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The civil global aviation market has experienced considerable economic growth in recent years and will keep increasing. It is estimated that around 1300 new international airports will be required, and the commercial aircraft fleet will double by 2050, with a projected passenger throughput of 7.2 billion in 2035.
This growth is desirable from an economic standpoint, but aviation is predicated on fossil fuels, which increase greenhouse gas and air pollutant emission.
Presently, Aviation Industry generates 2-3 percent of the world’s human-generated carbon dioxide emissions and 12 percent of the CO2 emissions from all transportation sources. It is projected to rise to 11% if new technology is not advanced in the next two decades to cope with the projected annual growth of the aviation industry.
To reduce its impact on the environment and improve the sustainability of its operations, the commercial aviation industry has committed to achieve net-zero air transport emissions by 2050.
Achieving these goals requires disruptive innovation in the propulsion system of aircraft. The need to optimize aircraft performance, decrease operating and maintenance costs, and reduce gas emissions is pushing aircraft industry to explore new concepts including more electric aircraft (MEA), and ultimately an All-Electric Aircraft. Electric propulsion can be powered by rechargeable batteries, fuel cells, or solar energy. Electric plane power is much simpler — batteries power an electric motor that spins a propeller.
By introducing electric battery-powered aircraft, the potential exists for charging batteries using power generated from low carbon sources, such as nuclear or renewables. Yet getting to that place presents many significant technological challenges
R&D is moving forwards too, as prototypes and test concepts are being rolled out. Recent large aircraft programmes such as the Airbus A350 and Boeing 787 have increasingly used batteries to power on-board systems. The 787 also exhibits greater use of electric power from engine installed generators, described as the ‘more-electric aircraft’.
This suggests future progression to electric propulsion could follow a phased approach. First, a hybrid option with energy still provided by hydrocarbon fuel with batteries also contributing to powering electric propulsion – and second, progressing to a fully electric system with only batteries providing the energy. We would start to see reductions in emissions even at the hybrid stage, with further gains from a move to full electric systems.
For more information about the technology and applications of Electric Aircraft please visit: Electric Skies: How Electric Airplanes are Revolutionizing the Future of Air Travel
In a conventional, large, civilian aircraft there are typically four sources of power derived from the engines: electrical, pneumatic, hydraulic, and mechanical. The electrical system is used to power loads such as the avionics systems, the lighting, and in-flight entertainment. The pneumatic system, taken as an air off-take from the engine, provides for loads such as cabin pressurization and air-conditioning as well as wing ice protection. The mechanical system is used for fuel and oil pumping, mainly local to the engine, and a hydraulic system is used for most of the aircraft actuation systems, both for flight control and auxiliary systems. The total maximum power level of these systems is usually in excess of 1MW, a large power system for a relatively small platform. However, when the aircraft is considered as a whole, it can be shown that efficiency and weight gains should be possible if just one power source is used for all systems.
Military Requirements
Military is also interested in the gains like obtaining the weight savings benefits of a full more electric architecture implementation. Joint Strike Fighter (JSF), C-141 transport aircraft, and UAV’s like Condor, Global Hawk and Dark Star are some examples where the MEA concept has been introduced. With MEA technology, the weight in an aircraft can be shifted from hydraulic systems and plumbing to passengers, fuel or mission payloads. MEA technology could dramatically reduce per passenger costs and ticket prices for commercial aircraft, while giving military planes more maneuverability and survivability due to less vulnerability to enemy fire, says Honeywell.
German said the trend in the military is for “more electric,” writes Stew Magnuson in NDIA. That is, jets need more power to run its suites of energy-hungry electronics, radars, and so on. It wants less fuel being diverted to these systems. “Another flight profile might be an unmanned aerial surveillance aircraft that uses the gas engine for the flight to a targeted area, then switches over to the much quieter battery in order to be more stealthy, or extend its range,” writes Richard “Pat” Anderson, professor of aerospace engineering and director of the Eagle Flight Research Center at Embry-Riddle Aeronautical University’s Daytona Beach, Florida, campus.
