Ground control

It’s a fascinating period in aviation history. Aerospace engineers, who were once only limited by their own imaginations and the laws of physics, must now face up to the well-known commercial and environmental concerns that will shape the industry’s future.

And while flagship aerospace projects such as the A380 and the Dreamliner, enjoy their day of glory on the runway, engineers operating behind the scenes in the parallel universe of the aircraft simulator are striving to match the latest aviation advances step by step.

Thanks to a range of developments and an increasingly fruitful exchange of ideas with the once exclusive domain of the military simulator, engineers are making ever-greater leaps in their ongoing quest for higher levels of realism. This quest begins with the corner-stone of any convincing full-flight civil simulator: the motion base, the spindly-looking unit that tilts, heaves and pitches the pod through a series of gravity defying manoeuvres.

For many years high-performance hydraulic systems have done the job admirably. But in the face of the industry’s increasing desire to improve efficiency while cranking up the realism levels another notch, simulator designers are now looking beyond the noisy, expensive and oily world of hydraulics for a different solution.

The EM2K, a new electro-hydraulic motion base developed by engineers at avionics giant Thales, could be just what they’re looking for. Claimed to use 90 per cent less oil and 80 per cent less power than traditional units, the system will make its debut on the Thales Boeing 787 (Dreamliner) simulator and will also be fitted to future A380 sims. It can be retrofitted to existing simulators and will, says the company, eventually become its motion base of choice on all of its civil units.

The Engineer was granted an exclusive look at the system last month as it was put through its paces at Thales’ simulation facility near Gatwick. Standing next to the device as it swings its dummy 14-tonne cargo of huge yellow girders effortlessly through the air, one of its attractions is immediately obvious: you can hear yourself think. It’s not perhaps the new system’s most critical feature — but it’s an obvious indicator that something new is going on here: traditional hydraulic simulators can produce a deafening amount of noise.

The system uses the same kind of hydraulic jacks that would be found on conventional systems, but the servo valves have been replaced with two hydraulic pumps on each jack that are driven by electric motors. To provide energy efficiency six accumulators, one for each jack, are precharged to a pressure that balances the weight of the simulator. In addition, the tops of the jacks are connected to a single large accumulator that gives a constant downwards force to balance the upwards force from the other accumulators.

Ken Cleasby, one of the engineers who helped develop the system, said the chief advantages of the design kick in when the simulator is flying straight and level which, in the case of a civil airliner, should be most of the time: ‘[in this state] the pressures in the accumulator exactly balance the weight of the simulator; there’s no net torque on the pumps, no net torque on the motor — there’s very little energy used to hold the simulator straight and level.’

To generate dynamic movements, the electric motors are called into play, and even in these circumstances EM2K is claimed to be considerably more efficient than traditional systems. Indeed, Cleasby said the design has enabled Thales to reduce the amount of oil from 2,400 litres to 240 litres of fully synthetic oil while the power consumption has been reduced from 42kW to 6kW.

But the quest for an oil-free simulator has been taken one step further by the other giant of the simulation world, Canada’s CAE, which has developed an all-electric motion system that also boasts huge efficiency improvements and, it is claimed, enhanced levels of reality. Earlier this year four civil aircraft simulators based on the so-called ‘True Electric Motion System’ became the first full-flight simulators with electric motion to receive Level D certification. This means pilots could fulfil their mandatory flight time in the simulator and fly their first commercial plane — with passengers — without ever having flown that particular aircraft before.

CAE motion systems engineer Peter Jarvis explained that the company was motivated by a similar set of concerns to Thales. It wanted to dispense with the inefficiencies of servo valves and the high operating costs and infrastructure requirements of hydraulic systems. But it wanted to go one step further and eliminate the use of oil.

Like Thales, CAE is claiming impressive energy savings. ‘We’ve measured energy savings of 75 per cent over a traditional, hydraulic-based simulator,’ claimed Jarvis, adding that with civil training simulators typically enjoying 6,000 hours of use a year, this could add up to a huge financial saving.

The company first looked into the potential of all-electric simulators in the mid 1990s, but the available technology had neither the payload capacity nor the low-vibration characteristics required by a high-fidelity simulator. Spurred on by recent progress in motor and ballscrew design, the firm decided the time was now right to revisit the idea.

Jarvis claimed that in addition to reduced power requirements, an all-electric system gets around two of the big disadvantages of hydraulic simulators. First, he said, the compressibility characteristics of oil affect the frequency response of the actuator. Second, such systems also encounter problems with what Jarvis terms cross-coupling: ‘With a hydraulic system, as you move the motion system around the loads on the actuators are changing, you have to compensate for these changes and control becomes more complicated.

‘With electric actuators, because there’s no oil it’s a much stiffer design and you don’t have the same cross-coupling characteristics. Plus, because of the motor characteristics, the frequency responses are much better.’

While agreeing that Thales’ decision to replace the servo valves with hydraulic pumps is a good way to reduce energy consumption, Jarvis suggested EM2K will not be entirely free from the problems that have bedevilled traditional systems. ‘They’re still dealing with hydraulic actuators and issues of compressibility and that impacts on the performance,’ he said.

But Thales’ Cleasby is adamant the electro-hydraulic solution is the most attractive technology. ‘The all-electric route involves a mechanical conversion of the rotary motion of the electric motions into linear motion of the jacks. We felt that method of conversion isn’t as reliable as we would like and produces more vibration and noise than we would like.’ Cleasby added that a system with a hydraulic element also has distinct advantages in the event of a power failure: a common occurrence in countries such as China or India. He said while the EM2K system will come down under its own weight, an electro-mechanical system is rated like a car-jack and requires a standby set of batteries to control the descent.