NASA Drop-testing Helicopters: If You Fly in a Helicopter, NASA Is Interested in Saving Your Posterior.

 - October 2, 2013, 5:10 AM
As part of its investigation into helicopter crashworthiness and accident survivability, NASA swung a Navy CH-46E like a pendulum before releasing it and allowing it to drop 30 feet to the ground. Onboard sensors and cameras recorded the deformation of the aircraft and the seat structures. Data from the experiment will be used to establish a baseline to test energy-absorbing floor structures to improve passengers’ chances of surviving a similar crash.

If you fly in a helicopter, NASA is interested in saving your posterior.

On August 28, the agency’s Rotary Wing Project drop-tested the hulk of a specially sensored surplus Navy CH-46E at its Langley (Va.) Research Center as part of its continuing investigations into crashworthiness and survival factors. Onboard computers recorded more than 350 data channels, and dozens of high-speed cameras filming at 500 images per second caught every movement of 13 wired and two unsensored crash test dummies and the deformation of both the aircraft and several different seat structure designs and configurations provided by the Army, Navy and commercial manufacturers. The fuselage was first pendulum swung by cables from a gantry and then severed free by pyrotechnics at a height of 30 feet before hopping across the ground and hitting a dirt pile at 30 mph. NASA claimed this simulated a serious but survivable accident as the majority of helicopter hard landings are into soil.

A preliminary analysis indicated that several of the “passengers” likely suffered significant and perhaps fatal injuries. While it will be months before NASA plows through and analyzes all the data, the agency intends to release a preliminary description of it at the American Helicopter Society’s (AHS) technical specialists’ meeting on rotorcraft structure and survivability in Williamsburg, Va., this month. A full report likely will be issued next summer after the data is analyzed and verified.

Energy-absorbing Floor Structures To Be Tested

The data will also be used as baseline measurements for the drop test of another CH-46E next summer at the same speed and angle. That test is being designed to evaluate the effectiveness of several different types of energy-absorbing floor structure, including some that can be retrofitted into existing helicopters.

“We’re going to look at advanced composite materials for the subfloor,” said a NASA spokeswoman. The goal is to measure the load-carrying capability of composite inserts as well as their ability to absorb crash forces using several different test designs NASA is manufacturing. “That’s the beauty of that large (45-foot-long) fuselage. We can put one design in the front and others in the middle and the end. We have a lot of real estate to do that kind of testing. We can look at the different designs that have the composite structure to see if it improves [reduces] the deceleration the occupants feel. We could then apply it to not only new designs but also as a retrofit to existing configurations.”

If the test is successful, the spokeswoman said, the composite flooring could be adapted by private industry. “We would expect a commercial company to pick that up and improve it by making it more efficient to produce. That is how we transition a lot of our technology. We demonstrate that the concept works and the primary characteristics and aspects you have to have to make it work.”

She expects next summer’s drop test to break new ground, so to speak, noting that predictive calculating of loads for composites is not as reliable as it is for metals. “The ability to calculate the impact-absorbing capability of composite materials is really in its infancy. Right now we can calculate a [predictive] number, but we don’t have confidence that the number will scale up to a full-scale vehicle with enough accuracy to quote that number. The results of our experiments and analysis should improve our confidence.”

While the 10,300-pound CH-46E fuselage is on the large end of the helicopter spectrum, the science from testing it has direct applications to all helicopter designs, said the spokeswoman. “We are not identifying the characteristics of that military configuration. It was much more generic. That fuselage is a common metallic structure. What you can learn from it is applicable to a broad range of rotary- and fixed-wing transport aircraft” regardless of size. She said the research will enable the airframe and seat structures of all size helicopters to be modeled and evaluated more accurately.

Removing Barriers to Rotorcraft in the NAS

In addition to enhancing safety, NASA believes that overcoming the noise and performance limitations of today’s helicopter designs may someday enable the next generation of rotary-wing aircraft to assume a more prominent role in the nation’s air transportation system, reduce congestion and increase airport throughput. That might mean the design of larger helicopters. Conversely, the development of more cost-effective and smaller unmanned platforms may make rotary-wing designs more commercially viable for remote sensing and package delivery. “We see the future of rotary-wing vehicles in a whole range of different sizes,” she said.

“We span a lot of different types of testing and research,” she added. “The main goal is to develop the tools and technology concepts that will overcome some of the key barriers for rotary-wing [aircraft], including noise and safety aspects as well as the performance and efficiency of the vehicles provided we can buy down the safety, noise, performance and costs.”

The NASA Aeronautics Research Mission Directorate’s Fundamental Aeronautics Program Rotary Wing Project began in 2006 and is investigating a variety of topics and technologies, including advanced propulsion, such as variable-speed power turbines and two-speed drive systems and active rotors. It is also developing better predictive models for rotor loads using computational fluid dynamics, and integrating rotorcraft into the NextGen ATC system. Government funding for the project varies but has averaged $22 to $30 million per year. Each year the program receives a five-year budget.

While helicopter OEMs have partnered with NASA on past crashworthiness studies, none has joined with it on the CH-46 tests.