The need to reduce gas emissions, optimize aircraft performance, decrease operating and maintenance costs, is pushing aircraft industry to progress towards more electric aircraft (MEA), and ultimately an All-Electric Aircraft. Due to the higher efficiency and better reliability compared to conventional combustion engines, electrical systems with no greenhouse gas emission and low noise and vibration attract much more attention.
Propulsion systems also enable UAV missions by providing them with the necessary power to propel the aircraft for forwarding flight or hover. Propulsion systems can advance the flight time or endurance of a UAV which is influenced by the propulsion technology used and is dependent on the aerodynamic design and amount of fuel carried. To fulfill the energy requirements of a large variety of UAVs, several variants of piston-engines and electric motors have been designed by the market players. Electric propulsion is also gaining interest in UAVs as they are increasingly employed by various industries and in Defense and Security missions.
Electric propulsion can be powered by rechargeable batteries, fuel cells, or solar energy. “Typical lithium-ion batteries in use today have a maximum energy density of around 1,000,000 joules of energy per kilogram, and while newer research promises the possibility of higher densities, these are not available commercially, says Dr Peter Wilson, professor of electronics and systems engineering at the University of Bath. A million joules sounds like a lot. However, compare this with 43m joules per kilogram for aviation fuel. Swapping the fuel tanks for a battery weighing 43 times as much isn’t a viable option: clearly there’s a significant storage problem to be solved before electricity can power large aircraft over long distances.
A fuel cell is a device that generates electricity by a chemical reaction. It converts hydrogen and oxygen into water, and in the process also creates electricity. Fuel cells provide many advantages, they are environment friendly as they don’t produce pollutants or greenhouse gasses, significantly improving our environment, high energy efficiency ( can be close to 80% where they generate both heat and electricity), scalable providing power from milliwatts to megawatts, and complementary i.e. readily be combined with other energy technologies, such as batteries, wind turbines, solar panels, and super-capacitors.
Hydrogen fuel cells can be used in a broad range of applications such as cars, buildings, electronic devices, trucks, and backup power systems. As these cells can be grid-independent, they are an attractive option for critical load functions such as telecommunication towers, data centers, emergency response systems, hospitals, and even military applications for national defense.
Benefits of fuelling drones with Hydrogen
Hydrogen fuel cells are demonstrated as the propulsion system for long-endurance, small, electric unmanned air vehicles (UAVs). Unmanned aerial vehicles (UAVs) are typically used for military operations where manned flights would be too risky or difficult. They send back real-time imagery of activities on the ground and are usually powered by batteries that last up to 30 minutes before they need to recharge. Hydrogen fuel cells can increase UAV air time to approximately 8 hours and, after landing, can be refueled in less than 15 minutes. Also, there are no moving parts—meaning the fuel cell-powered UAV requires less maintenance and zero lubricants.
1. Hydrogen is a clean energy source.
Hydrogen is a colorless, odorless, and nontoxic gas that won’t produce acid rain, deplete the ozone, or produce harmful emissions. When converted to energy it only has one byproduct: water. This makes hydrogen an incredibly clean fuel source. Plus, hydrogen can produce electricity and electricity can produce hydrogen, creating an energy loop that is renewable and harmless to the environment.
2. Hydrogen is the most abundant resource on Earth.
Hydrogen is the most abundant resource on Earth and throughout the entire Universe. Think you might fly a drone on Mars one day? Even on Mars hydrogen is still the most abundant resource.
3. Hydrogen fuel cells have a higher energy density than batteries.
Fuel cells use air for half of their reaction when converted to energy, producing a higher energy density than other batteries. This means a hydrogen tank attached to a drone will generate more energy than a LiPo battery of the same weight.
4. Hydrogen fuel cells enable longer flight times.
Due in part to benefit #3, hydrogen-fueled drones fly longer than LiPo powered drones. In addition to the high energy density of hydrogen, it’s unique method of creating and releasing energy impacts flight time a well. Regular batteries store energy and release it on demand, while hydrogen fuel cells produce energy only as required. This unique behavior has enabled hydrogen-fueled drones to fly for up to two and a half hours in the case of MCC’s HyDrone 1550 and up to two hours with BSHARK’s new Narwhal 2. Most LiPo powered drones have a maximum flight time of 25-30 minutes, but there are a few ways you can extend the life of your sUAS LiPo battery.
5. Hydrogen fuel cells refuel quickly.
In the past, Hydrogen fuel has not been readily accessible by the public, and it’s still difficult to find. However, BSHARK has just made Orca1, a mobile hydrogen fueling station with 99.999% output purity of hydrogen, available for hydrogen fueling at home. When compared to the time it takes to recharge a LiPo battery, a hydrogen fuel cell can be refueled much faster within just a few minutes.
6. hydrogen-fueled drones function in low temperatures.
Hydrogen fuel cells require the constant presence of oxygen but are not affected by low temperatures. This expands the use of drones into northern and southern latitudes. The ability to function in low temperatures will open up new applications for drones.
