When aircraft are in flight, vortices are generated behind them from the wing tips. These are known as wake vortices, and they can have safety implications for following air traffic. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has now tested the improvement of a wake vortex avoidance system in flight tests. Using only weather information and navigation data from the preceding aircraft, the system is able to predict potentially dangerous wake vortices, determine possible conflicts and propose avoidance manoeuvres.
Depiction of invisible vortices on the display
DLR's research aircraft A320 ATRA (Advanced Technology Research Aircraft) was involved in a total of five test flights in November and December 2016 to test the new avoidance system. "With the assistance of DLR's Falcon research aircraft flying at the same time, we initially tested how accurately the proposed avoidance manoeuvres circumvented the wake vortices," explains project manager Tobias Bauer from the DLR Institute of Flight Systems. "From the Falcon we received accurate information on position, speed and meteorological parameters, which the computer uses to calculate how the wake vortices evolve and move in the air." The interface with the pilot is a display that shows the position of the wake vortex and proposes an alternative flight path with minimal deviation.
Test case: scheduled flight
The vortex prediction software, developed at the DLR Institute of Atmospheric Physics, takes into account wind, temperature distribution and turbulence to calculate how wake vortices behave behind the aircraft. The less the local weather data available for this, the more difficult the calculation. "In four of the five test flights, we headed directly for the wake vortices from airliners," explains Bauer. "Currently, these aircraft only transmit part of the required data to -surrounding aircraft, forcing us to make assumptions for wake vortex predictions." Data collected from operational scheduled air traffic therefore forms a valuable basis for further system definition. Tests using the Falcon have already shown that the chosen approach delivers high-quality vortex predictions and improves the pilots' situational awareness.
"The test flights required precise coordination with the aircraft ahead," says DLR test pilot Jens Heider from DLR Flight Operations (FB). "This was well-rehearsed with the Falcon, but with the scheduled aircraft, which were selected ad hoc, we relied on the cooperation of the pilots from a number of airlines as well as the air traffic controllers, which fortunately worked very well." The avoidance manoeuvres were carried out in the airspace above north-east Germany. The research aircraft took off and landed at the DLR site in Braunschweig.
Swirling vortex at the wing tips
Wake vortices, also known as wake turbulence or wing tip vortices, are counter-rotating vortices of air behind flying aircraft. Their level of intensity depends on the size and weight of the aircraft. Particularly strong wake vortices are therefore generated by large aircraft such as the Airbus A380 or Boeing 747. Smaller aircraft must maintain an increased safety distance of up to 15 kilometres behind these giants of the skies. The lifespan of wake vortices is affected by wind conditions, turbulence and temperature stratification in the atmosphere. The vortices normally slowly descend before dissipating. Wake vortices are caused by the aerodynamics of the wing tips. Here, air from below the wing is drawn around the wingtip into the region above the wing by the lower pressure above the wing, causing a vortex to trail from each wingtip.
On-board warning and avoidance system for wake vortices
DLR scientists have been working on the basic functionalities of the DLR warning and avoidance system for wake vortices, known as WEAA (Wake Encounter Avoidance & Advisory System) since 2012. Their work has been spread across various projects including the current DLR project Land-Based and Onboard Wake Systems (L-bows). Led by the DLR Institute of Flight Systems, the technology is being progressively developed to predict wake vortices along the flight path, assess their impact, provide suitable avoidance manoeuvres and automatically carry these out as required. The DLR Institute of Atmospheric Physics has developed the software to acquire weather data from various sources and to predict wake vortices; part of the work has been carried out on behalf of Airbus. A follow-up project will see the suitability of the individual modules for daily use being advanced and technological testing further extended under operating conditions.