Hybrid-electric propulsion
Industries are now exploring Hybrid-electric propulsion systems that employ two or more distinct types of power, for example, power from an internal combustion engine and with electric propulsion systems in aircraft. These systems typically use a combination of electric motors and batteries, along with a gas turbine engine or another type of internal combustion engine.
One of the main benefits of hybrid-electric propulsion systems is that they can significantly reduce fuel consumption and emissions, particularly during the most energy-intensive phases of flight. Batteries can then, for instance, provide clean take-off and landing to reduce emissions near airports. They can also provide a backup power source in the event of an engine failure or other emergency situations.
Internal United Technologies Corporation studies indicate that commercial hybrid-electric and electric propulsion could: Reduce aircraft noise up to 85 percent, Improve fuel consumption up to 40 percent, reduce carbon dioxide emissions by more than 20 percent and Reduce airline operating and maintenance costs up to 20 percent.
Types of hybrid electric propulsion systems for aircraft.
Whilst full-electric flight in the civil aviation sector is still a long way in the future, electrically assisted engines, a hybrid technology step, will soon be possible and the consequences of this technology change in terms of aircraft engine design and aircraft efficiency improvements are important to the industry.
There are several types of hybrid electric propulsion systems for aircraft. Here are some of the most common ones:
- Parallel Hybrid Electric Propulsion System: In this system, both the electric motor and the internal combustion engine are connected to the propeller or fan, allowing for either power source to drive the aircraft. The electric motor can be used to provide additional power during takeoff or climb, and the internal combustion engine can be used for cruising.
- Series Hybrid Electric Propulsion System: In this system, the internal combustion engine is used to generate electricity, which is then used to power the electric motor that drives the propeller or fan. The electric motor cannot directly drive the aircraft and is only used as a propulsion system.
- Turboelectric Propulsion System: This system uses a gas turbine engine to drive a generator, which produces electricity to power the electric motor that drives the propeller or fan. The electric motor can also be used as a generator during descent or landing, regenerating energy to recharge the battery.
- Distributed Electric Propulsion System: In this system, several small electric motors are distributed around the aircraft’s wings or body, each driving a small propeller or fan. This provides greater control and maneuverability for the aircraft, as well as reducing noise and emissions.
- Integrated Electric Propulsion System: This system integrates the electric motor and internal combustion engine into a single power source, allowing for greater efficiency and flexibility in power management. The electric motor can be used to supplement the internal combustion engine during high-power demand, such as takeoff or climb, and the internal combustion engine can be used for cruising or recharging the battery.
There is not a unique solution for aircraft HEP. Some studies claim that actual technology HEPS in parallel architecture is best suited for aircraft with fluctuating power requirements, this means short duration of high-power requirements (Finger et al. 2020).
Hybrid-electric aircraft combine fuels with electric propulsion. This class of aircraft includes design without batteries, where the electric propulsion system serves to improve the thrust efficiency, reducing the amount of fuel needed. Hybrid-electric aircraft with batteries are also in development, where the batteries may provide extra power in specific circumstances. Batteries can then, for instance, provide clean take-off and landing to reduce emissions near airports.
More Electric Aircraft (MEA) are future-generation aircraft that are equipped with more electrical systems to minimize non-propulsive power systems, such as mechanical, hydraulic, and pneumatic systems including flight control actuation, environmental control system, and utility function. The removal of the pneumatic system removes the need for a bleed air system on the gas turbine, something which leads to a significant improvement in the efficiency of the turbine.
In the “No-Bleed” architecture, the pneumatic aircraft systems, namely engine starting, wing de-icing, landing gear deployment system, secondary flight control actuators, cabin pressurization, environmental control, and braking systems will be replaced by electrically powered machines. This has resulted in a reduction in the weight of the aircraft, usage of less fuel, and reduction in emissions, leading to a low cost of ownership and increased reliability.
Electric motors offer other advantages too compared to combustion engines, they don’t need air to produce power, so they can maintain their full rated punch even at high altitudes, where the air is thin. The use of electric power in airframe systems saves fuel and helps in cost reduction. Electric motors can be made quite light and small and still develop considerable power with high reliability—they scale well. Air-breathing engines, both reciprocating and turbine, have many more moving parts, are more complex. The more electric aircraft architecture also helps in reducing maintenance costs as it requires fewer moving or non-moving parts, as compared to the conventional aircraft systems.
