talking about having a dangerously slack harness. Nor even loose leg straps in the plane -- nor loose butt strap nor Y mod for that matter. Just the difference on the MLW & back diagonals, between comfortable to arch in, slightly snugger, and really snug hindering an arch. Which will translate into slightly looser conditions when seated under canopy. Their tightness also affects comfort for the student standing on the ground (affecting how tightly the leg strap dig into the crotch). We're discussing the minor tradeoffs here.

To expand on what you mentioned EvilGenius, I've seen different formulas and graphs for the typical variation of wind with altitude. Of course the numbers are a rough average to something that varies a lot -- sort of like saying the ICAO temperature lapse rate is exactly 1.98 deg C per 1000' altitude. What you actually get within the altitudes you jump at, may be quite different day to day. Getting back to the wind, one formula from the Iowa Wind Energy Centre gave these results: The below is for terrain that consists of high grass or low crops (which affects the friction of the air mass, eg, prairies and lakes are windier). The starting point is 20 mph wind actually measured at a standard anemometer height of 33 ft: 15 ft-----17.4 mph 33 ft -----20 100 ft-----24.4 200 ft-----27.7 500 ft-----32.6 1000 ft-----37 I don't expect their formula to apply very well at 1000' and more. While the winds at 13,000' can be quite a bit higher than at 1000', it isn't like we have 50 mph wind up there every day. Generally the shape of winds affected by friction with the earth will look like the below. This is the velocity gradient EvilGenius was talking about: [inline wind-vs-altitude-sketch.jpg] Now I wouldn't trust any graph to say what's happening on a particular day. Many of us have seen examples, like a student coming in to land when the wind has picked up a little too much for students. The student is coming straight down, straight down ... then magically at 200 ft or 100 ft or 50 ft, he starts to get a little forward speed and comes in for an almost normal landing! So all this does suggest a) Yes there is some shear, not necessarily sudden, with altitude b) Of course the biggest differences will happen when the wind speeds are higher c) The shear amount over any short distance one will fly the canopy through is moderate in size. So yes the wind might go down from 32 to 17 mph from 500 ft to when you are planing out during the flare. We're used to trying to account for dropping wind when planning our circuits or accuracy or swooping. Over a short distance though, the changes (in this average situation) aren't high: From 200 ft down to 100 ft the wind dropped only 3.3 mph. If you were swooping at 60 mph and let's say in a 20 degree dive it would still take 3 seconds to cover that vertical distance. That's about a 1 mph change to the canopy each second, a smaller change for a canopy already moving at 60 mph. (If the dive were as steep as 30 degrees, it would be about 2 seconds and about 1.6 mph change per second.) Which isn't a huge shear effect on the canopy, and gives the canopy a little bit of time to adjust to each bit of change. Will it affect the natural flight path of the canopy? Sure, a little. (The lower one is, the more the wind changes with a given change in altitude. But down low, you won't be in as steep a dive either, so the canopy will take longer to be exposed to those changes. So who knows where one might experience the most shear (per unit time), depending on how one flies or dives one's canopy. ) This 1 mph in 60, per second, isn't at all like a bad scenario of 5 mph instant change, when going 40 mph, as in my earlier examples. Those were used to show how the canopy behaviour changes (and thus differs upwind vs downwind) if one does indeed have a sudden wind shear. To sum up, we've looked at different levels of understanding of canopy flight: 1) At a first glance, start with assuming no wind speed change with altitude, and understand how that works. If you don't understand how canopies and air masses and air speeds work in that situation, your whole understanding of canopy flight will be messed up. 2) Next one can add on, "But what happens the wind does change suddenly with altitude?" and understand what that can do to a canopy, by looking at simplistic scenarios where the wind suddenly changes by a lot. 3) Next one can back off a little and see what is more likely to happen on a typical day: while the wind does drop off as one gets closer to the ground, the amount of wind shear your canopy experiences from second to second isn't huge. As far as how the canopy will behave, it is more like the original all-the-same-wind case. (Just trying to teach these things is a great way to focus ones mind, organize thoughts, and make some calculations one hadn't gotten around to before!)

Haha, yeah I wasn't trying to be exact. Move the x-axis to the very bottom of the sine curve, then one has a nice rise from zero up to some maximum value (and if its a gust, dropping it back down to zero) (In aerodynamics texts I've seen them use the "1 minus cosine" curve to be precise. Whatever.)

