From the sky, tomorrows airports might look more like racetracks than landing strips More people are flying than ever before. But the skies look set to get busier. The latest forecast from the International Air Transport Association (IATA) suggests that there’ll be 7.2 billion air passengers in 2035 – that’s almost twice the number of people who flew in 2016. More passengers will inevitably mean more aircraft, which poses a big challenge for air traffic controllers, airport designers, and urban planners. But one Dutch scientist has a radical idea that he thinks could herald the future of aviation. Henk Hesselink and his colleagues at the National Aerospace Laboratory in the Netherlands are working on a project called the Endless Runway, funded by the European Commission’s Seventh Framework Program. In it, they propose replacing the long straight strips of concrete that render airports instantly recognizable from the air, with a single circular runway that surrounds the terminal building.
According to Henk, the benefits of their design are manifold – for a start, because planes could take off from any point in the circle, they could avoid damaging crosswinds that can shut down linear runways. In order to manage the traffic of a multi-terminal airport, circular runways would need to be pretty big though – the NAL team suggest a minimum diameter of 3.5 km (2.17 miles)*, which compares pretty favorably with the ‘typical’ length of a commercial airline runway – in the range of 2.4 – 3.9 km. I can almost hear you thinking, ‘But a circle with that diameter would be huge!’ The resulting area (π x radius x radius) would be around 9.6 km2. This is actually significantly smaller than London’s Heathrow Airport, which covers an area of 12.27 km2, despite having just two runways (for now). So, circular runways could give us smaller airports, without sacrificing air traffic. In addition, the team say that up to three planes can take off and land on their runway at once, which could improve traffic flow. To see how it would work in practice, they looked at the flight patterns from Charles de Gaulle – a four-runway airport on the outskirts of Paris – and as reported in Fast Company, proved that a single “circular runway could handle the same number of departures and landings.” Their design is a little like a velodrome or a race track, only circular, rather than oval-shaped. The entire runway would be steeply banked, and to understand why, let’s think about how you’d drive a truck around a corner. While you instinctively know that you’ll need to slow down for the corner, you might not realize that it’s because you’re making use of friction (between the wheels and the road). This is the only force that helps you turn on a flat corner. If you’re going slowly, that force is more than enough to keep you on the road. If you hit a corner at a slightly higher speed, you might still make it, but you’ll find your weight – and that of the truck – shifts to the outside of the turn. This is inertia in action – in effect, you are forcing the truck to turn, but it is trying to resist you**. If you attempt the corner at an even higher speed, your truck may well just tip over***. So, flat corners on a runway of never-ending corners would be a terrible, terrible idea. However, by tipping the roadway inwards, so that the outer edge is higher than the inner edge, you get an additional force – the normal force from the road – acting on the truck / plane. This keeps you on the road, and allowing you to travel safely around the corner, even at much higher speeds. These same forces mean that as a landing plane decelerates, it would naturally move down the bank towards the center of the track, in the same way that a track cyclist does. In terms of what that’d mean for the passengers, Henk told the BBC that they “would experience a slight turn, similar to a turn in the air. Pilots and passengers would not feel like they are in a rollercoaster.” (CONTINUED...)