According to AHS International, more than 50 companies around the world are in the process of researching and developing electric vertical takeoff and landing (eVTOL) aircraft. The majority of these concepts are designed to travel at lower altitudes for a fraction of the cost of operating a fixed-wing aircraft.
Major OEMs are also showing interest in the future potential of electric-hybrid-propulsion aircraft. Boeing, for example, acquired Aurora Flight Sciences in 2017,. Aurora has been researching the use of eVTOL technologies in different configurations for several years. Airbus also has a future-focused division that is researching the concept with its Vahana air taxi in Silicon Valley right now.
Another type of 2020s airframes are being researched and developed for commercial and supersonic business jets.
Aerion, Boom Technology and Lockheed Martin have emerged as the biggest industry names behind supersonic development programs.
Both the supersonic and eVTOL concepts will provide a paradigm shift in commercial and private passenger travel, and both will require a new breed of avionics.
Making the biggest impact in driving the future possibility of eVTOL aircraft air taxis becoming reality is Uber, which in May held its second annual Uber Elevate Summit in Los Angeles. The ride-sharing company’s new aviation division envisions 2023 as the year for the beginning of a concept of operations that will feature a network of small, electric aircraft that take off and land vertically from a distributed network of vertiports. These vertiports will have multiple takeoff-and-landing pads and a charging infrastructure for eVTOL aircraft batteries.
While Uber is not developing an actual air taxi airframe internally, it is developing a comprehensive requirement set. Its Elevate Summit featured OEMs, such as Embraer and Pipistrel, unveiling new eVTOL designs.
It also used the summit to officially unveil its design specifications for its eVTOL common reference model. At a basic level, Uber is seeking an eVTOL air taxi capable of flying at cruising altitudes between 1,000 and 2,000 feet with a cruising speed of 150 to 200 mph. The air taxi will be fully electric using a distributed electric-propulsion architecture and four sets of electric-powered propellers dedicated solely to take off and land vertically. The company also describes an air taxi flight as achieving altitude vertically and using a tail-mounted propeller for forward-motion thrust.
At the summit, Stan Swaintek, head of operations for Uber’s aviation division, briefly described what the avionics of a future Uber air taxi would look like conceptually with a focus on the software component. The ride-sharing company wants to connect the cockpits of its future aircraft to what it describes as the Uber Elevate cloud services. Using two-way application programmable interfaces (APIs), the cloud-computing network would enable the exchange of aircraft health and trajectory data between pilots, aircraft and Uber’s ground-based network operations team.
“The continuously optimizing control system will coordinate flight clearances, upload mission trajectories and direct exactly timed taxi, takeoff and terminal flight procedures,” said Swaintek.
The system will also be capable of “dynamically displaying critical mission information for pilots through an avionics interface that provides enhanced situational awareness and a flight control integration that enables simplified vehicle control,” he added.
Uber is not the only company actively pushing the concept of eVTOL. At the 2018 Consumer Electronics Show (CES), Intel unveiled a video of its CEO, Brian Krzanich, flying the first Volocopter eVTOL aircraft. Volocopter is a fully electric VTOL aircraft featuring 18 rotors with no combustion engine. The aircraft, which is designed to fly autonomously or with a pilot in the cockpit, has 18 electric drives that are supplied by high-capacity batteries.
The German startup company behind Volocopter envisions the use of rooftop “Volo-ports” where up to 1,000 passengers per hour could board and de-plane personal air taxis.
“We actually see the biggest challenges in making this reality being more related to the battery capacity and power generation, not necessarily the flight control systems,” said Alexander Zosel, Volocopter’s co-founder and chief innovation officer.
On the software side of the Volocopter concept, Intel is providing its flight control and sensor technology that is based on what it already features the Intel Falcon 8+ commercial drone. The software is designed to capture environmental data with highly redundant sensors to provide an accurate reading of the in-flight position with the ability to compensate for certain flight malfunctions as well as unexpected wind gusts. The software is also designed to provide automated corrections of the Volocopter’s center of gravity to help stabilize the position of the aircraft as well.
“When you think about Volocopter’s avionics, the system status and everything else inside the cockpit, that is all being designed by Volocopter,” said Anil Nanduri, VP and general manager of the Intel Drone Group. “It will be a very software-intensive aircraft. The flight control software stack has to be capable of providing the health of the aircraft systems to the pilot. We have to develop the software so that the interface for the pilot is intuitive and easy to use.”
As noted by Volocopter’s Zosel, the battery density and source of power generation are major components of the future eVTOL aircraft as well. One company that could be key in providing power for future eVTOLs is Honeywell Aerospace.
