What are eVTOL Aircraft?

eVTOL Aircraft are essentially battery powered Electrical Vertical Take-Off and Landing aircraft.

Aimed at the Urban Air Mobility market, eVTOL aircraft aim to reduce traffic congestion by making airborne short-hop services achievable and affordable.  Particularly suited for air taxis and emergency response vehicles, an eVTOL is designed to allow quick access to areas at a much lower cost than a traditional helicopter.

These aircraft, which are currently in development, are designed to carry generally between 2 and 10 passengers, fly short routes within urban environments, provide quick turnarounds for arrivals and departures, and may even operate autonomously.

eVTOL aircraft differ from traditional aircraft and rotorcraft as they are powered by multiple battery driven rotorblades and offer vertical take-off and landing.  This does have an impact on safety, as during the take-off / landing phase, they will not have little (or no) forward momentum in order to generate lift; nor will they be able to use autorotation, which is used by helicopters to allow a controlled form of crash landing.

This exciting market has drawn attention from both traditional aircraft manufacturers, such as Boeing and Airbus, but also car manufacturers and the likes of Uber.

The emergence of eVTOLs could catalyze transformation across many different areas, with these being particularly pertinent:

  • Air traffic management system: Developing and deploying a new, complete air traffic management system is expected to be key. This system must span airspace allocation and management as well as airworthiness certifications and pilot requirements for unmanned autonomous aerial systems. National governments need to work together as well as in conjunction with local councils to settle upon a common operating concept and establish a universal set of requirements that would allow eVTOLs to be widely deployed. This includes ensuring interoperability with existing air traffic management systems globally.
  • Physical infrastructure: Significant capital is required to acquire the land/space necessary for building vertiports and other infrastructure components. Extending existing types of public/private partnerships or establishing new models will be needed  to secure adequate funding. Without this type of collaboration, infrastructure projects may not get off the ground, thus delaying, limiting, or entirely blocking the widescale deployment of eVTOLs.
  • Aircraft development: Current helicopter developers and manufacturers  are at risk of being disrupted, with the implications being similar to those incurred by the automotive sector when new entrants used electrification and autonomous capabilities to re-envision the automobile. Parallels can also be drawn with taxi and rental car industries when technology companies used apps and geo-location capabilities to reimagine ride-sharing services.The future market for eVTOL aircraft manufactures could be substantial. For example, the estimated market size for the US alone is approximately $17 billion by 2040.

Certification and Safety Requirements

At present there is no specific certification and safety requirements for eVTOL aircraft.  As with any aircraft, before they can be used in public service, they will need an airworthiness certificate to show how they meet the relevent safety standards.

The European Union Aviation Safety Agency (EASA) has been working on the certification of such aircraft since 2018 and Active VTOL Crash Prevention Limited is part of the team formulating the EUROCAE/EASA safety standards for eVTOL aircraft with specific responsibility for drafting new standards for both eVTOL Active Safety Systems and for Stroking Crashworthy seats.

Taking accident data for helicopters as a starting point, the two highest causes of accidents are Loss of Control-Inflight and System (Powerplant) malfunction, with Low Altitude Operations and Collision cited as two additional causes for accidents.

Fixed-wing aircraft already deploy a parachute in an emergency; inflating and slowing the descent to provide an acceptable touchdown condition.  Over 500 lives have been saved worldwide to date by whole aircraft recovery systems and these are becoming more standard in the redundancy systems of many general aviation aircraft.

There are dangers inherent in the design and operation of eVTOL aircraft:

  • eVTOL aircraft are designed to be flown at low altitude where the incidence of bird strike is higher due to the greater density of birds;
  • the increased number of take-offs and landings will result in additional stress for pilots, airframes and engines alike – remembering that pilots will need to consider potential traffic, obstacles and wildlife in all 6 directions;
  • the increase use of the eVTOL aircraft over towns and cities increases the risk to those on the ground as well as animals and property in the event of an emergency;
  • electrical power trains and the lithium batteries used to power eVTOL aircraft are at greater risk of fire / explosion if an emergency landing has to be made or the aircraft strikes an obstacle;
  • the lack of any (or minimal) forward momentum during the vertical take-off and landing phases means that there will be no normal lift under any wings; and no rotational effect which is used by helicopters to control emergency descents;
  • eVTOL aircraft are likely to appeal to a wider audience than standard helicopters and light aircraft which means that safety features will need to deal with a much wider range of parameters such as weights, sizes and the excitement of passengers

 

As part of this, it has become apparent that current Emergency Descent Arrest Systems designed for fixed wing and rotary aircraft will not work when it comes to eVTOL aircraft and a new approach is required.

