Richard Branson once said, “If you want to be a Millionaire, start with a billion dollars and launch a new airline.”  This is one of those sayings that falls into the category of, it’s funny because it’s true.  In fact, the saying applies equally to most new undertakings in aviation, including the design, certification, and manufacture of a new aircraft. In this three part series, we will be taking a look at one of the most ambitious initiatives in modern aviation, the electric aircraft and urban air mobility.

In this  first part, we will update readers on current developments in electric and hybrid electric aircraft, including what can we expect from the first generation of eco-friendly aircraft, battery technology, as well as the development of transport size hybrid-electric aircraft.  In Part II, we will take a look at eVTOL (electric Vertical Take-Off and Landing) aircraft and the developments occurring in Urban Air Mobility (UAM).  Finally, we will discuss in Part III the FAA certification process for electric aircraft and how the rewrite of the small aircraft certification rules (Part 23) directly benefits the development of electric aircraft.

THE HIGH COST OF BUSINESS AS USUAL

One of the main barriers to aviation innovation has been the aircraft certification process, which often stopped dead innovation in aircraft design before it even left the drawing board.  The Federal Aviation Administration’s (FAA) certification regulations – which provide IKEA®-like step-by-step instructions for building, designing, and testing an aircraft – often penalize the introduction of new technology.  If a design or technology does not fall squarely within the purview of the certification regulations, the additional time and cost necessary to satisfy the FAA’s inquisition (e.g., Issue Paper process, Equivalent Level of Safety (ELOS), Special Conditions…), and certify the damn thing dramatically reduces the profitability of, and scares away further investment in, the new technology.

Certifying an aircraft is an extraordinary feat, requiring countless engineering and flight test hours, thousands of regulations, and a very large checkbook.   A recent publication by Aerospace Testing International reported “certification costs around US$1m for primary category aircraft, which have up to three seats, US$25m for a general aviation aircraft and hundreds of millions of dollars for a commercial aircraft.”  Of course, this is just for certification and these figures do not factor in delays due to redesign changes, additional flight testing, special conditions, etc., which typically happen and can add millions more to certification costs.

Because of the high price of certification, the latest and greatest technologies often skips aviation, which is why a new Cessna 172 still looks pretty much the same as it did when the C-172 was type certified in 1955; a single engine propeller fixed-wing aircraft with the usual stick and rudder flight controls.  Don’t get me wrong, I love flying the 172 – it’s a great aircraft, and throughout the years, Cessna has produced upgraded models with improved avionics, but the C-172, at its heart, is still the same 1955 aircraft…. at least according to its Type Certificate (TC).

PLANTING THE SEEDS OF CHANGE

Come 2020, that’s all going to change (actually, it changed in 2017 with the rewrite to 14 CFR Part 23, but 2020 sounds much cooler)!   Companies like Eviation Aircraft with its all-electric fixed-wing aircraft and Uber Elevate are pushing a new technologically advanced class of electric aircraft into the aviation ecosystem.  But how close are we to the reality of commercial flight in an electric aircraft?  What can we expect for the first generation of hybrid and all-electric aircraft?

By late 2021 or early 2022, Eviation Aircraft expects 14 CFR Part 23 certification of its all-electric 9-seat aircraft, known as Alice, for IFR and known icing conditions.  Driving the two Hartzell propellers at the wingtips and one in the rear fuselage are three electric motors supplied by MagniX or Siemens.  Powering the all-electric aircraft will be a 900 kilowatt-hour (kWh) lithium-ion (Li-ion) battery system weighing 8,200 lbs., which accounts for 60% of the aircraft’s maximum take-off weight (MTOW).  Additionally, Alice will implement fly-by-wire technology and automated landing capabilities.

Photo Source: Eviation Aircraft – Alice Commuter

Eviation lists a cruise airspeed of 260 knots and a range of 650 miles for Alice, which is which is ideal for regional air carriers like Cape Air, which was announced as the first commercial customer for Alice.  Eviation also has plans for an upgraded 2.0 version of the Alice (Alice ER), which will have a pressurized cabin and an upgraded aluminum-air battery system, increasing the aircraft’s range to 738 nautical miles.  As of January 2019, Eviation secured $200 million in funding for certification and production of Alice.  Flight testing for Alice will take place at Moses Lake’s airport in Seattle WA.

