Aviation for Women

SEP-OCT 2018

Aviation for Women is the flagship member publication of Women in Aviation International. Articles feature women who have made aviation history, professional development ideas, and current-topic articles.

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36 AviationforWomen S E P T E M B E R / O C T O B E R 2 0 1 8 ra n a number of reefing lines through keep - ers— belt loops— around t he skirt where t he suspension lines connect to the canopy. "Orion has timed cutters on these cords that hold the skirt to a certain diameter," Elsa says. "They are cut in se- quence to help decelerate the spacecraft without overloading the chutes and their attach points." These belt loops evolved in her most chal- lenging project, a 39-foot chute for a Navy target drone. With its extra high-density pack, metal- reefing rings crushed the cutters. Elsa found the solution in a NASA project she was also working on, where the bungee cord that replaced the reef- ing lines didn't work well with metal rings. "So we routed structural Kevlar tape through Teflon sleeves to make it as slick as it could be. Every- one is using them now because they are a better way to pack a chute without metal components," she says. Testing is part of the engineering process, and Elsa was with a camera crew in a helicopter, awaiting Orion's return after its December 2014 launch. "I had to pinch myself; who gets to do that?" Elsa says. After evaluating their operation, "we brought the chutes back here, dried them out, and inspected them. We do the same for the SpaceX chutes, which are the same size and made by the same company." Before she started consulting on Orion in 2005, Elsa engineered the deceleration systems that landed the Pathfinder and Exploration Rover mis- sions on Mars, as well as the bailout system used by the shuttle astronauts. "Right now I'm working on a JPL parachute system where we're at Mars' rela- tive altitude. There's just not much there, and that changes everything. Sud- denly, you're going supersonic," Elsa says. Parachutes are multiphase aerodynamic systems, and designing them is, perhaps, the most vexing of aerospace engineering challenges. Velocity is a crit- ical concern. Drag is time dependent, and its coefficient depends on the type of parachute: flat circular, hemispherical, conical, poly conical, or extended skirt. Ram air parachutes create lift. The design employed depends on the need. Gravity is obviously a factor. So are the payload and its weight. Inanimate payloads "really don't care about landing velocity," she says. For humans, the "military maximum is 24 feet per second, which is like jumping off a 9-foot wall. It's not very comfortable, but you'll survive. We typically try to get close to 20 fps." When the atmospheric density is just a few molecules, "there's not a whole lot going on and the inertia of the materials is a factor," Elsa says. A parachute is an aerodynamic structure built of flexible textiles. "We have some, such as nylon, mostly used as the broadcloth for the parachute. It is very stretchy; good for that purpose because it absorbs a lot of energy." The structural grid, risers, suspension lines, and seam reinforcing tapes employ "high tenacity" textiles like Kevlar, Spectra, Vectran, and Technora. Given their strength to weight ratios, Elsa says, they don't stretch much. "Kevlar only elongates about 4 percent before it breaks." Thread unites the pieces. It's needled in a variety of zigzag patterns that accommodate stretching. Straight stitching, she says, is an invitation for failure along the dotted line.

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