7. BVLOS flights are more attainable with hydrogen-fueled drones.
Since hydrogen-fueled drones have longer-flight times and can operate in lower temperatures, they’re more reliable for beyond-visual-line-of-sight (BVLOS) flights. However, changes in regulation around BVLOS flights will need to occur first before we reap the full benefits of hydrogen-fueled drones.
Fuel cell demonstration on UAVs
Flight times of >24 hours have been demonstrated for the 35-lb Ion Tiger fuel cell UAV while carrying a 5-lb payload. The promise of hydrogen-electric power could shape the future of aviation. “It’s now possible to break past the endurance limits of battery-electric flight using HES’ ultra-light hydrogen energy storage in a distributed propulsion arrangement,” says Taras Wankewycz, founder of HES. “Element One’s design paves the way for renewable hydrogen as a long-range fuel for electric aviation.”
Unmanned Aerial Vehicles (UAVs)
At InterDrone exhibition in Las Vegas, two FCHEA member companies showcased hydrogen fuel cell power packs for commercial UAVs. Doosan Mobility Innovation’s fuel cell powerpack is refueled using a single, detachable hydrogen container, and the powerpack can keep UAVs flying for two hours on a single charge of hydrogen.
Intelligent Energy’s new 800W Fuel Cell Power Module (FCPM) was shown with the company’s 650W model, which was unveiled at the 2017 InterDrone exhibition. The 800W FCPM is 10% more power dense than the 650W model, and multicopter UAVs will be able to carry one kilogram of cargo for two hours, or two kilograms for one hour. Intelligent Energy will also work with customers who have the capability to combine two of the 800W models to provide 1.6 kW of continuous power building on the success and interest in UAVs, FCHEA member Alakai Technologies is going one step further, developing a hydrogen fuel cell-powered, four-passenger, long-duration, all-electric vertical takeoff and landing (eVTOL) aircraft in 2019.
Fuel cell for Aircrafts
Numerous airlines made strides towards reducing carbon emissions and investing in next generation air transportation technologies in 2021. Several airlines, including Virgin Atlantic, GOL, and Japan Airlines have pre-ordered electric vertical take-off and landing (eVTOL) vehicles from the company Vertical Aerospace.
Airbus has announced plans for the world’s first zero-emission commercial aircraft models that run on hydrogen and said they could be flying by 2035. Boeing, meanwhile, has done several tests of hydrogen-powered aircraft — both manned and unmanned.
United Airlines, has invested in electric aircraft startup Heart Aerospace and ZeroAvia, the hydrogen-electric aircraft engine company. The agreement brings the total investment in ZeroAvia up to $115 million, and it also includes a provision for United to purchase up to 100 of ZeroAvia’s hydrogen-electric engines.
Dan Steingart, an associate professor of chemical metallurgy at Columbia University, explained that “in a single hydrogen molecule, there is somewhere between one-fourth and one-eighth the total energy available in a single typical jet fuel molecule.” So, for the same amount of fuel, “planes would go one-fourth the distance.”
Obviously, that’s not ideal. So large aircraft meant to go any substantial distance would need much larger fuel tanks. And those tanks would need to be frozen to minus 420 degrees Fahrenheit — close to absolute zero — to liquefy the hydrogen. That is almost as cold as anything in the universe can get.
In today’s planes, wings are where the fuel is stored, and they are in no way large enough to store the hydrogen that would be needed for a long flight. “Yes, as far as hydrogen-powered, the planes will definitely look different,” said Bhupendra Khandelwal, an associate professor at the University of Alabama. So the hydrogen planes of the future could have extra-large fuselages, but more likely they will be what’s called blended wing, in which the planes are shaped like large triangles. This would allow them to store more fuel, “but also reduce fuel consumption to make the aircraft aerodynamics even better,” Khandelwal said.
It’ll be sometime in the 2030s that the cost of hydrogen becomes comparable to jet fuel, according to ICF, and the infrastructure to help make that happen would probably develop outside of aviation, said Eliot Lees, ICF’s vice president for clean transportation. “What you’ll see is the infrastructure for hydrogen becoming important for the on-road fleet of heavy- and medium-duty trucks, and from there it will make its way into aviation.”
World’s First Hydrogen-Electric Passenger Aircraft: Element One, unveiled in 2018
Singapore’s HES Energy Systems developed Element One, the world’s first regional hydrogen-electric passenger aircraft. The ultra-light Element One can take up to four passengers and is envisioned for fully autonomous flying. Element One is designed to fly 4 passengers for 500 km to 5000 km depending on whether hydrogen is stored in gaseous or liquid form. This performance is several orders of magnitude better than any battery-electric aircraft attempt so far, opening new aerial routes between smaller towns and rural areas using an existing and dense network of small-scale airports and aerodromes. HES Energy Systems said that it worked on the project for 12 years and intends to build the first flying prototype before 2025.
Designed as a zero-emissions aircraft, Element One merges HES’ ultra-light hydrogen fuel cell technologies with a distributed electric aircraft propulsion design. With virtually no change to its current drone-scale systems, HES’ distributed system allows for modularity and increased safety through multiple system redundancies.
