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Jeff Goin

 
 

Understanding Paraglider Collapses

Dec 15, 2006 | Chapter 4, 19 | Weight Shift

Related articles: fury of a dust devil video, Active Piloting, Attending a Maneuvers Clinic,
  Mid-Day Collapse Accident with video and diagram, and Reserve Parachutes.

It's one of the most-often cited fears of inquiring minds. "But can't that paraglider wing collapse?" they ask. Of course it can. But it turns out that the dreaded collapse has more bark than bite and most are easily avoidable. Even when it happens it's rarely more than a surprising sight. There are, of course, exceptions.

Gaining a mastery of the wing can dramatically reduce the chances of a collapse in the first place. But that mastery comes through sound training and experience. Not just experience boating around in smooth air, but exposing yourself to lower levels of turbulence and maneuvering. Don't think you can read about this here, in the Bible, or anywhere else and just go do it, either. Steep maneuvering in a paraglider is risky beyond its appearances, especially for those who tend to jump ahead of their capabilities.

Some good news: the wing is built to open and fly. Quickly. So even if part of it does fold down, once it's reloaded, normal lift returns pronto. Higher performance wings are notorious for getting their long, skinny tips caught in the lines (a cravat) and can be more challenging to recover.

What's surprising is how easily most wings can be controlled with up to half of their area folded up. In most cases, if the pilot minimizes brake pull, lets the remaining wing accelerate briefly and then steer, it's quite flyable, even landable like that.

Two rules should followed by new pilots:

  • Rule 1. Never have NO brake pressure, always have about pressure 2 or what many instructors call quarter brakes (about the weight of your arms). The wing is far more collapse resistant with some brake pressure but, beyond about pressure 3, the benefit goes away since you lose brake authority by being too slow.
  • Rule 2. if you feel something unusual, do the default action: reduce brakes, reduce power, then steer. Risk and reward has the refrain "Hands Up, Power Off" which means "Reduce Brakes, Reduce Power".

You're cruising along when bumps begin—how much brakes to pull? First, briefly go hands nearly full up then go pressure 2. If something unusual happens, reduce brakes a bit reduce power a bit, then steer. Remember, the vast majority of complications from collapses are not the fold itself, but rather the pilot's abrupt and excessive reaction to it.

See also the Bump Scale for a standard reference to turbulence strength.

Active Piloting

Here is a complete article on Active Piloting.

There's more than meets the eye but the skill is primal for those who want to really be able to master their craft. It's much more than riding the brakes and must be learned over time.

I've seen numerous accidents and collapses that were aggravated by the pilot's attempt at using brakes when the best action would have been simply reducing brake pressure to about pressure 2 (see brake pressures) and concentrating on direction.

You can do a lot to avoid collapses in the first place. Staying out of turbulence is the best prevention. Keeping the wing from going forward too much is the next best thing. The further forward your wing goes, the more likely a collapse is. 

Free flyers in strong thermal conditions get collapses a lot, relatively speaking, so avoid such conditions. A good start is to only fly in the first 3 and last 3 hours of the day. Don't fly in rotors—downwind of obstructions and remember that stronger wind means stronger mechanical turbulence.

Don't fly too slow. Speed is life especially once you're already in turbulence. If you're getting bounced around a lot hold pressure 2, as mentioned above, but reduce it if you feel the airflow on your face decrease or the wing goes back. One you give up too much speed, those brakes are nearly worthless. Except for heavily reflexed wings, have the trimmers set to slow and do not use the speedbar. Flying faster can dramatically aggravate a fold since the extra airspeed will tend to pull it under farther.

As an aside, cruising along in turbulence under power leaves you more susceptible to going parachutal—a rarity in free flight but more common in motoring, and another reason to remember "reduce brakes, reduce power, then steer" if you feel something unusual.

You are most susceptible to collapses when 1) lightly loaded, 2) accelerated, 3) hands up, 4) descending power off.

High Performance vs Reflex

High performance wings (higher than DHV 1-2 or equivalent), especially when lightly loaded, will behave the worst during large folds—they are more susceptible and less likely to recover cleanly. Their higher certification, in fact, comes significantly from how long they take to recover from various upsets. These long, skinny wings are favored by cross-country pilots for their great glide at the expense of higher risk. Don't think that skill alone will make them safe—it will make a difference but some awesome pilots have died in the thermic cauldron called "big-air." Small folds, less than 50%, seem to affect higher performance wings less than lower performance wings.

Having said the above, realize that any wing, when confronted with a sufficiently strong vertical gust will fold. A heavily loaded wing will be the most resistant but it's recovery will be sportier. A highly skilled pilot flying a small, moderate performance wing actively is quite resistant but only with appropriate active piloting.

