May 12, 2010
Crash and Learn: APL Torso Model Used in Helicopter Safety Tests
Head and torso injuries are the leading cause of death among individuals involved in helicopter crashes. Although such injuries are routinely studied in automobile accidents, no validated models exist for use in aviation. Over the past year, human-modeling experts from APL’s Biomedicine Business Area have worked with NASA and the Office of the Secretary of Defense to address this challenge, using human surrogates to investigate loads on the body during helicopter crash tests.
APL-developed head and torso models have already supported investigations of dynamic loading events on the body. “With our instrumented human torso, we’ve been able to study the ability of body armor to protect warfighters against blast and ballistic impacts,” explains Andrew Merkle, of APL’s National Security Technology Department. “Sensors are embedded within the torso to quantify the amount of energy transmitted into the body, allowing us to measure the energy-absorption capabilities of the armor.”
Merkle and his team of engineers and materials experts modified the human torso surrogate for use in two full-scale crash tests at NASA Langley’s Landing and Impact Research Facility in Hampton, VA. “This research should lead to changes in engineering design to improve helicopter crashworthiness and occupant protection,” says Merkle, the Program Manager for Biomechanics and Injury Mitigation Systems.
In December 2009, NASA researchers dropped a small MD-500 helicopter from 35 feet high to simulate crash conditions. Aboard the aircraft were three crash test dummies and APL’s Human Surrogate Torso Model, an anatomically correct model of an average-sized male made with simulated bones and organs—with sensors used to record their responses during impact.
The helicopter was retrofitted with a honeycomb-like deployable energy absorber (DEA), developed by NASA and designed to cushion the aircraft’s crash. Although the helicopter’s landing gear bent on impact, the DEA kept the craft’s bottom from touching the ground, and the dummies were only slightly battered.
Neither the dummies, nor the craft for that matter, fared as well during the second test in March. During that exercise, the DEA was removed from the helicopter. Once dropped, the helicopter crashed into the concrete, its skid gear collapsed, the windshield shattered, and the “occupants” pitched forward violently, suffering potentially spine-crushing injuries. NASA researchers say the helicopter experienced three times the g-forces recorded in the previous test.
Researchers will use data culled from the sensors in the torso to not only assess injury potential but also validate the models themselves. “We will work with NASA researchers to determine how efficient the deployable energy absorber had been in the earlier test and how much it might help reduce potential occupant injuries,” says project engineer Kyle Ott.
The team also recreated the crash conditions in APL’s Impact Biomechanics Laboratory, using sled tests to simulate the same impulsive loading and allow the study of multiple test parameters. A finite element model (FEM) of the Human Surrogate Torso Model was developed for incorporation into a full helicopter FEM developed by NASA. “This model will be validated using data generated from the full-scale test and the laboratory crash sled tests.” Merkle explains. A much more detailed model of the torso, with more than 200,000 elements, was developed to study specific injuries. This model will be used to assess the potential mechanisms and loading conditions that lead to certain traumatic injuries, including spine injury and aortic rupture.
APL’s Biomedicine Business Area staff members have conducted crash tests in their own facility for more than 12 years, progressively increasing their expertise in the critical area of impact injuries. Business Area Manager Dexter Smith sees more applications in this area: “This NASA project uses our human surrogate torso technology in a new test environment that could potentially reduce warfighter injuries in the future.”