The electric revolution is coming to aviation, that much we can say for sure! Across the world, big money is being poured into research and development. With the environmental impact of aviation becoming a major concern, and the airline industry’s ongoing quest for more efficient aircraft, investors have spotted a golden opportunity.
The ultimate goal of this electric revolution is to create not only small aircraft for local use, but to reimagine international airliners as well! Already, two-seat aircraft are available for pilot training, and we’re proud to say that Australia is one of the first countries in the world to embrace this technology. Electro Aero in Perth is just one example of this, offering the public a chance to experience electric flight through training sessions and trial flights.
The advantages of electric aircraft are huge. Not only do they offer pollution-free flying, but operating costs are lower and noise levels are dramatically reduced — a real bonus both for passengers and for people who live or work around airports.
However, achieving long distance flight in an electric aircraft is still the greatest challenge. There are currently three approaches to tackling this problem, battery electric, hydrogen fuel-cell electric, and hybrid combustion-engine electric. These three solutions will all feature alongside economy trial solutions in our 2019 Great Air Race, and could quite possibly go on to change the face of aviation forever!
Conceptually, this is by far the simplest solution. Not too dissimilar to an electric car, these aircraft have a large, lightweight battery and an electric motor.
The motor, which has very high efficiency (over 90%, compared to ~25% efficiency of a typical car engine) drives the propeller directly. Because the electric motor is much smaller, lighter, and more efficient than its fuel-burning counterpart, the aircraft can also be more aerodynamic — further increasing efficiency! It’s also possible to boost the energy stored in the batteries by placing a large array of solar cells on the wings and tail.
Despite this, Battery Electric solutions still face a major challenge. They’re still limited by the amount of energy that the battery can store. The best batteries on the market currently use lithium-ion technology, very similar to the batteries used in electric vehicles, laptops, and drones. Major improvements in battery technology — particular in the amount of energy they can store — have already been demonstrated in laboratories. The question is, will such batteries be ready in time for the 2019 rendition of the Great Air Race?
A cylinder of compressed hydrogen gas can carry much more energy than a battery of the same weight! So it’s no surprise that hydrogen fuel cells have garnered the interest of aviation heavyweights such as Boeing, NASA, and Airbus.
So how does it work? Simply put, hydrogen and oxygen are combined in a fuel cell, which produces electrical energy and water vapour. Batteries are then used to smooth out the load, with the system feeding an electrically driven propeller.
In many ways hydrogen is the ideal fuel. A hydrogen fuel cell produces only electricity and water vapour, and the hydrogen itself can be created from water, using only electricity. Therefore, the entire system is a closed cycle! As long as the electricity used to split, or “electrolyse”, the water to create hydrogen is generated by renewable sources, such as wind and solar, there are no greenhouse gas emissions at any stage of the operation. In effect, it becomes a “wind powered” or “solar powered” aircraft.
Whilst some small hydrogen fuel cell powered aircraft have already proven emission free flight is possible, the technology has a fair way to go before it’s able to take us around the world! Although hydrogen fuel only weighs about a third of kerosene jet-fuel for the same amount of energy, at normal temperatures hydrogen is a gas, rather than a liquid. To carry a usable amount of fuel in a reasonable volume, hydrogen must either by compressed to incredible pressures (350 to 700 times atmospheric pressure) — or cooled to -253 C to liquify it.
Either way, the specialised containers end up much heavier than they fuel they contain, greatly reducing the weight advantage of the hydrogen. Unlike most aircraft, where the wings are used for fuel storage, aircraft using liquid hydrogen will typically carry their fuel inside the fuselage, where the specialised storage tanks can be designed with minimum surface area to reduce boil-off. While the larger fuselage that results might increase skin friction drag and wave drag, reducing aircraft performance, innovative solutions are being explored where the super-cold hydrogen gas can help cool the electric motors, and even improve the aerodynamics of the wings.
It’s also worth noting that because hydrogen fuel is a relative newcomer, it is currently more expensive than fossil fuels. However, South Australia is installing some of the largest hydrogen electrolysers in the world, with a view to Australia becoming a major world producer of climate-friendly hydrogen fuel. This could have a major impact on the advancement of hydrogen fuel cell technology, but only time will tell if it’s ready in time for the 2019 Great Air Race!
In a hybrid aircraft, as in a hybrid car, both batteries and a combustion engine are used. This combines many of the benefits of both — the aircraft can take off and land on electric power alone with minimal noise, with the combustion engine giving plenty of range.
In the Great Air Race we have created a separate class for series hybrids. In this configuration, the combustion engine drives an electrical generator. The aircraft propeller is driven by an electric motor, with power coming both from the generator and from on-board batteries. The aircraft is therefore not only quiet when close to inhabited areas, but the efficiencies gained by designing the combustion engine for “cruise” power rather than “take off” power leads to major savings in fuel consumption – and hence greenhouse gas emissions.
Hybrid Electric aircraft could become a common sight quicker than you think. A prime example is the Equator Aircraft (pictured) produced out of Norway. This is the result of a need to reduce operational costs, and a call to cut down on airline emissions and noise pollution.
The European commission has stated (as part of its flightpath 2050 plan) that it wants to cut carbon dioxide emissions by 60%, nitrogen oxide pollution down by 90%, and noise pollution by 75%. In addition to this, airline fuel costs have been at the mercy of oil price fluctuations, and costs have varied anywhere between 17-36% over recent years. So, it’s clear to see why so many aviation titans are interested in Hybrid Electric solutions!
There are many ways to reduce the fuel consumption, and simultaneously the greenhouse gas emissions, of long-haul aircraft.
Aircraft designers are working hard not only on more efficient designs, but also on innovative concepts such as the Airbus E-Fan X. Extremely fuel-efficient light aircraft are already commercially available, making this class effectively open to anyone!
The 2019 Great Air Race will provide a proving ground for smaller aircraft with global capability, and could very well lead us into the future of aviation!