Alongside energy from the sun, then from the Li-Po, there is the potential from alternative forms of power sources to extend flying range.
At the start of the 20th century, three engineers had come up with the idea of extending automobile range with a hybrid-electric drive system. Harry E. Dey of Jersey City fitted a gasoline-powered, 6.5-liter, two-cylinder engine and a dynamo flywheel connected to an onboard battery into an Armstrong Phaeton; Ferdinand Porsche at the Lohner works in Vienna and Louis Kriéger of Paris achieved a similar drive train. In 1911, London engineer Jack Delmar-Morgan equipped his cabin cruiser Mansura with a gasoline-electric drive and went cruising out to lands beyond the Thames estuary.1 Yet nobody before World War I thought of extending the range of an airplane with an additional gasoline engine.
Then on April 10, 1920, an article was published in The Electrical Experimenter headlined “The Electrical Airplane.” It reported that an experiment in aviation had drawn up plans for an airplane with electrical transmission. A power of 6,000 hp would be provided by gas engines, then transformed into electric power distributed to engines powering the propellers. “This device in regard to the advantages it will procure will not go without causing a considerable increase in weight—the author envisages it for a giant plane which would carry 75 to 100 passengers, whose wingspan would be 72 m (236 ft), length 54 m (177 ft).” Could this be the first mention of a hybrid-electric airliner? The size is interesting compared to the 60-m (197-ft.) wingspan and 76-m (249-ft.) length of the Boeing 747 jet airliner a lifetime later.
Four years later, in 1924, Alphonsus Ligouri Drum of Chicago obtained U.S. Patent 1511448 for a hybrid-electric biplane with a central gas motor generating power to three electrically driven propellers: two mounted on the upper wing gave it vertical lift, while a third gave it traditional forward motion, so achieving improved stability in flight. As far as we know, the Drum hybrid was never built.
In 1943 a patent application, titled “electrical airplane propulsion,” was filed by a team working at the Westinghouse Electrical Corporation at East Pittsburgh, Pennsylvania. On the team: Frank W. Godsey Jr., Lee A. Kilgore (who had developed a variable speed motor drive), Frank B. Powers and Bennie A. Rose:
The principal object of our invention is to convert the perennial suggestions of electric power-transmissions in airplanes from the realm of impracticability to the realm of practicability.… In our design, we have moved the propeller driving engines of a multi-propellered plane, from nacelles or wing-fairings or bulges, to the fuselage, and we have replaced them with high speed, lightweight, small-diameter four-pole squirrel-cage electric motors and gear-units, which can be submerged entirely within the airfoil section of the wing, for driving the propellers. By taking advantage of the much lighter weight, per horsepower, of large-sized gasoline engines or turbines, developing more power than can be absorbed in a single propeller, and necessitating some sort of power-transmission from a single large prime mover to a plurality of propeller-shafts, we have produced a design of electrical airplane-propulsion which may actually increase the cruising-radius or the speed of the airplane, while reducing the amount of gasoline required per flight. In this manner, we have eliminated the 20% drag. In our design, we are enabled to utilize a large number of relatively small-diameter three-bladed propellers, which can be readily balanced. The use of a plurality of electric motors for driving a plurality of propellers distributed over the wing also reduces stresses and vibration in the wing-structure, which is at best quite flimsy in comparison with its size. The use of an electric power-plant makes it feasible, also, to utilize auxiliary propelling means during take-off, to supplement the propelling force of the propellers….
