Collapses and Turbulence
Posted Wed Feb 01 2006
Edited Feb 27, 2006
By Brian Germain
There are many variables to consider when looking
into a canopy collapse:
- What was the pilot doing?
- How fast was the canopy flying when it collapsed?
- Where was the pilot flying?
- What is the canopy design?
- What is the wing-loading?
- Was there any re-active solution employed?
These are the principle considerations, but not
the only ones. I will take each one separately.
The way in which a parachute is flown can increase
or decrease the "G" loading on the lines.
A rapid release of one or both brakes significantly
increases the chances that the canopy will collapse.
This allows the parachute to surge forward to a
lower angle of attack, decreasing the lift of the
parachute. This reduces the amount of energy exerted
by the parachute away from the suspended load, allowing
the "negative" portion of the lift to
take over and allow the wing to fly toward the jumper.
2) Airspeed is what creates lift. Lift
is what causes the wing to strive to fly up and
away from the jumper. This is the formula for line
tension and therefore stability. The slower you
are flying, the more likely your parachute will
collapse due to low internal pressure and low line
3) Was the wing flying in clean air when
the collapse occurred? This is an important
part of the question. All parachutes can collapse
in "bad" air. We must always fly considering
the invisible dangers that the sky presents us.
If you wouldn't fly a kite there, don't fly or land
your parachute there.
4) Certain parachute designs do better
in turbulence than others. I must avoid
pointing fingers here, as this is a volatile industry
that can be taken down by non-skydiving lawyers.
Nevertheless, certain wings have an increased propensity
to go "negative" when presented with adverse
condition, while others bump around a bit and keep
on flying. This is a complex issue, and the best
way to decide which parachute to fly is to listen
to the actual statistics, and to your own experience
when flying a particular design. I have not experienced
any kind of collapse on the parachutes I fly, ever.*
If you have on yours, you may want to reconsider
what is over your head.
*(This does not include nasty, ill-conceived prototypes
that seemed like a good idea at the time. I am talking
about production-model canopies here.)
5) Parachutes perform differently at different
wingloading. The lighter the wingloading,
the slower it will fly. This means that the internal
pressurization of the wing will be less on lightly
loaded canopies. Consequently, lightly loaded parachutes
tend to experience more small collapses than heavily
loaded ones. Not only is there less internal pressure
in the wing, but the dynamic forces are also less
with decreased airspeed. This means that the average
line tension tends to be less on a lightly loaded
wing, and the wing tends to have an increased propensity
to surge forward in the window when flying at low
airspeeds. This is why very small, highly loaded
parachutes tend to experience fewer distortions,
especially when flown at high speed. Flying at high
speed increases the drag of the canopy itself, relative
to the jumper, so the relative wind holds the parachute
back in the window, and at a higher angle of attack.
This is why I make smooth carving, high "G",
high speed turns to final approach heading, especially
in turbulence. The speed actually reduces the chances
of a collapse by increasing the forces that keep
the parachute at the end of the lines. I am literally
increasing my wingloading by flying fast and at
high "G's", and the increased velocity
reduces the amount of time that I fly in bad air.
*I am not saying that you should downsize just
to increase your stability. I am saying that until
your skills and knowledge are ready to fly smaller,
faster parachutes, you should stay out of the sky
until the winds come down. I still haven't been
hurt by a jump I didn't do.
6) This is all about "Pitch Control".
If you are flying a good design with lots
of airspeed and significant line tension and in
a reasonable location that has no obvious precursors
for collapse, you can only deal with turbulence
in a re-active manner, as you have addressed all
of the relevant variables up to this point. If your
wing tries to aggressively surge forward in the
window, you must notice it and quickly stab the
brakes to bring it to the back of the window. A
collapse always begins by a surge to a low angle
of attack, but there is very little time to deal
with the problem before I folds under. Here are
a. The first sign is a change in Pitch. The wing
moves forward in the window. This is the limited
flying space over your head. Too far forward and
it collapses. Too far back and it stalls.
b. The "G" loading drops dramatically
and almost instantly. In other words, your apparent
weight in the harness drops because the wing is
producing less lift.
This is the time to jerk on your brakes: quickly,
sharply, but not more than about 50% of the total
control stroke. This action is to pull the wing
back in the window, not to stall the parachute.
By putting the wing further back in the window,
we are increasing the angle of attack. This increases
the lift, and forces the wing to fly away from the
suspended load and thereby increase the line tension.
This can prevent a collapse entirely, or cause the
wing to recover to stable flight before things get
really out of control. Once you have flown past
the bad air, smoothly and slowly release your brakes
back to full flight so that you may maintain your
If the wing is allowed to collapse, it may recover
quickly on its own. This is why the more modern
airfoils have the fat point (Center of Lift) so
far forward. It causes the wing to pitch nose-up
when it begins to fly again, bringing it back to
the end of the lines. Nevertheless, parachutes can
still collapse fully, which often involves significant
loss of altitude and possibly a loss of heading.
*If your wing goes into a spin because of a collapse,
your job is to STOP THE TURN FIRST, and
then increase the angle of attack. If it is spinning,
there is less chance of recovery until the flight
path is coordinated and the heading stable. Most
modern airfoils will recover as soon as the heading
- Don't fly an unstable parachute. If it is prone
to collapse, ground the parachute. Do not sell
it to an unsuspecting jumper at another drop zone.
These people are your brothers and sisters.
- Don't fly in crappy air. Land in wide open spaces,
in light winds, and never directly behind another
- Practice stabbing your brakes in response to
forward surges on the pitch axis. This must become
a "learned instinct" that requires no
thought at all. Like pulling emergency handles,
pulling the wing to the back of the window when
the lines get slack is essential for safe skydiving.
- Keep flying the parachute. If your parachute
does something funny near the ground, don't give
up. If you keep your eyes on YOUR ORIGINAL HEADING,
you will unconsciously do things that will aid
your stability and keep you from getting hurt.
Looking toward what you don't want is how you
make it occur.
I hope this little article helps you understand
the phenomenon of collapses a bit better. I know
as well as anyone how painful a collapse can be.
I do not want to go back to that wheelchair, and
I don't want anyone else to have to experience that
either. You morons are my family, and if information
can help protect you, I will give it until my lungs
are out of air.
Blue Skies, Sky People.