Flying in turbulence (long)

[billvon 2,434]

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.

[sunshine 2]

Thanks Bill. Turbulence has always scared me, perhaps now when i'm stuck in it, i'll handle it a bit better.

___________________________________________
meow

I get a Mike hug! I get a Mike hug!

[dterrick 0]

Um, wow, Bill great essay. Yes I did read it all and I may go looking for 'the book'.

At our wee DZ at Gimli, Mb, we have wacky wind conditions. It's flat like a pancake but we're 3 miles off a Great Lake sized lake (L. Winnipeg). As warm summer conditions also brings storms, and they typically circle back on us from over the lake, we also have the treat of WWII sized hangars causing turbulence about 500 ft from our landing area. Oh ya, and the general gust range is about 10 mph from base windspeed ... so 5-15 is common and 15 gusting 25+ grounds almost everybody with a conscience.

Thankfully I haven't seen anyone actually collapse a canopy at low altitude but I know I've flown through distrubing burbles as low as about 100-150 ft and it makes for some excitement. It's too bad there's no good way to practise being in such conditions and surviving them -except not to be in them to begin with.

Book learnin is great but it sure is no match for experience in these types of conditions. Yes I read lots but when my mentors decide to sit out due to conditions.... I take the opportunity to ask for a story and I learn even more! Thanks for telling yours.


Keep it up

Dave

Life is very short and there's no time for fussing and fighting my friend (Lennon/McCartney)

[robskydiv 0]

Thankyou for such an in-depth description and explanation of turbulence and how it affects our canopies. Your article let me know that so far I have reacted correctly to it and more importantly what to do if the canopy should collapse.

***"A more informed canopy pilot, makes for a better canopy pilot."

[Push 0]

Great reading. Do you mind if I print it and show it around my DZ?

-- Toggle Whippin' Yahoo
Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you.

[markbaur 0]

Quote

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.

I'm not sure I understand this. Both canopies should turn the same amount, since they are weathervaning into the same relative wind. But the angular difference between the pre-gust flight path and the relative wind created by the gust is less for the faster canopy. Wouldn't that mean a less violent weathervane for the faster canopy?

Quote

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.

Is this a common occurence in weather we jump in? It seems like a vertical gust of 30fps (18 kts) would be hard on the jump plane, too. I was wondering also about the size of your micro-burst. Did you choose 25 feet (radius? diameter?) for the sake of your example, or is this the generally accepted size?

Thanks for an excellent essay. The best explanation of turbulence effects I've read.

Mark

[WeakMindedFool 0]

I'm officially impressed and would like to come learn more stuff from you! Thank you for the info!

Faith in a holy cause is to a considerable extent a substitute for lost faith in ourselves.
-Eric Hoffer -
Check out these Videos

[billvon 2,434]

> Both canopies should turn the same amount, since they are
>weathervaning into the same relative wind.

Well, the faster you fly the less change in relative wind direction you see for a given gust. However, that doesn't neccessarily mean that the smaller canopy will react less violently - a Stiletto 120 will dive harder in a sudden 45 degree turn than a PD190 will after even a sudden 90 degree turn. Whether that ends up being a bigger problem depends on how you handle the sudden turn; if you can act fast and there are no other problems with turbulence, you might be able to pull it off in both.

>Is this a common occurence in weather we jump in? It seems like a
>vertical gust of 30fps (18 kts) would be hard on the jump plane, too.

Yep. Fortunately, they're pretty rare, and a well-behaved one of the type described is even more rare. I think most serious turbulence that parachutes see are a combination of the three things I listed.

An otter wouldn't have too much trouble with the downdraft during climb (they can climb at 20-30fps) but the main problem with microbursts for aircraft is that they can fool you, especially during landing:

1. You approach it, and the wind spilling off it is seen as a headwind. This increases airspeed, and the plane "balloons" or climbs a bit as it enters the headwind. A pilot might reduce power to compensate, since he wants to remain on his glidepath.

2. The plane hits the downdraft. He's at low power levels now and it might take a second for him to react. The plane drops.

3. The plane leaves the downdraft, and sees the tailwind. The plane sees this as a loss of airspeed. Now the plane is low _and_ slow, the worst place to be for a plane on approach. This has caused a lot of crashes.

[billvon 2,434]

>Do you mind if I print it and show it around my DZ?

No prob.

[poohbeer 0]

bill,

I'm a complete idiot at skydiving (hoping for my first jump tomoroow ) but I was reading the other topic ion turbulence asswell and there someone gave a link to http://www.performancedesigns.com/faq.htm#4.
There it states:
"Contrary to what some people have been told, flying in brakes does not necessarily help keep the canopy pressurized. Aerodynamically, the canopy is actually more susceptible to turbulence in brakes. Years ago, flying in half brakes seemed to make some older ram-air canopy designs more stable in turbulence, though they were obviously very different from modern canopies. Flying in brakes is definitely not the best technique to use with the canopies we're flying today, although a lot of skydivers are still told to use this technique.".