Sure, the shear will happen over some distance, which will take a certain amount of time to fly through. Assuming that there's an instant change is a simplified, worst case way of looking at it. In actuality there's typically a little more time for the parachute to adjust to gradual changes in wind or gust speed, taking the edge off whatever they would do if they really changed instantly. (Still, if you've been hit by gusty, turbulent winds, it can seem pretty sudden at times, and not just a gradual bumping around.) Even aerodynamics books, when looking at the effect of a vertical gust on an aircraft, tend to start with the idealized case of an instant change from zero to the maximum. It's easier to write out some equations. If one uses some smoothly curved, sine curve style shape, then one would need to do a simulation over time. The sharp edged gust is still a valuable simplification to help understand a gust's effects.

Ok I'll give it a shot. Since it gets mathy it's always a compromise between getting too wordy, or leaving out all sorts of calculation and explanation, which would then make it tough for anyone to follow the logic if they tried. This is all for the situation where there is a wind shear -- wind speed dropping off sharply as one goes lower -- not the steady wind conditions discussed in much of the thread: 1) I've said before that it all depends on the vectors relating to relative wind and how that affects airspeed, angle of attack, and thus lift. And it is messy. That's both correct, and a vague answer that doesn't help much. But if nobody else has done the calculations, I'll at least do a couple. I'll talk about airplanes first because it turns out the standard wisdom in aviation doesn't always work out for parachutes. 2) For airplanes, when one talks about encountering wind shear on approach, to be clear we're usually talking about the normal 'flying into the wind' and 'wind decreases as one gets lower'. Standard wisdom is that the plane will tend to sink, because one will lose airspeed and thus lift. This seems to be borne out. Calculations: Say the airplane is flying 80 mph on a 10 degree descending flight path. Yeah that's a bit steep but whatever. Angle of attack (relative to zero lift angle) is say 10 degrees, as a rough rough guess. When wind shear hits, lets say there's a sudden 5 mph drop in the wind. Doesn't matter what the wind is. Wind shear in reality isn't usually an instant jump in the wind speed, but for a quick look at the issue that's sufficient, a sort of worst case for any given change in wind speed. Vector addition shows the airspeed changes to about 75 mph, and angle of attack changes to about 10.7. Lift goes up with the relative change of angle of attack (10.7/10)(linear lift curve slope in the normal range of operation), and down with the square of the change of airspeed (75/80, squared). Net result is the lift being 94% of original. Thus for the light airplane on approach, a sudden loss if some headwind does result in a loss of lift. The airplane will drop faster, pitch nose down, and eventually recover to steady state flight at 80 mph again. 3) Now to try the calculation for a parachute. There are an infinite number of possible cases to try, but how about this: Medium sized canopy in a 30 degree dive, some sort of swoop, is at 40 mph (not a fast swoop canopy). Say 5 degrees angle of attack since it is moving fast. It gets hit by the same sudden loss of 5 mph wind. Vector addition this time shows airspeed dropped to 35.7 mph. (Would be exactly 40-5=35 if flying horizontally, but it isn't doing that.) Ok, so the airspeed did of course suddenly drop when the headwind dropped. But then the angle of attack: With the headwind dropped by 5 mph, the relative wind on the canopy is now from 34 degrees down not 30. A big 4 degrees increase in angle of attack. (Vector sum 40@-30 deg, plus 5@ 180 degrees = 35.7 @ -34 deg. Where 0 degrees is horizontally into the wind) The lift from speed is at a 0.79 factor (35.7/40, squared), while the lift from angle of attack is up by a 1.8 factor (9/5). Multiply the two and one has a 1.42 factor. Thus