[INNOVATIONS]
the fabric, but that also aff ects the porosity of that panel. So with more or less air being let through the cloth, the opening at the top must be adjusted or the slider reefi ng method used has to be adjusted, or some combination of the two in order to maintain the same parachute performance. All the radial seams between the panels were
reinforced with Kevlar tape, and the circumferential seams between panels were reinforced with either nylon or Kevlar tapes depending on the strength requirements. Nylon thread was used throughout with stitch pattern and density playing critical roles in the fi nal strength of the part. With an increase in the size and weight of the parachute, the extraction system components, consisting of the rocket, the pickup collar, cable, thermal protection, incremental bridle and a deployment bag, also had to change. T e deployment bag, what holds the packed parachute, is removed from the parachute during the extraction sequence, allowing the parachute to unfold in an orderly sequence. “Although it would seem that this bag should be fairly straightforward, during parachute testing, we were fi nding that the extraction sequence was so fast that we were burning the parachute on the way out. So a natural PTFE twill weave Tefl on fabric was sewn into the bottom of the bag to prevent damage to the parachute during the extraction,” notes Timmerman. Due to the heavier weight, the rocket size also had
to increase. Early development testing showed that this extra force was more than the incremental bridle could handle. T e incremental bridle is made from nylon webbing overlapped and stitched together, which acts as the shock absorber between the accelerating rocket and the stationary parachute pack allowing the rocket to smoothly pull the parachute pack from the airplane. T e incremental bridle accomplishes this by having the stitches tear away as it loads up. Several dynamic tests were done in the lab to determine the load characteristics of thread type and stitch type. Based on this testing, two diff erent stitch types and densities along with two diff erent nylon threads were used in the fi nal design to smooth out the load.
A thin thermal protection layer of Kevlar cloth
existed over the incremental bridle to protect it from the exhaust plume of the rocket, but the bigger
rocket meant a longer exhaust plume and the thermal protection was found to be insuffi cient in development testing. Initial redesign eff orts focused on protecting the link between the pickup collar cable and the leading edge of the thermal protection and incremental bridle. A thermal boot was designed to defl ect the bulk of the exhaust plume, however the fabric protecting the incremental bridle remained insuffi cient. After several tests using layers of diff erent materials such as silicon-coated fi berglass, an outer layer of Nextel cloth was sewn over the top of a layer of Kevlar fabric. T e thermal sheath was reverse stitched so that no seams were directly exposed to the exhaust plume. Ultimately, this design proved successful. T e fi nal link to the rocket was the pickup collar.
T is is an aluminum sleeve around the rocket that is attached to a 1/8” stainless steel wire rope. T e size of this wire rope was increased from the original design and the bend radius was also increased signifi cantly to enhance the strength of the assembly to withstand the acceleration of the rocket. T e CAPS redesign successful, the ‘Generation 5'
aircraft was introduced with the hard-sought weight increase in early 2013.
RECOGNITION OF SAFETY T e achievements of the original and ongoing engineering designs are probably best exemplifi ed by the Cirrus SR-series Engineering and Design Team having been recently recognized as the recipient of the prestigious 2013 Joseph T. Nall Safety Award, for pioneering a wide array of safety features designed for single-engine aircraft. T e award is presented annually by the International Air & Transportation Safety Bar Association (IATSBA) to honor industry leaders who have made noteworthy contributions to aviation and transportation safety. From the inception of the SR-series aircraft,
CEO Dale Klapmeier and the design team challenged conventional wisdom and industry design standards while exploring ways to build a better, safer airplane. “We have the deepest regard for the aviation leaders who have received this award in past years, and Cirrus Aircraft is honored to join them,” Klapmeier said. “However, our work is far from done as we continue to challenge ourselves to make fl ying safer and more secure for new and seasoned pilots alike.” y
1, 2 Fallows, James. Free Flight. New York: PublicAff airs, a member of the Perseus Books Group, 2001. Print.
Wire Rope Exchange would like to thank Tim Timmerman at Cirrus Aircraft and Ernie Villanueva at Free Flight Enterprises for their contributions. The images were courtesy of Cirrus Aircraft. For additional information on Cirrus Aircraft and its products, please visit
cirrusaircraft.com. For additional information on Free Flight Enterprises, please visit freefl
ightent.com
32 MAY-JUNE 2014 WIRE ROPE EXCHANGE
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