AIN Blog: NASA's "Copter Crashing" Continues

 - September 12, 2013, 3:16 PM
NASA researchers swung the fuselage of a CH-46E like a pendulum from a height of 30 feet before releasing it, allowing it to hit the ground at 30 mph.

A large helicopter crashed last month near Norfolk, Va., and not only wasn’t the National Transportation Safety Board mobilized, but it probably even had advance warning. The planned wreck was part of a continuing series of rotorcraft crash tests sponsored by NASA in partnership with the FAA, the U.S. Navy and the U.S. Army, dating back to 2009. Those first two tests involved a lightweight ex-Army OH-6 (MD500), which was hoisted 35 feet in the air on cables at the agency’s Langley Research Center and let go. Think trapeze with an abrupt stop at the bottom of the arc. This initial test investigated the efficacy of a deployable energy absorbing (DEA) composite honeycomb “cushion” installed underneath the fuselage, and whether it would protect the cabin occupants in the event of crash. According to the report following the test, “the probability of injury in the pilot, copilot or rear passenger is below the low category, indicating a very low probability of risk.”

As for the helicopter itself, the cushion did protect it enough to allow it to be recycled the following year in another drop, this time with no protection. The flight path angle (33 degrees) and speed (33 mph) were the same as in the first drop, approximating a “relatively severe but survivable helicopter crash.” Packed with instrumentation and sensors as well as four crash test dummies (including one equipped with fake internal organs), the helicopter swung forward and smacked into the concrete with enough force to crush the skids, crack the windshield open and inflict potentially paralyzing injuries to the passengers, according to the instrumentation. This time the helicopter suffered enough damage to be excused from further abuse.

For the crash test held on August 28 at Langley’s historic Landing and Impact Research (LandIR) Facility (which began life nearly 50 years ago as the Lunar Landing Research Facility, helping Apollo program astronauts learn to land on the Moon) NASA moved up in weight class. The sacrificial victim this time: one of two retired CH-46E tandem-rotor troop helicopters provided by the Navy. The stated goal of the test was not only to evaluate how improved seat belts and seats affect passenger survivability in the event of a crash, but also to establish a baseline for the crash next year of the second CH-46 fuselage, which will be outfitted with additional equipment, including composite airframe retrofits. The former Marine transport in this test was painted with a dot-matrix-like pattern: the black dots on a white background serve as part of a photo technique known as full-field photogrammetry. During impact, each dot or data point is tracked by high-speed cameras recording the event at 500 images per second, to measure the distortion of the fuselage precisely. Engineers also installed a video game motion sensor inside the cabin in an attempt to track the movements of the dummies in the cabin.

As the “Phrog” fell earthward at about 30 mph with all the aerodynamic grace of a 45-foot-long brick, cameras recorded the action from multiple angles:

While the helicopter’s rugged airframe seemed to have fared well in the simulation, you likely won’t be seeing a version of this thrill ride any time soon at your local amusement park. As evidenced by footage from the onboard camera, the 13 mock passengers inside most certainly did not enjoy the violent impact. “We designed this test to simulate a severe but survivable crash under both civilian and military requirements,” said NASA lead test engineer Martin Annett. “It was amazingly complicated with all the planning, dummies, cameras, instrumentation and collaborators, but it went off without a hitch.” The researchers will now have a year to review and digest the 350 channels worth of recorded data in preparation for next summer’s sequel.