Technology is being developed that could see electric aircraft in our skies within just 10 years. Magnetic gear manufacturer, Magnomatics CEO, David Latimer explores how pressures to reduce noise and carbon dioxide emissions is driving the innovations that will make this possible.
Magnomatics proprietary Pseudo Direct Drive technology will be showcased at the Farnborough Airshow
It is fast becoming a matter of when, rather than if, a short-haul electric aircraft will take to our skies. The pace of innovation is accelerating as more organisations bring their R&D resources to the goal of creating the all-electric aircraft.
As in the automotive sector, the aviation industry is turning to electric and hybrid technology to reduce environmental impact, as a future without jet fuel becomes a real possibility.
A range of possible solutions currently exists, from hybrid configurations to pure electric. Established names such as Airbus, Rolls-Royce and the e-Aircraft division of Siemens are set to work together to develop a hybrid aircraft with a central electrical generator running distributed propulsive electric motors.
In fact, the three companies have signed a deal to develop this form of technology. It is envisaged that batteries will be used to provide the peak power required for take-off and climb – when aircraft requires double the amount of power needed for it to cruise. Using electricity during this phase of the flight will significantly reduce both noise and fuel consumption. The gas turbine powered generator then runs at it most efficient operating point for the cruise.
This aircraft seems to be aimed at relatively short-haul flights – the optimum range is judged to be around 500 nautical miles, or 926km, with the technology working best between 300km and 1,000km.
Tests are planned for next year on an older aircraft – a BAE 146 commuter plane – that will carry two tons of batteries and a powerful generator in the fuselage. One of its four engines will be converted to operate on electricity, enabling evaluations to be carried out to assess the engine’s efficiency and safety.
Moving to electric aircraft from those powered by conventional engines would help the aviation sector meet EU targets of a 60% reduction in CO2 emissions, 90% less NOx and 75% less noise by 2050. The technology would see batteries that were put inside a plane’s wings instead of being slung underneath them, making the aircraft more aerodynamic.
All of these initiatives are supported by the relevant governments. In the UK, the Aerospace Technology Institute (ATI) has been established to stimulate and steer the technical innovation required to maintain the UK as the number one in the European aerospace sector. It is set to allocate £150 million per annum of funds to innovative projects and has secured a total of £3.9 billion research and technology funding.
Magnomatics has built a number of prototype electric motors as part of the Electro-Mechanical Magnetic Actuator Systems project
Highly reliable flight actuator
Whether pure electric or hybrid, industry experts agree that there will also be the need for reliable all-electric actuators, for control surfaces and other systems.
Most large aircraft currently use hydraulics but these systems are inefficient and carry the risk of leaks of potentially harmful fluids with pipes route around the aircraft.
Thanks to a project partly funded by Innovate UK, a reliable electric aerospace control surface at just a fraction of the volume and mass of current technology looks like a real possibility in the coming years.
Magnomatics has been working with collaborators Triumph Aerospace, Romax and the University of Sheffield to develop a highly reliable and compact flight aircraft control surface actuator.
For the more-electric aircraft, existing electromechanical actuator systems, both rotary and linear are prone to mechanical jamming events caused by failures in the mechanical drivetrain, for example the mechanical gearbox in the rotary topology and the screw/gearbox in the linear topologies.
These failures can be caused by a combination of shock loads such as wind gusts or object strikes and the kinetic energy in the rotor of the high-speed motor driving the actuator. The large mechanical gear ratio employed between the motor and the control surface has the benefit of reducing the volume/mass of the actuator motor, but results in an increase in the kinetic energy stored in the output rotor of the electrical machine.
Magnomatics has designed, built and tested a number of prototype electric motors as part of the Electro-Mechanical Magnetic Actuator Systems (EMMAS) project. The electric motors use Magnomatics proprietary Pseudo Direct Drive (PDD) technology. This technology will be showcased at this year’s Farnborough Airshow on the ATI stand.
The PDD integrates a permanent magnetic motor and a magnetic gear, resulting in a very compact electric motor. When compared with current benchmark technology, the results look very promising indeed.
Compact, and less weight
Two variants of the PDD have been designed, a basic machine and a second one using a fault tolerant (FT) stator winding and a fault tolerant control system developed by University of Sheffield. Even with the fault-tolerant winding, the PDD is around half the mass of current technology with a conventional winding.
The PDD has a further benefit, low inertia. This results in a very good response rate, making it suitable even for military applications on unstable aircraft where a high bandwidth is required.
The low inertia and inherent torque fuse also protect the actuator system from jams or impacts. Rather than failing, the magnetic gear in the PDD simply slips until the problem is removed. This takes place without damaging the system components, which in turn means other actuator components such as end stops can be light-weighted, bringing further benefits for this type of actuation system.
This slipping function has already been shown to be of great benefit in difficult applications in other sectors. In the oil and gas sector, a pump driven by a Magnomatics magnetic gear has been installed in a particularly difficult oil well in California by artificial lift specialist ZiLift, which is based in Aberdeen.
All these features suggest that a PDD based actuator for flight control surfaces will be at least as reliable as the traditional hydraulic systems used today. This is a key step on the way to the all-electric aircraft. A number of aircraft manufacturers and leading suppliers are showing interest in this exciting new technology.