For decades, NASA has been working to solve safety and performance challenges in commercial aircraft. One idea, which was originally intended to cushion the next-generation space capsule, is being tested for potential use in helicopters.

According to Newton's laws of motion, an object moving at a constant velocity continues at the same velocity unless an external force acts upon it. This means that during a car crash, a body inside the vehicle continues moving forward at the same velocity as the vehicle was moving prior to the collision. The body stops only when it hits some object in the vehicle—like the steering wheel, the dashboard, or the seat in front of it. When the force of impact against an object is large enough, injuries can occur. Deployment of a protective device called an airbag can help reduce injuries. By absorbing the kinetic energy (energy of motion) carried by the body and distributing this energy over a larger surface area, the airbag lessens the force that may cause an injury.

An energy-absorbing airbag like that installed in cars can also be used in helicopters. But conventional airbag designs have some important shortcomings. When a helicopter crashes, it’s not just moving downward, but also forward. This may produce a higher crash force as well as shear force, which is a lateral force in any material that causes it to change its shape. In the video demonstration, shear force is what causes the balloon that represents a conventional airbag to pop.

To learn whether an expandable cushioning device called a deployable energy absorber (DEA) could lessen the destructive force of a crash—including the shear force—NASA conducted some tests. Engineers performed two drop tests: the tests were identical, except that technicians mounted a DEA to the belly of the test helicopter in the first test alone. In both tests, the helicopter was equipped with more than 100 sensors to collect crash data. Because researchers also wanted to examine the injury risk for passengers, they wired four crash test dummies with sensors.

Results from the first drop test showed that the DEA softened the blow of the crash so much that the helicopter needed only minor repairs prior to the second test run. The dummies also held up well. In fact, the probability of injury was measured as very low. However, when the second crash—without the DEA—was performed, the helicopter exhibited quite a bit more damage. The bottom of the windshield shattered, several bulkheads buckled, and the floor of the helicopter pushed through into the cabin. The dummies experienced forces powerful enough to break human necks.

Using the crash test results, NASA engineers can refine the design of the DEA to further improve its safety. In any case, the tests demonstrated that this type of device could make helicopter crashes survivable for passengers.

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