lift has increased 42%. Despite the airspeed decrease, the loss of 5 mph headwind significantly increases the angle of attack since the canopy is in a steeper dive, suddenly increasing the lift even more. What does the canopy do? It will clearly lift away from its existing flight path. Better to say 'lift up' than 'pull up', as the latter may suggest pitching up the canopy. So it wouldn't be like hammering the brakes, because brakes have a big pitching effect on a canopy. Maybe more like a rear riser recovery from a dive... That's adding extra lift and effective angle of attack through changing the airfoil shape, but not causing much pitching up. What happens next isn't exactly clear to me on first thought. How does the flight path continue to change? The canopy's natural stability would tend to slowly pitch it back down to a more normal angle of attack. While at the same time, the extra G loading (and drag on the canopy with increased lift) might cause the jumper beneath the canopy to get swung forward. Hard to tell without a full simulation to tell what exactly would happen, but in any case the canopy would get some extra, unexpected lift while in the dive. 4) If one were flying downwind instead, the effect would be roughly reversed. My numbers gave a 43% lift loss. Extra airspeed suddenly, but because of the steep dive, a big loss in angle of attack. Note that exact lift losses and gains do depend on the assumption of the angle of attack. Which aerodynamically will be somewhere between 0 and 15 degrees, roughly, when flying 'normally' and not collapsing or starting to mush and stall. ===== So -- if I'm correct -- we have a result of a canopy in a decent little dive, losing headwind suddenly as it descends to land. It actually picks up lift and starts to lift up compared to the expected flight path, pulling out in less vertical distance. ===== 5) I hesitate to give answers like the above , as it might make some who made incorrect claims think they were right all along, when they weren't. Say someone said, "When I'm diving into wind and hit wind shear behind the tree line at the the DZ, it seems like I recover faster from my dive. I can't figure out whether that's true or figure out an explanation." That's ok. But if one says, "I think the if I dive into a headwind, I pull out faster, and it is because of ..... [a mess of logic about momentum and the chute catching more air etc that is completely wrong and doesn't explicitly involve wind shear]" ... then it is still wrong. 6) The faster recovery from a dive into wind shear could have other undesired effects: Wow cool, you dove into the wind shear and lifted up from the normal flight path and thus recovered in less distance. .... But you're still at a lower airspeed, and a higher, draggier angle of attack, so the canopy pick up less speed in the rest of the dive. Almost like you started rear risering out of the dive too high and then let up again. So you may end up with less speed for the swoop in the end, messing up your plans. Even if you did somehow start the dive lower to account for the faster expected dive recovery. One isn't likely going to say, "Because there's a strong headwind today, and that increases the chances of significant wind shear, I'll start my swoop 50 ft lower, expecting that to happen." Is one? There's going to be more mental energy expended adjusting the swoop anyway to get the horizontal positioning right, to hit the gates right, if dealing with high and changing winds. 7) Wind effects from shear or gusts clearly change with the direction relative to the canopy. So the result can be vastly different depending on the angle of dive. As we've seen, a headwind loss when in a moderate dive has one effect (increased lift). While if one were already in a horizontal flare, there would be no angle of attack change, just a sudden loss of airspeed and lift. And if one were in the middle of a steep dive, towards 90 degrees, a change in the wind (horizontally) would affect angle of attack without directly affecting airspeed at that moment. If anyone has better insight or calculations... give it a go.

