Stories of new applications for unmanned aircraft are now regular features in newspapers - from aerial photography to parcel delivery and personalised air transport. What seemed like a surreal future-scape just 10 years ago is fast becoming reality. The challenge is how to keep all these aircraft away from each other in the sky. EU-funded researchers have used simulations and visual modelling to find a solution.
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Named after the 1927 expressionist film, the Metropolis team set out to investigate the influence of airspace structure on capacity, complexity, safety and efficiency for high-density air traffic management. Their findings, published in the Journal of Guidance, Navigation and Control and elsewhere, upend traditional notions about handling extreme traffic in the skies above our cities.
“Does adding more structure increase airspace capacity? This was our starting question in the Metropolis simulations and, to our surprise, using data based on today’s air traffic densities, we found the opposite to be true,” says project coordinator Jacco Hoekstra of TU Delft in the Netherlands.
Many of the models and predictions from the project are now making their way into advanced technologies being developed for the market, he adds.
“The project ended less than two years ago and yet we’re already seeing many of our models and predictions play out as advanced technologies speed to market application,” says Hoekstra. “Package delivery by drones is likely to be scaled up by Amazon, personal air transport vehicles will soon be flying in Dubai, and Airbus is developing prototypes of its ‘Citybus’.”
Less structure, higher density
Higher density can be achieved by having a completely unstructured airspace using what Hoekstra calls “free routing and decentralisation” techniques which spread high-volume traffic more evenly over the available space and reduce conflicts between aircraft. But would free routing still be feasible if traffic increases by, say, a thousand times compared to current levels?
Metropolis researchers tested this predicted volume increase in simulations of Paris’ airspace. They applied a branch of mathematics to define four conceptual models for structuring and managing airspace in urban areas. In general, and in increasing order of complexity, the models are described as:
- layers — according to altitude bands
- full mix — all vehicles share the same airspace, without any structure, while flying an optimal route
- tubes — airspace is segmented into a fixed, but dense, tubular route structure
- zones — segments of airspace are reserved for different types of vehicles, speed ranges and global direction
The project found that the less structured models such as ‘layers’ and ‘full mix’ did not result in a concentration of traffic — and the potential for routing conflict that could lead to a collision — as the more structured ones.
“Analysing the data, we believe the ‘layers’ concept strikes the best balance between efficiency (allowing direct lateral routing) and safety (reducing relative speeds and hence conflict rates),” notes Hoekstra.
Keeping a safe distance
The project carried out a total of 6.5 million simulated flights with different separation parameters. Three patterns were flown to simulate different traffic scenarios during the morning, lunch-time and in the evening.
To keep pace with such rapid change, the researchers have carried out further data analysis to come up with a solid mathematical description of the capacity of any airspace and under varying traffic loads and circumstances.
“Even with a partially complete picture of the airspace load and conditions, we can now estimate mathematically the capacity without having to run new simulations. As this works for both structured as well as unstructured scattered demand patterns, one of the first applications will be to determine the capacity of unmanned vehicle airspace concepts,” Hoekstra says.
Metropolis not only explored new models for air traffic management on the near horizon, it also contributed to a deeper, understanding of how to efficiently and safely expand airspace capacity. This understanding lays the foundation for the future, when unmanned and personal vehicles become technologically and economically feasible.