In 2020, Dubai passed a new regulation “to help flying taxis and drone deliveries to take off” alongside a network of mini-airports within the city. For a long time, there have been helicopter services from airports to city centres. Advances in battery and electric propulsion technology, and Vertical Take-Off and Landing (VTOL) design have supported Urban Air Mobility (UAM) and now given a flip. Tilt-rotor systems have been tried and tested and will support regional connectivity till 300 km. UAM envisions a safe and efficient aviation transportation system that will use highly automated aircraft that will operate and transport passengers or cargo at lower altitudes within urban and suburban areas.
UAM will be composed of an ecosystem that considers the evolution and safety of the aircraft, the framework for operation, access to airspace, infrastructure development, and community engagement. It will envisage commercial inter-city travel (like air taxis), cargo delivery, public services, and private or recreational vehicles.
The initial UAM ecosystem will use existing helicopter infrastructure such as routes, helipads, and Air Traffic Control (ATC) services. Looking toward the future, the agencies are evolving infrastructure specially designed for UAM. It would mean designating routes along the main city arteries and developing new vertiports. On 2 March 2022, the US Federal Aviation Administration (FAA) issued draft interim guidance, to support the design and operation of facilities that electric VTOL aircraft will use for initial operations. Many companies are developing the next generation VTOL vehicles.
Passenger acceptance and potential passengers' value of time are the two key factors for going ahead. The UAM vehicle could either be rotary-wing, fixed-wing or hybrid cruise vehicles. There is the need to understand the landscape of relevant questions surrounding the implementation of UAM. The urban airspace would have to look at safety factors, social aspects, system and aircraft issues.
Unmanned Aerial Vehicles
The unmanned aerial vehicles (UAV) have been flying since the 1970s, and the safety record has been continuously improving. Removing pilots dramatically increases payload and reduces personnel costs. Also there has been a boom in less expensive civil travel and light personal jets. UAM is the next logical step. UAM evolved from the Advanced Air Mobility (AAM), a joint initiative of the FAA, NASA, and the industry to develop an air transportation system that moves passengers and cargo with new electric (i.e. green) air vehicles to places previously under-served by traditional aviation. Nearly 150 companies worldwide are in the race with under-testing UAM prototypes. The UAVs had to be made more robust for passenger flights.
Hybrid Propulsion
Electric motors in multi-rotor designs for “lift-and-cruise” have started maturing. More efficient rotors are using lightweight materials. Hybrid-electric turbo-generators are being combined with rugged turbine engines using conventional or bio-derived jet fuel that power motors or high-capacity batteries. The battery endurance is increasing, and the same is evolving further by the surface transport industry. The electromechanical actuators would be very important for UAM aircraft. Since the flight will be at low heights, they will experience thermals and the unusual winds caused by buildings. The pinpoint landings dozens of times a day would require fly-by-wire computers to make hundreds of small adjustments every second. The actuators would make these movements maintaining the highest degrees of precision and reliability.
Flight Safety Issues
Unlike a traditional helicopter, the UAMs will use multiple motors and propellers, electric engines, and lighter materials, which make them cheaper, quieter, and more efficient. The operations will be both urban and regional. Limited airspace and a larger number of operators would cause congestion. It may push the industry to adopt smaller separation standards. The safety record and acceptable risk models for hobby drones are clearly unacceptable. The on-board systems will have to have quadruple safeties and high reliability.
Since the UAM vehicles will have more degrees of freedom to freely choose their position, altitude, heading, and speed, this will require safety clearances. That would also require high technological capabilities, such as dynamic geo-fences and advanced sense-and-avoid capabilities, to maintain the required safety levels. Some such features already exist in drone swarms. Collision avoidance algorithms, avoidance maps, and path-planning would be required. Very compact traffic collision avoidance system and enhanced ground proximity warning system, including avoiding buildings, made up of multiple electronic beams using a small phased array, are under testing.
Flight and Weather
Tall urban buildings create wind gusts and cause significant turbulence in their proximity. This can affect aircraft’s ability to maintain position, altitude, and stability. Even the autopilot may be overtaxed and cause divergences. Precipitation can increase resistance or could affect on-board electronics. Low temperatures can reduce battery life. Icing can affect airframes or propellers and increase drone weight. Visibility and low ceiling could reduce the effectiveness of sense-and-avoid avionics. Close monitoring weather is thus required.
Traffic Challenges and Control
The UAVs used for recreation, policing, infrastructure inspection, forestry and agriculture purposes remain in specific geographic regions and require limited traffic management. Accommodating exponential UAM traffic will require solutions for communication, navigation, surveillance, and overall air traffic management. Differences in air vehicle designs and sizes and performance will make it complex. Higher numbers, greater density, lower altitudes of operations, will need handling.
