Crashing: Part of the process?

Vertical Aerospace crashed its prototype last week during a motor failure test scenario. 

It is not the first time an eVTOL has crashed during flight tests and it probably won’t be the last. So is crashing an integral part of the eVTOL certification process? It may not be. But successful navigation of all phases during which a crash is possible is and accidents are likely along the way — that is why we have prototypes. 

The Vertical crash happened on August 9, at Vertical’s flight test centre on the grounds of Cotswold Airport. The company confirmed the aircraft was remotely piloted and there were no injuries during the accident. 

In a SEC filing, filed after the accident, Vertical stated: “Our flight test programme is designed to establish the limits of the aircraft’s performance, and the incident occurred during an uncrewed test of the aircraft’s manoeuvrability during a motor failure test scenario, which is a key requirement to progress to crewed operations.”

A week before the crash Vertical published their second-quarter results. CEO Stephen Fitzpatrick said: “We have seen fantastic momentum at Vertical in the first half of 2023 across our testing, certification, and commercial efforts. We have conducted our first untethered flights of our full-scale VX4 and been granted a design organisation approval from the CAA.”

Other manufacturers, including Joby have reported prototype crashes before. Whilst BETA Technologies has dropped their battery packs from 50ft to prove durability. And NASA has crash tested an eVTOL aircraft to see what happens. 

In the UK in April 2021, ZeroAvia’s testbed Piper Malibu, which had been partly converted to run on a hydrogen fuel cell propulsion system, crashed near Cranfield Airport, UK. According to an AAIB report, the electrically-powered aircraft was undertaking experimental flight tests when power to the electrical motors was lost. A forced landing was carried out during which the aircraft was severely damaged.

“The loss of power occurred during an interruption of the power supply when, as part of the test procedure, the battery was selected ‘off’ with the intention of leaving the electrical motors solely powered by the hydrogen fuel cell. During this interruption the windmilling propeller generated a voltage high enough to operate the inverter protection system, which locked out the power to the motors. The pilot and observer were unable to reset the system and restore electrical power,” stated the AAIB. 

credit: ZeroAvia

In February 2022, Joby reported an accident during flight testing of its prototype when the aircraft was flown at over 270mph (435kph), far beyond its purported top speed of 200mph (322kph). Disclosed again in an SEC Form 8-K filing, Joby stated: “There were no injuries. Safety is a core value for Joby, which is why we have been expanding our flight envelope with a remote pilot and in an uninhabited area, especially as we operate outside expected operating conditions.

“Experimental flight test programmes are intentionally designed to determine the limits of aircraft performance, and accidents are unfortunately a possibility. We will be supporting the relevant authorities in investigating the accident thoroughly.”

Then over the festive period last year, NASA crash tested its eVTOL concept, developed by its  Revolutionary Vertical Lift Technology (RVLT) project. The aircraft, designed to represent a six-passenger vehicle with multiple rotors, was filled with crash test dummies in a range of sizes and multiple seat configurations. NASA also tested a modular energy-absorbing composite subfloor on the aircraft.

The crash provided researchers with over 200 channels of data and more than 20 camera views. NASA said: “The subfloor and energy absorbing seats functioned as intended and limited the effect of the impact on the crash test dummies.” It also said that “the vehicle was destroyed beyond expectations which gives researchers valuable data when planning to make AAM vehicles safe for public use.” 

NASA is planning a second drop test of an eVTOL test article to take place some time towards the end of this year. 

Justin Littell, Research Engineer in the Structural Dynamics Branch, NASA said: “We are trying to convey that there is a lot of the technology available for use in occupant protection already in existence, and that by utilising a few small steps, the level of protection in the vehicle can be improved.”

Joseph Pellettiere, Chief Scientist and Technical Advisor for Crash Dynamics at FAA, added: “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, utilisation rates, you can begin to project out that accidents may occur. Crash safety is the last line of defence 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.”