Hard Openings

Chances are that any jumper reading this has either experienced a main canopy that opened hard or will at some point in the future. Although the definition of a hard opening is very subjective (what one person may consider a hard opening, another may call normal), it is actually possible for a parachute to open so hard that it can cause severe physical trauma or even death. The range of possible injuries is wide, from minor strains and pulled muscles to broken necks and backs to torn aortas.

How much force does a jumper experience during a hard deployment? Dr. Jean Potvin and Gary Peek of the Parks College Parachute Research Group tried to answer this common question by collecting data on the g-forces (measurements of acceleration felt as weight—one g represents the normal force of gravity on the earth’s surface) that jumpers experience.

Potvin and Peek arranged for jumpers to wear g-meters on test jumps using Performance Designs Stiletto 150s. During the test jumps, a relatively soft opening registered a maximum g-force of about 3 g, while a harder but not unreasonable opening registered 6 g. To provide comparisons, they also made test jumps using a Para-Flite Stratocloud with no slider, which registered a bone-jarring 12 g, and another drop using a Para-Flite Cruiselite, which resulted in a whopping 18g.

Peek found that the biggest factor in preventing hard openings was correct placement of the slider in the pack job, saying, “Jean Potvin and I have discussed this many times and have come to the conclusion that when a normally soft-opening canopy opens very hard, it is because the slider got out of position for some reason or the canopy opened very asymmetrically.”

John LeBlanc, vice president of Performance Designs, provides lots of helpful information on packing for soft openings in a video he posted to YouTube titled, “Hard Openings.” He states, “In order for the slider to do its job properly, it needs to start in the right place, and the basics of that means that it has to be right up against the slider stops. And also it’s wise to quarter the slider, so when the four line groups start to separate from one another early on in the deployment of the canopy, the slider is right there in the middle, ready to do its job.”

How you fold the parachute into the bag is another critical factor in ensuring the slider stays where it belongs. You must s-fold the canopy so that the slider stays up against the slider stops, exactly where it was before you started folding the canopy into the bag. This is called “presenting the slider” and is a crucial step.

Proper packing—particularly slider placement—is essential for a soft deployment of your main canopy, but that alone will not ensure that your parachute opens correctly. Other major factors include:

  • Pilot chute size and condition
  • Canopy design and suspension-line types
  • Line stows
  • Freefall speed and deployment position
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A critical factor for soft openings is slider placement. The packer should quarter the slider between the line groups with its agrommets up against the slider stops and must ensure that it stays in that position through the entire pack job. Photo by David Cherry.

Pilot Chutes
The main pilot chute’s size and condition have a big effect on your deployment. According to LeBlanc, “One common error is in pilot chute size. You have to have a pilot chute that is of sufficient size to deploy the parachute but not so large that it generates too much force. Usually, the 27- to 30-inch range is good for most parachutes.” Additionally, if your pilot chute is worn or damaged, it will not function as designed. So keep an eye on the condition of your pilot chute, and replace it as necessary.

Canopy Design and Line Type
To maximize the chance for soft openings, jumpers need to consider canopy design. For example, canopies designed for canopy formation jumping and fixed-object (BASE) jumping are designed to open much more quickly (and therefore harder) than sport canopies intended to open at terminal freefall speeds. But although some non-specialty canopies have a reputation for opening hard, it is usually packing technique that is the cause. “If a parachute opens soft one time, then it is capable of opening soft every time,” states John Sherman, parachute designer and owner of Parachute Labs, Inc. (aka Jump Shack). “Assuming that logic, in order to repeat soft openings, we must control all variables involved.”

Some jumpers have modified their parachutes to produce softer openings by installing a larger slider or adding a pocket to the front of the slider, which helps the slider stay higher up on the suspension lines for longer, thereby slowing down the inflation of the canopy. If you think that the design of your parachute or one of its components is causing hard openings, consult with the manufacturer to see how to best proceed.

Jumpers may also want to consider switching to Dacron suspension line. Dacron suspension line stretches some during deployment. Spectra, HMA and many other popular types of suspension lines do not stretch, which causes the force of a hard opening to transfer directly to the jumper. Many jumpers who use heavy video equipment opt for Dacron lines to help soften their openings. However, not everyone agrees that Dacron lines really change what your body might experience during a deployment. Sherman states, “I accept the fact that there may be an effect from line type or weave or the friction of pulling the lines from the rubber bands, but I don’t see it in data acquired during many opening shocks recorded. If there is an effect, it must be minor.”

Line Stows
Sherman states that there are two deployment issues that jumpers need to consider: the initial forces placed on the main bag and lines as the deployment begins (snatch force) and the speed of the inflation itself (inflation force). To minimize these forces, the packer must stow the lines so they’ll stay in place as the inflated pilot chute pulls the main bag from the container pack tray. The packer must also carefully stow the line bights at the proper length to ensure the lines are not stripped from the bag during deployment. Line strip (sometimes called line dump) occurs when the line stows release from the main bag prematurely. This allows the canopy to rapidly inflate while the lines are still slack, bringing the jumper to an abrupt halt.

LeBlanc says, “Regardless of the type of line you are using (whether it is the biggest, heaviest type of Dacron or the very lightest competition 300-pound line), whatever you are using for each line stow needs to hold each and every stow with adequate tension.”

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To keep lines in place during the deployment, line stows should be equal in size, the bights should be about two inches long, and the stow bands should hold the lines with enough tension so the bights don’t prematurely slip out. Photo by David Cherry.

