Canopy control by definition is not swooping

[diablopilot 2]

I think it's luck of the draw. The same turbulence that affects the straght in, could hit just intime to fold your canopy up just as you are bottoming out your recovery arc.

I think when it's time to stand down, it's time to stand down.

"Swoopist"? Hmmm.....I guess I qualify.

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You're not as good as you think you are. Seriously.

[kimemerson 7]

There are definitely times when no one should go up regardless of skill level. Agreed. But there are times when only the highly skilled should consider it and indeed, they prove it load after load. I have mentioned to beginners, "When you have a question (about the wind) you have your answer." In other words, if you have to ask, you can't afford it. And I refer not exclusively to cross-braced swoopistos as I've seen it happen back when Sabres were considered the highest performing canopy available. While so much succeses in turbulent winds is attributable to the canopy construction, solid canopy control and skill level can puill more performance out of 'standard' cell canopy than a lack of skill will ever do under a cross-braced canopy.

[billvon 2,436]

>but has anyone mentioned that a good hook and swoop is sometimes
> the only thing that will get you through winds on landing?

No, because it's not true.

>That a straight-in approach sometimes won't cut it?

If a jumper cannot do a straight-in approach on a given canopy, then they should go back up a size and practice on the larger canopy until they master that skill.

[kimemerson 7]

We're talking winds here. And it is absolutely true that SOMETIMES a hook, thereby generating speed and followed by (maybe) a swoop, will indeed slice through turbulence when others doing standard straight in approaches are much more vulnerable to those same winds. It's the speed more than the hook. But it is the hook that gets you the speed. A straight in approach is not as effective under turbulent conditions. Granted, if a jumper cannot do a straight in approach... But we're not talking doing straight in approaches in good conditions. We're not talking about one's overall ability to do a straight in approach. We're talking about the nature of the approach under certain conditions. ANYONE doing a straight in approach in turbulent winds is far more vulnerable to unfavorable wind conditions than that same person would be with enough speed to slice through the winds. In this instance I'm talking about the type of approach - speed vs sloth. No straight in approach will generate speed in and of itself. Some input is required to get speed beyond that which the canopy creates in full flight. And speed deals with turbulence when slow will not. So, I repeat, SOMETIMES a good hook and swoop IS the only thing that will get you through winds on landing. Seen it a million times. But I only needed to see it the first several thousand times over almost twenty years to convince me. But you know, I haven't been jumping very long. I'm a newbie, so what do I know? Could be wrong. And I can accept that.

[billvon 2,436]

>SOMETIMES a hook, thereby generating speed and followed by
>(maybe) a swoop, will indeed slice through turbulence . . .

Sorry, that has no basis in fact. Increasing your speed through a turbulent area increases the turbulence you see, and the term "slicing through turbulence" has no meaning. That reasoning ("swooping makes you safer in turbulence") is often used because a) it sounds good and b) it justifies swooping.

[kimemerson 7]

"Slicing through turbulence... " oops, I shouldn't have used such colloquial language here. I just don't have the technical language skills required. However, I stand by the gist of my statement that speed will penetrate turbulence when slow will not. And no, I cannot prove it by providing "basis in fact' the way a scientist might. I don't know anything about an "increase of speed through a turbulent area increasing the turbulence we see." Especially because I don't see any turbulence, I see it's effects. And the effects on a fast canopy are not as troublesome as they are on a slow canopy. I also don't know a whit about a) or b) because I have never relied on either to make my point. I just spent a lot of time taking notice and actually experiencing exactly what I'm talking about. At the Ranch it's almost a daily thing. But, for our esteemed readers, please offer some basis in fact for the opposite arguement. I'm just talking about what I've observed and experienced over 18 years, many of which were full time. year round. Maybe someone - anyone? - could offer some technical input, some diagrams and charts, facts, figures, testimonials. Anything but this paying attention and taking notice shit.

[greybeard 0]

You guys are 'off topic' again. I'm celebrating the art of flying backwards for 1000 yards, playing with the wind and enjoying every controlled and demented pleasure of sinking and sashaying, and driving, and flying to the max in the most challenging conditions. Slip your canopy like a real wing. Stall and dive, rotate out of a stall. Climb a bit .

