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Understanding Paraglider Collapses
By Jeff Goin |
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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 is easily avoidable.
First, the wing is built to open and fly. Quickly. So even if part of
it does fold up, 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 and then steer,
it's quite flyable, even landable.
The million dollar question is how much brake is too much? The best
answer is first go hands nearly up, where you have minimal pressure, for
about one full second then start trying to steer. In fact, the vast
majority of maladies that arise from collapses are not the fold itself,
but rather the pilot's abrupt and excessive reaction to it. |
Active Piloting
The PPG Bible goes into great detail about this. Besides avoidance,
there is no better prevention of collapses than active piloting: the
fine control inputs required to keep your wing overhead in a smooth
fashion. The book details how to practice, what to practice and
how to know when you've mastered it.
Here's an
important point: if you don't know how to do active piloting,
trying to do so in strong turbulence will likely make matters worse!
Use constant pressure instead.
Active piloting should be practiced in light turbulence until keeping
the wing overhead, using minimum brake input, is second nature.
The the dynamics are such that body movement is opposite the wing in
turbulence, rendering your natural reaction to be exactly wrong. The
other common malady is using too much brakes which slows down your
wing's airspeed to the point where the brakes become ineffective or
worse.
And I've seen numerous accidents and collapses that were aggravated
by the pilot's attempt at using brakes when he would have been far
better served by reducing brake pressure to let the wing fly and
concentrating on direction.
You can do a lot to
avoid collapses in the first place. Staying out of turbulence is the
best prevention.
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.
Stronger wind=stronger turbulence.
Don't fly too slow,
though. Speed is life especially once you're already in turbulence. If
you're getting bounced around a lot, reduce brake pressure a bit,
especially if you feel the airflow on your face decrease. After all,
once you give up speed, those brakes are worthless. Except for heavily
reflexed wings, have them trimmed slow and do not use the speedbar.
Flying faster means that, once a fold starts, the extra airspeed will
tend to pull it under farther.
You are most
susceptible to collapses when 1) lightly loaded, 2) accelerated with
speedbar, 3) hands up, 4) descending power off.
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Resistant Wings & The Reflex
High performance wings (higher than DHV 1-2 or equivalent),
especially when lightly loaded, will behave the worst during large folds
(collapses)—they are more susceptible and less likely to recover
cleanly. Their higher certification, in fact, comes 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, either.
It will certainly make a huge difference but free flight has lost some
awesome pilots in the powerful 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 if he is actively piloting it.
A reflex wing, trimmed so the reflex is engaged (trimmed fast) but
with no speedbar 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. |
Recovery
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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 in the
collapsed side comes back 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.
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. |
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 to a rapid
recovery. Here's why.
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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 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.
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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.
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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.
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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.
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. |
Cravats, Complications
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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.
It's important that,
after reducing brake pressure momentarily, you steer, especially before
it wraps up into a steep turn. That can happen fast.
Such problems are
incredibly rare except for those exploring the boundaries of conditions
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.
A Reflex style wing 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.
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
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
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