Isn't that from (I take) thé experts saying the opposite from what you say? Or do I miss something?

*hats off* anyways to you.. you do come over like someone to stop for and listen to!

singing off now.. go to get going for my theoretical AFF woohoooo!!!

------- SIGNATURE BELOW -------
Complete newbie at skydiving, so be critical about what I say!!
"The only thing necessary for the triumph of evil is for good men to do nothing."

[diverdriver 5]

Bill, that's the most excellent post I've seen on canopy flight in turbulence. Well done. I think it gets across the point that going into breaks should be done AS the turbulent event starts near the ground. You don't want to get to the turbulent event in 1/2 breaks because your momentum will be less especially on the smaller/faster canopies.

I just hope people take the time to read the whole thing. I fear that some only read Talk Back and that's it. Again, excellent post Bill.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[diverdriver 5]

Actually you need to read the whole thing. Don't quote just one part and think that it supports a certain view. Keep it all in context. This part of that same article supports what Bill says and completes the picture.

Quote

Pumping doesn't re-inflate the canopy, although holding both toggles down for a moment can help the end cells re-inflate more quickly if you are at a high enough altitude. If you are close to the ground, your main priorities should be keeping the canopy flying straight, flaring as well as you can, and making a PLF if necessary.

note: emphasis is mine

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[markbaur 0]

Bill:

I guess I'm still wondering about how realistic your micro-burst example is. I thought they'd be much larger. What you've described sounds almost like an upside-down dust devil, without the rotation.

Mark

[bwilling 0]

Great explanation Bill!

I saw someone fly thru really bad turbulence one day, and it was one of the scariest thing that I've seen skydiving... the jumper ended up with a normal standup landing, but only because he didn't panic, and he continued to fly the canopy every step of the way, using the techniques you described in this article! But man, was it ugly! He actually got a standing ovation for his landing!

Thanks for helping to make skydiving a safer sport for all of us!

"If all you ever do is all you ever did, then all you'll ever get is all you ever got."

[diverdriver 5]

Quote

Bill:

I guess I'm still wondering about how realistic your micro-burst example is. I thought they'd be much larger. What you've described sounds almost like an upside-down dust devil, without the rotation.

Mark

I know I'm not Bill but I'll try to answer anyway. Let's say you have air flowing over a large hanger. It may be of such size and form that it can act like Bill's "microburst" example. The air flows over the top of the hanger and then down the other side and then "splashing out". You get the flow seperation and some rotors on either side.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[billvon 2,434]

>I guess I'm still wondering about how realistic your micro-burst
>example is.

It's not that realistic as stated. A 'true' microburst of the type that brings down MD-80's is massive. But the other examples (like a sudden 90 degree 20 knot change in wind direction) aren't that realistic either. Turbulence is pretty chaotic; you get winds coming from all over. I tried to 'isolate' three examples so I could talk about them without saying "but if the wind's coming from a little above, unless there's a downdraft too . . ."

There are basically three cases you have to worry about. Turbulent tailwinds that can cause you to lose flying speed. Side winds that can cause a sudden turn, or even a partial collapse. Downdrafts that can cause your canopy to collapse completely, or at least to descend more rapidly. (Downdrafts also have that 'splash' problem near the ground.) Most dangerous turbulence you feel will probably be a combination of these. Downdrafts can be caused by many things, including dust devils on a partly cloudy day - if all that air is going up, it has to come down somewhere. Sometimes it comes down in a small area, especially if the sun is heating some areas and not others.

[riddler 0]

Quote

wondering about how realistic your micro-burst example is.

I can give you an example of one:

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=410515;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;;page=unread#unread

Winds were squirrely all day, and one unfortunate person got caught in a downdraft, while an instructor landed safely close by.

Great post, Bill. You explain things very clearly. It's my belief that airlocks help in more than just "minor" ways with collapse (but not line slack), but that's definitely a non-expert non-pilot newbie opinion. I'll let you know after a few thousand jumps

[Meathorse 0]

Wow, nice Bill! Thanks for taking the time!

There's one thing I'm having trouble grasping, though. When the larger canopy has a tailwind it's suggested to use the brakes (anywhere from 1/4 to full). Since the lack of airspeed is the problem in the first place how is this helping?

[billvon 2,434]

>Since the lack of airspeed is the problem in the first place how is this
>helping?

Because if your airspeed drops, the canopy will dive at the ground to recover its airspeed. Going to 1/4 brakes can help keep it from diving as hard and potentially pounding you into the ground. If you're high enough, it doesn't matter as much - the canopy will recover and level out on its own eventually.

