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By Elan Head

An award-winning journalist, Elan is also a commercial helicopter pilot and an FAA Gold Seal flight instructor with helicopter and instrument ratings. Follow her on Twitter @elanhead

q-and-a

Q-and-A on eVTOL crash safety

No aircraft developer or operator wants to believe that their aircraft will crash. But aviation accidents can and do occur — and the stakes are high. When all other safety measures fail, an aircraft’s occupant protection features can make the difference between passengers walking away from a crash, or suffering serious or fatal injuries. For the eVTOL industry, which aims to win public acceptance for very high volume flight operations, crash safety is simply too important to ignore.

In the United States, NASA and the Federal Aviation Administration (FAA) have been leading efforts to create standards for eVTOL crashworthiness, and to educate eVTOL developers on steps they can be taking to make their vehicles safer. COVID-19 concerns forced the postponement of an in-person workshop on eVTOL crashworthiness originally scheduled for April 7 at NASA Langley Research Center in Virginia. Instead, organizers conducted a virtual meeting that served as an introduction to the topic (presentation slides from that event can be downloaded here).

For anyone who might have missed it, we asked NASA’s Justin Littell and the FAA’s Joseph Pellettiere to recap some of the key points related to eVTOL crash safety. Littell conducts research into aircraft crashworthiness as part of the Structural Dynamics Branch at NASA Langley. Pellettiere is the chief scientific and technical adviser on crash dynamics for FAA Aviation Safety.

NASA Landing and Impact Research Facility
The Landing and Impact Research Facility at NASA Langley in Virginia is used for crash safety research, as with this controlled crash of a CH-46E helicopter fuselage in 2013. U.S. Air Force Photo by Staff Sgt. Stephanie Rubi/Released

eVTOL.com: What is the role of NASA and the FAA in aviation crash safety?

Justin Littell: NASA has been involved in aircraft crash safety for the past 40-plus years. We have unique facilities and resources that are able to be used to conduct various research programs which feed into the development of the regulation development efforts. Additionally, we develop in-house technology that is able to be spun off into industry.

Joseph Pellettiere: The FAA’s mission is to provide the safest, most efficient aerospace system in the world. Part of this involves developing the requirements and regulations that support crash safety — whether it be accident prevention and the identification of precursors to incidents, or the investigation of accidents to develop lessons learned that can be shared with the community. In addition, as aerospace and occupant safety experts, we are well positioned to promote concepts to achieve a high level of crash safety.

Justin Littell eVTOL crash safety panel
Justin Littell discusses eVTOL crash safety at the Vertical Flight Society’s annual Electric VTOL Symposium earlier this year. VFS Photo by Warren Liebmann

eVTOL.com: What specific efforts related to crash safety are you making in the eVTOL world?

Joseph Pellettiere: While eVTOLs are new types of vehicles entering the national aerospace system, they have many features of existing types of aircraft. For example, they do have vertical take-off and landing capability, much like existing rotorcraft, with some differences, however. Others have wings and a capability to glide. The FAA has knowledge and experience in accident prevention and safety analysis for both of these types of systems. As such, we can leverage the lessons learned and adapt them to these new vehicles.

One of these areas is in promoting crash safety as a system level concept as opposed to each individual component. We are looking at ways to leverage the recent revisions to [Federal Aviation Regulations] part 23 to promote and incorporate design features that are crashworthy. Part of this involves industry outreach to share our experience and hold discussions on how crash safety can be met for the eVTOL world.

Justin Littell: Currently, we are researching the current technology and regulatory gaps that exist for eVTOL crashworthiness. We are working with the industry and standards organizations to best determine where NASA research should be focused. Once we have determined what the gaps are, we will focus our efforts on addressing them.

eVTOL.com: What are some of the challenges associated with occupant protection with these novel types of aircraft?

Justin Littell: eVTOL vehicles today, while having some similarity to current general aviation aircraft and rotorcraft, are also unlike these current vehicles, so it is uncertain how they will perform both under normal mission profiles, and also in a mishap event. The use of novel materials such as composites, electric power, and autonomy are three areas where there is no historical data to support, and thus determining levels of performance and safety is difficult.