The British engineer Lorne Campbell has commented:
They claim a number of advantages like small nacelles for the motors in the wings, hence less drag; lighter weight in the wings so that there is less strain on wing structure; the capability of running the motors at different speeds from the engines so that both can be operated at their most efficient speed, etc. The engines are mounted in the fuselage, and they claim this, also, is an advantage because it will mean the main weights are around the Centre of Gravity and the plane will be more manoeuvrable. They also say that having fewer, large engines is more efficient than having more, smaller, engines from the power to weight point of view. The big disadvantage that I see is that they don’t mention (as far as I have read) the losses in the conversion of the power from the main engines to the electric motors and the elephant in the room, in my opinion, is that mounting the engines in the fuselage takes up a great deal of passenger/cargo space—this, to my mind, is a big disadvantage. Chucking the engines out on the wings opens up all this space.2
It is interesting to note that the filing date for this Patent was February 2, 1943. On exactly the same date, one of the co-inventors, Frank W. Godsey Jr., filed another patent for an airplane engine “in which air is drawn through a tube and discharged in a jet or blast at the rear of the aircraft”; in other words, a turbojet engine. Indeed, history records that Westinghouse Electrical Corporation developed and built their J30, the first American-designed turbojet to run, and only the second axial-flow turbojet to run outside Germany. The patent for the turbojet (U.S. 2404954 A) was published in 1946, while the patent for the electric airplane design (U.S. 2462201 A), again never built, was only granted in 1949. Frank Godsey Jr. went on to accumulate 100 patents in fields that included radio aviation and undersea warfare. He later became a consultant to James E. Webb, administrator of NASA. Lee Kilgore continued to develop lesser-known but reliable electric motors for wind tunnels. In IEEE interviews about their careers recorded in the 1970s, neither Godsey nor Kilgore made mention of their involvement in the electrical airplane transmission.3 Their ingenious idea would only be resurrected some seventy years later.
Unknown to these men, in 1945 Stanley Bizjak, a humble corporal in the U.S. Army, based at his family dairy farm in Crivitz, Wisconsin, received U.S. Pat. No. 2,368,639 for an electrically powered glider. He had applied for the patent on June 3, 1943, specifying that its electric propulsion should be driven in part by gasoline. We do not know whether it was ever built. Bizjak also patented a motorized sledge.
Hybrid philosophy for mass-produced gas automobiles returned some fifty years later with the release of the Toyota Prius in Japan in 1997, followed by the Honda Insight in 1999. Meanwhile, aviation was looking at a variety of options, one of them hybrid.
In February 1943, Frank W. Godsey Jr., Lee A. Kilgore and a team working at the Westinghouse Electrical Corporation at East Pittsburgh filed a patent for this hybrid-electric “multi-propellered” airplane. Patent U.S. 2462201 A was finally granted in 1949, and then forgotten.
In 2003, a team of researchers led by Dave Bushman at the Marshall Center, NASA’s Dryden Flight Research Center in Edwards, California, and the University of Alabama in Huntsville flew an 11-ounce (312 g) model airplane with a propeller powered with solar panels illuminated by a laser. The plane with its five-foot wingspan was constructed from balsa wood and carbon fiber tubing and was covered with Mylar film, a cellophane-like material. The photovoltaic cells had been selected and tested by team participants at the University of Alabama in Huntsville. The prototype was flown indoors at Marshall to prevent wind and weather from affecting the test flights. After the craft was released from a launching platform inside the building, the laser beam was aimed at the airplane panels, causing the propeller to spin and propel the craft around the building, lap after lap. When the laser beam was turned off, the airplane glided to a landing.
Another exponent of laser-powered airplane concepts is Leik N. Myrabo with his LightCraft, a 1-kg. (2-lb.) launch vehicle, made from high-temperature ceramic materials, that could fly into space on a megawatt laser beam. Myrabo first got the idea in 1988 while working on the “Star Wars” anti-missile shield. A LightCraft channels the heat generated by a laser into its center, heating the air to about 30,000 degrees and causing it to explode, generating thrust. Small jets of pressurized nitrogen spin the LightCraft at 6,000 rpm to maintain stability. It was all just theoretical research—which the U.S. Air Force, NASA and the Strategic Defense Initiative provided $600,000 to help finance—until July 1996, when Myrabo, working with the U.S. Army at the White Sands Missile Range in New Mexico, propelled a small LightCraft prototype, measuring 6 inches long and weighing ounces, 50 feet into the air. After that, Myrabo conducted 24 test campaigns at HELSTF using the PLVTS 10-kW laser. On October 2, 2000, sponsored under a nonprofit grant to his company LightCraft Technologies, Inc., Myrabo, using a 10-kilowatt pulsed carbon dioxide laser, saw the LightCraft climb to 233 feet (71 m) during a 12.7-second flight. This experiment established a new world altitude record for laser-boosted vehicles in free flight. On December 2, 2002, having made 140 test flights using small prototypes, LightCraft Technologies Inc. of Bennington, Vermont, was awarded U.S. Patent #6488233—“Laser Propelled Vehicle.” Myrabo’s challenge since then has been to find the finance to build the first full-scale craft. Once achieved, Myrabo sees laser flight carrying people around the globe and into space by 2020. Ground-based lasers called LightPorts would provide the energy needed to propel the aircraft. One is reminded of Nikola Tesla’s patent of a century before.