[JJohnson 0]

You have jumped a LP, so you know the kind of winds I'm talking about. (Not that LP has the worst winds, but they can be fierce, inconsistent, gusty and from multiple directions)

If landing into the wind, like a nice calm gusty 20 mph LP day....and say about 20 feet off the deck, while riding in about 1/4 brakes...your wind that you are landing into decides to quit on you?

My perception is that the canopy is going to surge forward (less resistance to it's forward progress) and drop like rock at first until it gets it's speed back.

In this case how would you fly your canopy...being only 20 feet or so up? Under these exact conditions I got slammed last year. As soon as the wind died I went to a full flare trying to slow the initial drop. But it felt like there was nothing there.

This left me with the thought that coming down on front risers, with so extra speed would have at least left me with some flare. It was like hitting a vacuum....

Your take on it??

JJ

"Call me Darth Balls"

[billvon 2,434]

>like a nice calm gusty 20 mph LP day . . .

"nice calm gusty?" Well, OK . . .

>and say about 20 feet off the deck, while riding in about 1/4 brakes...

If it's nice and calm, but a little gusty (with no gusts affecting you at the moment) why would you be in 1/4 brakes?

But if you were, and that wind quits, about the only thing you can do is bury the toggles. Flying at normal speed, or with a little tension on the toggles, will give you more speed with which to flare.

>This left me with the thought that coming down on front risers . .

In the situation you mentioned it might help. If there's any downdrafts, that could leave you at front-riser descent speeds with a collapsed canopy. You'd have to drop the front risers and go to 1/2 brakes instantly, and at those speeds you don't have a lot of time to do that.

And if it's a severe and sudden tailwind, then nothing you do is going to help. In those cases, being in 1/4 brakes will mean you impact with less forward speed since you had less to start with. It might make the difference between two broken legs and a broken neck.

It's all a game of odds. In most cases of no to mild turbulence, full flight works pretty well and gives you the most options. In severe turbulence, 1/4 to 1/2 brakes can help keep a collapsing canopy open, can help prevent a dive at the ground, and may give you more control options. (Severe meaning turbulence where you fear for your safety, and are seeing your canopy start to collapse/stall.)

[JJohnson 0]

Thanks.

And YES dammit...A nice NORMAL calm gusty Lost Prairie day....

JJ

"Call me Darth Balls"

[sducoach 0]

Chris,
?????
Relative wind and effective wind equal performance?Turbulence is a result of fluid dynamics?
Does an airfoil have a positive AOA when inverted?
Does gravity/centrifugal force maintain tension on the lines?

Wind shear (a.k.a. microburst) equals decrease in performance. Response/prevention.........POWER.
(can't find the power levers on my Vengeance)

AIM 7-1-31-d
The microburst downdraft is typically less than one mile in diameter as it descends from the cloud base to about 1,000-3,000 feet above the ground. In the transition zone near the ground, the downdraft changes to a horizontal outflow that can extend to approximately 2 1/2 miles in diameter.

Unless you have a TDWR at your DZ.............

James 4:8

[diverdriver 5]

Quote

Chris,
?????
Relative wind and effective wind equal performance?Turbulence is a result of fluid dynamics?
Does an airfoil have a positive AOA when inverted?
Does gravity/centrifugal force maintain tension on the lines?

Wind shear (a.k.a. microburst) equals decrease in performance. Response/prevention.........POWER.
(can't find the power levers on my Vengeance)

AIM 7-1-31-d
The microburst downdraft is typically less than one mile in diameter as it descends from the cloud base to about 1,000-3,000 feet above the ground. In the transition zone near the ground, the downdraft changes to a horizontal outflow that can extend to approximately 2 1/2 miles in diameter.

Unless you have a TDWR at your DZ.............

JE, I think you are reading too much into this example. No one would actually be jumping during a real Microburst condition. At least I hope they wouldn't. We're talking about downdrafts that hit the ground and spread out (splash out). This can happen by different causes like Bill said.

And there is no such thing as centrifugal force. It is a myth. It is only used to describe what we feel but not a true force. Centripital force is the true force.

Now what was your question again?

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[CRWBUDDHA 0]

I would recomend you contact Para Flite and ask for a copy of their manual on Canopy Flight. It's over 20 years old and to date I have not found a better tutorial on basic technique which may very well fit the circumstances you are concerned about, and a lot more too.
One thing for sure, if you posess a working knowledge of the techniques in that manual, you will survive to jump another day and twenty years from now, you will be able to better judge whether the wealth of information in the community has any real value.
I donot believe anyone is intentially out to hurt you however, instant gratification in this sport has shown that it doesn't work as well as tried and tested methods that have been duplicated by thousands for hundreds of thousands of jumps over 40 years of recording.
Cheers and remember if what you are told seems unclear, it may very well be. The manufacturers have more information available and that information can be fully substantiated.
Check this out, you'll be glad you did.

Buddha

1-609-663-1275 Para Flite......New Jersey Home Offices