The heart of the Active VTOL Crash Prevention system is the retro rocket array, which can be associated with a ballistic parachute or mounted in the skids of an air taxi. Image: ABBS

British startup offers retro-rocket safety system for cargo drones, air taxis

Equipment & systems Passengers • air-taxi

Active VTOL Crash Prevention Ltd., a subsidiary of Advanced Blast & Ballistic Systems Ltd. (ABBS) founded in 2008 in the UK, presented a patented solid-fuel retro-rocket safety system for aircraft at the Vertical Flight Society Forum 75 convention in Philadelphia on May 16. Designed to assure soft landings of electric vertical takeoff and landing (eVTOL) aircraft and heavy cargo c-drones in case of catastrophic failure such as loss of power or control, the “zero-altitude/zero-speed” system’s inventor said the technology could also be adapted to existing light aircraft and helicopter airframes.

Heavy c-drones under development as well as electric powered air taxis on the drawing boards or in prototype phase will fly at low altitudes over populated areas, presenting safety challenges both for passengers and people on the ground. At very low altitudes — from ground level to about 250ft (75m) — a parachute cannot deploy in time to prevent a crash. This “safety gap” means a serious incident — loss of power or control, foreign object debris (FOD) damage, bird or small c-drone strike — could cause injuries or fatalities.

Roger Sloman, inventor of the system, explained in a technical presentation and later in an exclusive interview how the technology was first developed to counteract the deadly effects of improvised explosive devices (IEDs) of the type detonated by insurgents in Afghanistan or Iraq under armored vehicles. A novel form of rocket motor with a linear array of nozzles along the side of a square-section tube is paired with sensors which can detect and measure an explosion underneath a vehicle within three milliseconds and fire the rockets for a small fraction of a second, with sufficient thrust to keep the vehicle glued to the roadway while a vehicle belly plate then deflects the force of the blast outwards. This application is currently being evaluated by the American and Israeli militaries. The linear rocket motor casings designed for vehicles can also potentially be mounted under the skids of a conventional helicopter.

On a heavy c-drone or eVTOL passenger air taxi, the AVCP safety system is designed to be incorporated in the harness of a ballistic parachute. When sensors indicate an emergency condition, the parachute is launched upward above the aircraft by a small rocket and opens, slowing the descent; when the craft is about 15-30ft (5-15m) above ground level, the retro rockets fire for about 1 second, slowing the descent to a soft landing. A key feature of the system is that it turns the nozzles from the vertical position to horizontal when the aircraft contacts the ground, to avoid lifting the aircraft back into the air, and to burn all the propellant to reduce the risk to passengers and first responders.

In the airline industry, where safety is paramount (a targeted accident rate probability of less than 1 x 10-9 occurrences per operational flight hour is often cited), the safety of the industry’s new eVTOL designs remains unproven. These aircraft differ from traditional helicopters which are designed to “autorotate” in a controlled descent during an emergency; eVTOL craft are generally using highly automated flight controls and distributed electric propulsion (DEP) powering multiple rotors or ducted fans. The Vertical Flight Society maintains a list, now numbering over 175 eVTOL designs, in all stages from conception to prototype. None are certified yet by regulators such as the US Federal Aviation Administration (FAA), UK Civil Aviation Authority (CAA), or European Aircraft Safety Association (EASA).

Heavy c-drones such as Boeing’s Cargo Air Vehicle (CAV), with a 500 lb (227 kg) payload, and the Autonomous Pod Transport (APT) series by Bell, with varying sizes and payloads, will precede eVTOL aircraft; the safety systems on heavy cargo drones certified to fly over people and urban areas could well influence regulators evaluating the safety of flying passenger vehicles for certification.

ABBS is seeking to partner with aircraft and drone manufacturers to test and deploy the AVCP safety system.