Another option is the fuel cell.
In the early 1950s, an English engineer, Professor Thomas Bacon of Cambridge University, was making considerable progress developing the first practical hydrogen–oxygen fuel cell to present large-scale demonstrations. One of the first of these demonstrations consisted of a 1959 Allis-Chalmers farm tractor powered by a stack of 1,008 cells. With 15,000 watts of power, the tractor generated enough power to pull a weight of about 3,000 pounds. Allis-Chalmers maintained a research program for some years, building a fuel cell–powered golf cart, submersible, and fork lift, but not a boat. Interestingly, the U.S. Air Force also participated in this program.
The first experimental fuel cell airplane came thirty years later, with the Soviet Tupolev Tu-155, a Tu-154 airliner retrofitted by the Kuznetsov Engine Design Bureau. After two years of R&D, it made its first flight on April 18, 1988, by a crew under the command of Andrei Talalakin. The liquid hydrogen–fed engine was tested at altitudes up to 7,000 m (23,000 ft.) and speeds up to 900 kph (560 mph). In-flight starts and failures of the experimental engine were simulated, and the fire extinguishing system also was tried.
It made another four flights before the fall of the Soviet Union and it is currently stored in the Ramenskoye Airport near Zhukovskiy. The Tu-156 was intended to fly commercially around 1997 but was canceled due to the fall of the Soviet Union. At the beginning of the new millennium, the economic situation in Russia stabilized, and interest in cryogenic fuels was reignited. Financing of a new project—the Tu-2016, a modified Tu-204K—began in 2002 with approximately 50 percent coming from the state budget.
In 1997, Klaus Graage of Ballard Power Systems and Daimler-Benz combined their vehicular PEM fuel cell and fuel cell system businesses to form dbb GmbH. The following year, they expanded to take in the Ford Motor Company and dbb became Xcellsis. Although the plan was to develop PEM fuel cells for autos and trucks, an additional patent was obtained in 1999 (DE19821952A1) for the energy supply on board an airplane.
Ever at the cutting edge, in 2001 Paul MacCready and his team at AeroVironment (see Chapter Five) applied for a patent for a fuel-celled flying wing. Their system would use liquid hydrogen as fuel, but gaseous hydrogen in the fuel cell. A fuel tank heater would be used to control the boil-rate of the fuel in the fuel tank. Although Patent U.S. 20020005454 was obtained in 2002, it was not until 2011, three years after MacCready’s death, that AeroVironment’s Global Observer took off with a hydrogen-fueled propulsion system.
In 2006, a team led by Professor Giulio Romeo at the Department of Aerospace at Turin University, funded by the European Commission, began a UAV program called the VESPAS (Very Long Endurance Solar-Powered Autonomous Stratospheric), a fleet of whose Heliplats (Helios Platforms), using a combination of solar and fuel cell technology, would be able to monitor the Mediterranean Sea from Turkey to Spain. By October 2007, a Super Dimona 2400 model motor-glider with a 7-m (22.9-ft.) span modified with solar lithium technology made its maiden flight. From this, the Turin Polytechnic—supported by 11 partners, including Israel Aerospace Industries, Evektor, Metec, Air Products, Enigmatex, Infocosmos, and Intelligent Energy, Brno University of Technology in the Czech Republic, and the Université Libre de Bruxelles in Belgium—adapted a Jihlaven Rapid 200 two-seater light plane into their ENFICA-FC (Environmentally Friendly Inter-City Aircraft powered by Fuel Cells) prototype. From 2010, the fuel-cell airplane was successfully tested at the Reggio Emilio Airport by POLITO during six experimental flights, lasting a total of 2 hours and accumulating 147 miles (237 km). Climbing was obtained at a combined fuel cell and battery power of 35 kW. Level flight was attained up to 100 mph (160 kph) using only a fuel cell power setting. A new world speed record of 84 mph (135 kph) and an endurance of 39 min were established for the airplane during several flights conducted in the FAI Code Category C for motorized aircraft. The next step would be for an 11–16 passenger ENFICA-FC commuter.
