Phase 1 included tethered flights, ground taxi testing and high-powered ground runs, all with a pilot on board.
Vertical is now preparing to progress to piloted untethered thrustborne testing, as soon as it receives permission from the UK Civil Aviation Authority (CAA).
The VX4 went from its first powered ground test to ‘wheels up’ in just one week – three times faster than the previous prototype.
During Phase 1, the VX4 prototype conducted multiple piloted tethered flights and ground runs, across
20 piloted test sorties, completing a total of 70 individual test points. Together, these tests simulated
various aspects of flight and operational situations needed to validate the prototype’s safety in real-world
flight scenarios, including those outside of its expected operating conditions. By intentionally testing the
aircraft’s ability to handle failures, Vertical demonstrated the underlying safety of its design.
One of the most important tests successfully carried out included simulating the failure of one Electric
Propulsion Unit (EPU) – inoperative testing – while in piloted tethered flight, to ensure the aircraft responds
correctly and continues to be safe while in flight conditions.
These tests have enabled Vertical engineers to collect and measure 35,000 flight and system parameters
and verify that all systems are operating correctly and safely in different conditions ahead of further
expanding the flight test envelope to piloted thrustborne flight.
Alongside Phase 1 testing, Vertical’s engineers also completed more advanced low and high-speed taxi
tests, including deliberately failing EPUs at high taxi speeds to confirm controllability and safety. This
verified ground handling characteristics throughout the taxi envelope, as well as aerodynamic characteristics
for increasing speed, while in a safe, ground test environment.
Vertical is continuing to work closely with the UK Civil Aviation Authority (CAA) on expanding its Permit to Fly
as it prepares for Phase 2 of testing which will see the VX4 prototype undergo piloted thrustborne flight tests.
Vertical is currently developing an identical full-scale prototype which will accelerate the VX4’s flight test
programme and demonstration capability. The company will take flight test learnings from both prototypes
into the design and development of the certified VX4 model.
CEO of Vertical Aerospace, Stuart Simpson, said:
“It took us just one week to go from our first ground test to our chief test pilot flying the VX4, and we have
been making outstanding progress since then. We continue to prove the safety and performance of our
design and technology, which we believe to be market-leading. Completing this first phase of testing is a
significant feat for any eVTOL company and shows the strength of our aircraft, team, and our partners as
we progress through our flight test programme and head towards our goal of creating a better way to travel.”
Phase 1 of testing included:
• Piloted tethered flight: performed using closed-loop flight control to ensure the aircraft’s stability and
safety in a controlled environment. Also included simulated failure testing to validate one EPU deliberately
failing and assessing automatic aircraft response to bring other engines to maximum power output while in
tethered flight.
• Ground vibration testing (GVT): Working with specialists from world-leading ATA Engineering – who
performed GVT testing on the $10 billion James Webb telescope - eight heavy-duty shakers were installed
on the VX4 while it was suspended in the air to stress test the aircraft in different situations when flying,
such as turbulence. 350 accelerometers - devices that measure the aircraft’s movements and vibrations
during testing - were installed on the inside and outside of the aircraft to collect the data.
• Powertrain testing: Understanding how the powertrain is operating and evaluating all the components that
generate and deliver power to the propellors. This includes a High Voltage (HV) ripple test to measure and
analyse voltage fluctuations (ripple) generated on the powertrain and ensuring the battery can handle it, even
at low charge, while providing a stable power supply. This is carried out while the aircraft is tethered in hover.
• Dynamic testing: Ensuring all systems are functioning correctly before they are put into use in flight in
real-life conditions – such as powering up, checking the parts are installed and connected correctly and
the systems and components work.
• Propellor testing: Propeller balancing and spinning tests to measure weight distribution of each
propeller blade to ensure vibrations are minimised for smooth, stable flying.
• Taxi testing: VX4 is piloted at low and high speeds on the ground to test the aircraft can move forwards
and backwards effectively, testing brake performance and direction of control using differential thrust.
New VX4 prototype
This next-generation VX4 is more powerful than the previous full-scale prototype, with an impressive 20%
increase in the power-to-weight ratio, enabling the aircraft to reach speeds of up to 150mph – the certification
aircraft’s intended cruise speed.
The aircraft has been designed and built alongside global aerospace partners, including GKN Aerospace,
Honeywell, Hanwha, Molicel, Leonardo and Syensqo. It features Vertical’s next-generation propellers and
new proprietary battery technology, capable of delivering 1.4 MW of peak power and which has been
designed and built at the state-of-the-art Vertical Energy Centre near Bristol, the UK’s most advanced
aerospace battery facility
