FEATURE GEARS & GEARBOXES


ELECTRIFYING AVIATION


The electrification of transport industries is not a new development. Aerospace companies, however, have not been so quick to follow suit. Here, Graham Mackrell, managing director of high precision actuator manufacturer Harmonic Drive UK, explains the design challenges for electrifying aviation


E


lectrification 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, however, many aerospace companies are struggling to envision how they can electrify their modern and complex systems. It’s predicted that over seven billion


people will fly annually by 2034, double the number of travellers recorded in


“When integrating electric actuators, engineers should consider gears like those offered by Harmonic Drive.


Designed to be a rotary configuration, the gears feature high single-stage reduction ratios with zero backlash”


2016 by the International Air Transport Association (IATA). These figures, 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 for each passenger by 75%, and a reduction in nitrogen oxide (NOx


) per passenger by 90%. 34 NOVEMBER 2018 | DESIGN SOLUTIONS


DESIGN CONSIDERATIONS Aerospace engineers can take one of two approaches when looking to electrify their aircraft. The first is focussed around lightening the overall load of the aircraft by replacing heavy mechanical systems with electrical components. However, 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. While an all-electrical future for


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


companies have built test rigs to prototype newer designs, many industry executives believe that physical prototyping like this are 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 have more electrical features have been prone to mechanical jamming because of the rotary or linear actuators installed, causing additional faults to the 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 such as actuators that are used in safety critical applications like aerospace need to be able to withstand high loads. When integrating electric actuators,


engineers should consider gears like those offered by Harmonic Drive. Designed to be a rotary configuration, the gears feature high single-stage reduction ratios with zero backlash. The company recently collaborated with


UK-based Ametek Airtechnology group to create an all-electric rotary actuator that is both highly compact and reliable, offering 650Nm output torque and weighing just over 5kg. This has received full certification from aerospace authorities and is qualified for use in helicopter landing gear. The actuator has been designed to operate in temperatures between -40 and +70˚C, with survival temperatures ranging from -55˚C. In years to come, we will undoubtedly


see the next generation of cleaner and quieter aircraft. 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. By working with companies like Harmonic Drive in the design of an application, engineers can shorten the development process and begin championing environmentally friendly alternatives, like electrification.


Harmonic Drive http://harmonicdrive.de/en/home


/ DESIGNSOLUTIONS


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44