The Endless Runway
The airports capacity is determined by the capacity of its runway system. The real capacity is usually lower than the declared capacity because of weather restrictions (cross- and tailwind and visibility) and because of dependencies between runways.
Aircraft need to take off and land within defined cross- and tailwind limits. The direction of the runway determines the cross- and tailwind components. With changing wind (direction and speed), other runways in other directions need to be used.
Endless Runway investigates the use of a circular runway. Starting anywhere in the circle, aircraft can take off from the point where the crosswind is at minimum (or zero). Just as well, they can land at the point where they fly exactly headwind and continue their landing roll in the circle, exiting anywhere where they are closest to their gate. This will create a runway that can be used under any conditions without loss of capacity.
Circular runways may improve air travel
The idea of a circular runway for airports could help revolutionise air travel, shortening flight times, saving fuel costs and promoting airport efficiency.
The design of airport runways has remained largely unchanged ever since aeroplanes were created. The EU-funded project 'The endless runway' (http://www.endlessrunway-project.eu/ (ENDLESS RUNWAY)) conceived a revolutionary design for a runway, based on a circular track that runs around the airport. Such a runway could enable planes to take-off in any direction and land from any direction, shortening trajectories, avoiding runway crossings and facilitating landings in any weather.
More specifically, the project team proposed a circular runway that would have a radius of 1.5 to 2.5 km, which enables changes to existing airports more readily. Such a runway would also be 400 m wide, striking a balance between limiting centrifugal forces and safety considerations. Interestingly, several aircraft can operate such a 10 km runway at the same time.
To achieve its aims, the project evaluated three operational models. The first was designed for low-wind scenarios where any part of the circle can be used in any direction. The second, on the other hand, involved a high-wind scenario that was similar to an airport with two parallel runways. Lastly, the third model considered changing winds, involving an aircraft sequence that gradually 'moves' with the wind direction.
With these scenarios in mind, the project team found that the concept could shorten take-off and landing tracks overall by 10 % in comparison to straight runways. The model fosters more sustainable operations that don't always rely on the wind, with total land use being smaller than that of conventional airports. While construction costs will be 10–60 % higher, the concept offers benefits in terms of shorter trajectories, less taxi time and continuous capacity, ideal for increasing air capacity in the world.
ENDLESS RUNWAY has successfully demonstrated the feasibility of the circular runway project, highlighting benefits, future requirements and outlook. If Europe's airports shift to such a model, they could realise significant fuel savings and streamline air travel. Exciting possibilities are in store for air travel in Europe.