ELECTRIC VEHICLES TAKING FLIGHT

PROF M. Goosey

​In the last year or two, governments around the world have announced their commitments to ending the sale of petrol and diesel powered cars by setting deadlines for when all new vehicles will need to be, at least partly, electrically powered. We can thus now know with some certainty that the days of the purely internal combustion engine powered vehicle are limited, even if it is something like 20 years in the future.
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However, there is another area of transport that is also receiving increasing interest from environmentalists and those keen to minimise its contribution to global warming. The area in question is air transport, which is another big user of hydrocarbon fuels. Jet engines are the main culprits and, although they have been made much more efficient in recent years, they are still a major cause of concern, especially as the number of aeroplanes in service continues to increase.

​Not surprisingly, therefore, interest is growing in the possibility of using electricity to power aircraft, as is currently possible with small model aircraft, drones and UAVs etc. The use of solar cells on a very lightweight electrically powered plane enabled Solar Impulse 2 to circumnavigate the world in 2015. This was an important demonstration of the possibility of electrically powered flight, even if the journey did take over 500 days at an average speed of just 45 miles per hour. Since then, there has been rapid growth in global electric aircraft development activity, and it is estimated that there may now be as many as 100 projects underway around the world aiming to develop some form of new electrically powered aircraft.

To achieve the performance and range that is expected, and currently possible using conventional jet engine powered aircraft, there will need to be a major advance in battery technology, in order to provide the levels of energy needed at a much lower battery weight. Inadequate battery energy density is already an important consideration for electric vehicles, as it is a key factor in limiting range. For aircraft, the issue is really about weight, and with one tonne of aviation fuel offering around 14 times the energy of a one tonne battery, it is clear why electric aircraft development is currently limited to very small aircraft, such as two seater trainers that carry a limited payload over a short range. In an electric aircraft, without much improved battery energy densities, a plane with sufficient useful range may simply be too heavy to get off the ground.

One compromise solution, as is already the case with the automobile industry, may be to develop hybrid aircraft with dual power sources. This approach could lead to aircraft being built, where combinations of electric motors and conventional jet engines provide a viable and attractive power solution for some applications.
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Many aviation experts now believe that there will be a role for electric aircraft in the not too distant future as the technology continues to improve. For example, the Norwegian government has stated that it will require all internal flights to be electrically powered by 2040. More specifically, it wants aeroplane makers to develop a 25 to 30-seat aircraft that are powered by electric motors and, to show the level of ambition, it wants the first ones in service by 2025. Norway is already leading the world in the adoption of electric vehicles, so it seems that there is a good chance they may also achieve this more difficult objective.