Airliners’ reliance on hydraulic fluid could drastically decrease if the aviation industry develops technologies to convert the hydraulic systems used in large aircraft to run on electricity, says aviation services company National Airways Corporation (NAC) senior production manager of fixed wing maintenance Mike Mayers.

He believes a 50% decrease in the dependence on hydraulic systems can be expected in large aircraft, if electric aircraft are introduced.

The use of hydraulics in small electric aircraft can be eliminated sooner, as significant advancements have already been made in this field, Mayers notes.

Small electric aircraft with up to four seats are able to run on battery-powered electric systems that drive an electric motor, which drives the propeller. These aircraft have to be charged by either a 220 V plug-in when they land or an air turbine.

“Currently, there are many developments and trials under way on small electric aircraft, such as the Puffin, which is designed by the US National Aeronautics and Space Administration, and the All-electric Airplane, which is built by the University of Cambridge,” he says.

Mayers explains that large aircraft use bleed air power – the hydraulic process whereby energy is diverted from the engine to the motor to propel the aircraft.

“Bleed air power is an economically viable process for airliners, as it is easily available, reliable and assists in stabilising various parts of the aircraft. “It is also commonly used to keep ice off of the wings.”

He adds, however, that engine power extraction increases fuel consumption, which contributes to higher levels of carbon dioxide (CO2) emissions and adds to the cost of flying.

Electrically powered aeroplanes will hold significant cost and environmental benefits for the aviation industry, states Mayers.

However, the industry does not currently have the technology available to allow large aircraft to run only on electricity.

Mayers explains that electric aircraft run on electric motors rather than internal combustion engines, with the electricity generated from fuel cells, ultracapacitors, solar cells, power beaming or batteries.

Further, it is also easier to work with hydraulics, owing to the efficiency of fluid pressure.

In addition, electric power generation requires big electrical motors to do the tasks currently being undertaken by hydraulic power.

“Increasing the size of an electric motor increases the weight, which causes battery challenges, as a large number of batteries are required to store the same amount of energy as that stored by a hydraulic engine.

“That leads to an increase in the weight of the aircraft and will prevent it from taking off. “Weight and space are also limited on large aircraft.

“Therefore, large electric aircraft are currently not an economically viable option,” Mayers notes.

He points out that the realisation of large electric aircraft will require advanced technology and smaller motors.

“It will be quite a few years before this technology will be viable for airliners,” he says.

He adds that there is still a need for hydraulics in electric aircraft. “Hydraulic fluid is more efficient for certain aircraft systems, such as the brakes.”

Further, Mayers notes that the conversion from using hydraulic aircraft to using electric aircraft will bring about many changes in the aviation industry.

“There will be a switch in trades from mechanical to electrical engineers for aircraft maintenance and service, and a new skills base will need to be created for airline crew to understand the basics of electric aircraft.”

Environment-friendly

Greenhouse-gas (GHG) emissions from aircraft contribute significantly to global climate change, says the International Air Transport Association (Iata).

In September 2010, the association reaffirmed the aviation industry’s commitment to capping net CO₂ emissions by 2020 and to cutting its CO2 _{emissions by half by 2050, compared with 2005 levels. The industry’s CO2 footprint stood at 625-million tons in 2009.}

“A switch to electrical power will be more environment-friendly, as there will be no CO2 emissions and the aircraft will be powered by propeller,” Mayers states.

A switch from hydraulic aircraft to electric aircraft will not lead to an increase in electricity consumption, as renewable-energy electricity generation options, such as electrical turbines, can be used to charge the aircraft, he says.

“Electric aircraft will also be a more affordable option than hydraulics, as the cost of generating renewable energy will be a fraction of the money spent on fuel. “These aircraft will, therefore, be cheaper in the long run,” Mayers comments.

A large aircraft, such as a Boeing 747, requires about 220 000 ℓ of fuel to fill its tank and uses 10 t of fuel an hour.

“This greatly contributes to GHG emissions and will, hopefully, become a thing of the past,” says Mayers.

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