The electrification of transport industries is not a new development – automotive manufacturers have spent the last decade investing in the development of electric powertrains. Aerospace companies have not been so quick to follow suit. Graham Mackrell, Harmonic Drive UK, explains the design challenges for electrifying aviation.

Electrification has gripped the imagination of companies looking to make a fundamental change in the way we power the world around us. Revolutionising the design of everything from motorways to transportation, electrification offers a more sustainable means of powering a system.

It’s been over 130 years since the first electrically propelled aircraft was prototyped by French chemist and aviator, Gaston Tissandier. Today, many aerospace companies are struggling to envision how they can electrify their modern and complex systems.

New pressures

It’s predicted that over seven billion people will fly annually by 2034. This is double the number of travellers recorded in 2016 by the International Air Transport Association (IATA).

An increase in the number of people flying, alongside the growing calls for businesses to reduce carbon emissions, put additional pressure on aerospace and aviation manufacturers as they develop the next generation of aircraft.

Initiatives like Flightpath 2050 highlight the importance of the aerospace sector embracing electrification to meet environmental targets, outlined by the European Union (EU). This includes reducing carbon emissions by 75 per cent for each passenger, and reducing nitrogen oxide (NOx) per passenger by 90 per cent.

Aerospace engineers can take one of two approaches when looking to electrify their aircraft. The first is focused around lightening the overall load of the aircraft by replacing heavy mechanical systems with electrical components. The challenge with this is that a lot of the world’s existing electrical technology has yet to handle the power densities and voltages needed to meet the safety standards required for certification.

Alternatively, aerospace companies can consider replacing traditional propulsion systems with electric or hybrid options. Both offer greater benefits for the environment, but electrical propulsion has been known to make aircraft not only quieter, but also more efficient.

Design considerations

While an all-electrical future for aviation looks promising, there are several design considerations that engineers need to bear in mind. For example, design engineers must integrate reliable, all-electric actuators for control systems on the aircraft.

Traditionally, aerospace companies have built test rigs, much greater than Tissandier’s, to prototype newer designs. The push towards electrification and the fast-changing market demand have made many industry executives believe that physical prototyping like this is no longer viable.

Currently, most large aircraft actuation systems use hydraulic or linear actuators. In fact, the design space within an aircraft has evolved with aircraft design and developments over the last few decades to perfectly accommodate linear actuators.

This has presented a further challenge for engineers when designing components for aerospace applications, as they have to effectively manage and optimise the limited design space.

While these existing systems may not be the perfect solution, they are widely used. So, despite hydraulic systems being identified as inefficient and at risk of leaking harmful fluids, many engineers have continued to integrate these systems to avoid complicating the design process.

In addition to this, aircraft that predominantly feature more electrical features have been prone to mechanical jamming because of the rotary or linear actuators installed, causing additional faults to the applications gearbox.

Issues like this can be the result of shock loads such as wind gusts and the kinetic energy in the rotor of the high-speed motor driving the actuator.

Components for success

Components such as actuators that are used in safety-critical applications like aerospace need to be able to withstand high loads.

Harmonic Drive recently collaborated with UK-based Ametek Airtechnology group to create an all-electric rotary actuator that is both highly compact and reliable, offering 650 Nm output torque and weighing just over 5kg. The product has received full certification from aerospace authorities and is qualified for use in helicopter landing gear.

Considering the harsh environments and weather that aircraft endure, the actuator has been designed to operate in temperatures between -40 and +70 degrees Celsius, with survival temperatures ranging from -55 degrees Celsius.

The next generation

In years to come, we will undoubtedly see the next generation of cleaner and quieter aircraft fly high above our heads. To meet and comply with EU targets, aerospace companies need to begin making the shift to electrify their applications sooner rather than later.

For any component in the aerospace industry, engineers need to factor the load limits, failure scenarios and efficiency changes over a varying temperature range into the design phase.

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