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Circular Airport Runway 

In the last few months, more and more articles were published and posted on a revolutionary idea for airport optimization: the endless runway.

As I am not an expert on aerospace technology – or have any actual knowledge on it at all – and still am a student, I usually have two people I go to for a first impression on technical ideas and innovations I read about. My father – a mechanical engineer with an open mind – and my grandfather – a mechanical engineer as well as a former licensed pilot. Their view on this topic was quite similar: how can an airplane land on a round landing strip? It sounds very dangerous and the physics behind the take-off and landing of commercial airline flights does not seem to go well with the forces that would be generated by the use of a circular runway. After starting my online research, I noticed that this opinion is shared by many – people were even considering it to be an April fool’s due to the unfortunate publication dates around April 1st. The circular airstrip seems unfeasible, impossible and complete non-sense – this actually made the “endless runway” more intriguing to me.

So what is this circular airport runway?

As the picture shows, the airport has a completely new design: A circular runway is built around a central airport infrastructure. The circle has a diameter of about three to four kilometers creating a runway length of approximately 10 km. International airports usually have landing strips of maximal 5km length, meaning that one round runway would have the length of three conventional ones; thus, managing to operate several aircrafts simultaneously. The width of the potential runway is about 140 m with a banked lateral profile (with increasing angles to the outside) that ensures safety and limits the centrifugal forces created by the landing and take-off procedure on a round airstrip. The runway is divided into 18 segments to simplify the organization of landing and take-off points on the circle.

To access the inside facilities two possibilities are developed: one for employees and suppliers of the airport through a tunnel under the runway and one for passengers with an underground train or other automated people mover (APM).

The main advantage behind this innovation is that airplanes can land independently from where the wind is coming – with strong winds (stronger than 20 knots) airplanes can land and take-off without having to be concerned about dangerous crosswinds as the right segments of the circular runway can be chosen where the wind comes from an acceptable angle. With winds weaker than 20 knots, the airplanes can use any segment of the circular lane making the distribution of landings and take-offs on the track easier and more balanced.

Furthermore, other advantages were analyzed:

• Less space needed – the circular airport is 36% smaller than an airport with similar flight power
• Shorter flight routes and times – the airplanes don’t have to circle around the airport anymore in order to reach the airstrip from the right angle and time distance between airplanes can be shortened as wake turbulences between airplanes can be avoided
• Shorter taxiways – the airplanes will have shorter distances between airport docking station and runway segments
• Noise around airport distributed evenly – the airplanes can get to the airport from any direction thus not passing over the same area every time

Since the research report has been published, many concerns have been made public. Many readers of online articles are unsure on how the forces acting on the airplane while landing can be handled in a circular runway. They fear that the runway would make the landing and take-off procedure unsafe and less controllable.

On an organizational level, other concerns emerge; it seems that the airport would need an elaborate information and control system in order to process and organize the incoming and outgoing flights. Current software would be useless thus making the implementation process of the innovation even longer, more expensive and more unpredictable.

In case the runway will be built and used in the future all pilots would have to be trained for this new landing and take-off technique.

Lastly, a cost analysis shows that the building of the project would cost 10% to 60% more than traditional airports. It might be more cost efficient in the long term as airplanes will have shorter flight distances without having to circle around the airport to adjust the trajectory, but high initial costs are a major potential obstacle.

Is it worth it?

At this moment, it does not look like the advantages of such a project overweigh the disadvantages, making it unattractive for stakeholders and potential investors.

The researchers motivate the necessity for this innovation with the fact that air traffic will increase drastically in the next decades; unfortunately though, one of the main disadvantages of the circular runway is that it can not be expanded. On a normal day basis the amount of flights that can be operated on the endless runway is approximately 80-87 per hour (in comparison the Paris Charles de Gaulle airport has a capacity of 115 movements per hour). No additional airstrip can be built within an existing circle and the airport infrastructure at the center is limited as well. Thus, making the endless runway less efficient in case of an increase in air traffic.

Additionally in their report they introduce a new airplane that would make the new airport more efficient, although they have tested and ensured that current airplanes would be able to land on the endless runway. This makes me question if the endless runway actually can be feasible and safe for existing airplanes.

It is not the first time that in the aerospace field the possibility of a circular runway has been researched. In the early 20th century, the first idea of a circular runway on top of skyscrapers in the city center was developed for businessmen who would want to get to the office in a fast and direct way.