Chopper drop tests new technology: Expandable honeycomb cushion could make helicopters safer

NASA aeronautics researchers recently dropped a small helicopter from a height of 35 feet (10.7 m) to see whether an expandable honeycomb cushion called a deployable energy absorber could lessen the destructive force of a crash.

On impact, the helicopter's skid landing gear bent outward, but the cushion attached to its belly kept the rotorcraft's bottom from touching the ground. Four crash test dummies along for the ride appeared only a little worse for the wear.

Researchers must analyze the test results before they can say for sure whether the deployable energy absorber worked as designed.

"I'd like to think the research we're doing is going to end up in airframes and will potentially save lives," said Karen Jackson, an aerospace engineer who oversaw the test at NASA's Langley Research Center in Hampton, Va.

According to the National Transportation Safety Board, more than 200 people are injured in helicopter accidents in the United States each year, in part because helicopters fly in riskier conditions than most other aircraft. They fly close to the ground, not far from power lines and other obstacles, and often are used for emergencies, including search and rescue and medical evacuations.

For the test at Langley, researchers used an MD-500 helicopter donated by the U.S. Army. The rotorcraft was equipped with instruments that collected 160 channels of data. One of the four crash test dummies was a special torso model equipped with simulated internal organs. It came from the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

Technicians outfitted the underside of the helicopter's crew and passenger compartment with the deployable energy absorber. Created by engineer Sotiris Kellas at Langley, the device is made of Kevlar and has a unique flexible hinge design that allows the honeycomb to be packaged and remain flat until needed.

Kellas initially came up with the idea as a way to cushion the next generation of astronaut-carrying space capsules, but soon realized it had many other possible applications. So the concept became part of a helicopter drop test for the Subsonic Rotary Wing Project of NASA's Aeronautics Research Mission Directorate in Washington.

Jackson said researchers tested the deployable energy absorber under realistic conditions. "We crash-tested the helicopter by suspending it about 35 feet (10.7 m) into the air using cables. Then, as it swung to the ground, we used pyrotechnics to remove the cables just before the helicopter hit so that it reacted like it would in a real accident," she explained.

The test conditions imitated what would be a relatively severe helicopter crash. The flight path angle was about 33 degrees and the combined forward and vertical speeds were about 48 feet per second or 33 miles per hour (14.6 meters per second, 53.1 kph).

"We got data to validate our integrated computer models that predict how all parts of the helicopter and the occupants react in a crash. Plus the torso model test dummy will help us assess internal injuries to occupants during a helicopter crash."

Engineers say the MD-500 survived relatively intact as a result of the honeycomb cushion. They plan to recycle the helicopter and drop it again next year, but without the deployable energy absorber attached, in order to compare the results.