[greybeard 0]

And something called 'modulating the brakes', so you back up without losing relative altitude. I've seen it close up while being 'top-docked', but it still boggles the mind.

[billvon 2,436]

>But, for our esteemed readers, please offer some basis in fact for the opposite arguement.

Here's an article I wrote for a dutch skydiving magazine. It's long but it answers your question:
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Over the years I've seen a lot of skydiving myths start up. Pumping the brakes makes you go farther, putting all the weight in the plane forward helps it climb, wait until the group before you makes a 45 degree angle with the horizon and you'll have good exit separation. Some of these are good myths - the CG-forward doesn't neccessarily make the plane climb faster but can help avoid a too-far-aft CG. Some are neutral, like the pumping the brakes thing. It doesn't do anything, but so what? Some actually hurt the cause of safety - the 45 degree angle thing might cause a group to get out too soon in strong-upper conditions and potentially collide with the previous group, and a jumper might ignore advice to "leave more time" because they trusted in a myth that didn't work.

The same thing seems to be happening with turbulence. I've heard all sorts of explanations about how going fast makes turbulence less dangerous - one person even suggested using front risers to increase speed, allowing a canopy to blast through turbulence unscathed! Another suggested that ram-airs are somehow different now, so what worked 10 years ago doesn't work any more. This is getting well into myth status.

Why do myths start? I think they start because people desire a simple and straightforward plan to deal with problems. In skydiving there are a lot of these - emergency procedures are very simple and straightforward in most cases, and that's a good thing, because the lack of ambiguity saves a lot of lives. If you have a lineover you know exactly what to do. In some cases it's not so clear (PC in tow) but either choice (cutaway first or not) works more often than not, so it's not a big deal.

Other issues are not so clear-cut. Exit separation is complex, for example. It's possible to do the math and know exactly how far you'll be from someone else, but few jumpers do it. Fortunately the simple rule "wait longer if headwinds on jump run are strong" works well. So why do things like the "45 degree" rule seem to propagate? I think it's because it makes a sort of intuitive sense, anyone can do it, and it seems to 'solve' a difficult problem. The problem is that we are land animals, and while our intuitions apply well to things like jumping out of a tree, throwing a rock or chasing a dog, they don't apply well to flying or jumping out of airplanes. We just aren't set up to have good intuitions about aerodynamics or ballistics in moving frames of reference.

So on to turbulence.

First off, what is turbulence? For a detailed explanation I highly recommend Dennis Pagen's book "understanding the sky." It was written for hangglider pilots, and there is no better book I've found for understanding micrometeorology, or the winds and weather of local areas.

In general, turbulence is air moving relative to other air. Many people visualize turbulence as "pockets" of air that are somehow different, but it's all just moving air. If the air moves and changes direction and speed slowly, we call that normal wind. If it changes direction/speed more quickly we call that gusty. If it changes even more quickly than that we call it turbulence. If you fly through those changes and they happen slowly, you feel light turbulence. If you fly through them more quickly, you feel serious turbulence.

The most basic idea behind turbulence is the idea of wind shear. All turbulence is essentially wind shear, although the term is usually used to describe a large change in windspeed/direction over a short distance. A body moving through the air sees the wind of its passage (the relative wind.) If that body moves into an area that has a different wind, it sees that relative wind change. If it is relying on that relative wind to keep itself in the air, as parachutes and airplanes do, then the wing must adjust to the change in relative wind. If the wind change is dramatic the adjustment must also be dramatic. This is how we feel turbulence, through our wing's adjustment to the new relative wind condition. That new condition can be from any direction. It can come from below, from above, from the sides, even from in front or behind, which is seen as a transient increase or decrease in airspeed.

So how do we fly safely through turbulence? Let's start with a hypothetical light airplane. Like most normal category airplanes, this one has a +6.6G -3.3G design limit for its wings; the structure of the wings can take that much load at max gross weight, but beyond that, they may collapse. It can cruise at 160kts. It stalls at 50kts, and it's structural cruise, or turbulence penetration speed, is 100 kts at this weight. The plane weighs 2000 lbs.