A reflex wing, trimmed so the reflex is engaged (trimmed fast) with speedbar applied will have the greatest resistance to collapse. I have experience with these unusual wings since I found their claims a bit hard to swallow. So I did some experimentation and back-to-back comparison with existing wings. It was enlightening. Eventually, that experience will be included in another article. Note that if one does collapse at such high speed, all bets are off.


Many instructors prefer calling them wing folds or asymmetric tip folds or asymmetric wing folds.

Turbulence means a downward vertical gust that causes all or part of the leading edge to fold under. It then blows back and lift is lost. Depending on severity, the glider will turn towards the folded portion since the open part is lifting.

If the whole leading edge folds under, it's called a frontal collapse. If a tip folds it's called an asymmetric collapse or asymmetric tip fold.

 

JeffCollapse3byStan.jpg (68228 bytes)

During the fast half of a slow/fast task at the 2005 USPPA competition, at about 1.5 meters high, I hit turbulence. 40% of the left wing folded as my left side brake went limp. It only took a couple inches of brake with my right hand to steer and keep it tracking down the lane. This technique allowed me to keep from hitting the ground and within the 5 meter wide lane.

Another important response to turbulence is to get off the speedbar. I didn't since I had no idea how bad it was! It happened while nearly fully accelerated, trimmers at 3/4 out in moderately turbulent air: a very, very, VERY susceptible condition.

Photo by fellow competition pilot Stan Kasica.

 

A Reflex style wing courtesy www.FlyParamania.com

These wings load the A's and B's very heavily with the trimmers set to fast. They are less prone to collapse in that condition because the leading edge is less subject to "blow down," where relative wind aggravates the collapse as the leading edge is blown down and back, taking more of the wing as it goes. The effect is seen in all three of these pictures and the video below.

But any wing, going real fast, will be wilder on the recovery. So even the reflex wings will frequently earn (or deserve) a DHV 2 or performance rating at their faster settings.

Recovery

For most collapses, here is the best bet for recovering. 

1. Let it fly first by reducing brake pressure slightly for a second. The good side will accelerate some.

2. Add the least amount of pressure required to steer your course straight. The hand on the collapsed side will be loose, there is no point pumping it in most cases. However, one large pump can sometimes clear things up AFTER some speed is gained. But always use pressure—as the pressure builds in the collapsed side you MUST let that hand go up.

3. For smaller collapses, weight shift away from the turn, if able. Don't waste time with it, though, during a large collapse, unless you can do it instinctively.

4. React to pressure. If you feel the pressure build, in most cases it is best to let your hands up to allow the wing to accelerate.

5. React to fore/aft swing. If you're pointed at the ground, you may need FULL brakes. As soon as you start swinging back under though, you must get off the brakes. More advanced techniques exist for dissipating the energy resulting from such a dive but you certainly won't remember that from a one-time read here. That requires expert instruction and practice.

6. In a severe collapse there are many potential complications that may defy correction. Each situation is different, that is why avoidance is so important. There are thermals and windshears and rotors out there that no amount of pilot technique will counter. A good SIV (maneuver/safety)  course will help prepare you but, even then, without rehearsal it's doubtful you'll be that much more prepared for the most severe deformations.

Realize that these maladies are incredibly rare. Most paramotor pilots have never even experienced a significant collapse (less than 30% is almost un-noticable) but that doesn't mean you shouldn't be prepared. What has happened is pilots over-reacting with too much brake input too quickly. That has caused a number of crashes!

The pilot was about 200 yards inland from the the Salton Sea which exhibits calming on-shore winds like an ocean beach. He was descending on speedbar which is a more vulnerable condition.

Pilots had been reporting only light thermal activity and wake turbulence did not appear to be a factor. This was a fluke. 

Fortunately, he was a very competent pilot who managed this properly, keeping his cool and using the minimum brake pressure required to recover which he did with about a 30 foot altitude loss. This was on a DHV 1-2 wing. 

Photo by Jim Farrell

Weight Shift (skip this if time is important)

Conventional wisdom suggests weight shifting to steer during a collapse and, to the extent possible, I agree. During smaller collapses it is quite beneficial—I've demonstrated turning away from a 50% collapse using weight shift alone on the Spice. However, experience and observation suggest that for large collapses it's impractical and even contrary (because of time wasted trying) to a rapid recovery.  Here's why.

  1. In a truly large collapse your body will fall towards the folded side. A turbulence induced collapse is quite different than an intentional one. When you induce it, usually by pulling the A's down on one side, you know it's coming and will likely start weight shifting immediately if not a hair in advance. Plus, just hanging on those A's gives some support and you won't fall as much, if at all. 

  2. The surprise version will give neither support nor warning. You won't prepare and will likely fall towards the down side making it harder to move back up for effective weight shift. 