THE NEED FOR IMPROVED LI-ION BATTERY TECHNOLOGY

Plans are underway for developing even larger capacity aircraft (100+ passengers) by several aerospace companies, but initial designs will be hybrid-electric rather than all-electric due to current limitations in battery technology.  In a nutshell, current Li-ion batteries do not provide the same bang for your buck as hydrocarbon fuels.  The power provided by today’s Li-ion batteries is suitable for smaller aircraft with a 5 or less passenger capacity, but gravimetric energy density (battery power expressed as watt hours per kilogram (Wh/kg) is not sufficient for an all-electric transport category size aircraft.

The best Li-ion batteries currently have energy densities of about 250 Wh/kg, which, depending on the aircraft design, equates to a range of around 300-600 miles for electric aircraft (less for non-wing-born lift designs, such as multi-rotors) on a single charge.

Graphic Source: M. Hepperle, “Electric Flight – Potential and Limitations“,  AVT-209 Workshop on Energy Efficient Technologies and Concepts Operation, Lisbon, 22.-24. October 2012.  Reprinted with permission.

The above chart is somewhat dated but still valid.  It represents essentially where we are in battery technology and how far we still need to go before batteries become a suitable replacement for all aspects of aviation transportation.  As of recent reports, companies like TerraWatt Technology achieved an energy density of 432 Wh/kg for its Li-ion Terra 3.0 batteries which is about 3.2% of the gravimetric energy density of jet fuel (kerosene = 13,500 Wh/kg).  The current Terra 3.0 batteries will be available in 2021/2022, and are intended for consumer electronics and small mobility devices.  The company website states it is developing a 500 Wh/kg Terra 4.0, intended for electric vehicles (perhaps aircraft?), which will be a significant improvement in current EV battery technology.  By comparison, Tesla’s most advanced Li-ion batteries have an energy density just shy of 250 Wh/kg.  All-in-all good news, but we are still a long way from the energy density of jet fuel at 13,500 Wh/kg.

Innolith, a Swiss tech startup, recently announced its non-flammable inorganic Li-ion battery achieved an energy density of 1,000 Wh/kg.  If confirmed, the Innolith battery will be a major breakthrough in Li-ion technology that speeds up the current battery development trend, which currently tracks a 5 to 8 percent increase in gravimetric energy density annually.  The next generation Li-ion batteries (e.g., lithium-air or lithium-sulfur) intended for electric aircraft are expected to reach energy densities of 750-1000 Wh/kg.

TRANSPORT CATEGORY ELECTRIC AIRCRAFT  

Larger transport category size aircraft (i.e., regional and large commercial aircraft) are unlikely to make the leap directly to all-electric propulsion.  Rather, the first steps will likely be a hybrid system (think Prius rather than Tesla) that utilizes both conventional and electric engines in parallel or series hybrid configurations.  One such initiative – Project 804 – undertaken by United Technologies (UT) Research Center, and UT subsidiaries Collins Aerospace and Pratt & Whitney, involves the conversion of a Dash-8 Series 100 aircraft to a hybrid-electric demonstrator.  Project 804 is expected to take three years to construct and fly the aircraft and is intended to develop and demonstrate the viability of hybrid-electric systems for 30-50 passenger regional aircraft.

Similarly, Airbus, in collaboration with Rolls-Royce and Siemens, is developing a commercial 100-passenger hybrid-electric aircraft known as the E-Fan X, scheduled to take its first test flight in 2021, with expectations of commercial passenger flights in the 2030s timeframe.  The E- Fan X is more of a “let’s dip our toes in the water” approach, since only one of its four engines is hybrid-electric.

On the more ambitious side is EasyJet, a British low-fare airline carrier, who announced in 2017 that it had partnered with Wright Electric to develop a 150 seat electric plane with a range of 300 miles.  This aircraft is expected to cover EasyJet’s short haul routes by 2027.

If it were up to me, I’d make this one really long post, but blog etiquette insists that I do not subject today’s online reader with too lengthy of a post.  In Part II, we will focus a bit more on electric aircraft capable of vertical take-off and landing (eVTOL), and Part III will touch briefly on the FAA certification rules applicable to electric aircraft.