Let's say our pilot is cruising along at 160kts. The wing is generating 2000 lbs of lift, as it must to keep the plane in stabilized flight. (Note to purists - yes, I'm neglecting tailplane and fuselage lift.) A wing can generate more lift by going faster or by increasing its angle of attack. Since he's going pretty fast, the wing's angle of attack is pretty low. If he slows down, he has to increase his angle of attack to compensate, so the wing still generates 2000 lbs. If he slows down below about 50kts, the angle of attack the wing needs to fly is so dramatic that the air no longer "sticks" to the wing, and the wing stalls.

But for now he's just cruising along at 160. He starts to feel turbulence. First he flies through an area where the wind suddenly comes from the left at 20 kts. The plane, since it's stable in yaw, 'weathervanes' into the new wind, and the plane continues along happily, but now heading slighlty to the left of where it was a moment ago.

Now he flies through an area where the wind is coming from _behind_ him at 20kts. He perceives this as a drop in airspeed from 160 to 140kts, and the plane starts to descend a bit. He might adjust power or pitch to compensate. He gets back to 160kts.

Now he flies through an area where the wind comes from beneath him at 20kts. He perceives this as a change in the relative wind from dead ahead to a wind that comes from slightly beneath him at 7 degrees. The wing doesn't know this; it just sees a change in angle of attack. 7 degrees is a big AOA change, so the wing starts generating a tremendous amount of lift - say 6000 lbs. The pilot feels 3 G's as the plane starts climbing. He quickly uses the yoke to level off.

At this point he's going to slow down. Why? Two reasons. First, because if he hits a strong enough upward gust, the AOA will change even more, the wing may generate more than 6.6 G's (13200 lbs) of lift, and the wings may fail. Similarly, if he hits a strong enough downward gust, the wing may generate more than 3.3G's of downward lift, and may likewise fail.

Secondly, wind shears are rarely 100% discontinuous. Often, the wind will change over the course of some distance, say 100 yards. If he traverses that 100 yards quickly, it will tend to hit the plane all at once. If he traverses it more slowly, the plane will see the change in relative wind more slowly, thus giving the plane (and the pilot) more time to get the nose down, add power etc.

Anyway, he slows to 100 kts. At this speed, the worst-case gust will make the wing go to 15 degrees AOA and cause a load of 6 G's or so. If it gets stronger, the wing will stall. Stalling isn't the best thing in the world but it's better than having the wings come off.

Now he's coming in to land. He's flying at 70kts. It's still turbulent. A gust from the side will cause the plane to weathervane into the wind, a bad thing when you're landing - so he's quick on the rudders to compensate. A gust from below will cause him to generate more lift and climb - so he's fast with the yoke and throttle to get the nose down to compensate. A 20kt gust from behind causes his airspeed to fall to 50kts. His stall warning horn goes off, which worries him, so he increases his speed to 80kts. That way, if that 20kt gust hits again, he will only drop to 60kts, and he won't stall. Stalling isn't _too_ big a deal at 1000 feet in the pattern (if he recovers quickly) but is a very big deal at 100 feet so he doesn't want to risk it. Note at this point he is no longer worried about his wings collapsing - he's worried about stalling.

That's an airplane. On to parachutes:

A parachute has almost infinite (for our purposes) positive load limits. There's no way you're going to tear the parachute to shreds by starting a hook turn and burying the toggles. They are built to withstand even hard (10G or so) openings, and you still have all that strength available when you're flying it. However, being a flexible wing, it has a zero negative load limit. At the slightest hint of negative lift (i.e. if the angle of attack ever goes negative) the lines will go slack and the parachute will collapse. It has no effective way to prevent this.

A parachute is relatively stable in yaw - it just turns into the relative wind. That's good since you have no rudders to control its yaw. It's very stable in pitch, which for a parachute also means stable in airspeed - if you let go of the toggles (or if airspeed changes through turbulence) it very rapidly returns to its trim airspeed and pitch.