Generally speaking, a line stow bight that will hold lines in place for a properly staged deployment is approximately 2 inches long and will require a pull force of eight to 12 pounds to pull loose. Sherman explained how inertia causes line strip by saying, “Newton said, ‘Bodies at rest tend to stay at rest; bodies in motion tend to stay in motion.’ A body is a unit of mass. Line stows are divided into three units of mass. They are the bights (two each) and the span or the part of the lines between the bights. Each of these components, separated by the stow rubber bands, is a unit of mass within itself. The mass of the two bights must equal the mass of the span. In terms of percentage, the span should make up 50 percent of the entire line stow from side to side. We want 25 percent in each bight so as to equalize the tendency of the span to ‘drop out’ or ‘dump’ or ‘strip’ or pull the bights out of their stows upon extraction from the container by overcoming their mass.”

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The principles of packing lines on a standard deployment bag also apply to stowless bags: The folded lengths of line should be neat and roughly equal and the closing bands should hold the lines with adequate tension. Photo by David Cherry.

Sherman also talked about the importance of deployment-bag design, saying, “The d-bag is used to prevent the canopy from taking any air or opening prior to an orderly, properly sequenced line deployment. We use the suspension lines stowed in rubber bands to keep the bag closed. (There are other devices designed to do the same job, and the phenomenon described here is applicable to all of those devices.) If the bag is allowed to open prematurely, exposing the canopy to inflation, you will have a very hard, canopy-first opening. These openings may vary in intensity depending on exactly when in the process of deployment the canopy inflation begins. We want inflation to be the last thing that happens. This malfunction is referred to as line strip/dump or out-of-sequence deployment.

“The lines being released from the bag prematurely and allowing the canopy out is, in and of itself, not the complete cause of these catastrophic openings. The slider being allowed to fall down the lines away from the bottom skin, allowing the initial inflation to occur simultaneously or prior to the lines extending fully, is the cause.”

Freefall Speed and Deployment Position

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Photographer Karen Lewis holds her head in a spine-neutral position with her ears above her shoulders, a position many experts recommend to decrease the chance of neck and spine injuries during deployment. Photo by Mike McGowan.

Body position is also an important factor in the quality of your deployment. According to a study by the Air Force Research Laboratory, the position of the heads of fighter pilots greatly affected the ability of their necks and spines to resist g-forces. Researchers found that the cervical spine could support up to 30 g if the pilot’s head was in a neutral position. However, if the pilot twisted his head around (for example, if he was looking behind the plane to try to keep an eye on another aircraft), it would only withstand as little as a 7 g load. And loads as small as 4 g could injure the neck muscles and soft tissue if the head and neck were in positions other than neutral

Ideally, you want to provide a solid platform with your body during the deployment sequence. Keep your shoulders square and level to allow the lines and risers to unstow evenly. As the canopy is inflating, protect your spine by keeping your head directly above your shoulders.

The weight of your head and helmet can apply significant force to your spine during a hard opening. The more weight you have on your head, the harder it can be on your spinal column. Jumpers wearing camera helmets are at an increased risk of suffering neck and spine injuries due to the added weight of the equipment. Veteran videographer Mike McGowan says, “I have found that a neutral head position and slightly tensing my neck muscles during the deployment works best.”

Chiropractor and skydiver Joe Santarsieri agrees. “It is always best to hold your head in a spine-neutral position, where the ears are directly over the shoulders,” Santarsieri says. “With normal biomechanics, you are only imposing about 20 pounds of pressure on the lower part of the neck. However, when the head is forward, bringing your ears in front of your shoulders, you are imposing about 200 pounds of pressure on the lower part of the neck (due to the additional pressure placed on the discs and vertebrae when the neck is bent forward). With that being said, and taking into consideration extra force from opening shock during deployment, It would be very damaging and harmful to the discs and ligaments of your neck to open your parachute system with your head hanging down. To prevent neck injury, it is best to keep your gaze at the horizon and keep your ears over your shoulders during deployment.”

However, where videographers are concerned, head position is just one issue among many that they must consider. Highly experienced cinematographer Norman Kent says he spends a lot of time discussing deployment issues during his video workshops. “There are so many variables and so many things to consider on body position and technique to avoid injury during deployment when wearing a helmet-mounted camera (helmet type, weight balance, weight amount, deployment technique...) that I think to address head position alone is a bit irresponsible. When I teach my workshops, we go thoroughly into this subject and techniques, and I can assure you it is not as simple as head position,” says Kent.

Industry experts state that freefall speed can also play a role in experiencing a hard opening. LeBlanc recommends that jumpers break off from formations with enough altitude to allow not only for plenty of separation but also time to slow down before throwing the pilot chute. “Slow down with enough time remaining before your pull time, with a flatter body position,” LeBlanc suggests. tions other than neutral.

Many jumpers consider hard openings to be an unpleasant but somewhat common part of skydiving. However, brutally hard slammers can cause serious, long-term damage and may even be fatal. With a thorough understanding of what causes hard openings, we can take action to avoid them entirely. Proper packing techniques combined with careful equipment maintenance and good deployment practices can help ensure that your spine and the rest of your body stay happy for your entire jumping career.

About the Author
FEATURE20139-30In the mid-1990s, USPA Director of Safety and Training Jim Crouch, D-16969, had two openings so severe that they caused lower back and neck damage that required surgery to repair. Now, 18 years later, he is facing two more surgeries: one to fuse several vertebrae in his neck and another for his lower back. The MRI image shows the disc and vertebrae damage that stemmed from the hard openings, injuries that just recently forced him to retire from jumping.

 

 

 

More detail on information presented in this article is available at the following websites:

Parks College Research Group g-force study

Hard Openings” video by John LeBlanc

Force Transfer in the Spine” research paper by Dr. Douglas Orndorff

Air Force Research Laboratory study “Acute Neck Injuries” by Russell Burton

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