Joseph Pellettiere: We know how current general aviation and rotorcraft fail and crash. But what will these failure modes of the eVTOL aircraft encompass? Will we need to look at other crash modes? What will their performance entail? How do batteries affect post crash hazards and egress?

Joseph Pellettiere eVTOL crashworthiness
Joseph Pellettiere speaking on the crashworthiness panel at the Vertical Flight Society’s 2020 Electric VTOL Symposium. VFS Photo by Warren Liebmann

eVTOL.com: Why do eVTOL developers need to be thinking about crash safety now?

Joseph Pellettiere: This is the time for eVTOL developers to be thinking about crash safety as they are early in the development process. If you view crash safety as a system level concept, many small design changes now can pay great dividends later that would be more difficult in the future. For example, if you incorporate crush space into the fuselage for the purpose of absorbing impact energy, you can design that fuselage and space. However, if you decide you need it later on, it will be much more difficult to change the shape of the fuselage to build in this new space. It is anticipated that these vehicles and designs will be around for many years, so taking advantage of these early stages of development will pay many dividends in the future.

Justin Littell: Because we essentially have an “open canvas,” so to speak, with the vehicle design, many of the crash features that already exist and are understood can be implemented and utilized beforehand. Items such as subfloor and landing gear crushable/collapsible structure, frangible joints, and airframe geometry can all be adapted and optimized prior to the first passenger riding.

eVTOL.com: What are some of the biggest misconceptions related to crash safety that you’ve encountered among eVTOL developers?

Joseph Pellettiere: I think there is this general perception that these vehicles are extremely safe and as such, they will never crash. However, if you begin to look at the number of operations, take-offs, landings, utilization rates, you can begin to project out that accidents may occur. Crash safety is the last line of defense in the failure chain. An event has happened, let’s plan to do all that we can to make sure it is a survivable outcome.

Justin Littell: We are trying to convey that there is a lot of the technology available for use in occupant protection [that] already exists, and that by utilizing a few small steps, the level of protection in the vehicle can be improved.  This was the intent of the recent virtual workshop we held on April 7, and more of the intent of the in-person workshop later this year. The virtual workshop was to provide a brief overview of the background of crashworthiness with some specific examples of how crashworthiness can be utilized in aircraft fleets.

We hope that the developers which do not have a detailed background in crashworthiness realize that there are resources out there to help. The in-person workshop [date still to be determined] will expand upon this premise and will allow industry, regulators, independent and government researchers to come together in an open forum and discuss the current issues.

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4 Comments

  1. A question quoted was not answered … the one regarding post-crash implications of batteries.
    I’d add a supplementary to that … are there any known significant differences among the crashworthiness of lithium ion, carbon and other battery materials anticipated for application in eVTOL?

  2. A device creating lift by inertia change will be much safer than aerodynamic devices having exposed high speed moving parts. PDF copy of the concept drawing can be presented if the email ID is informed.

  3. In most cases the goal is not to save the batteries but the occupants in a crash. If you want the batteries to survive there would be a heavy weight penalty unacceptable to anyone trying to lift cargo or passengers. Usually the loads from a crash are far above what the plastic based battery shells can withstand. Now you have the combination of a potential crash vertically as well as forwardly.

  4. I’m glad that people are thinking about eVTOL crashworthiness now. Those of us who have worked in crashworthiness for the last 50 to 60 years have never had the pleasure of working on a helicopter that wasn’t overweight, underpowered, and in single rotor helicopters, tail heavy. Especially in smaller aircraft, the weight restrictions resulted in cockpits and cabins far too short to permit the inclusion of comfortable seats which are also a major contributor to crashworthiness. The addition of a few inches of cockpit length would have required lengthening the fuselage with its unacceptable weight penalty. The weight limitations and cramped space resulted in both reduced crash safety and especially comfort of the seats while large ballast weights were needed in the nose of some aircraft to offset the “tail heavy”” problem. It would have been very beneficial to comfort, as well as crashworthiness, if ballast weight could have been used to improve those features instead of being carried as dead weight.
    Perhaps eVTOL aircraft will have configurations that eliminate at least some of the basic complications besetting helicopters, I hope so. But now is the time to think about it, to learn from the helicopter experiences that preceded eVTOL, and try to not repeat mistakes!

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