The same approach was taken up by the major airliner builder Boeing. From 2003, during the formative stages of the project, it became clear that a NASA-funded U.S. effort, led by Worcester, Massachusetts-based Advanced Technology Products, had come to many of the same technical conclusions as the Boeing team, developing a similar fuel cell–powered electric aircraft based upon a French DynAero airplane. Instead of working in parallel, a decision was made to combine the two teams’ efforts in order to speed up progress and take advantage of mutually beneficial funding opportunities. A four-strong research team, Elena Bataller, Jonay Mosquera, Nieves Lapeña-Rey and Fortunato Ortí, engineers at Boeing Research & Technology Euro in Madrid (part of the Boeing Phantom Works advanced research-and-development unit), began to work around an Austrian Diamond HK-36 Super Dimona motor glider. For the motor, proton membrane fuel cell, and li-ion batteries, they worked with Advanced Technology Products of Massachusetts, then Aerlyper of Spain integrated the propulsion package into the airframe. In February and March 2008, the Boeing Fuel Cell Demonstrator, piloted by Cecilio Barberan Alonso of Senasa, achieved three successful straight-level flights out of an airfield at Ocana, south of Madrid. The aircraft took off on a combination of battery power and the fuel cell, but used the fuel proton membrane cell alone to cruise at 3,300 feet (1,000 m) and about 55 knots for 20 minutes.4
As Boeing, so Airbus: Deutsche Aerospace AG had cooperated in a German-Russian effort started in 1990 to investigate an environmentally compatible airliner using fuel other than kerosene. A two-year feasibility study by Deutsche (later Daimler-Benz, then DaimlerChrysler) Aerospace AG, completed in September 1992, concluded that liquid hydrogen is safer than natural gas, kinder to the environment, and more readily available over the long term. Following this feasibility study, a new three-year phase was begun to develop critical technology and components such as tanks for liquid hydrogen storage at -253° C at 1.5 bars (21.75 lb./sq in), together with pumps and seals. This was supported by the German Ministry of Economics. Participants in the Cryoplane project included Tupolev, Samara, Daimler-Benz Aerospace, Munich, Linde, MAN Technologie, Messer-Griesheim, UHDE, Honeywell, Bodenseewerk, Drägerwerk, Deutsche Lufthansa, Munich Airport, Berlin Airport Corporation, and Hamburg’s Max Planck Meteorological Institute.
In 2002, Koni Schafroth of Zurich, Switzerland, inspired by the shape of a tuna fish, began flights with an unconventional low aspect ratio model airplane he called SmartFish. It was initially powered by batteries, but following successful flights, the transition was soon made to a fuel cell plant. For this, Team SmartFish joined forces with the Institute for Technical Thermodynamics of the German Aerospace Centre (DLR) in Stuttgart with the goal of adapting the SmartFish’s impeller engine to run on hydrogen fuel cell power as developed by Horizon Fuel Cell Technologies of Singapore. So the name chosen was HyFish. In addition, Schafroch was joined by Ulrich Scheifer, a former aerodynamics expert on BMW’s Formula One team. Following a successful flight in April 2007 in Bern, Switzerland, the team began to plan a 20 Pax full-scale airplane.
In 2005, financed by the European Commission, Airbus launched the CELINA (cell in airplane) to investigate the complete fuel cell system including kerosene reformer, fuel cell stack, air supply and all subsystems based on simulation models and tests. By 2008, Airbus, DLR and Michelin had progressed to performing flight evaluations on a testbed A320. The earlier fuel cell was installed on a cargo pallet and produced some 25 kW of electrical power—operating the electric motor pump for the aircraft’s back-up hydraulic circuit, and controlling the spoilers, ailerons and elevator actuator. It has now partnered with the DLR German Aerospace Centre and Parker Aerospace to study usage of a Multifunctional Fuel Cell (MFFC) system on aircraft to replace today’s gas turbine–based auxiliary power units. The system could provide an estimated 100 kW of electricity, acting as an independent source capable of providing power throughout an aircraft.