In particular, in the NASA Langley Research Center’s paper on “Challenges in Vehicle Safety and Occupant Protection for Autonomous electric Vertical Take-Off and Landing (eVTOL) Vehicles” by Justin Littell; the author concluded that a Ballistic Recovery System should be a required piece of equipment but notes that existing systems do not advertise operation below 400 feet.

There have been some improvements since that paper was written, with one Ballistic Recovery System claiming to work at heights of 100 feet and over.  However, this still leaves a safety gap should an emergency occur below that height. We have created our own white paper outlining the various Emergency Descent Arrest Systems which currently exist and how they can be applied to eVTOL aircraft.  This white paper was presented to EASA in February 2021.

Standard parachute / ballistic recovery systems are normally reliant on some forward momentum for proper and expedient deployment of the parachute – this is the reason why revovery parachutes are not found on helicopters.  The parachutes also take time to deploy and hence require sufficient lateral airspeed and altitude to allow them to work (for example, the Cirrus aircraft needs to be 920 feet in the air) – well above the ceiling for eVTOL aircraft.

This is where the AVCP Zero-Zero Safety System comes to the rescue.

How the AVCP Zero-Zero Safety System Works

In the event of a system or power failure…

Total launch system/parachute/rocket motor weight is just 110lbs/50kg for a 3310lb/1500kg aircraft.

At whatever height the emergency occurs, the motors and small drogue parachute are actively launched.

In-line solid composite propellant rocket motors fire for approx 1 second at a height between 5m and 15m, and rotate on landing so that the aircraft does not take off again

At the moment of impact, AVCP’s stroking, lightweight shock absorbing seats provide the primary shock absorption.Our fire resistant prepreg composite system contains any potential battery compartment fire

AVCP’s technology suite will allow passengers to walk away from any almost any eVTOL uncontrolled landing, from any height, with only minor injuries at worse.

What AVCP Can Offer to eVTOL Manufacturers

Here at Active VTOL Crash Prevention Limited, we have a wide range of expertise in safety systems:

  • Our CEO (Roger Sloman) founded the Advanced Composites Group in 1975 by introducing carbon fibre into F1 motor racing – he developed the business into a global operation based on novel prepreg materials for the tooling, aerospace, and motor racing markets.
  • We have wide experience of developing novel uses for rocket motors, such as the use of LRMs to protect land vehicles against mine blast and IEDs
  • Our team includes Dr Brian Coaker who has recognised expertise in the development and delivery of electronic safe arming and ignition sub-systems, high-power microwave and microwave electronics, in the defence, commercial and medical markets.

We use our technical expertise to deliver all elements of the Zero-Zero Safety System:

  • Environmentally friendly composites specifically designed to protect the battery box in the event of a fire
  • Safe arm and initiation automated control systems to ensure that rocket systems do not deploy accidentally in the event of lightning strike and/or impact
  • Rocket motor technology development to ensure the optimal choice of fuels for a controlled descent of the eVTOL aircraft in the event of an emergency

Performance Characteristics

In-line rocket motor reduces ground contact velocity under conventional ballistic parachute from 5-7m/s to 1-2m/s maximum. (Target is less than 1m/s) System is deployed in less than 0.5s and fully effective in approximately 1.5s. Effective at only 5-10m altitude with target ground contact speed of 1-2m/s worst case maximum. Aircraft attitude automatically controlled by parachute.

eVTOL Aircraft are essentially battery powered Electrical Vertical Take-Off and Landing aircraft.