  3. When the wing initially folds, in most cases your body will actually swing briefly away from the fold and then you'll fall towards it. It can be quite confusing. A simple procedure, such as "reduce brake pressure for a second then steer with the least input required," will yield more consistent results until you've gained experience with the requisite timing. More steering inputs may certainly be required in some cases, but in most cases, they are way overdone.

  4. Weight shift works by differentially moving the risers. Cool foot crossing and body contorting may impress the babes, but if the risers don't move, neither will the wing. In a large collapse, the collapse-side riser is barely in play, if at all.

  5. Most motors don't have enough weight shift capacity to make a huge difference. Even those that do are probably half as effective as free flight harnesses.

I've never been able to induce a collapse as bad as what nature has. Even pulling down one side as fast and hard as possible has never done more than about 60%. While that was attention-getting and turn-inducing, it was not as bad as what Mother Nature's turbulence served up. So we shouldn't think that just because we can handle self-inflicted versions, we'll easily tame natures fury. Prevention is still the best medicine. 

In the 3 major asymmetric collapses that I've experienced, two during thermal free flight and one while motoring, I fell immediately to the down side and recovered from that position mostly using the above technique. One was from launch at Marshal. Alan Chuculate, launching behind me, described that event as a 70% collapse. Another, also at Marshal, cascaded. That is, one side folded then the other. Airspeed dropped and I was successively falling to each side. That side would load and the other side collapsed. After 3 repetitions I dropped out of the harness into the landing configuration to prevent weight shifting and the cascading stopped. Scary. In that case eliminating the possibility for weight shift allowed a recovery. Of many dozens that I've induced, mother nature took the cake for collapse severity.

My advice: don't mess with mom.

Weight shifting here would likely be worthless since there is no load on the collapsed side. This is a 70% fold and there is no cure but to use just enough brake on the good side to let it accelerate and inflate the left side.

 

InducingCollapse.jpg (104840 bytes)

Here I am just starting to induce a 50% collapse and steering with only weight shift (the other hand is operating the camera). My right hand is pulling down the entire right A riser (on the left side of the picture). A hard, fast pull can induce over 50% which will be sporty. If done accelerated it will probably be violent with a lot of turn. Don't try this unless you're ready for a wild ride!

Cravats, Complications

Severe wing deformations can defy correction. For example, while most cravats (where a tip gets tangled in the lines) are non-events, some can quickly induce a spiral. Even small ones can be problems if the pilot allows a spiral to develop. Same with severe collapses (as shown below). 

It's important that, after reducing brake pressure momentarily, you steer to prevent it from wrapping into a steep turn. That can happen fast and the only option is to pull as much brake as you have available.

I highly recommend the Instability II DVD. You'll see video illustrations from experienced acro paraglider pilots who rented a helicopter and filmed various maladies. These are experts with the intent to illuminate the problems in ways that everyday pilots will benefit. Very instructional. 

Severe complications are incredibly rare except for those exploring the boundaries of turbulence or maneuvering. If you've seen Risk and Reward then you've seen some examples of this. Minding the conditions and flying only when it's mellow (and forecast to remain so) will avoid the vast majority of this kind of risk.

This is a small cravat—no big deal unless a spiral takes hold. A large cravat will cause fabric to block the air over a large area and induce a rapid bank. Speed increases in a spiral which makes the cravat even more powerful which causes the spiral to steepen and make it even draggier. Photo by Tim Kaiser

Paraglider Collapse Video

An amazing video captured the worst collapse I've ever seen. It would have been harmless up higher but still a shorts-emptying experience. 

While the pilot had apparently been warned about flying in the rotor of a large stadium, he either forgot or felt his skills were up to the task. It's an assessment that every pilot makes every time he flies, some more conservative than others. I've seen many, many pilots fly where I would have expected a tumble but they slipped by merely bumped.

1. The 15 mph wind coming from the stadium off his right side was serving up a powerful swirl.

2. The pilot suddenly sinks then, just as suddenly starts a climb.

3. Deformation starts on the middle-right leading edge. At this point the pilot has no idea what's happening to his wing. There was likely nothing he could have done in this severe situation. His fate was sealed by the decision to fly there. By the time he realized there was a problem, it was too late.

4. The leading edge is forced down by the vertical gust. Relative wind from forward speed blows it back and down.

5. It's just about here where the pilot probably realized something is terribly wrong. Bereft of lift and being pulled back by the crumpling wing, he is swung forward and starts falling. 
Only the left tip retains it's shape which rapidly spins the glider around, up and over.

6. After about 15 feet of fall the pilot has come around and is facing the ground as his wing begins to recover.

7. The wing has almost recovered. 8 & 9 In spite of pulling hard on the brakes there just isn't enough room. 
Another 20 feet would have let this swing out into a recovery. The pilot apparently survived this with significant injury.

Click below to see the entire entire video sequence.


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Remember, If there's air there, it should be flown in!