Endless Runway concept could pave the way for future airports
An innovative research project from the Netherlands Aerospace Centre has put forward the concept of a circular runway. Hoped to provide a breakthrough in airport safety, capacity, noise and fuel burn, the Endless Runway is being pursued as a model for aviation beyond 2050.
Two years ago, Henk Hesselink, senior R&D engineer for the Netherlands Aerospace Centre (NLR) was tasked by the European Commission (EC) with finding a solution to recurring runway issues, such as cross and tailwinds, as well as long-term airport capacity constraints – one of the primary global challenges facing the industry in the years to come.
In response, Hesselink brought forward a daring concept: the Endless Runway. The idea is built around a compact airport, consisting of a circle measuring 3km in diameter with a 10km-long runway, and the taxiways, aprons, terminals and all other airport facilities all located within the circle.
One of the revolutionary aspects of the layout is that it promises independence from wind conditions. Today, traditional runways are heavily dependent on wind, which leads to delays and safety issues.
On the Endless Runway, researchers argue that the aircraft could always operate with a headwind during take-off and landing, meaning that planes could depart safely in any direction at all times.
“One of the problems that runways face is wind,” Hesselink says. “And I was thinking: would this still be a problem in 2050? In these many years, this problem should have been solved – but how? One answer is the circular runway.”
The project, currently in its trial phase, promises further advantages such as improved aircraft trajectories, efficiency of transport from gate to gate, and a compact airport footprint.
What would the Endless Runway look like?
“At first we thought we can maybe have some kind of extensions to this runway, where you could land on a straight part, and then enter the circle after some time,” Hesselink explains, “but that doesn't really work, because you have the problem that the aircraft is suddenly in a curve, which isn't very comfortable.
“So the practical solution is to already start taking the turn in the landing phase. Just before landing, [the pilot] should initiate the turn. There are of course centrifugal forces we have to cope with, and if you look at trains and roads, you can see they are banked to the outside, so we have also designed a banked circle.”
This new navigation model would do away with one of the oldest causes of delays at airports across the world, namely tailwinds and crosswinds, which determine whether runways can be used or not. The fixed direction of traditional runways means they are completely dependent on wind direction. Due to its shape, the Endless Runway would avoid such constraints.
“Aviation has been the same for a very long time,” Hesselink says. “Even though nowadays it's a bit more automated in order to handle large numbers of people, the principle is still the same.”
"The fixed direction of traditional runways means they are completely dependent on wind direction."
“In most airports today, if there is a storm, capacity drops significantly, so you should really look at how we can ensure that capacity is always maintained at a certain level. I think this solution will guarantee that,” Hesselink says.
A report detailing the airport infrastructure notes that “the terminal building is the nexus between the airside and landside facilities [and] their design must be flexible, balanced and visionary in order to adapt to changing needs of airlines, aircraft and passengers.”
When it comes to access to and around the airport, design reports dating from 2012 explore possibilities such as curb-side roadways leading to the airport, and “Automated People Mover vehicles” to be used to transport users inside the Endless Runway.
Asked whether retrofitting existing airports would be a possibility, Hesselink said he thinks the concept should be first proved as a stand-alone structure, to gain more experience and a better understanding of the challenges.
“If the experience is positive,” he says, “we can consider retrofitting existing airports later on.”
A recurring concept in aviation
The Endless Runway project was developed under the EC’s 7th Framework Programme, which set out to search for tomorrow’s breakthrough technologies.
A consortium made up of the respective national research centres for aeronautics in the Netherlands, France, Germany, Spain and Poland worked together in researching and testing the concept.
But this is not an entirely new idea.
Circular runways have been explored since the early days of aviation. In France, the first circular take-off took place at the end of the 19th century, followed by a flurry of articles, reports and patents on the idea submitted over the course of the 20th century.
In 1960, US Navy pilot James R. Conrey put forward a patent for the concept, in the belief that it would allow aircraft to land in any wind condition – much the same reason that inspired Hesselink to revive it.
“Videos on YouTube depicting scary crosswind landings just show that crosswind is a big problem, so if you could solve that, it would be a great improvement in safety,” Hesselink says.
Following Conrey’s death, a project was launched by the US Navy, and between 1964 and 1965 successful landings and take-offs with propeller and jet planes were made by seven different pilots on a General Motors track.
“After their tests, they reported that the first time they landed on the runway felt a bit strange, but after a few approaches, they concluded it was pretty easy to do.”
Simulating the runway using record numbers
The concept was simulated by Hesselink and his team in three stages, looking at issues with air traffic management, infrastructure and aircraft modelling.
For assessment purposes, take-offs and landings on the Endless Runway simulation were compared with traffic conditions at Paris Charles de Gaulle on 1 July 2011, the busiest day ever at the airport, when it handled an all-time record of 8.9 million passengers. Researchers believe that if the novel concept is feasible under such high-stress conditions, it could then work for almost any other airport in Europe.
“We designed the runway as a number of segments that could be used for take-off and landing and we scheduled the aircrafts as such that they would all be free of conflict,” Hesselink says.
“Another thing we simulated was the aircraft. If you have the bank on the runway, the wingtip or the engine may touch the surface, so the design of the runway was based on the calculations we made with aircraft simulator.”
The third aspect tested was the design of the airfield. The maximum allowed centrifugal forces as they are now in trains served as the basis for establishing the size of the circle for the most comfortable take-off and landing conditions.
A mixed reaction and hopeful outlook
Looking towards 2050, the European Research Establishments in Aeronautics (EREA) puts the number of air passengers at almost 14 billion per year, which would put serious strains on airports and restrict growth.
Ongoing programmes such as SESAR (Single European Sky ATM Research) are currently working on modernizing air traffic management infrastructure to achieve both safe and environmentally friendly operations. However, even though advanced technologies and automation help with processing the increased flow of passengers and goods, more is needed.
But why hasn’t the circular runway concept taken off until now?
According to a 2014 report published by EC’s Community Research and Development Information Service (CORDIS), the circular runway has so far remained at experimental level due to high costs and the need to introduce new landing procedures and techniques.
"The circular runway has so far remained at experimental level due to high costs."
The report argues that construction costs would be higher than for conventional runways, because of the requirement for precise banking of the runway and for larger runway width and length.
Another challenge would be the necessity to develop new landing techniques, as well as up skilling pilots in the new procedures.
“There are a lot of questions on the forces on the landing gear and the tires, as well as the training of the pilots, which are indeed things that need to be considered in follow-up work,” Hesselink says. “What we've done so far is a computer-based simulation, and we have proven that it is possible.”
The next step for Hesselink and his team is to try testing the track in real life, ideally on a car track with similar characteristics. The preliminary trials could use large drones for cargo delivery.
“The reaction so far has been mixed, but many people are very happy that we have come up with an innovation in aviation,” he says.
“I sometimes compare this with a car exhibition: the final product will not look exactly how we have defined it, but it will give a lot of food for thought for new ideas in aviation and I hope that a lot of spin-off ideas come from this.”