Electric Propulsion Energizes Aviation
The revolution towards electrically-powered vehicles continues in all areas of transportation, from those that drive on land, to those that float, to those that fly. Tesla and the legacy automotive companies (that are playing catchup, for the most part, outside of Toyota and a few others) seem to get most of the attention for their electric-powered cars and trucks. It seems that nearly every mode of transportation is exploring how to move away from fossil fuels to electric or electric hybrid propulsion systems.
The Revolution Has Been Uneven, But it is Here
While electric vehicles have been around for quite some time, most had been vanquished by their petrol-powered competitors to exile or specific niches. Well, what comes around, goes around. Electric propulsion is back in vogue, and in some cases provides for a much better economic argument that those old gas guzzlers due to advances in battery technology, lightweight materials, and new propulsion systems. As mentioned above, cars and trucks have gotten most of the press, but buses are quietly (pun intended) becoming battery-powered all over the world in large numbers due to economic and environmental reasons, as are other local fleet vehicles. Maritime transport has been going electric, and ferries are a key example of this. Ferries are primed for electrification due to their regular and often short routes, and now cargo ships are now also exploring various types of hybrid propulsion (and other technologies such as sails). Trains and urban transport (trams, trolleys) had also moved in this direction where it made sense in the past, and locomotives continue to move away from diesel globally. The worlds first ultra-fast electrically-powered hyperloop will begin to be built in the third quarter of 2019 by a U.S. company (HyperLoopTT) in Abu Dhabi. Things are happening, and most of these things are being enabled by electrical power.
Batteries — The Greatest Challenge
The number one challenge to design an electric aircraft is the current state of battery technology. In general, batteries cannot provide the power-to-weight ratio needed for electric aviation to be feasible for a significantly-sized aircraft. According to reports, jet fuel yields approximately 43 times more energy than the equivalent mass of battery. Those working on electric aircraft are wholly dependent upon the never-ending march of technology to improve the energy storage technology quickly. Battery energy density has been increasing rising by 5 to 8 percent per year (according to industry pundits), but some battery companies such as Panasonic have projected much faster increases. Battery technology still needs to be improved further to where it is economically feasible to work in smaller aircraft. Estimates are that they will need to achieve approximately five times their current density. Some of this will be mitigated with aircraft re-designs to make use of the smaller electric motors and related components.
“Electric propulsion permits new design architectures,” says Venkat Viswanathan, a battery scientist at Carnegie Mellon University, in a recent article in Wired magazine. “Future electric aircraft will look nothing like the aircraft of today, and they will be able to fly with much less energy — as little as 400 watt-hours/kg — thanks to distributed motors and reduced drag. We’ll redesign aircraft around electric motors.” This is an interesting comment, and this may allow new aircraft OEMs to enter the market due to this technological shift, since each time there is a major evolutionary change in an industry, new entrants seem to enter it.
Some of the challenges for engineers and support personnel at airports to develop mechanisms and processes to swap out batteries quickly so that aircraft can continue with quick turnaround times, and in adverse weather conditions. An entirely new support infrastructure will be needed by airports, operators, and MROs to manage all of this.
Electric Aircraft Will Come Along Slowly
The electric and electric-hybrid projects in aviation are being driven incrementally by smaller aircraft initially, which is partially due to limitations of the current state of battery technology, and in other cases, purely economic reasons. We are seeing a gradual movement towards how newer aircraft will be powered, with short-range vehicles looking at electrical or some type of hybrid technologies, and longer range aircraft mainly staying with legacy fuels (outside of the biofuels being used by some airlines).
It is worth noting that electrically-powered long-haul flight is feasible, but due to aircraft being rather well maximized for their use, this will delay any significant changes to such aircraft. Much of the industry expects that the first electric vertical take-off and landing (eVTOL) vehicles to be air taxis (i.e., Uber in the skies) for our local mobility needs. Regional aircraft for ~100 passengers and between 300–1000 miles are already being worked on. While smaller aircraft will seemingly face evolutionary changes, larger aircraft will see more Incremental changes (at least initially).
Each of the major engine manufacturers is working on solutions in this area, and many of the initial advancements are either ready for use, or nearly ready.
The United Technology Research Center is developing an eVTOL (electric vertical take-off and landing) battery-assist system and a platform that re-optimizes turbofans in cruise mode and indicate that the overall energy reduction has been up to 5% so far. According to a recent article in Flight Global, the chief technology officer at United Technologies was interviewed at the Farnborough air show and stated that the company is developing a number of hybrid-electric demonstrators. While there is some speculation whether UTC will look to build its own aircraft in the future (perhaps due to the ongoing pricing squeeze that the OEMs are putting on suppliers, as well as how Boeing is working on bringing in some aircraft parts development and manufacturing in-house), only time will tell.
