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 progression of a wake vortex avoidance system in flight tests. Using only weather information and navigation data from a preceding aircraft, the system is able to predict potentially dangerous wake vortices, determine possible conflicts and suggest avoidance manoeuvres.
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 suggested avoidance manoeuvres circumvented the wake vortices," explains project manager Tobias Bauer from the DLR Institute of Flight Systems. "We received accurate information from the Falcon in terms of position, speed and meteorological parameters, which the computer uses to calculate how the wake vortices move in the air." The interface with the pilot is a display that shows the position of the wake vortex and suggests an alternative flight path with minimal deviation.
Test case: scheduled flight
Software used to predict vortices 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 scheduled aircraft," explains Bauer. "Currently, these aircraft only transmit part of the required data to all surrounding aircraft, which means we had to make assumptions for wake vortex predictions." Data collected from operational scheduled air traffic therefore forms a valuable basis for further defining the system. 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's Flight Facility. "This was well-rehearsed with the Falcon, but with the scheduled aircraft, which were selected over a short term period, 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 extended 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 subside 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, with the current DLR Land-Based and Onboard Wake Systems (L-bows) project. Led by the DLR Institute of Flight Systems, the technology is being progressively developed, which predicts wake vortices along the flight path, assesses their impact, suggests suitable avoidance manoeuvres and automatically carries these out as required. The DLR Institute of Atmospheric Physics has produced 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 being advanced and technological testing further extended under operating conditions.
More information on DLR Portal: "Flying around wake vortices - new system tested in flight tests".