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Crew's Control: Smart Integrated Wing Demonstrator gets into gear

Clean Sky's Smart Integrated Wing Demonstrator (SIW) is a ground-based demonstrator platform integrating electrical and hybrid electro-hydraulic actuation technologies and equipment that have been developed, matured and tested through a series of synergistic enabling projects.

The SIW Demonstrator is located at Lindenberg im Allgäu, Germany © Liebherr-Aerospace Lindenberg GmbH
The SIW Demonstrator is located at Lindenberg im Allgäu, Germany © Liebherr-Aerospace Lindenberg GmbH

Feeding into Clean Sky’s electrification objectives and the European Green Deal ambitions, the core of the activity is oriented around a fully digital 'control network’ developed at Liebherr – a high integrity, versatile and modular network for flight controls (primary and secondary in one network) but also for other systems such as landing gear actuation and 'smart' power supply solutions.

Control network concept evolution

Now, under Clean Sky 2's Smart Integrated Wing Demonstrator project umbrella, the flight controls system is being developed and expanded to the next level.

The focus is on the signal electronics and control network to support fly-by-wire flight controls and actuations, with demonstration of the concept and its innovations to TRL5 at relevant scale and context within Clean Sky's Systems ITD initiative. 

The initial set-up focused on infrastructure and primary flight control components on test rigs for ailerons and spoilers, directed and monitored via a 'cockpit' control room. Hardware-in-the-loop simulation equipment developed in Clean Sky Systems ITD is being integrated to enable virtualisation of equipment, insertion of failure cases and visualisation of controls, parameters and system status. 

How the signal electronics work

A key feature within the control network system is the way that the electronics architecture is configured. Signals are digitised at source by very small remote electronic units (REU) which then connect the equipment with the network. Each actuator or other equipment in the aircraft wing is fitted with a dedicated REU, or an REU integrated into a motor control unit, such as an electromechanical actuator or an electro-hydraulic actuator.

The analogue interfaces of the REU can be customised within the software to operate with any relevant equipment. For example, a traditional electro-hydraulic servo actuator (EHSA) can be exchanged with an electromechanical actuator easily, and any cockpit controls can be flexibly integrated the same way directly into the network. The architecture also facilitates the distribution of functions and ‘computing power’ over the network.

Liebherr flight control actuator with Remote Electronic Unit on top to connect with the digital bus. - © Liebherr
Liebherr flight control actuator with Remote Electronic Unit on top to connect with the digital bus. - © Liebherr

Get the picture

‘The demonstration platform includes an aircraft model to simulate flight physics and related systems and functions via devices such as an air data unit or inertial reference unit,’ says Christoph Budzinski, Clean Sky 2 Programme Manager at Liebherr-Aerospace. ‘Consequently, the demonstrator will offer a representative hardware-in-the-loop (HiL) testing environment, where the installed hardware can interact with aircraft behaviour in real-time.’

The demonstrator will offer a representative hardware-in-the-loop (HiL) testing environment, where the installed hardware can interact with aircraft behaviour in real-time

Additional combinations of computing hardware and software allow the simulation of additional equipment, such as extra actuators, which can be integrated into the rig, while a flight simulator visualisation system translates the internal ‘physical’ data into a visual representation of the aircraft and/or a view from the cockpit on a screen.

The demonstrator is able to replicate a broad mixture of features, including several primary flight control actuators such as force-fight-control to operate actuators of different technologies – both electrically and hydraulically powered – applied to the same surface using ‘all-active operation'.

The rig also demonstrates secondary control surfaces and flap actuation including a new electronic torque sensing concept, plus a high-voltage DC (HVDC) supplied electromechanical actuator in spoiler configuration.

Budzinski says that the SIW Demonstrator has been so versatile that after the closure of Clean Sky 2 the rig ‘will remain an important tool for Liebherr to demonstrate capabilities of new equipment and systems, which can be integrated flexibly.’

Hydraulic Power Pack  

The hydraulic power pack (HPP) concept is another main feature of the SIW, designed with the next more-electric aircraft generation in mind. It facilitates the supply of hydraulic power locally to a set of consumers using HVDC electric energy while other functions can independently be realised with electromechanical actuation. This enables future architectures without engine-driven-pumps and centralised hydraulic circuits to offer localised hydraulic supply with a higher efficiency and less moving parts. 

In practical terms this means that major mechanical assemblies requiring hydraulic actuation, such as landing gear assemblies, can work off a localised rather than an aircraft-centralised hydraulics system.

Because the hydraulic power pack is located closer to where power is needed (e.g. next to the landing gear or tail surfaces), there’s a reduction in the length of the hydraulic lines (and their fluids), while the control network concept can decrease the amount of wiring needed. Both of these factors result in considerable weight savings in line with Clean Sky’s objectives and the EU’s green ambitions. 

‘Liebherr calculations showed that for a large aircraft the benefit could reach up to 200 kg. This would correspond to saving approximately 120 kg CO2 on a flight from Frankfurt to New York,’ Budzinski points out. He adds that ‘the new concept of electronic torque sensing for high-lift surfaces enables a much earlier detection of jamming with a quicker response to it.’ 

‘Consequently, the structural loads in failure cases can be lowered considerably, allowing for a reduction in stress to overload and thus a reduction in weight of the high-lift-system structure, by up to 130 kg for a large aircraft.’ This equates to roughly 75 kg additional CO2 savings on a Frankfurt to New York flight.

One important element of the demonstration is the versatile electronic control network © Liebherr-Aerospace Lindenberg GmbH
One important element of the demonstration is the versatile electronic control network © Liebherr-Aerospace Lindenberg GmbH

Achievements so far

So far, the electro-mechanical actuator with remote HVDC supply has been verified. The force-fight-control of hybrid configurations electro-hydraulic servo actuator (EHSA), electro-mechanical actuator (EMA) and electro-hydrostatic actuator (EHA) were tested concurrently, while they were in all-active configurations controlled via a remote electronic unit (REU), and the local control loop was verified.

The electronic torque sensing and related monitoring have been verified and cockpit controls have been integrated into the network, proving its versatility. The electronic control system is working and viable, and the ‘Stick-to-Surface’ function of flight controls has been shown to work properly.

Additionally, essential key features of the electronic control network have been demonstrated, showing good results for redundancy, stability and failure cases — for example the 'take-over functionality' when one of the components fails, has been established. 

Ongoing activities

Remaining challenges for the project in 2021 focus on the electronic control network, which will be expanded with added components to create a more representative environment demonstrating its full capacity. Safety-critical communications, particularly for flight surface controls, need to be guaranteed to be free from delays and prove unimpaired by a wide range of failure-cases.

‘In order to support the integration phase of the demonstrator, including the HPP, the user interface has to be optimised for automated and more efficient testing tasks, such as introducing failure-scenarios into the communication or equipment to demonstrate behaviour and robustness,’ says Budzinski. 

‘This step will also include an improved system visualisation to enable keeping track of the system parameters. It opens the path to the final demonstration, so that the entirety of the equipment installed will be represented.’

Liebherr’s new Remote Electronic Units enable easy integration of any equipment into the control network. - © Liebherr
Liebherr’s new Remote Electronic Units enable easy integration of any equipment into the control network. - © Liebherr