Back in August 2017, GE Aviation released a white paper outlining the substantial work it said it was doing on hybrid-electric motor-generators. In one ground-based experiment, GE Aviation used a motor rated at 1 MW to turn a 3.3-meter (11-foot) propeller. In another experiment, it used the compressors of a GE F110 jet engine to power a generator rated at 1 MW; meanwhile, the engine continued to produce thrust.
Let’s take a look at some of the noteworthy efforts underway.
Zunum Electric Aircraft (backed by Boeing / JetBlue / Safran)
One of the companies which has attracted much attention is Seattle/Chicago-based Zunum. Their initial offering is the Zunum Aero ZA10 12-seat, 700-mile commuter aircraft. Zunum envisions that this aircraft will reduce travel times on regional routes in half and emissions by up to 80% while reducing seat-mile costs (with estimates of $250 per hour for the aircraft or ~8 cents per available seat mile). This firm is backed by Boeing, JetBlue Ventures and the US Dept of Commerce Clean Energy Fund, and has now added Safran Helicopter Engines (France) to its team. Safran will develop and certify a 1,700–2,000 shp (shaft horsepower) Ardiden 3 turboshaft version to power the ZA10.
This turbine is already in use, but will be modified to produce up to 500 kW to re-charge the battery packs and provide power the electric propellers. The Zunum solution has ducted fans driven by electric motors. The motors get their energy from batteries, that are charged while on the ground, and are used for climb. While in cruise the onboard jet turbine will recharge the batteries and the electric motors spinning.
Ground and flight testing is scheduled to begin in 2019. Zunum and the FAA are working together to develop certification standards for electric aircraft. It expects to start operating its first planes in the early 2020s, though those initial units will only have an operating range of 700 miles, and eventually be able to reach a 1,000-mile range by 2030. Zunum has made use of a Rockwell Turbo Commander 840 as its flying testbed aircraft.
Charter provider JetSuite will be the launch customer of the Zunum Aero hybrid-electric airplane, with a planned entry date as early as 2022. JetSuite has signed on to purchase up to 100 planes from Zunum but will customize the interior to a more spacious six- or nine-passenger configurations.
Airbus Ventures
In late 2017, Airbus, Rolls-Royce, and Siemens came together to develop a near flight demonstrator for hybrid-electric propulsion for commercial aircraft, named E-Fan X. It is projected to fly in 2020 on a BAe 146 flying testbed. Initially, one of the aircraft’s four engines will be swapped out for a 2MW electric motor, with a second engine being replaced with an electric motor once system maturity has been proven.
Airbus will oversee the overall integration effort, and the control architecture of the hybrid-electric propulsion system and batteries. Siemens will provide the 2MW electric motors and their power electronic control unit, as well as the DC/DC converter, inverter, and the power distribution system. Rolls-Royce will provide the turbo-shaft engine, power electronics, and 2MW generator.
This project follows a previous collaboration between Airbus and Siemens which began in 2016 and focused on the development and maturation of various electric propulsion system components.
Sometime in late 2018, Airbus Helicopters will flight-test the four-passenger, self-piloted eVTOL (electric vertical takeoff and landing) CtyAirbus vehicle, which is specifically designed for urban air transportation. The aircraft will have a four-ducted propeller configuration which is intended to provide a high degree of safety and low noise, and have a cruising speed of 120 kilometers per hour, with a typical one-way flight lasting about 15 minutes, with a range of approximately 30 km.
Uber
While Uber will not build any aircraft for its flying air taxi service it is working with five manufacturers who will: Bell (formerly Bell Helicopters), Aurora Flight Sciences (part of Boeing), Embraer, Karem (based in California), and Pipistrel (based in Slovenia). The company is forecasting that by 2020 it will have test flights of its electric-powered VTOL aircraft (which of the manufacturers will be ready by this date was not identified). Uber plans to launch an aerial taxi service by 2023.
Uber has been showing demonstration aircraft already and has a goal to operate its vehicles at an elevation of 1,000 to 2,000 feet. The goal is to operate thousands of its flying taxis ferrying passengers between rooftop “skyports” and landing sites in urban areas, each of which will be equipped to handle 200 takeoffs and landings every hour. Humans will initially pilot these aircraft but eventually will fly autonomously once the technology matures.
Uber is also working with NASA on Space Act Agreement to develop a new air traffic control system to manage these low-flying, (and eventual autonomous) aircraft.