What makes it structurally stable? The primary thing that keeps a parachute stable is the constant tension between the jumper's weight and the lift/drag generated by the canopy. A downward force on the canopy is resisted by the lift in that area of the canopy, an upward force is resisted by the tensile strength of the line (hundreds or thousands of pounds.) Cell pressure is a secondary effect; no canopy will remain stable with a lot of broken lines. Note that there are plenty of parachutes (rounds, the Paradactyl, the PC) that don't have _any_ cell pressure, since they have no cells, and they still inflate and fly. Indeed, even something like an air mattress, something that can be pressurized far more than any canopy, is no match for even a 20kt wind - but a round canopy in the same wind will inflate and remain quite stable. It is tempting to think of a pressurized canopy as a solid wing, resistant to turbulence through its rigidity, but that's just not reality. What keeps it above your head in turbulence is primarily lift, drag and the tension on the lines, and if that tension goes away, it will collapse no matter what the pressure in the canopy.

When we think of canopy instability in turbulence, we're really talking about several different things. One is canopy collapse. This is the worst result, since the wing stops flying, distorts, and must redeploy before it can generate lift again. Another is a canopy stall. In this you lose lift, but the canopy remains above your head and fully deployed, thus reducing recovery times. A third is canopy instability, where the canopy seems to want to dart in every direction. Oddly this is often due to the canopy's _stability_ - the turns and dips you feel is the parachute wanting to face into the wind and resume its previous airspeed and attitude.

So let's consider two people trying to land their canopies at a DZ. One has a large 7-cell, the other has a small 9-cell. The small canopy is twice as fast as the large canopy at trim speed - 30kts vs 15kts. There is an infinite number of types of turbulence we can consider, so let's concentrate on three: a tailwind gust, a side gust, and a downdraft.

If both people are near the ground and get hit by a very sudden 10kt tailwind, the larger canopy will immediately be near stall, with an airspeed of 5kts. The jumper could respond by burying both toggles, which will give him a little bit of flare - but probably not too much. If he's high enough the canopy will recover before impact. If he's really low (10 feet) it will just drop him on his butt. At 30 feet he might be seriously injured. The guy on the faster canopy will be much better off IF he responds well. His canopy will lose some airspeed and drop. If he adds a little less brake than is needed to arrest his descent, the canopy will not dive too hard and will recover. If this happens below 50 feet he'll have to do a braked approach, which he will probably survive uninjured if he's done it before. Since his canopy had more speed to begin with, the gust affects him less.

A side gust is similar, although the larger canopy now has something of an advantage. Both canopies will weathervane into the wind. The larger canopy will turn more degrees but the smaller canopy will react more violently. The jumper has to be _very_ quick to turn the sudden swerve into either a flat turn or a flare turn. The larger canopy will turn more but not dive very much, giving the jumper more time to deal with the problem.

It may be, of course, that the gust is so strong or so sudden that the canopies cannot weathervane quickly enough to keep the relative wind flowing over the tops of their noses, and will instead suffer partial collapses from the unexpected side loads. If that happens near the ground, the jumper going slower will make out better, due to simple physics. He will hit at a slower speed.

The final turbulence example takes some explaining. There's a 30fps downdraft that both canopies fly through near the ground. When downdrafts hit the ground, they don't just disappear - they sort of "splash out" and create winds flowing away from the downdraft. This low level tail/headwind is part of what makes microbursts so dangerous to pilots. Around the shaft of the downdraft is a 25 foot area where the downdraft transitions from zero to 30fps.

The fast canopy hits it and is through the transition area in less than a second. Even in freefall you can't pick up more than 20 feet per second every second, so even if his canopy dives hard, by the time he hits the center of the downdraft the wind is coming from _above_ him by about 5fps. His canopy collapses; there's no way around that. His momentum carries him forward, and he continues to drop. Once he exits the downdraft he has to get his canopy open again and get 10-20 kts of airspeed to let him land safely. Unfortunately, on the far side of the downdraft, he's got that wind 'splash' that he sees as a tailwind. His best chance of survival will be to hold 1/4 to 1/2 brakes - that's the brake position that canopies open best in, which is why brakes are stowed there for opening. If it does open, that's also the best compromise between a stall (full brakes) and a sudden dive for the ground (no brakes.)