Axel Lange, one of the pioneers of the e-assisted sailplane, also decided to pursue the fuel-cell flight path. On July 7, 2009, the German took off from Hamburg airport in his fuel-cell powered Antares DLR-H2 for a 10-minute maiden flight to an altitude of 837 feet (255 m). Designed as a flying test bed for fuel cell technology aimed at civil aviation (APU replacement), the heavily modified Antares 20E has a top speed of 170 kph (105 mph). Commissioned by the Stuttgart-based Institute for Technical Thermodynamics of the German Aerospace Center (DLR), Lange strengthened the structure of the Antares 20E, added two underwing external pods and integrated an HT-PEM fuel cell system designed by Serenergy in Denmark, with additional input from BASF and Airbus. Pressurized hydrogen was used for fuel. Three years later, the aircraft was re-equipped with LT-PEM fuel cells and a larger pressure vessel for fuel storage. Located in the starboard external pod and weighing some 95 kg (210 lb.), the new tank holds some 5 kg (11 lb.) of hydrogen at 350 bar (5,076 pounds per square inch), compared to the 2 kg (4.4 lb.) capacity of the previous tank. To achieve this weight-saving, they wrapped hydrogen-trapping magnesium with an atom-thick layer of graphene. These changes yielded a maximum range of 500 km (270 miles) and an endurance in excess of 5 hours.
Next followed the Antares H3, whose target was to set range and endurance benchmarks beyond those accomplished by its predecessor: higher-performance and more compact fuel cell systems were incorporated in cooperation with Hydrogenics. The additional option of hybrid operation using storage batteries installed in the wings maximized the aircraft’s peak power. A transatlantic crossing was even planned. It was hoped the Antares H3 would demonstrate significantly increased performance—the developers planned to achieve a range of up to 3,700 miles (6,000 km) and endurance of more than 50 hours. For the Antares H2, these values had been only 430 miles (700 km) and 5 hours respectively. The aircraft would have a wingspan of 76 feet (23 m), a maximum takeoff weight of 1.25 metric tons (2,200 lb.) and it would carry payloads of up to 450 lb. (200 kg). It would use four external pods to house the fuel cells and fuel.
Fuel-cell electric airplane progress has gone on elsewhere with the HY4 as presented by H2FLY at the German Aerospace Center, Deutsches ZentrumfürLuft und Raumfahrt (DLR), working with Hyrodgenics. The HY4 is a four-seat hydrogen fuel cell electric air taxi, equipped with a low-temperature fuel cell with a proton exchange membrane (PEM) and an electric motor with a power of 80 kW that allow a maximum speed of about (125 mph (200 kph) and a cruising speed of 90 mph (145 kph). Depending on the speed, altitude and load, the autonomy of HY4 can vary between 750 and 1,500 km (450 and 930 mi) away. In cruising flight, the fuel cell will only power the electric motor; it will be helped by a 21 kwh Li-Po battery to provide the extra power required during takeoff and climb in altitude. Using the airframe of the Pipistrel Taurus G4, the HY4 eventually appeared at the 2016 Hannover Trade Fair. During the spring of 2016, the DLR research team successfully tested the drive train in the laboratory. In order to take off, the engine must reliably provide a maximum takeoff output for three minutes. This has already been successfully demonstrated for more than 10 minutes. The interaction of the fuel cell and the high-performance battery, used as a buffer and additional safety system, has also been successfully demonstrated in a simplified form in the laboratory. Hence, the road is clear for installing an initial version of this propulsion system in the four-seater HY4 passenger aircraft. The first short 15-minute demonstration flight of the HY4 was made on September 29 at Stuttgart Airport above the public and the media; air traffic control had all the other air traffic stopped, so spectators could appreciate the almost complete silence of the fuel cell airplane, flown by pilots Johannes Anton and Nejc Faganelj in one cockpit, with two dummy passengers in the other.5
Antares H2 flying over Zweibrücken, Berlin (courtesy Lange Aviation GmbH).
