Vertical Aerospace has pinned the 9 August crash of its VX4 prototype on a faulty propeller blade which failed during a power-out test.

However, the UK start-up insists the goal of obtaining certification in 2026 for its electric vertical take-off and landing aircraft remains unchanged even though the arrival date for the next prototype appears to have slipped.

VX4 Kemble-c-Charlotte Bailey

Source: Charlotte Bailey

Incident took place at Kemble airfield on 9 August

Flight testing of the VX4 had been taking place at Kemble airfield in southwest England when the incident occurred.

Having completed in July an initial uncrewed flight-test campaign with the aircraft in thrust-borne mode, Vertical was proceeding with follow-on tests to “understand how the aircraft performed outside of its expected operating conditions”.

During the 9 August flight, when one of the aircraft’s electrical propulsion units (EPU) was intentionally disabled – what Vertical has described as a “motor failure test scenario” – one of the front propellers connected to a separate EPU was “released”.

“This resulted in an excessive out-of-balance load, which caused the failure of one of the supporting pylon structures.

“The aircraft entered a stable descent due to loss of thrust, suffering damage on contact with the ground,” says Vertical.

It says the root cause of the incident was a “bonding issue within the propeller blade itself”.

Vertical says the “early generation propeller” had been redesigned prior to the crash and the modified part has been incorporated in its next flight-test aircraft, an update on the first prototype, which is currently under construction.

Vertical untethered-c-Vertical Aerospace

Source: Vertical Aerospace

Untethered flight tests of the VX4 began in July

The second-generation prototype had been expected to fly at the end of this year, but the developer now says it will not make its maiden sortie until early 2024.

Construction of an additional flight-test asset has also been approved, says the company, “and is expected to be flying in the second half of 2024.”

Vertical says it has submitted a report of its findings to the UK Air Accidents Investigation Branch (AAIB) and will issue a further update once the agency completes its probe.

Vertical intends to use the incident aircraft for further ground tests but will not repair it to an airworthy standard, it says.

Further recommendations from the investigation are also being implemented by Vertical.

Noting that an accident of this nature was not “wholly unexpected at this stage of testing a novel aircraft”, Vertical’s founder and chief executive Stephen Fitzpatrick adds: “Our planned second upgraded prototype, which will include most of our top-tier partners’ technology, will have us in the air early next year and we remain on track for our certification timelines.”

Vertical says it has sufficient funding to continue development work into the second half of 2024.