The joint research flights being conducted by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and the US National Aeronautics and Space Administration (NASA) are now half complete. Today, on 24 January 2018, the fourth of eight planned joint flights took off from Ramstein Air Basein Rhineland-Palatinate, Germany. The measurement flights are predominantly taking place in restricted airspace over Mecklenburg-Vorpommern. "DLR and NASA have combined their research resources, aircraft and measuring instruments to study the potential of alternative fuels for environment-friendly aviation and their impact on the atmosphere in more detail," says the DLR Executive Board Member responsible for aeronautics research, Rolf Henke. The international team of researchers conducted previous joint research flights on 17, 19 and 23 January.
"We have successfully collected emission and contrail data for the DLR A320 ATRA, which initially used conventional Jet A-1 kerosene fuel and then switched to a blend of kerosene and biofuel, flying under contrail-forming and non-contrail-forming conditions," says Hans Schlager of the DLR Institute of Atmospheric Physics. "In addition, we managed to collect measurement data relating to the properties of cirrus clouds on the transit flight from California to Germany," adds NASA scientist Bruce Anderson.
Climate impact research issue
One key question for the research flights, which will continue until early February, is whether it can be shown that the lower soot emissions produced by the use of alternative aircraft fuels has an impact on the ice particles in contrails, thus resulting in a lower warming effect on the climate due to long-lasting contrails. “We are also interested in finding out whether, with a targeted fuel design, a markedly more economical addition of 30 per cent biofuel will generate a similarly low level of soot emissions as a 50 per cent mixture with conventional Jet A-1 kerosene," explains Patrick Le Clercq of the DLR Institute of Combustion Technology. "We are building on the results of the ECLIF I campaign, in which two DLR aircraft, the A320 ATRA and the Falcon, were deployed in 2015 and also assisted NASA with the ground measurements."
For the ND-MAX / ECLIF 2 (NASA / DLR-Multidisciplinary Airborne eXperiments / Emission and CLimate Impact of Alternative Fuel) measurement flights, DLR’s A320 ATRA and NASA's 'flying laboratory' take off with a total of 14 measuring instruments on board, of which around half have been provided by DLR. DLR’s A320 flies in front, using an alternative fuel, while the NASA DC-8 flies a few kilometres behind and 'sniffs' the exhaust. The emissions generated by two mixtures of alternative fuels are measured at different altitudes and flight speeds, along with the resulting contrails and contrail cirrus clouds.
Flight test sequence
Each joint research flight takes off in the morning from Ramstein Air Base. "The NASA DC-8 and DLR Airbus fly some distance into an airspace reserved for flight tests," explains DLR test pilot Stefan Seydel. "So far, this has been an airspace over Mecklenburg-Vorpommern." Once there, the two aircraft fly up to 15 circuits per flight, following one another. "After a straight flight path, where we fly in the contrails of the A320, we perform a 180-degree turn, then we dive with the DC-8 onto another straight path, flying in the exhaust streams and contrails, before the next 180-degree turn," says NASA test pilot Wayne Ringelberg, describing the exercise. "We generally fly these measurement circuits for four to five hours before embarking on the return flight to Ramstein."
The NASA DC-8 lands in Ramstein shortly after the DLR A320. Final exhaust gas measurements are taken on the taxiway, before the aircraft taxi to the hangar. In addition, the researchers carry out separate static tests in which the exhaust gases of the DLR A320 ATRA are studied using ground-based measuring instruments. The researchers expect to have the results of the studies in the next few months.
The cooperation between DLR and NASA has a long-standing tradition. Having been active in the field of spaceflight for a long time, DLR has been able to establish very good relationships with NASA in aeronautics in recent years. "DLR and NASA co-founded IFAR, a forum that connects 26 aeronautics research centres worldwide. In addition, projects with NASA have been initiated via existing bilateral cooperation agreements between individual DLR institutes," says Henke. "One example is the DLR-NASA Design Challenge, a competition that runs simultaneously and with the same specifications at German and US universities and is currently entering its second round." Both partners are particularly involved in aviation research, in joint research projects in the areas of aeronautics, air traffic management and low-noise and low-emission flying.