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Designs float from the skies

Designs float from the skies

Wanted: one 80-ft2 piece of cloth to safely land a 275-lb person traveling 120 mph through Category 3 hurricane force winds and falling about 10,000 ft/min on a 5-cm wide target. Such are the design requirements confronting today's parachute engineers. And they are being met using improved manmade fibers, computers, and better designs.

Once thought of as a dangerous, daredevil sport, skydiving now boasts of its safety and gentle landings as 99-year-old women jump tandem from planes. "The advances in skydiving equipment in the last 20 years are nothing short of miraculous," says Kate Cooper, vice president of Square One, a skydiving equipment distributor in the U.S. And she should know. Cooper has made 6,000 jumps since she started parachuting in 1978.

Gone are the 24-ft-diameter, 40 lb, round, ripcord activated parachutes, with rough landings. Today's sport parachutes, including harness, hardware, and two canopies, weigh less than 20 lbs on average. Skydivers wear stronger, lighter nylon harnesses with stainless-steel hardware; fiberglass or carbon-fiber helmets instead of leather; audible altimeters; and automatic reserve parachute activators.

"Before, skydivers had to take what the military used, and like it. But today, people in the sport drive the equipment advances," says Cooper.


Credit: "Parachuting: The Skydiver's Handbook" by Dan Poytner and Mike Turoff.

Better canopies. John LeBlanc and William Coe are two such examples. LeBlanc, vice president with an aerospace engineering background, and Coe, a mechanical engineer, started Performance Designs (DeLand, FL) 17 years ago. Thanks to computers and old-fashioned engineering, the company is "the largest ram-air inflated canopy manufacturer in the world," says LeBlanc.

Ram-air inflated canopies are colorful rectangular or elliptical shapes, resembling a large air mattress with the front or leading edge cut open. As the skydiver falls, air is literally rammed into the individual cells creating a wing. Jumpers can steer and flare the parachute, controlling it much like an airplane. The canopies range in size from 100 to 200 ft2, to match the jumper's weight, size, and skill-the smaller the "wing," the faster one travels. As the sport becomes safer, says LeBlanc, jumpers demand smaller chutes for faster, flashier landings.

Although, in some companies, the individual panels of the chute or canopy are still sewn by hand, cutting and much of the design are computerized. Coe and LeBlanc moved from pencil-and-paper to CAD when the company purchased its first package of AutoCAD from Autodesk (San Rafael, CA) in 1990. Equipped with a couple of Silicon Graphics and Sun workstations, and an Okidata plotter, LeBlanc and Coe drew their design, then printed each parachute cell full size. "From these, we would cut templates for the actual design," says LeBlanc. Today they run their operation on PCs with Mechanical Desktop, the 3D CAD program from Autodesk. "Now that PCs are faster, we don't need workstations anymore," adds LeBlanc.

Nor do they need templates. The implementation of a computer-operated laser-cutting table, designed and manufactured by Coe, allows the parachute engineers to design a canopy in CAD and convert the drawing directly to computerized cutting instructions. LeBlanc says, "This reduced a great deal of time and labor."

Designed in AutoCAD and constructed in the company's machine shop, the table is basically an air hockey table in reverse. Air, sucked through little holes on the 108-ft long, 72-inch wide cutting surface, pulls the canopy taut and holds it flat. A spreader carriage runs horizontally, smoothing out the fabric evenly. A 100W CO2 laser travels up and down on a toothed carriage that parallels both sides of the table. A servomotor with a controller inside the drive carries the laser left to right across the table, creating an x and y motion.

CAD-generated computer files dictate the x-y coordinates for each individual part. In addition to cutting the outside perimeter of each panel, the laser marks where the material needs to be sewn with needle-sized holes. "By matching up these little marks from one part of the canopy to the next, we guarantee that everything lines up properly and the canopy goes together the way we want," LeBlanc says. A third-generation cutting table, complete with faster motors and carriages, went on line late last year.

Another major advance was Coe's customized CAD system based on parametric modeling. The software, a preprogrammed routine based on Autolisp commands, allows LeBlanc to insert the variables he wishes to change. "Say that I want to change the canopy shape by increasing the wing span. I change that one variable, expressed in a ratio of wingspan to length of wing from front to back. I input the data, kick off the program and go skydiving! When I come back, I have a new canopy, compete with exploded views, and all the files necessary to run the laser table."

Automatic openers. One of the many technologies making parachuting safer are automatic activation devices (AAD). Required for students, they release the reserve if the jumper fails to activate his or her main parachute. Although some AADs operate using a mechanical or electro-mechanical system, the Cypres, developed by Airtec GmbH, (Wunnenberg, Germany) uses a microprocessor to calculate the jumper's altitude and rate of descent on the basis of barometric pressure.

A jumper switches Cypres on in the morning prior to the jump. The device begins calibrating to ground elevation by measuring the air pressure several times in a short period of time, taking the average as the value for ground level. Before takeoff, the AAD continuously checks the ground air pressure, adjusting to changing weather if necessary.

Once in freefall, the device checks the altitude and rate of descent of the jumper. If there are signs that she is in a dangerous position, like being in freefall at a low altitude, the processor triggers the release unit to open the reserve.

The mother of invention. Materials play a big part in modern day chutes. The first advance in materials came on Dec. 7, 1941, says Dan Poynter, author of The Skydiver's Handbook. Up until then, parachutes were made from silk. But when the Japanese cut off the silk supply at the start of War World II, Allied countries scrambled to find alternative materials. Nylon came up the winner. "And nylon was even better than silk," says Poynter. "Silk has many natural enemies, such as mildew. But nylon only has two...ultraviolet light (sun) and acid."

However, untreated nylon can have a high permeability that negatively affects the performance of the chute by creating a less efficient airflow. "We need the air to go over and under the air foil (or canopy) instead of through the fabric," says LeBlanc, so the canopy will act more like an airplane wing. To decrease fabric permeability, the fabric is calendered or run through heavy rollers at high temperature.

However, as a canopy is used, permeability increases. So Performance Designs uses a silicone-based compound to coat the chute, bringing the permeability of the material down to zero without affecting the fabric's tear strength or opening characteristics.

Suspension lines, once made from nylon, were too elastic for ram-air parachutes, causing serious changes in the trim angle of the canopy due to each line supporting a different load, says LeBlanc. Looking for a high strength material with low drag, Performance Designs wove spectra fiber from Honeywell, formerly Allied Signal, into a hollow core braided line for a low drag, low bulk, abrasion-resistant line. Today, this is the industry standard.

Oldies but goodies. Despite all these changes, round canopies are still used, particularly by the military. Parachuting can be the fastest, safest, and simplest way of getting soldiers down in many situations. And because round chutes basically fall straight to the ground, that is they drift evenly with the wind, Poynter says, a large number of solders can be deployed at the same time without flying into each other.

Primarily due to this improved equipment, sport jumping is growing. Approximately 3.4 million jumps were made in 1999; 2.8 thousand were first time skydivers.

So why does someone jump anyway? It is an addiction. "I've been doing it for over half my life and find it to be an incredible physical, emotional, and mental high," says Cooper.

TAGS: Aerospace
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