In March 2017, Professor Josef Kallo, head of the Institute for Energy Conversion and Storage at Ulm University, describing this flight, announced plans to test the technological platform over the coming years before the target will be upped to six or eight seats. He explained: “Recent studies on commercial aviation show that there are indeed feasible propulsion designs for regional air travel with up to 40 seats and a range of 435 miles (700 km) or below, even though the technical challenges are significant.”6 During the summer of 2017 the HY4 continued to make a large number of short proving flights.
The origins of the Thevenot fuel-cell E-Trike go back to 1974, when Gérard Thevenot of Fontaine Les Dijon in the Côte-d’Or Department, while still a student at the engineering school of Nancy ISIN, acquired the plans of the Seagull (an American-manufactured glider) and decided to build his own wing, based on this model, in order to fulfill his wishes to become airborne. He called the wing “La Mouette” (Seagull in French). By mistake he built the leading edges stronger than required due to the materials he had at hand, thus improving the wing’s stability and performance. Enthusiasm about hang-gliding and the new wing spread rapidly among his friends, who begged him to build some for them. Thevenot built a 13 kW Flytec-engined Mouette E-Trike, which could be folded up and put in a car trunk. In July 2009, Thevenot flew his hydrogen-powered ultralight “trike” across the English Channel, with a Geiger/Eck HP-10 electric motor powered by a hydrogen fuel cell, without the onboard presence of an accumulator or battery. Its light weight allowed a consumption of only 550 grams per flight hour, and the craft’s 5-liter tank allows about one hour flying time. In an environmentally friendly hint of its passing, the craft leaves behind only a mist of water vapor.
On January 8, 2017, a test flight of 350 yds (320 m) made in Shenyang, Liaoning, by an RX1E, equipped with 20 kilowatts of hydrogen fuel cell power supply, made China the third nation in the world to successfully test an airplane using hydrogen fuel. With a charging time of 90 minutes, the airplane is designed to be able to fly at a maximum altitude of 3,200 feet (3,000 m), for 45 to 60 minutes.7
Both photographs: Axel Lange in Antares H2 fuel cell aircraft (courtesy Lange Aviation GmbH).
At the time of writing, Axel Lange is working on his next electric aircraft, the Antares E2. While not being a competitive aircraft on its own, the Antares H2 had shown that if the fuel storage problem can be solved, then fuel cells can work in aviation. The Antares E2 solves the problem of fuel storage by carrying a liquid hydrocarbon fuel and reforming it into hydrogen onboard the aircraft. This solution results in a higher empty weight compared to IC. However, the high fuel efficiency of a fuel cell means that the system becomes more and more weight-competitive as the endurance increases. With a planned endurance in excess of 32 hours, it goes without saying that the E2 must be operated as an unmanned air vehicle (UAV). The aircraft targets the civilian market, with the goal of fulfilling hitherto unfulfilled sovereign and industrial requirements. As with the Antares H2, fuel cells and fuel are once more housed in underwing pods, leaving the fuselage for flight controls and payload. The fuel cells are of the HT-PEM variety, and once more, Serenergy is delivering the fuel cell systems. The battery pack of the Antares 20E is maintained, making hybrid operation possible. This allows for high peak power consumption during takeoff and in adverse weather. Contrary to the previous gliders, the Antares E2 will be equipped with anti-icing and lightning strike protection. The Antares E2 has a MTOW of 1650 kg (3640 lb.), of which 300 kg (660 lb.) are fuel, and 200 kg (440 lb.) are payload. The motor installation Antares 20E and 23E had been optimized for climb and soaring flight. This resulted in a high-torque electric motor with a large-diameter propeller located on a pylon over the center fuselage. For soaring flight, motor and pylon are retracted into the center fuselage, yielding a pure sailplane. For the Antares E2, which is to operate under continuous power, this propulsive solution does not represent an optimum. The increase in power required would result in an unacceptably large propeller diameter, and the propeller wake would continuously hit the empennage, resulting in deteriorated aerodynamics. This problem was solved by distributing the power over six motors mounted on pylons above and behind the wing trailing edge. Altogether, this results in a unique aircraft that may very likely prove to be another milestone of electric flight.