However, more importantly, electrical systems offer far more options for re-configurability as well as for advanced prognostics and diagnostics. These prognostics and diagnostics systems could help to improve aircraft availability and reduce the need for unscheduled maintenance. There is a potential for equipment on an aircraft to monitor its use and environmental conditions and use profiles of its own failure mechanisms to predict end of life, leading to preventative maintenance based on usage rather than simply age or flying hours.
Brian German, associate professor at the Daniel Guggenheim School of Aerospace Engineering at Georgia Tech, said there are no distinct lines in the sand yet for aircraft categories, but generally researchers are looking at all-electric, or battery only, systems for smaller aircraft and various hybrid or turbo-electric systems to power the larger ones.
All Electric Aircrafts
Using electrical power to actually propel planes, however, is a more complicated challenge. In a conventional jet airplane, the engine sucks air in through its front, a compressor squeezes it, and fuel is sprayed in and lit, creating burning gases and forward thrust. Electric plane power is much simpler — batteries power an electric motor that spins a propeller.
It’s more efficient but involves far less thrust, which is why electric planes tend to be slow. In July 2015, the E-Fan, an Airbus design with batteries, crossed the English Channel, however Airbus’ two-seat electric plane could only go a maximum speed of about 136 miles per hour.
A solar-powered plane that completed an around-the-world journey had an average airspeed of 47 miles per hour. The plane, called Solar Impulse 2, had more than 17,000 solar cells that powered four electric motors. “But solar power, while an interesting technical challenge, is not a particularly realistic option for mass transit of passengers. As can be seen from the Solar Impulse aircraft, the power output from the Solar Panels on a very wide wingspan is able to transport only the aircraft and the pilot for any significant distance,” writes Dr Peter Wilson.
While we have been able to modify cars, trains, trams, and boats Electric we are not yet seeing large electric aircraft. The main reason is that Land vehicles can easily cope with the extra mass from electricity storage or electrical propulsion systems, but aircraft are much more sensitive. For instance, increasing the mass of a car by 35% leads to an increase in energy use of 13-20%. But for a plane mass is crucial, energy use is directly proportional to mass: increasing its mass by 35% means it needs 35% more energy (all other things being equal).
However, today’s best available lithium-ion battery packs provide around 200 watt-hours (Wh) per kilogram, about 60 times less than current aircraft fuel. This type of battery can power small electric air taxis with up to four passengers over a distance of around 100km. For longer trips, more energy-dense cells are needed.
Aircraft also travel much further than ground vehicles, which means a flight requires far more energy than an average road trip. Aircraft must store onboard all the energy needed to move its mass for each flight (unlike a train connected to an electrical grid). Using a heavy energy source thus means more energy is needed for a flight, which leads to extra mass, and so on and on, writes Dries Verstraete, The Conversation. Hence fully electric large aircraft require a major, yet-to-be-invented shift in energy storage.
“For an electric airplane, the top three priorities are weight, weight and weight,” said Cory Combs, co-founder and chief technology officer of Los Angeles-based Ampaire, Inc. “It has to spend a lot of its energy just keeping itself in the air.” The fundamental challenge, he explained, is that an electric plane has to carry enough battery power to allow it to take off carrying a nominal payload of passengers or cargo, fly at a reasonable speed, then travel a sufficient distance, notionally 100 miles, to make it commercially viable. If its battery packs become too large or too heavy, the aircraft will have a limited ability to carry passengers and cargo.
This energy requirement is exacerbated, Combs added, by the Federal Aviation Administration (FAA)’s requirement that all aircraft must carry at least 45 minutes of reserve fuel, enough to divert to another airport or go around for another landing attempt.