I wonder whether the passenger harness loosens off slightly over time, as harnesses tend to do (depending on the webbing and buckles and tension involved), when the student moves around on the ground. I've never really tested it with the student harnesses. Has someone? I use the Sigma system and admit to snugging the harness up a little on the plane, not aggressively though, even though the student is in a seated position (Caravan with benches) which "takes up" less length of the harness than when standing or arched. Less so for the thin and light; more so for the bigger people where it can be harder to get the leg straps really tight or they are going to sink more into the harness. In those cases I'm less concerned with a bit of an arch problem than the whole sinking into the harness issue on opening. So yeah I sometimes wonder if I'm slightly improving the situation or making it slightly worse. (Maybe 3 chuckers/heavers in 1000 or so tandems.)

Jakee keeps the answer simpler but anway: Sorry, nope. Curiously, some think there's "extra push" if going downwind, while you were suggesting there's and "extra push" of the wind against the canopy because it's going upwind. The canopy doesn't see either. Remember the canopy is always in the same wind. It's not as if it is flying along and suddenly dropped into a headwind or tailwind. This is of course for the basic case where the wind isn't changing over time or altitude. If there's a sudden change, sure the lift can change.

I have mixed thoughts about these things. It reminds me that when Bob Hoover gave up flying the P-51, he said it was because he couldn't handle the rudder loads any more. Even if he thought he was mentally good enough for the game. That was in 1996 so he would have been 74. As Jeff Ethell might say, twin engine aircraft are even trickier. [Ref: Smithsonian Air & Space Magazine, May 2010 article on Bob Hoover, online]

The key early paragraph is this: That is indeed interesting. (So what happened to the other five? It doesn't say.) The article at the end mentions this: So there's more to be heard from all this, just what the acquittals and those 11 guilty pleas really mean. But at first glance it does seem to suggest they were OK to take guns to a federal facility because (a) it's acceptable to use a thread against the law, to prevent oneself being arrested, and (b) those silly little rules, equivalent to "No food on the premises" are unimportant compared to the more compelling argument that one was doing a sit-in. Little different than hippies in the '60s, but with more guns. Obviously further news will clarify the situation more.

I believe Beatnik has one. (The manual, and a Paraplane too.) Check with him, although some of his stuff might be in storage at the moment.

Guess a simple explanation is that as with most flying vehicles, a parachute (with jumper) has speed stability. If it is flying faster than its equilibrium trim speed, it will slow down. And vice versa. How it does that is partially a function of basic aerodynamics of the airfoil (in which we get into pitching moment coefficients, aerodynamic centre etc), and of course for a parachute, a jumper hanging down below, which adds a bunch of pendulum stability. Lift being created up above, weight down below. As for what is dampening the oscillations, its.... well.... just the overall aerodynamics and dynamics of the system. I at least can't explain it better on short notice. How quickly a parachute swings out of a dive will depend on airfoil design, trim angle, line length, speed, etc. If it swings out faster, it is more likely to overshoot (leaving you at less than normal speed for a bit), before settling down to steady flight again. As a jumper one generally only needs to know a little about the various factors. What really matters is getting used to the speed and altitude lost in coming out of a dive, on whatever canopy you fly. (If you want to check out equations galore, and some simulations of dynamic response to gusts etc, look at the paper Ram-Air Parachute Design by JS Lingard 1995, available somewhere on the web free.)

As others are pointing out, you're still having an issue with the "swinging into a headwind" thing. You aren't swinging into any sort of wind as you are already in the same wind no matter which direction you face. Now if you were to talk of different layers of wind, so that there's a change during your flight, of course there will be different effects. If you are descending in still air and suddenly drop below a shear layer into a sudden headwind, or sudden sidewind, certainly all sorts of things can happen to your parachute. There it is more like the feather and bowling ball example you gave where there's no wind, then suddenly they "encounter" a 200 mph wind. Just that airfoil aerodynamics are more complex. (If you are flying your parachute along and DROP INTO a layer with a headwind, you need to do a vector analysis of the change in relative wind. You'll likely get increased lift coefficient from increased airspeed coming at the canopy, but a reduction in angle of attack which is also needed for lift. The net result could be more lift on your canopy ... or less lift ... or even the nose of the canopy folding under. Depends on the details.) But we're supposed to be still working with the basic situation of you flying in a constant wind situation. As for momentum: The jetliner slowing has nothing to do with some notion of momentum, although you might use the term. You could be standing in the jetliner when it is stopped on the ground. A ground tug suddenly pushes the plane backwards out of the gate, and you fall towards the front of the plane. Exact same result, whether you are standing still with zero "momentum" or flying 600mph. So "momentum" doesn't matter. It is just an acceleration of one object affecting another. Ok, I'm finished lunch, so that's enough for now.

Keep working on thinking about being in a 'block of air' that you're in. It doesn't matter if the ground is sliding by at 1, 15, or 100 mph. (In reality of course there may be some turbulence etc) If you were in a balloon in that block of air and closed your eyes, you wouldn't know whether it was a windy day or not. Everything would be calm, with no wind in your face no matter which way you faced. The balloon would be serenely drifting in the air mass at the same speed it is moving. If you now jumped out and opened your parachute, it wouldn't know which way the wind was blowing either. Only when you look at the ground do you notice your block of air is sliding over the ground. What if you jumped from the balloon in a jet stream doing 200 mph? And you open your canopy above a high stratocirrus cloud layer, so you can't even see the ground. If you turned your canopy one way, would it pitch up out of the dive crazy fast because of facing a 200mph headwind? Or super slow in the other direction? No it wouldn't. Your canopy may be doing 170mph groundspeed flying upwind or 230mph groundspeed flying downwind, but the parachute isn't in any way affected by what the ground is doing down below. You'd also owe beer for your first jetstream balloon jump.