Chap 19: Spot
Stretching Glide II
Deep Stall / Parachutal
When Ship Hits the Fan
fury of a dust devil
Dec 15, 2006 |
Chapter 4, 19 | Weight Shift
articles: fury of a dust devil
Attending a Maneuvers Clinic,
Collapse Accident with video and diagram, and
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.
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
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,
reduce pressure then go to 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.
Here is a complete article on
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. Depending on your wing, immediate
responses may be in order, almost jabbing at the brakes. You learn by seeing
how much pull it takes to reduce the wing's forward darting when it hits a
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.
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.
had been reporting only light thermal activity and wake turbulence did not
appear to be a factor. This was a fluke.
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.
by Jim Farrell
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
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-noticeable) 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!
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
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!
3. 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
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
impractical to waste much time on trying. Here's why.
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.
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.
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.
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.
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.
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
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.
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.
below to see the entire entire video sequence.