Challenges
The operating environment on an aircraft can be very harsh as well as the hours of operation and expected lifetime being long in comparison to many industrial and automotive applications. The limiting factor for an electric-powered aircraft is the battery challenge is to like develop lightweight batteries that can store enough electricity for long distance flights. Batteries are heavy, and their energy storage capacity increases only at an average of eight percent or so a year.
Therefore biggest challenge ‘all-electric’ aircraft are faced with is the question of power to weight ratios: a fully electric propulsion system requires batteries with greater energy densities than those currently available that are fully reliable and have a sufficient life.
More Electric Aircraft (MEA) applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. However, the MEA puts some challenges on the aircraft electrical system, both in the amount of the required power and the processing and management of this power.
The most significant limiting factor at this point is not the weight of the engines, or the design of the aircraft, but rather it is the batteries. Batteries at this point cannot provide the power-to-weight ratio needed for electric aviation to be feasible. Currently, jet fuel yields about 70 to 80 times more energy than an equivalent mass of battery. In addition, Batteries have a higher maintenance costs than gas turbines, and on top of that require replacement after only 1,500 charge cycles.
Short-range electric commuter aircraft that carry up to 30 people for less than 800km, for instance, specifically require between 750 and 2,000Wh/kg, which is some 6-17% of kerosene-based jet fuel’s energy content. Even larger aircraft require increasingly lighter batteries. For example, a plane carrying 140 passengers for 1,500km consumes about 30kg of kerosene per passenger. With current battery technology, almost 1,000kg of batteries is needed per passenger. To make regional commuter aircraft fully electric requires a four- to tenfold reduction in battery weight. The long-term historical rate of improvement in battery energy has been around 3-4% per year, doubling roughly every two decades. Based on a continuation of this historical trend, the fourfold improvement needed for a fully electric commuter aircraft could potentially be reached around mid-century.
“Lithium (Li) ion batteries are the current state-of-the-art stored energy technology for aviation,” said Dr. Ajay Misra, deputy director, Research and Engineering Directorate, NASA’s Glenn Research Center, “the same type of technology used in cells phones and electric cars.” For aviation, Misra added, the relevant measure of battery suitability is called pack specific energy, also referred to as pack gravimetric energy density. A pack contains thousands of battery cells. The units of pack specific energy are watt-hours per kilogram (Wh/kg). According to Misra, the pack specific energy of the most commonly used Li-ion batteries today is about 150 to 170 Wh/kg. By contrast, the specific energy of jet fuel is nearly 12,000 Wh/kg, or about 70 to 80 times more energy dense than Li-ion batteries.
Industry experts predict that batteries for all-electric larger aircraft won’t be available for another 15 to 20 years, with full integration going beyond that. A hybrid-powered solution is likely to be available sooner if this is deemed a worthwhile step towards a full electric solution. This could deliver real benefit through reduced emissions and would also allow for the development of high-power electric propulsion motors and power electronics so that these would be ready for the switch to full electric operation. Aviation engineering giant Rolls-Royce announced it had delivered more than a megawatt of power from a hybrid-electric propulsion system, followed by a new partnership announced between magniX and Brazilian aeronautical company DESAER to develop a hybrid-electric aircraft.
Another challenge that exists is creating a practical cooling system that can be used. Thermal management for these systems will require a system that can reject anywhere from 50 to 800 kW of heat in flight. A cooling system is required for the integrated power module used for high-power electronics. Materials will need to be developed for improved thermal performance, and a lightweight system developed for the power electronics cooling. Superconductivity and supercooled electronics will be required to reduce the electrical resistance of the aircraft.
More Electronic technologies
The step-change in technology for commercial flight of civilian aircraft using just electrical energy will require a step change in technology in many areas. This includes the storage of electrical energy where there will need to be significant improvements in rechargeable battery or fuel-cell techniques in order to store enough energy for a long range flight. The equipment used for propulsion will also need to be small, lighter and more efficient than anything available today.
Batteries
“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 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.
To make all-electric aviation viable, the researchers say, the energy density of batteries will have to increase at least fourfold, from today’s 250 watt-hours per kilogram to 800 watt-hours per kilogram. That would make it possible to create all-electric aircraft able to carry 150 passengers up to 600 nautical miles (1,111 km), which could replace half of global aircraft departures. Boosting this to the stretch goal of 1,200 nautical miles (2,222 km) could replace more than 80 percent of departures.