The main challenge for fuel cell aircraft will be the constrained durability and instability of nanoparticles. The robustness of fuel cell systems is lower compared with the internal combustion engines, particularly in the specific temperature and humidity ranges in which an aircraft driven by a fuel cell would operate. The durability of a commonplace fuel cell stack is half the optimum durability required for its use in commercial aviation.
In Israel, aerospace engineers led by Dr. Shani Elitzur at the Technion-Israel Institute of Technology have developed and patented a process that can be used onboard aircraft while in flight to produce hydrogen from water and aluminum particles safely and cheaply. The hydrogen can then be converted into electrical energy for in-flight use. According to the Technion researchers, fuel cells can even play an energy-saving role in airline and airport ground support operations when they are also used for systems such as de-icing and runway light towers.8 Non fuel-cell hybrid-electric research has continued in parallel.
In late 2016, a team led by Pat Anderson at Embry-Riddle Aeronautical University’s Eagle Flight Research Center, at Daytona Beach, Florida, announced that it was developing a nine-seat hybrid electric turboprop aircraft.
Another hybrid-electric prototype developed by a team at University of Cambridge’s Engineering Department led by Dr. Paul Robertson was given flight tests in late 2015 at Sywell Aerodrome in Northamptonshire, England. The Cambridge demonstrator used a Honda engine in parallel with a custom lightweight electric motor while a set of 16 large lithium-polymer cells was located in special compartments built into the wings. These tests consisted of a series of “hops” along the runway, followed by longer evaluation flights at a height of over 1,500 feet (460 m).9
In 2013, General Electric opened the $51 million Electrical Power Integrated System Center (EpisCenter) on the campus of the University of Dayton, Ohio. The facility was sized to test electric power systems ranging in size from 500kW to 2.5MW. In the lab, university researchers and students began to work side by side with GE Aviation scientists and engineers to create new advanced electrical power technologies such as new power systems for aircraft, longer-range electric cars, and smarter utility power grids for more efficient delivery of electricity. On August 25, 2017, the GE EpisCenter published a white paper reporting how they had modified an F110 engine, a propulsion option for the Boeing F-15 and Lockheed Martin F-16, to generate 1MW of electric power. By siphoning compressed air from the core, GE had extracted 250kW from the high-pressure turbine and—an industry first for a two-shaft engine—750kW from the low-pressure turbine, according to the white paper. As a megawatt of electric power is equivalent to 1,341 hp, the F110 still has plenty of thrust to continue powering even in a single-engined aircraft. They had also produced an advanced electric motor in a separate project where the 1MW motor drove a propeller designed by Dowty, another GE subsidiary. When coupled with a gas generator, such a hybrid propulsion system could produce the same thrust as a large version of the Pratt & Whitney Canada PT6A turboshaft engine. Whereas most aviation motors are designed to achieve 90 percent efficiency, the new motor demonstrated by GE is 98 percent efficient. Such efficiency means a 1MW motor produces only 20kW of waste heat, rather than at least 100kW if a conventional aviation motor is used. GE Aviation did not reveal the size or weight of the device, but announced that they were currently engaging with several prospective companies on hybrid electric aircraft concepts.10
GE is also running a lightweight megawatt-class power inverter, which is a key step toward development of a viable hybrid-electric aircraft propulsion system. Tests of the liquid-cooled inverter, conducted at GE’s Global Research Center (GRC) in Niskayuna, New York, form the next phase of an accelerating company-wide drive to perfect technology for hybrid-electric, turboelectric and all-electric aircraft.
Also in England, with the Griffon Hoverwork 995ED, another air cushion vehicle also known as the hovercraft, whose origins go back fifty years, finally embraced electric power. Designed by a team led by Mark Downer in Woolston, Southampton, southern England, the 28-ft (8.6 m) 8-seat craft sees two standard hybrid power modules containing a 67kW Ford Tiger diesel engine providing lift through highly efficient fans and supplying the two 45kW lightweight axial thrust electrical motors. No batteries are involved. The 995ED went on trials in August 2016 and since then shakedown trials have continued.
The success of one-off electric airplanes, be they supported by solar panels or hybrid fuel cells, is one thing. Taking them to the stage of commercialization is another.