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Melding Old and New Technology: Impact Testing for Crash Safety
  • 13 Mar 2023 12:07 PM
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Melding Old and New Technology: Impact Testing for Crash Safety

While NASA ponders the fate of the Gantry, tests continue with this unique historic structure.

By Robert W. Moorman
Vertiflite March/April 2023

Featured Image: NASA’s generic eVTOL cabin model rests on the ground after impact. (NASA photos by Dave Bowman except as noted)

The NASA Langley Research Center in Hampton, Virginia, has a noteworthy dilemma: to keep and refurbish the Landing and Impact Research (LandIR) facility — typically just called the Gantry — or dismantle the structure that has served as a valuable aircraft and spacecraft testing facility since it was constructed for the Apollo program in the 1960s.

At 240 ft (73 m) tall and 400 ft (122 m) long, the Gantry (see sidebar)  is a mammoth, crane-like structure used to simulate various situations, including aircraft crashes and space capsule splashdowns.

As this article was being compiled, NASA Langley had completed a planned drone inspection of the Gantry. A Skydio X2D (see sidebar) uncrewed aircraft system (UAS) performed a 3D-mesh scan of the structure, demonstrating use of new technology to conduct the inspection.

The NASA Lift+Cruise Model at the LandIR facility at Langley Research Center The dots facilitate 3-dimensional photogrammetry.

 

The test model hoisted into position on the Gantry.

 

The Gantry is inspected for corrosion damage and routine maintenance items annually but is currently in need of advanced treatment to counteract years of usage. NASA is evaluating internally whether there are customers or a mission need that can sustain the facility into the future, according to Susan Gorton, NASA project manager for the agency’s Revolutionary Vertical Lift Technology (RVLT) project.

eVTOL Drop Test
For the past three years, the RVLT project has been planning for a drop test of a generic electric vertical takeoff and landing (eVTOL) aircraft fuselage. NASA and the US Federal Aviation Administration (FAA) held a series of joint workshops — as well as presentations at several VFS meetings — to provide information on test and evaluation requirements, vehicle safety system development, and certification challenges for eVTOL aircraft.

In November 2020, NASA released its Announcement of Collaborative Opportunities for its Advanced Air Mobility (AAM) National Campaign 1, which had numerous opportunities for companies to partner with NASA through non-reimbursable Space Act Agreements, including for crash testing.

Although no eVTOL companies responded for crash testing research, NASA continued to forge ahead on its own.

On Nov. 9, the LandIR was used to drop a full-size composite cabin section of the NASA Lift+Cruise Reference Vehicle, which measures 18 ft (5.5 m) long and 6 ft (1.8 m) tall. The “proof of concept” cabin section was created in-house as representative of a six-passenger configuration and not for a particular eVTOL aircraft, according to Langley public affairs. 

“The test was a great success for the crash-worthiness team at Langley,” said Justin Littell, lead RVLT researcher in eVTOL crash safety and a member of Langley’s Structural Dynamics Branch, in a NASA news release. “We successfully tested the eVTOL vehicle concept representing a six-passenger, high wing, overhead mass, multiple rotor vehicle, obtaining more than 200 channels of data, and collecting over 20 onboard and off-board camera views.”

NASA emphasized that the drop test was not performed to determine the airworthiness of the structure, but rather to collect data. A variety of experiments were included on the test article. These experiments included several seat configurations including a NASA energy-absorbing concept, various sizes of crash test dummies to study the effects of the crash loads on all sizes of occupants, and a modular NASA-developed energy-absorbing composite subfloor.

Data have not been thoroughly analyzed, but the results have shown some unexpected failures of the structure.

“We haven’t gone through all the data yet and figured everything out,” Littell told Vertiflite. “The subfloor of the cabin was crushed [to absorb the impact but] the overhead structure collapsed. That is what happened. Our composite material models didn’t quite capture the failure mechanisms that occurred.”

NASA’s statement on the initial test added the following:
“The subfloor and energy absorbing seats functioned as intended and limited the effect of the impact on the crash test dummies.”

“Our intention was to generate data,” said Littell. “We did. We want to shed light on the idea of designing crashworthiness in these vehicles. We built our own [cabin section] so we could publish the data from these tests.”

For this test, NASA designed the overhead mass to represent the wing structure, rotor and battery with all of the weight over the cabin. “There are many other overhead-mass configurations which may behave differently in a crash,” NASA noted in the news release.

Justin Littell speaking at the VFS Electric VTOL Symposium in January 2020 on the importance of impact testing. (VFS photo by Warren Liebmann)

NASA plans a second Lift+Cruise drop test — tentatively scheduled for late this year — which will incorporate updating the computer simulations based on the first test data. Overhead mass and seating configuration, and energy absorbing structure could change for the second test, said Littell. Specific information will be released once the data from the first test is fully analyzed.