The use of the More Electric Aircraft concept obviously puts a significantly larger load on the electrical system. The typical installed capacity of the electrical system on an existing medium range aircraft such as a Boeing 737 is about 100kW, for the Boeing 787 this power level increases to over 1MW. To reduce the current in the electrical system, and hence the cable weight, higher voltage electrical systems are considered. Some of the emerging standards include: 540V DC (+/- 270V); 230V AC at 400Hz; and 230V AC Variable Frequency (for example 320Hz to 800Hz).
Key components and functions include engine starting, electrical power generation, power conditioning and routing, air cycle environment control, avionics, fuel/oil cooling, ventilation, flight control actuation, and overall vehicle & propulsion system thermal management – especially waste heat recovery and/or rejection.
Future gas turbine aero engines will be more efficient, compact and will have more electric parts.As a result, more heat will be generated by the different electrical components and avionics. More Electric Aircraft (MEA) with higher demands on engines for thrust and power generation resulting in hotter fluids, higher components temperature and higher heat generation, which means critical thermal management issues. The TMS utilizes engine fluids to transfer excess heat from the engine heat sinks like bearings, accessory gearbox, pumps, generators, constant speed drive and power gearbox in new geared turbofans.
Moreover, taking the new advances in material sciences into account, it could be seen that the turbine entry temperature has had an average increase of about 8 °C rise per year over the last 20 years. It is due to the new advanced materials used for the turbine manufacturing in new aircraft engines (e.g., SC cast alloys and ceramics). So, more increase in thermal loads is expected for the future engines. Consequently, designing an optimal thermal management system architecture is a key factor for the heat management in future civil engines. Therefore, alternative methods should be used to dissipate this extra heat as the current thermal management systems are already working on their limits.
Distributed propulsion
One of the ways the technology can be applied for larger aircraft is distributed power systems, German said. For example, the larger a gas-turbine engine is the more efficiency can be squeezed out of it. That’s why there tends to be only a few massive engines hanging off aircraft such as the C-17. Researchers have known for many years that putting many smaller propellers or engine fans, distributed at key areas would be even more efficient. Every aircraft has a boundary layer, an area of dead air above the wing that builds up and creates drag as the plane flies. By placing several smaller fans along the aircraft, the boundary layer is “ingested” and almost disappears, making the aircraft faster or more energy efficient, German explained.
Engineers look at this one of two ways. It’s either making the engine fans more efficient, or creating less drag on the wing. Both effects are at play, German said. This is the principle behind DARPA’s LightningStrike vertical takeoff and landing X-plane that it is developing with Aurora Flight Sciences. An artist’s rendering of the plane shows 26 hybrid-electric propulsion fans distributed on the aircraft. The program has flown a 325-pound scale model and expects to build a full-scale version within the next two years, the company said in a statement. Operating from austere landing zones is the requirement the program is seeking to fill, it said.
One key aspect of design is in the distribution of the energy supply system. Aeroplane wings are tuned to withstand aerodynamic and mass loads – today, they carry distributed jet fuel – but what could be the effects on wings if they have to carry batteries, instead of fuel? One possible answer could result in a very positive side-effect. Currently, jet fuel in the wings depletes as the flight continues and the structure of the wing accounts for that. Batteries could help in a future wing because they would be a fixed mass throughout the flight and adding their mass into the wing could help with aeroelastic tailoring. That means there’s a possibility of tuning the wings to make them more aerodynamically efficient by allowing them to become longer and thinner.
While, historically, this type of shift in design would have made a liquid-fuelled aircraft more prone to ‘flutter’ – a physical phenomenon whereby a build-up of wing oscillations can break them away from the main structure – with the strategically-placed, immovable, batteries on thinner wings, a more efficient, aerodynamic shape could emerge that won’t succumb to flutter and improves aerodynamics. The change to an electrical system could also enable distributed propulsion allowing radically different aircraft configurations.
