Vertical Aerospace Cites Propeller Fault In eVTOL Flight Test Accident


Vertical Aerospace has identified a propeller issue as the most likely cause of an Aug. 9 flight testing accident involving its VX4 electric vertical takeoff and landing (eVTOL) prototype. According to the company, “an unexpected fault occurred causing the aircraft to enter a stable descent, before being damaged on impact with the ground.” Vertical reported that the propeller in use was an early generation model that had “already been redesigned prior to the incident.”

“We are pleased with our flight test progress to date and the data, insights and invaluable learnings we have collected,” said Vertical founder and CEO Stephen Fitzpatrick. “While a fault of any sort is disappointing, it is not wholly unexpected at this stage of testing a novel aircraft. … 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 is also in the process of implementing additional undisclosed recommendations stemming from its investigation. The company noted that it has submitted a report to the U.K.’s Air Accidents Investigation Branch (AAIB) and intends to provide an update once the AAIB has concluded its own investigation. As previously reported by AVweb, the accident took place at Vertical’s flight test center at Cotswold Airport (GBA) in the U.K.

Kate O'Connor
Kate O’Connor works as AVweb's Editor-in-Chief. She is a private pilot, certificated aircraft dispatcher, and graduate of Embry-Riddle Aeronautical University.

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  1. When you buy a small drone you almost always get a set of replacement propellers “free”.
    For good reason, they are thin and fragile and designed to flex as they turn to cope with sudden power changes.
    And if by mischance you happen to hit a leaf, or land in slightly long grass, the advice is to check for any nicks or cracks, because it is annoying to see a drone shred a bit of plastic and fall like a stone.
    Of course the manufacturers of the “air taxis” and “personal transporters” say they will never have those problems.

    • Other sources have reported that it wasn’t the loss of a propeller itself that was a problem, but that the loss of the prop caused the pylon that it and the motor were mounted on to fail, and that took out the data bus for other motors on that wing. That’s almost a more disturbing problem to me–your motors shouldn’t snap off if you lose a prop blade, and the even if they did, the loss of that connection shouldn’t break the connection with the other motors. I’m sort of reminded of the Electra whirl mode problems, UAL 232, etc.

      Multiple motors/props can provide great redundancy and protection, provided you make sure the failure of one of them doesn’t take out the others…

  2. For the concepts that involve “parking” some number of rotors during forward flight, has there been any flutter analysis…and for every possible “parked” rotor position?

  3. For myself alone, I will NEVER fly in one of these things unless I’m unconscious and PUT aboard. As a former PHI A&P I I know that rotary wing is complex enough but these multi bladed electrics take that to an absurd level. Guess the KISS principle doesn’t have currency with this industry?

    • I’m going to assume that ALL the rotary wings that you worked on required not only transmitting power from one or more ICE power plants to the rotor, but allowing both cyclic and collective control as well. An electric copter with direct drive, fixed pitch props is mechanically way simpler than a helicopter.

  4. “Necessity is the mother of invention.” The helicopter has already filled the void for vertical take off. Can anyone explain the necessity for these eVTOL machines? Just because you can, is not a reason to fill a market that is not there. “Why” has always been the most embarrassing question ever asked!

    • I am a helo guy and love them. However, I’d gladly take the following improvements offered by Joby and others:

      1) Much quieter. Fenestrons help, but helicopters are still just plain loud. Joby’s noise tests are outrageously good.

      2) Eliminate “Loss of Tail Rotor Effectiveness”. A quartering wind from just the right direction can make things bad really fast. See:

      3) More torque. Always want more torque.

      But your point is well taken. I watched a video showing the current state of the art of drone package delivery systems. The video of 23 drones delivering simultaneously is genuinely terrifying–I would not want them wizzing over my head delivering ranch dressing of all things. Amazon’s current drone is *80 pounds*. I can’t imagine the FAA certifying an unmonitored, unmanned thing that will literally kill someone if it just suffers a power failure. Zipline looks impressive.

    • Theoretically, an aircraft that can takeoff or land vertically yet fly like an airplane during cruise would be more efficient than a helicopter and won’t need a runway. It’s supposed to be a “best of both worlds” design. The FAA created the powered lift category for these, but there are no civilian examples.
      In reality, it’s a big compromise. See the V-22 Osprey and all the problems the military had with it. Textron has yet to get a tiltrotor certified for the civilian market. Many “e-vtol” designs are tiltrotors, which should be in the powered lift category. I suppose that the reason they are trying to do that instead of a “helicopter, but electric” is because the endurance of an electric aircraft is so low. An electric helicopter will have even less utility than an electric airplane.
      Some “e-vtols” are just drones large enough to carry people, which could also be considered multirotor helicopters.

  5. Noise: Point well taken, however, helicopters are not delivering packages all day long.
    Counterrotating blades can eliminate the tail rotor blade.
    Currently, eVTOL’s offer 20 to 30 minutes of fun for those with pockets deep enough.
    The only way they will ever be practical is if they use a highly efficient generating system that greatly reduces the battery weight.

  6. Ford is “abandoning its EV truck project” by tripling production capacity at the Lightning factory in Dearborn, where they just hired 1200 additional workers. Try again, Zeca.

  7. They must be very noisy as so many propellers are never exactly in sync.
    I would also NEVER ever sit in such a contraption with a motor ripping out the whole electrics connected to other ones, what a stupid design that is.
    I have worked on real aircraft, (Dash 7) and besides fly electric powered models, they need a lot of wiring especially twins like a big Twin Otter, and plenty redundancy.
    Such a hype about eVTOL machines carrying fearless pilot and a few passengers .. good luck eh.