Flying without a motor, inspired by birds

Human beings have succeeded, through their curiosity and genius, in flying like birds. However, this comes at a significant energy cost: a Boeing 737 consumes about 750 gallons (2840 liters) of fuel per hour. This need for energy also has an environmental effect. We know that the transportation industry leaves a significant ecological footprint, moreover, the industry is aware of this and is increasingly trying to adopt "eco-friendly flying." For example, some are dreaming of more fuel-efficient aircraft, A German student has thought about an aircraft, the Flying V, that uses 20% less gasoline which has excited some airlines.

All very good solutions to reduce air pollution. Nevertheless, a question arises: would it be possible one day to fly without any engine? It seems crazy and yet present and future engineers are likely to look into this topic.

The inspiring technique of the albatross

In fact, birds have demonstrated their ability to move over long distances by saving energy. While in the early days of aviation, humans tried to mimic the wing flapping of hummingbirds or passerines with dramatic results, they didn't really observe the larger species. The latter hardly flap their wings at all. Yet, some of them can spend hours and even days in the air while gliding.

Among the known large gliders, we find the Andean condor, pelicans, storks and especially the champion: the albatross. The latter records exceptional statistics. Researchers have noted that they spend only between 12 and 14.5% of their flight time making their wings go. To achieve this, they use a technique called "gradient flight" or "dynamic soaring" in the English literature. Thus, they let themselves be transported by the different currents over the oceans and the earth's gravity. Those who observe them notice that these birds rarely glide in a straight line, but rather, mimic skiers by slaloming to reach their destination. His method is so perfected that scientists are still analyzing their energy-conserving mechanics.

The Dream of Perpetual Flight

The various approaches to albatrosses, including gradient flight, have some dreaming. If the aircraft of the future were capable of flying without engines and without stopping until they reached their target, for some, this is even the likely future of aircraft: perpetual flight. Obviously, we are still far from the cup to the lips but research tends, little by little, to affirm that this could be done by responding to the laws of physics. With gliders that would be able to change the direction of its wings like the bird, it would be possible and the whole thing would even respect the laws of gravity.

Besides, this idea born in many theses and studies, materialized on January 19, 2021: a radio-controlled aircraft without a propeller or engine succeeded, through the technique of gradient flight, to reach a speed of 882 km/h! Launched from Parker Mountain north of Los Angeles, all it had to do was loop down the slope and thus feed off air currents. A feat made all the more impressive by the fact that at times the machine was only a few meters from the ground. Therefore, a good visual acuity is required to manage to establish such speeds with a small device.

Of course, these modest gliders are a far cry from the aircraft we would need for individuals to travel en masse from one country to another. It must also be said that this would require a total reinvention of the airspace that would have to take into account the different currents. Nevertheless, these breakthroughs and this interest by engineering faculties in gradient flight give hope possibly for even more energy-efficient future aircraft.

Illustration : S. Hermann & F. Richter from Pixabay

References :

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