There are many more factors to consider alongside the aircraft itself, such as its maintenance, repair and overhaul, and the massive physical infrastructure that will be needed to support this game-changing, new technology; from supporting spare battery capacity to locating recharging points. Also, could quieter, zero emission, aircraft in our skies mean more runways are built to connect major cities, asks James Domone, Principal Engineer, Atkins?
Challenges and technologies of Solar Impuse , All Electric Aircraft
Solar Impulse 2, is certainly a feat of engineering. The plane boasts a wingspan larger than a B-747 jumbo jet, but only weighs around 5,000 pounds, which is comparable to an average family car. A staggering 17,248 photovoltaic solar cells—each one roughly the thickness of a human hair—blankets the delicate wings and fuselage. These cells bask in the sunlight, charging the plane’s four lithium batteries to keep its propellers spinning through the dark nighttime hours.
The weather became the team’s biggest foe. Because the plane travels on a sinuous path—climbing to nearly 30,000 feet elevation during the day but slowly descending to roughly 5,000 feet at night to save energy—the team has to forecast wind, humidity and temperature at multiple elevations. And the swirling weather system is constantly evolving and changing. Weather conditions delayed their departure from China, later forcing the team to abort their initial Pacific crossing and land in Japan. But then more foul weather began to churn over the Pacific, causing two canceled departures.
Piccard and Borschberg traded off flying the plane for the 17 legs of the venture. Each slept only in short intervals to tend to the plane’s demands. Its wings couldn’t tip more than five degrees, otherwise the craft might spin out of control thanks to its low weight and expansive size. This airy construction also meant that even a small spot of foul weather or winds would easily whip the plane off course.
The duo turned to shipyards, chemical companies and more to seek out potential materials and solutions for their aircraft. The ultra thin carbon fiber that makes up the body of the plane, for instance, was created by the same company producing hulls for the sleek sailing boats the European Alinghi team race in the America’s Cup.
Some of the biggest impacts of Solar Impulse may actually be found on the ground. The flight has pushed cross-discipline advancements in many industries, according to Piccard and Borschberg. The materials development company Covestro, a Solar Impulse partner, is adapting the ultra-low weight, high-performance cockpit insulation for more efficient refrigerators. According to Piccard, a startup company in India is also planning to use the high-efficiency engines of the plane in ceiling fans that consume 75 percent less electricity.
Power Electronics
Power Electronics has been one of the most important enabling technologies for the Electric Aircraft. Without the use of power electronics to convert and control electrical energy none of the benefits of the More Electric Aircraft would be possible. However, aerospace applications present some challenging operating conditions for power electronics and there are still a number of areas where improvements must be made in terms of the weight, volume, cost and reliability of power converters and their associated systems.
When replacing hydraulic actuators with electrically powered actuators, the most obvious choice is to use an Electro-Mechanical Actuator [EMA]. Using an EMA system an aircraft control surface can be controlled by simply controlling the motor. As the motor turns it moves a ball-screw, often through a reduction gearbox. Each turn of the motor displaces the actuator by a fixed amount due to the direct connection between motor and ball screw. However there is a problem in using EMAs for primary flight control applications on large aircraft as to date it has been very difficult to guarantee that the ball-screw will never jam. A jam in an actuator for a flight critical control surface would cause problems in the current design of aircraft as the surface would not be controllable unless a benign failure mode can be guaranteed. A jam in a ball-screw is not a benign failure as another actuator on the same control surface would not be able to move the surface if one actuator has jammed.
In addition to the solution to the energy storage issue there is a need to meet demanding targets for the weight of power converter and electrical machines which will have to be used for future aircraft propulsion.
Some of the technologies which can be deployed in the design of electrical machines to obtain the power densities needed to meet the medium-term goals include the integration of the electrical machine, mechanical system and power electronic converters associated with the control. New materials will also play a large part in this technology development including new thermal, magnetic and structural techniques. Higher speed machines using power converters with emerging wide-bandgap semiconductors (SiC and GaN) may also provide benefits at a system level
Rolls-Royce has been developing world-first engine technology for the Tempest fighter jet programme over the last five years.