Asked if eVTOL companies would participate in the second test of the structure, Littell said, “I hope they would want to. There are different ways to address this [subject]. How crash safety is addressed in the regulations is where you need to start.”

He added, “The idea that you could conduct a full-scale test as your means of compliance would be interesting to see. That’s for FAA to decide. We are trying to provide the data to help with the discussions.”

Prior to the initial test, the proof-of-concept test article was equipped with energy absorbing systems, seats and crash-test equipment.

NASA Langley will present the data and analysis from the drop test in May in two papers at the Vertical Flight Society’s 79th Annual Forum and Technology Display in West Palm Beach, Florida.

Gantry’s Future
Within NASA, there is a discussion on the future of the LandIR. Various items must be discussed before a decision is reached on whether to keep the Gantry or decommission it, according to a NASA Langley spokesperson.

The Gantry is a national historical landmark, so federal historic preservation laws and regulations must be considered, and NASA headquarters also has an office that reviews the facilities and operations of the facilities at each NASA center.

The additional reviews and oversight add to the complexity of the operation and future of LandIR.

Has computer technology advanced to the point where the Gantry is a relic? Vertiflite posed this question to Littell: “I think we’re far along, but not ready yet,” he said. “For example, we ran this test and [the outcome] was different from what our computer models predicted. Our intent [now] is to determine why our models weren’t predictive. And we need to develop methodologies toward that goal.”

Within the agency, there are two views on whether the Gantry should stay or go. One camp believes the device is an important safety and technology-advancing tool and should be refurbished.

The vehicle was destroyed beyond expectations, which gives NASA valuable data to incorporate into its crash simulation models.

 

The NASA Lift+Cruise Model after suffering a devastating crash. Tests like these enable researchers to understand how a vehicle's structure reacts to a crash.

 

The other group maintains the device, which was built in 1963 to model lunar gravity, is too expensive to maintain and that these tests can be done virtually for less cost. The problem with virtual testing for some technologies is that there isn’t adequate data on which to build a virtual model, according to sources familiar with the science.

“I fully support the idea of maintaining the Gantry for performing future space-related impact testing, and for certification of aircraft crashworthiness,” said Dr. Karen E. Jackson, the former senior aerospace engineer for the Structural Dynamics Branch at Langley, now retired. “The [LandIR] Gantry is truly a unique facility that has been utilized to perform a wide variety of tests including Apollo crew module landings under simulated lunar gravity [and] a series of general aviation (GA) aircraft full-scale crash tests (data from which were used to establish seat impact criteria used today).”

Jackson was the 2017 VFS Alexander A. Nikolsky Lecturer; she condensed her lecture as an article in the Sept/Oct 2018 issue of Vertiflite, “Advances in Rotorcraft Crashworthiness: Trends Leading to Improved Survivability.” The Lecture and the article summarized some of the rotorcraft testing over the years.

Several research programs were sponsored by the US Army to encourage the use of advanced composite materials in rotorcraft structural design. The first program was the Advanced Composite Airframe Program (ACAP), whose goal was to demonstrate the potential of advanced composite materials to save weight and cost in airframe structures while achieving systems compatibility and meeting military requirements for vulnerability reduction, reliability, maintainability and survivability. The ACAP began in 1979 and concluded in 1987 with full-scale LandIR crash tests of the Bell and Sikorsky static test articles.

In March 2010, a full-scale crash test of an MD 500 helicopter was performed at the LandIR facility. The purpose of the test was to evaluate the performance of an external Deployable Energy Absorber (DEA), aka helicopter air bags.

In 2013 and 2014, in cooperation with the US Navy, US Army and FAA, a CH-46E Sea Knight helicopter was painted with 1-inch (2.5-cm) diameter black dots in a random pattern on one side of the airframe. This helicopter was crash tested at the LandIR facility as part of the Transport Rotorcraft Airframe Crash Testbed (TRACT) program. During the crash test, the position of each dot was tracked in time using 3-dimensional photogrammetry.

Safe to say, the LandIR facility has had an outsized impact on the design and regulation of aircraft crashworthiness. These latest tests of the eVTOL cabin will allow NASA to update its tools and provide all aircraft developers with the latest insights into how to prevent injuries in the event of an accident.


About the Author

Robert W. Moorman is a freelance writer specializing in various facets of the fixed-wing and rotary-wing air transportation business. With more than 30 years of experience, his writing clients include several of the leading aviation magazines targeting the civil and military markets.  He can be reached at rwmassoc325@gmail.com.

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