Aimed at the Urban Air Mobility market, eVTOL aircraft aim to reduce traffic congestion by making airborne short-hop services achievable and affordable.  Particularly suited for air taxis and emergency response vehicles, an eVTOL is designed to allow quick access to areas at a much lower cost than a traditional helicopter.

These aircraft, which are currently in development, are designed to carry generally between 2 and 10 passengers, fly short routes within urban environments, provide quick turnarounds for arrivals and departures, and may even operate autonomously.

eVTOL aircraft differ from traditional aircraft and rotorcraft as they are powered by multiple battery driven rotorblades and offer vertical take-off and landing.  This does have an impact on safety, as during the take-off / landing phase, they will not have little (or no) forward momentum in order to generate lift; nor will they be able to use autorotation, which is used by helicopters to allow a controlled form of crash landing.

This exciting market has drawn attention from both traditional aircraft manufacturers, such as Boeing and Airbus, but also car manufacturers and the likes of Uber.

The emergence of eVTOLs could catalyze transformation across many different areas, with these being particularly pertinent:

  • Air traffic management system: Developing and deploying a new, complete air traffic management system is expected to be key. This system must span airspace allocation and management as well as airworthiness certifications and pilot requirements for unmanned autonomous aerial systems. National governments need to work together as well as in conjunction with local councils to settle upon a common operating concept and establish a universal set of requirements that would allow eVTOLs to be widely deployed. This includes ensuring interoperability with existing air traffic management systems globally.
  • Physical infrastructure: Significant capital is required to acquire the land/space necessary for building vertiports and other infrastructure components. Extending existing types of public/private partnerships or establishing new models will be needed  to secure adequate funding. Without this type of collaboration, infrastructure projects may not get off the ground, thus delaying, limiting, or entirely blocking the widescale deployment of eVTOLs.
  • Aircraft development: Current helicopter developers and manufacturers  are at risk of being disrupted, with the implications being similar to those incurred by the automotive sector when new entrants used electrification and autonomous capabilities to re-envision the automobile. Parallels can also be drawn with taxi and rental car industries when technology companies used apps and geo-location capabilities to reimagine ride-sharing services.The future market for eVTOL aircraft manufactures could be substantial. For example, the estimated market size for the US alone is approximately $17 billion by 2040.

Prevention is better than cure.Make all Crashes Survivable

The eVTOL Safety System concept was originally proposed as Linear Rocket Motors installed in the skids of a helicopter and activating automatically during final 1-2 seconds of an un-controlled descent to slow the descent rate before landing or preventing a CFIT accident.

After the eVTOL market activity began developing rapidly in 2016 the concept was further evolved by the addition of a rapid-opening ballistic parachute, and some major developments of the Linear Rocket Motors to suit the specific requirements of the eVTOL application.
The latest design (2020) uses a small drogue parachute which can be opened fully at any aircraft speed, and which controls the aircraft descent rate to 25m/s and also maintains a level aircraft attitude during the descent.  The retrorockets then reduce the aircraft descent rate from a maximum of 25m/s to 10m/s on landing, which is then dealt with mainly by the stroking crashworthy seats
In all versions an Autonomous Sensor/Control/ Initiation System (ASCIS) for the rocket motors remains in Safe Mode until below about 10 - 15m altitude and the aircraft height and descent data indicates a hard landing or crash may occur.
When the data indicates that the system needs to be fired it arms within 1ms and if the data continues to indicate a crash will occur the rocket motors will then be fired. Immediately on landing at a controlled 1-2m/s, or just before, the rocket motor direction is adjusted to prevent the aircraft taking off again. (Installed thrust has to be about twice the weight of the aircraft in order to counteract both gravity and the momentum due to the descent rate of the aircraft.)
The ultra-rapid control and EFI (Exploding Foil Initiation) system is already used in air-launched missiles, and is designed to be a 100% safe system, immune to any radio-frequency interference and even lightening strikes.
The Linear Rocket Motor design is patented globally, is currently at about TRL 6,  and is being further developed for both the Active Mine Protection System for armoured vehicles and the eVTOL applications.

T: 01335 360 663E: info@advanced-blast.com

T: +44 (0)7989 381057E: info@advanced-blast.com

T: +44 (0)7989 381057E: info@advanced-blast.com

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