Honeycomb reduces crash destruction

NASA aeronautics researchers have dropped a small helicopter from a height of 35ft (10.7m) to see whether an expandable honeycomb cushion, the ‘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 that had been placed in the craft appeared only a little worse for wear.

Researchers at NASA’s Langley Research Center in Hampton, Virginia are testing the deployable energy absorber with the help of a helicopter donated by the army, a crash-test dummy contributed by the Applied Physics Laboratory in Laurel, Maryland and a 240ft (73.2m)-tall structure once used to teach astronauts how to land on the moon.

Researchers must analyse the test results before they can say 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 the centre.

According to the US National Transportation Safety Board, more than 200 people are injured in helicopter accidents in the US 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 US 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 from the Johns Hopkins University Applied Physics Laboratory.

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 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 realised it had many other possible applications. The concept then became part of a helicopter drop test for the Subsonic Rotary Wing Project of NASA’s Aeronautics Research Mission Directorate in Washington.

Jackson said that researchers tested the deployable energy absorber under realistic conditions. ‘We crash tested the helicopter by suspending it about 35ft (10.7m) 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 said.

The test conditions imitated what would be a relatively severe helicopter crash. The flight-path angle was about 33deg and the combined forward and vertical speeds were about 48ft/sec or 33mph (14.6m/sec, 53.1kph).

‘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 without the deployable energy absorber attached, in order to compare the results.