Before being certified for use, aircraft must undergo a standard test to assess their tolerance to bird strikes. In the case of drones, however, there are no such regulations. In the interests of safety, researchers at Germany’s Fraunhofer Institute for High Speed Dynamics would like to see the rules changed 

The rise in popularity of drones worldwide has brought an increasing number of reports of near misses with commercial aircraft. In 2018, German aviation authorities reported 158 cases of drones being sighted in the vicinity of the country’s airports and, in May this year, flight operations at Frankfurt Airport were shut down for a short period following the presence of a drone.

The total number of drones in private and commercial use in Germany is forecast to rise to 847 000 by 2030 – an increase of almost 80 percent. Drones endanger not only aircraft coming into land, but also low-flying helicopters. Pilots are said to live in fear of a drone strike, and safety experts warn that a collision with a drone would cause more damage to an aircraft than the impact of a bird strike.

Before being certified for use, aircraft must undergo a standard test to assess their tolerance to bird strikes. In the case of drones, however, there are no such regulations. Researchers from the Fraunhofer Institute for High-Speed Dynamics in Germany are keen to see aviation rules changed.

“From a mechanical point of view, drones behave differently to birds and also weigh considerably more,” explains Sebastian Schopferer, one of the scientists working on the project. “It is uncertain whether an aircraft that has been successfully tested against a bird strike would also survive a collision with a drone.”

Fragments of a drone battery following impact with an aluminium plate on a test bench

In order to fundamentally understand the consequences of a collision between an aircraft and a drone, the Fraunhofer Institute is planning to build a test bench to simulate a variety of impacts. Initial tests using drone batteries and motors have confirmed the danger.

“Using compressed air, we accelerated these two components to speeds ranging from 115 to 255 metres per second and fired them at aluminium plates up to eight-millimetres thick that were mounted in a test bench,” Schopferer says. “Given their weight, both battery and motor caused major damage including substantial deformation and indentation of the plates. In the process, the battery and engine were completely destroyed.”

The outcome of the tests was recorded using a high-speed video camera with a view to determining the transfer of momentum at the instant of impact and to investigate associated damage to aircraft materials such as aluminium alloys and fibre composites. In parallel to the dynamic research, specialists also conducted a number of quasi-static pressure tests in order to determine the strength and rigidity of drone components.

These results will play an essential role in the derivation of numerically efficient, predictive simulation models that the aviation industry can then use to ascertain new and important findings about the impact behaviour of drones. Using such models during the design phase, it will be possible to assess the resistance of new aircraft components to the impact of a drone.

In order to simulate realistic impact scenarios, researchers are now planning to construct a new type of test bench for investigating the impact of complete drones with a maximum weight of three kilogrammes and flying at speeds of up to 150 metres per second.

“We will be able to investigate the impact and fragmentation of complete drones during collision with both rigid and flexible targets and thereby study the effects of a drone strike on an aircraft,” Schopferer explains. “Tests in this weight class of drone have never been carried out before.”

The tests will be conducted with a variety of drones, including both amateur and semi-professional models, weighing between one and three kilogrammes. In addition to aircraft manufacturers, these investigations will also benefit aviation authorities, providing them with important information for a more in-depth assessment of the danger to aircraft posed by drones.

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