The slow canopy hits the same downdraft and takes two seconds to pass through the transition area. In that two seconds you could pick up 40fps if the canopy dove hard. You only need to pick up 30fps to 'match' the speed of the downdraft, so you have a good chance of keeping a canopy above your head. Once in the downdraft you may still have an inflated canopy, but you're still not that happy, because you're descending at 35fps. Once you start leaving the downdraft you are not only descending at 35fps but you now have a tailwind, which could potentially cause a stall. 1/4 to 1/2 brakes will help keep the canopy in the air. You're near stall now but at least you're still flying; with some luck and a PLF you may pull it off.

These are just a few cases. You can make up a lot of them. Generally, if your concern is survival after getting hit by a downdraft, canopy size is your friend. A larger canopy will do a better job of saving you if you have to land without your normal flare, or in an unusual state (stalled.) If your concern is survival after a stall due to a sudden tailwind, then speed is your friend. A smaller canopy will carry more speed to prevent a stall. In the downdraft example, had the smaller canopy made it through the core without collapsing, it would have had more airspeed to work with. A smaller canopy, however, is a lot more dangerous if you stall it at 20 feet. They stall more abruptly, and take much longer to recover, than a larger parachute.

The advice I usually give to people is to let their canopy fly - canopies are generally most stable at full flight, since the loadings on their lines are close to design specs at full flight, and it's that loading that helps keep them stable. The extra speed may help them if they get a tailwind that threatens to stall their canopies. I also tell people to make very smooth and gradual corrections, and don't be afraid to let the wind push you around a bit. Those little twists left and right are not your canopy screwing up, it is your canopy doing its best to stay headed into the wind. As long as you keep yourself on an approximate heading (into the wind for landing, for example) you can deal with a 5 degree turn without too much worry.

If they start feeling really bad turbulence then I usually suggest going to a little (1/4 or so) brakes. This slows down their canopies and thus gives the canopy more time to adjust to the new wind direction. If they have to steer to remain into the wind, having some tension on the brakes also helps the canopy make smooth corrections. Also, if it gets really bad and the canopy is beginning to collapse, 1/4 to 1/2 brakes is the best position to get a rapid reinflation.

And, of course, if they ever feel a sudden drop, IMMEDIATELY go to 1/4 to 1/2 brakes to get reinflation and/or lift. What they feel at that point will tell you a lot. If they feel little to no resistance in their brake lines, their canopy may well not be flying any more. If they feel normal resistance, they may have survived entry into a downdraft - and have a good shot at flying out of it. They can go back to full flight, but be prepared for a hairier than normal landing.

Front risers in _any_ sort of turbulence is a really bad idea. Using front risers distorts the canopy and unloads some lines (C's and some D's.) Since that play of line tension vs lift is what gives you stability in the first place, avoid front and rear riser manuevers in turbulence.

The effect of things like airlocks is minor, but it is there. Samurais and the like are slightly more resistant to turbulence than their equivalent elliptical nine-cells, but pilot skill is much more important - both in avoiding turbulence and handling it once you're in it. Aspect ratio seems to matter, too. 7 cell canopies are slightly more resistant to turbulence than 9 cells of equal loading.

So if anyone's still reading by this point, there are a lot of considerations for flying safely in turbulence. Despite some people's beliefs, ram-airs still fly the same as they did 10 years ago. 1/4 to 1/2 brakes still work under some conditions, and may save your life if you _do_ find yourself with a collapsing canopy above your head. Full flight, or a slight amount of brakes, works in most moderate turbulence. Front riser is almost never a good idea. But the main skills you need to fly in turbulence are just basic canopy flying skills - make small smooth corrections, let the canopy weathervane and bop around to adjust to new winds, and be ready to flare, flat turn, flare turn or PLF if something unexpected happens.

[ozzy13 0]

If I heard this once I have heard it a 1000 times

Never give the gates up and always trust your rears!

[brenthutch 388]

"It's like saying "I bench press 150lbs, and I think I'm going to try 155."

What a girlie man!