Lillium
This German-based startup is developing an on-demand air mobility service with its all-electric VTOL vehicle, the Lillium Jet. It is aiming to compete with cars and taxis, and the Uber-in-the-sky service. Its 5-person vehicle will be ordered the same way you order Uber or Lyft today, via an app, and you pay-per-ride. The service will have a network of localized landing pads and jets, so you can quickly reserve a ride for a desired time. Lillium will work with local mobility service providers to provide a seamless user experience from booking through to landing.
A prototype is being flight-tested already, with the first manned flight being projected for 2019, and an in-service date in 2025. Projections call for the Lilium Jet to travel as fast as 186 mph and have a range of 186 miles on a single charge. The Lillium Jet will have 36 electric jet engines embedded in the wing flaps, enabling the aircraft to transition from hover mode to horizontal flight.
The company has also recently hired a renowned car designer who has worked with Maserati, McLaren, Ferrari, and BMW to redesign the interior and the exterior in order to provide for a higher-end user experience.
Kitty Hawk
Google’s Larry Page formed this venture to develop an electric VTOL, and has already begun to offer its short-range, one-seat Flyer. It weighs just 250 pounds, has 10 battery-powered propellors, and is controlled by two joysticks. It has the appearance of a bobsled attached to a couple of pontoons encircled by drone rotors. It has a maximum elevation of 10 feet and a top speed of 20 mph. Seems like a nice toy to play around with. The Flyer will have an Ultralight classification from the FAA, so a pilot’s license is not required, but we highly recommend to not skimp on the training.
But Kitty Hawk has bigger dreams and is developing the Cora, a two-seat VTOL electric aircraft which has 13 rotors to serve as an air taxi service. Cora will have a wingspan of 36 feet, have a speed of 110 mph, and have a flight range of ~62 miles.
The company has come to an agreement with the government of New Zealand to test autonomous air taxis for official certification there. The goal of Kitty Hawk is to provide an Uber/Lyft-type app to customers to make it rather easy to order one of these air taxis.
EHang Personal Drone
This Chinese company is one of the earlier pioneers in developing an electric VTOL autonomous air taxi two-person personal drone named the EHang 216 (they also have a one-person aircraft as well, the 184). EHang 216 is doing flight testing in Dubai now, and has conducted over 1,000 test flights with human passengers as of July 2018, including a 984-foot vertical climb, a weight test carrying over 500 pounds, a routed test flight covering 9.3 miles, and a high-speed cruising test that reached ~80 mph. It has 16 propellers and uses an app to order it (a command center oversees all details).
Both of these aircraft have been extensively tested in Guangzhou, China and in Dubai, and EHang had autonomously flown Dutch Prince Pieter Christiaan into the Amsterdam Arena in April 2018. No date has been announced on when the 216 is expected to enter commercial service.
Eviation Aircraft
This is a startup based in Israel that is targeting the short-range regional market, specifically hoping to replace trips made in an automobile. It is developing Alice, a nine-passenger, self-piloted, all-electric aircraft with a range of 100 to 600 miles and possibly more. It seems that it is primed to compete with Zunum and its hybrid aircraft. Eviation has plans to fly a full-scale prototype by early 2019.
Israel Aerospace Industries (IAI)
IAI is working on an all-electric aircraft and projects to have an initial prototype which will fly in approximately three years. The company has stated that the new aircraft will have a maximum take-off weight of 10,000–15,000lb — approximately the size of a Beechcraft King Air 350. Range will be about 500nm, against 1,800nm for the King Air, and the aircraft is aimed at the regional use.
IAI has indicated that it may also partner with another company to bring the aircraft to production
Many Others
This column could go with more examples of companies which have announced either electric or hybrid approaches, and we will just list a number of the companies here:
· Ampaire
· Blackfly
· HoverSurf HoverBike
· Joby
· MagniX
· Volocopter
· Wright Electric
I am certain that I missed a few others, but it seems that every month or so a new entrant is announced.
Final Thoughts
For all of the naysayers regarding electric and hybrid aircraft, it is worth noting it took decades for early cars and aircraft to become more than novelties and enter commercial use. In today’s world, we have sped up the development of new products, and often due to unforeseen technology breakthroughs, and such innovations are able to come to market significantly more quickly than in decades past.
We will have incremental innovations in battery technology, propulsion, and materials, and through the progressive hybridization of aircraft, we will eventually reach pure electric propulsion. Nearly every major aerospace company is participating in this area, as no one wants to miss out and be left behind.
Short-range electric small aircraft are already pretty much here, and once personal drone/air taxi services identify how they will safely operate in urban environments, we will see a real evolutionary change to travel. And cheaper travel (hopefully) to go along with cleaner skies. Viva la innovation!