Rules of air, routes, and scheduling would have to be evolved. Traffic management would mean flight path clearance, time slot scheduling, and at times first-come-first-launch approval. The routes will be based on demand and social factors. Separate corridors would have to be designated. It may be interesting to follow the main-road as an axis. UAM aerodromes would be nearer to the main roads. Streetlight poles and electricity transmission towers would be a factor. Two-way traffic lanes would need horizontal and vertical separation. Tall building rooftops may be the UAM ports for ease of climb and descent.
Building UAM Infrastructure
The UAM ground infrastructure will have to dovetail into the other urban and regional transportation system. Maintenance and battery management would have to be factored. Vertiport sites will emerge based on estimated air taxi demand. Take-off and landing pads, communication, navigation, surveillance infrastructure, and seat-booking will have to be evolved, and fit into the overall urban plan. Air taxis may require booking like car aggregators Ola and Uber, including ride-sharing. The initial air taxi service would be on manned aircraft and later shift to unmanned. Cargo movement through UAM will be a good starting point.
Technologies and Certification
LTE and 5G-and-beyond cellular technologies and secure satellite links will be required for communication. Assured accurate GPS and backups will be crucial. Battery and hybrid fuel cell technologies will be important. Lighter yet stronger materials must keep evolving. The UAM certification and regulations have to evolve through global standardisation. Volocopter eVTOL pilots and maintenance technician training is being evolved. There will be demand for pilots and they would need certification to operate an eVTOL and remote eVTOLs. The International Civil Aviation Organisation (ICAO) and FAA are leading the process. UAM transportation policy and aircraft certification guidelines have to be in place first.
Public Confidence and Social Factors
The public is still sceptical about getting into an unmanned air taxi. Very few feel comfortable flying alone in an automated aircraft, even though accompanied by other passengers. Public acceptance will increase once self-driven cars become common. Since UAM will operate at low flight levels, closer to residential areas, communities will be concerned about security, privacy, liability, and noise, visual, and air pollution.
UAM rotor sound can at times be irritating, both in volume and frequency. It would affect sleep. Quieter air vehicles would need to be designed. Drone equipped with cameras could capture images that impact privacy. People, in general, have positive attitudes towards innovation and new technology, but expect high safety assurance. Cost of transportation and ticketing will be an issue. Time-cost saving analysis would be made with other modes of travel.
Portable Personal Air Mobility System
The Defence Advanced Research Projects Agency (DARPA) is in the process of granting contracts for construction and flight demonstration of “Portable Personal Air Mobility System” that can be used by soldiers for shorts hops of around 10 km. These will be mobile, small, light-weight, and compact. One can assemble them in a short time with minimal training. Once successful, it would be available for civil use akin to the bicycle of the air.
A Bright Future Ahead
Automation and electricity storage technologies, and higher flight safety will spur urban unmanned aviation. Rotary or fixed-wing cruise vehicles are already past the prototype stage. The UAM are currently in the “honeymoon” phase. UAM will be safe, sustainable and convenient. By 2030, 60 percent of the world's population will be urban, and this will create UAM demand. Hundreds of start-ups are evolving new automated aircraft. Issues related to regulation, air-traffic management and public perception are being addressed.
A holistic approach to urban air mobility, would mean seamlessly integrating a variety of critical components. Most commercial airports are currently located in the suburbs. The vertiports will mostly be located in more densely populated areas. NASA, FAA, including India’s DGCA, are actively involved. The aircraft will be initially owned and operated by professional operators, as with taxis, rather than by private individuals. Big players in UAM include Amazon, Boeing, Airbus, Embraer-X, Uber elevate, and Singapore UTM, among others. Maximising safety and capacity after understanding technological complexity, noise, and privacy is the essence.
For UAM aircraft to be most efficient, recharging, swapping batteries, and hydrogen refuelling must be done as quickly as possible. If it is safe to travel to space in an automated unmanned craft, so will it be in case of UAM. Some cities are encouraging the idea of inexpensive, point-to-point air travel as a way of reducing traffic congestion and moving goods. A European Aviation Safety Agency (EASA) survey showed that 83 per cent of respondents had a positive attitude towards UAM, while 71 per cent were ready to try UAM services.
Emerging big economy like India would have to get on-board early and reap the benefits. India must also try to become a manufacturing hub and support the huge automation software demands. Notwithstanding the Shatabdi trains and newly developed expressways, it may be more interesting to take an unmanned air-taxi from Faridabad to Karnal. It may also be a better way to travel from Greater Noida to Gurgaon on a Friday evening. And as it becomes possible, the loved ones will not be too far away.
The writer is Director General, Centre for Air Power Studies. Views expressed are personal.
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