In order to make the engine more electric, intelligent and harness more power, the company recognised that any future fighter aircraft will need new levels of electrical power demand and thermal load. Before the launch of the Tempest programme, Rolls-Royce had already started to address the demands of the future. In 2014 the company took on the challenge of designing an electrical starter generator that was fully embedded in the core of a gas turbine engine, now known as the Embedded Electrical Starter Generator or E2SG demonstrator programme.
Conrad Banks, chief engineer for future programmes at Rolls-Royce said: “The electrical embedded starter-generator will save space and provide the large amount of electrical power required by future fighters. Existing aircraft engines generate power through a gearbox underneath the engine, which drives a generator. In addition to adding moving parts and complexity, the space required outside the engine for the gearbox and generator makes the airframe larger, which is undesirable in a stealthy platform.”
NASA innovations
NASA can’t change the future of flight alone, so the agency has teamed up with two industry partners to transform its approach to aircraft propulsion. These agreements are aimed at designing more efficient aircraft engines, while also addressing several technical challenges: weight, power extraction and storage, and thermal management. The power extraction challenge is especially important for future hybrid-electric aircraft concepts where the energy requirement becomes even greater, as extra power is needed to drive electric fans used for additional inflight thrust. NASA and its industry partners have identified turboprops, regional jets, and single-aisle aircraft serving the thin-haul (very short flights), regional, and single-aisle markets as targets of opportunity for this technology.
NASA is working on advancing the design and modelling tools pertinent to future aircraft products with an Electrified Aircraft Propulsion (EAP) system. These EAP electrical systems are being developed to replace or boost fuel-burning aircraft propulsion systems, analogous to how electric or hybrid motors are used in automobiles. The US space agency is also seeking proposals in 2021 for ground and flight demonstrations of integrated megawatt-class powertrain systems for subsonic aircraft. The demonstrations will help rapidly mature and transition integrated EAP technologies and associated EAP vision systems for introduction into the global fleet by 2035.
Through its Hybrid Thermally Efficient Core (HyTEC) project, NASA is aggressively pursuing next generation aircraft engines that use less fuel and produce more power, by increasing the bypass ratio. This means making the fan – the one on the front of the engine – bigger, thereby increasing airflow, while shrinking the engine’s core which reduces fuel consumption.
“The question becomes how do we shrink the core of the engine, while maintaining performance and increasing the electric power available?” said Tony Nerone, HyTEC project manager at NASA’s Glenn Research Center in Cleveland. “As aircraft become more electric, we’ll need to address the traditional power needs – running subsystems like flight controls, air conditioning, and so on – but we also need to tap more power for the newer electric systems that we’ll be adding to the aircraft. Current state-of-the-art engines can extract about 5% of power and we’ll need to jump up to 10% to 20% in the future.”
Through a Space Act Agreement with Honeywell, NASA engineers will work with a team from Honeywell, to perform technology development and testing on an advanced low-pressure turbine. The data from the test will allow the combined engineering team to establish a turbofan power extraction baseline while also developing computational prediction tools. Ultimately, this test will provide essential data for the HyTEC project and advance Honeywell’s technology development of higher efficiency turbines that could impact its future gas turbine product line.
NASA has also entered into a contract with GE to demonstrate and assess turbofan power extraction and integrating electric machines like motors and generators. The goal is to significantly increase power extraction at relevant commercial engine operating conditions from a thrust, weight, efficiency, operability, and durability for future electric propulsion systems.
These efforts aim to introduce cleaner, more efficient and cost-effective aircraft in the near future. Core power systems technology development and testing are just the start. NASA will need to demonstrate the benefits in flight before eventual commercial aircraft integration. “Once HyTEC and its partners demonstrate power extraction, these new engines can be combined with other megawatt-class components we’re developing for electrified aircraft propulsion,” said Barbara Esker, AAVP’s deputy program director. “Together with advances in high-rate composite aircraft manufacturing and innovative configurations like the transonic truss-based wing, NASA can transform the long-term sustainability of commercial aircraft.”
