Electric planes - the future or science fiction? Max Rosenblatt Lower Sixth
Whether one watches the news every morning on a TV, or still prefer a newspaper, it seems that we are constantly bombarded by the same prevalent problems. I’ll refrain from mentioning the bureaucracy of the “B-word” and turn to something else that is completely unavoidable - climate change. Every day there seems to be a new story about Greta Thunberg, or another celebrity denounced for flying first class, or how we seem to be ploughing towards a “point of no return”. It’s clear that actions are being taken internationally towards reducing the rate of this possibly apocalyptic change, and it feels like something is looming which could be nothing short of revolutionary - electric planes (i.e. planes in which propulsion comes from an electric motor, not an internal combustion engine). Some knowledge of current plane engines is useful when evaluating how an electric plane would be structured. Today, plane engines can be categorised into three main categories: Turbofan (the simplest form of engine, used in present-day military jets), turboprop (in which the engine drives a propellor to generate thrust, most efficient at slower speeds) and turbofan (designed to merge the best features of the turbojet and
turboprop, used in modern day passenger planes). A plane’s efficiency is often characterised by its engine’s bypass ratio, that is, the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core. One of the main aims for aircraft manufacturers over the last few years has been to fit planes with engines that have high bypass ratios - leading to better fuel economy. Notably, Boeing’s 787 Dreamliner, commonly fit with either Rolls Royce or General Electric engines (both of which have high bypass ratios), is being used in place of larger aircraft like Boeing’s 747 or Airbus’ 380, as the 787 can be more easily filled, and so can operate more bespoke routes with the same
range as its larger counterparts. On the subject of size, larger planes can often be burdens for airports and airlines. For example, the Airbus 380, the largest current passenger aircraft, theoretically should have a wingspan of 90 metres for optimal efficiency, but airport restrictions (maximum size of 80 metres by 80 meters) have forced Airbus to shorten this to less than 80 metres, which reduces the 380’s fuel efficiency. With this in mind, we can see that airlines prioritise efficiency over size, which is important when theorising about a new form of aircraft.
[A]irlines prioritise efficiency over size, which is important when theorising about a new form of aircraft.
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The other issue that plagues the concept of electric planes (or rather, electric vehicles in general) is the extremely low energy density that is currently achieved by cuttingedge batteries compared to fossil fuels such as kerosene. For comparison, one kilogram of aircraft fuel will store around 42.7MJ of energy. The current “best” battery, in terms of energy capacity, will hold only around 1MJ per kilogram. That being