NASA backs development of cryogenic hydrogen system to power all-electric aircraft in 2019
The University of Illinois has announced that NASA is underwriting a project to develop a cryogenic hydrogen fuel cell system for powering all-electric aircraft. Funded by a three-year, US$6 million contract, the Center for Cryogenic High-Efficiency Electrical Technologies for Aircraft (CHEETA) will investigate the technology needed to produce a practical all-electric design to replace conventional fossil fuel propulsion systems.
The jet engine in all its variations has revolutionized air travel, but with airline profit margins running wafer-thin in these ecologically conscious times, there’s a lot of interest in moving away from aircraft powered by fossil fuels and toward emission-free electric propulsion systems that aren’t dependent on petroleum and its volatile prices.
Artist’s rendering of commercial transport aircraft concept utilizing CHEETA systems
The CHEETA project is a consortium of eight institutions that include the Air Force Research Laboratory, Boeing Research and Technology, General Electric Global Research, Ohio State University, Massachusetts Institute of Technology, the University of Arkansas, the University of Dayton Research Institute, and Rensselaer Polytechnic Institute. Although the project is still in its conceptual stage, the researchers have a firm vision of the technology and its potential.
“Essentially, the program focuses on the development of a fully electric aircraft platform that uses cryogenic liquid hydrogen as an energy storage method,” says Phillip Ansell, assistant professor in the Department of Aerospace Engineering at Urbana-Champaign who is the project’s principal investigator. “The hydrogen chemical energy is converted to electrical energy through a series of fuel cells, which drive the ultra-efficient electric propulsion system. The low temperature requirements of the hydrogen system also provide opportunities to use superconducting, or lossless, energy transmission and high-power motor systems.
“It’s similar to how MRIs work, magnetic resonance imaging. However, these necessary electrical drivetrain systems do not yet exist, and the methods for integrating electrically driven propulsion technologies into an aircraft platform have not yet been effectively established. This program seeks to address this gap and make foundational contributions in technologies that will enable fully electric aircraft of the future.”
The team points out that though progress has been made, there are many basic problems that need to be overcome before we see such electric aircraft taking to the skies.
“Advances in recent years on non-cryogenic machines and drives have brought electric propulsion of commercial regional jets closer to reality, but practical cryogenic systems remain the ‘holy grail’ for large aircraft because of their unmatched power density and efficiency,” says Associate Professor Kiruba Haran of the Department of Electrical and Computer Engineering at the University of Illinois. “The partnerships that have been established for this project position us well to address the significant technical hurdles that exist along this path.”
Boeing’s Insitu advances its fuel cell technology; LH2 fueling, reported in March 2021
Insitu, a wholly-owned subsidiary of The Boeing Company, announced new details about its latest efforts to advance hydrogen fuel-cell propulsion for Unmanned Aerial Vehicles (UAVs).
In December 2020, Insitu completed the first flight of the ScanEagle3 UAV powered by an all-electric, hydrogen-fueled, PEM fuel cell. The 30-minute flight confirmed initial performance characteristics including power output, climb rate, and intrinsic aerodynamic flight characteristics for the UAV in preparation for test flights using a Liquid Hydrogen (LH2) storage tank on the aircraft that are planned for later this year. For our global Defense customers, fuel-cell-powered UAS in this Group 2 space represent a significant game changer in the battlespace. Operationally, fuel-cell-powered platforms provide the potential for longer endurance missions, increased power availability for payloads, as well as significant reductions in noise signature. —Andrew Duggan, Managing Director Insitu Pacific
The 3-D-printed LH2 tank is an industry first, and is expected to support 10+ hours of endurance for ScanEagle3. In February 2021, a Liquid Hydrogen (LH2) flight tank designed for the ScanEagle3 UAV successfully completed liquid hydrogen fill, pressure and vapor generation testing at Washington State University’s Hydrogen Properties for Energy Research (HyPER) Lab. The tests verified operation performance metrics of the LH2 tank in preparation for upcoming flights of ScanEagle3 equipped with a PEM fuel cell power system. The LH2 Tank Integration project is part of a larger development effort to compare acoustic and thermal signatures of a small UAV powered with an internal combustion engine versus an all-electric power system.
The defense industry is growing increasingly interested in the benefits of hydrogen fuel cell technology, which range from environmental to operational. Fuel cells support better ISR data collection because PEM fuel cell stack emissions are limited to small amounts of H2O and trace amounts of H2. The fuel cell and electric motor thermal and acoustic signatures are significantly lower than traditional internal combustion (IC) engines, enabling mission routes closer to targets. The PEM fuel cell / electric motor combination also decreases platform vibration and enables excess power to support greater payload diversity. Fuel cells also deliver improved reliability and significantly lower logistics costs relative to small IC engine propulsion solutions. Tests are expected to continue in Q2 of 2021 with the first liquid hydrogen flight planned for late summer 2021.