Electric motor driven smart pumps support More-electric Aircraft
Commercial aircraft original equipment manufacturers (OEMs) have been building more-electric aircraft – or MEA – for over a decade. MEA are aircraft that rely on electric power to operate non-propulsion systems such as those for lubrication, flight control, fuel, thermal management, and more.
Today’s aircraft makers are collaborating with their suppliers to design new systems and implement new electrical-intensive architectures that are key to unlocking such efficiency improvements as lower aircraft weight, better fuel consumption, reduced total life-cycle costs, and enhanced maintainability and reliability.
One such supplier collaboration supporting the move to MEA has been launched by Parker Aerospace Gas Turbine Fuel Systems Division (GTFSD).
GTFSD is breaking new ground through its development of electric motor-driven smart pumps that can accommodate a wide range of voltage to the digital controller. The motor speed can be controlled by sensors or sensorless, depending on the application.
Electronic controllers interpret system signals, enabling a pump to respond with a specific flow to meet a specific system demand. Whether for more fuel, enhanced cooling, or greater pressure, this demand flow results in a highly efficient use of the aircraft’s finite energy resources, creating less fuel burn and fewer engine emissions.
Parker Aerospace’s auxiliary power unit (APU) fuel metering unit for the Boeing 787 Dreamliner is one such electric motor-driven smart pump already in service. The APU pump unit builds on GTFSD’s experience with electric motor-driven pumps, which includes those for missiles and military UAV applications, as well as for large transport turbine engines.
“The innovative APU fuel metering unit replaces conventional engine fuel control for the Boeing 787. Featuring an impeller boost pump and a high-pressure gear element, the two-staged pump assembly integrates 13 components into one and uses an AC- or DC-powered dual-processor digital controller with CAN bus interface to provide precise fuel flow in response to engine demand,” said Rick Mossey, engine systems business development manager, Parker Aerospace, Gas Turbine Fuel Systems Division
Alternative propulsion systems are being looked at as a means of achieving fuel savings, lowered emissions, and reduced noise. One such alternative approach uses hybrid gas turbines. A highly efficient gas turbine engine and electric motor are paired to provide thrust via combinations of both sources.
The electric power can be used for the duration of a flight or when added power is required. Since Parker Aerospace’s electric motor-driven smart pumps are able to vary their routines almost infinitely based on the requirements of the systems they serve, they are readily adaptable for such next-generation applications.
Bye Aerospace’s Sun Flyer 2 completes first flight with Siemens electric propulsion motor
Bye Aerospace’s electric Sun Flyer 2 successfully completed the first official flight test with a Siemens electric propulsion motor in February 2019 at Centennial Airport, south of Denver, Colo. The Sun Flyer family of aircraft, including the 2-seat Sun Flyer 2 and the 4-seat Sun Flyer 4, aims to be the first FAA-certified, practical, all-electric airplanes to serve the flight training and general aviation markets.
This successful test flight is a proud moment for the Siemens and Bye Aerospace teams and marks a milestone in bringing the age of electric flight to life. The Siemens electric propulsion system offers a clean, cost-efficient and silent propulsion alternative to the flight training market without compromising performance or safety, said Dr. Frank Anton, Executive Vice President and Head of eAircraft, Siemens.
Siemens will provide electric propulsion systems for the Sun Flyer 2 airplane—the 57 lb. SP70D motor with a 90 kW peak rating (120 HP), and a continuous power setting of up to 70 kW (94 HP). The company has previously equipped European light and sport aircraft with electric propulsion systems up to 260 kW for test purposes and is also developing propulsion technology in power classes up to 10 MW to enable electrification of aircraft in the commercial air transport sector.Siemens electric motor technology has powered aircrafts to set two speed records, achieve the world’s first aero tow by an electric plane, and set a new world climb record with an altitude of 3,000 meters in four minutes and 22 seconds.
Bye Aerospace is developing the Sun Flyer family of aircraft in addition to a family of advanced, high-altitude, long-endurance solar-electric unmanned aerial vehicles called “StratoAirNet.”
References and resources also include:
https://www.adsadvance.co.uk/electrification-of-future-flight.html