Prior to the Defense Advanced Research Projects Agency (DARPA) ending its VTOL X-Plane program, Honeywell was supplying the Aurora X-24A subscale demonstrator’s three 1-megawatt generators. The X-24A’s 24-ducted fans were fed AC power from electricity produced by the generators.
Though the X-Plane program is no longer funded, Honeywell sees the potential of its generators for commercial eVTOL concepts.
“We could be ready to have a prototype on an aircraft within probably eight to 12 months — a full hybrid propulsion system prototype,” said said Amanda King, senior director of breakthrough technologies for Honeywell. “With our Megawatt generator, for ground applications we think that could take somewhere around 18 to 24 months, depending on how quickly we can get certification.”
Is the traveling public ready for commercial supersonic air travel? Several companies designing supersonic airframes certainly believe so. Airlines have shown major interest as well.
At the end of 2017, Boom Technology announced a $10 million investment and a preorder for 20 supersonic aircraft from Japan Airlines (JAL). Under the agreement, JAL will help to refine the aircraft design and define the passenger experience for supersonic travel. Conceptually, Boom is designing its airliner to carry up to 55 passengers at speeds of up to 1,451 mph, or Mach 2.2. Boom has repeatedly said its first supersonic jet will be ready to enter service by 2023.
Several weeks after the JAL-Boom investment agreement, two other major OEMs announced a new partnership designed to accelerate the entry into service of the next civil supersonic aircraft. Aerion, which first launched its supersonic business jet program in 2014, formed an agreement with Lockheed Martin to develop a framework on all phases of the program, including engineering, certification and production. Aerion already counts Airbus and GE Aviation as engineering and engine partners as well.
Months later, NASA also showed its commitment to helping supersonic air travel become a reality in the 2020s by awarding a $247.5 million contract to Lockheed Martin for the development of a supersonic X-plane. Under the contract, Lockheed must build a low-boom flight demonstrator that will have a cruising altitude of 55,000 feet with a top speed of Mach 1.5. The aircraft will have a single-pilot cockpit based on the T-38 training jet design.
On the regulatory side, the FAA is showing how serious it is about providing certification for the next generation of supersonic aircraft. In May, the agency said it will initiate two rulemaking activities on civil supersonic aircraft noise. The first activity is a proposed rule for noise certification of supersonic aircraft, and the second is a proposed rule to streamline and clarify the procedures to obtain special flight authorization for conducting supersonic flight-testing in the U.S.
All of this activity around enabling supersonic commercial air travel in the 2020s begs the question as to what type of avionics will be featured on supersonic jets. Based on ongoing research, supersonic cockpits might not need technology that is overly advanced in comparison to what’s in service today.
As an example, in 2017 NASA and Honeywell completed a two-year test that integrated the use of predictive supersonic software and cockpit display technology on a business jet cockpit. That test demonstrated how pilots could predict where and how sonic booms generated by business jets flying faster than the speed of sound would impact populated areas on the ground within their flight paths. While the test flights did not actually fly at supersonic speed, the demonstration simulated supersonic travel in real airspace using real interaction with flight dispatchers and air traffic controllers.
Boom’s chief engineer, Joe Wilding, said one of the main computing components needed to enable supersonic travel will be an upgraded air data computer. That perspective was also confirmed in a recent interview with Thommen Aircraft CEO Stephane Jaquier. According to Jaquier, the Swiss avionics manufacturer’s AC32 digital air data computer has been upgraded to extend the operational airspeed computation range to Mach numbers greater than 1.
Airspeed calculation is based on measurements of the impact pressure — the difference of pitot and static pressure. The calculation of airspeeds depend on the Mach regimes and aerodynamic effects, which are different depending on whether you are flying at subsonic (Ma < 1), transonic (Ma 0.8 < Ma < Ma 1.3), supersonic (Ma > 1.0) or hypersonic (Ma > 5.0) speeds, Jaquier said.
“When flying above Ma > 1, a bow shock is formed in front of the pitot tube, which creates a sudden drop of total pressure. The conventional subsonic formula cannot be applied in such a case to calculate the airspeed, as the total pressure changes across the normal shock. So we needed to apply a supersonic calculation formula, which would take this dynamic effect into account, in order to precisely compute the Mach number and airspeed information. Our software then automatically and constantly checks whether subsonic or supersonic formulas are applicable and selects the applicable Mach number calculation, based on a critical pressure ratio,” said Jaquier.
While Thommen’s air data computer is not currently featured in the development programs at Boom or Aerion, the company is actively pursuing supersonic unmanned aircraft system opportunities, said Jaquier.
“The other good thing is that the addition of the supersonic capability is essentially a software-based modification of the existing subsonic air data computer, hence it does not need any other external sources to enable this function,” he said. AVS