https://hdl.handle.net/20.500.12738/2 Publications with full text files / Publikationen mit Volltext(dateien) 2026-09-21T07:31:24Z https://hdl.handle.net/20.500.12738/20039 Title: Determining recorder distances from multicopters to avoid bat disturbance Authors: Huamán Roswag, Marc; Fietz, Joanna; Roswag, Anna; Kunz, Veit Dominik; Taefi, Tessa T. Abstract: Introduction: This study examines the impact of two multicopters, differing in size and weight (ConVecDro hexacopter, DJI Mavic 2 Pro quadcopter), on the activity of bats assigned to three distinct echolocation groups. The objective was to define thresholds (in decibels) below which bat echolocation groups show weak or no impact on activity. Using the known noise profile of the multicopter and a model of sound attenuation in air, these thresholds were then used to determine optimal recording device placement distances by estimating frequency-specific sound levels at increasing recording distances. Directional properties of the recording device were also considered. Methods: Bat activity was recorded at distances 10.0 m, 12.2 m, 14.8 m, 17.4 m and 20 m, with the recording device oriented towards and away from the multicopter. We analyzed the effects of noise emissions from the multicopters in relation to the distance between the recording device and the multicopter to identify their influence on the recorded bat activity. Results: The study shows the differences in recorded bat activity between two multicopters with different noise profiles. The larger and heavier ConVecDro produced louder, and potentially more deterrent noise emissions, for Pipistrelloid and particularly for Nyctaloid groups. In contrast, the DJI Mavic 2 Pro had a weaker deterrent effect on bat activity, and only the Nyctaloid groups were affected. Based on our observations of both multicopters, the threshold value below which no echolocation group showed any detectable impact was 4.5 dB at 23 kHz. In our setup, where the recording device was oriented towards the multicopter, it should be placed at 20 m for the DJI Mavic 2 Pro and at 36.0 m for the ConVecDro. Discussion: The findings indicate that multicopter noise exerts a significant influence on bat activity, with the magnitude of the impact varying depending on the echolocation group and the specific characteristics of the multicopter noise profile. The ability to define noise threshold values for the different echolocation groups suggests that beyond a certain point, multicopter noise has no discernible effect on bat activity levels compared to a control group. 2026-09-18T10:21:04Z https://hdl.handle.net/20.500.12738/20040 Title: Aircraft cabin air contamination events : an engineering view Authors: Scholz, Dieter Abstract: Air conditioning in aviation means temperature control, pressure control and ventilation. The cabin is vented with a certain percentage (e.g. 50%) of fresh outside air. The remaining part of the air for cabin ventilation is provided as air from the cabin, filtered and recirculated back into the cabin. At cruise altitude, ambient pressure is below cabin pressure. Hence, the outside air needs to be compressed before it is delivered into the cabin. The air is compressed in the engine compressor and tapped off as "bleed air" at temperatures reaching 400 °C or more. Hence, bleed air cooling is necessary. The engine shaft is supported by lubricated bearings. They are sealed against the air in the compressor usually with labyrinth seals. It is explained why jet engine seals leak oil by design in small quantities. The amount of oil leakage can be estimated with a new equation. The estimate shows the same order of magnitude as measured in flight (Cranfield study, EASA study). The oil leaking into the compressor contains problematic additives which get pyrolized (burned) at the elevated temperatures in the compressor, leaving more than 100 substances behind, some of them hazardous and some known as Volatile Organic Compounds (VOC). An alternative source for the compressed air is the Auxiliary Power Unit (APU). Like the aircraft's jet engine, it is a gas turbine, built much in the same way when it comes to bearings and seals. For this reason, also compressed air from the APU is potentially contaminated. Engineering standards from SAE contain guidance about sound engineering design principles for air conditioning systems of airplanes. Also, certification standards give some guidance, however, more general. In essence, bleed air systems as we see them on today's passenger jet aircraft should not be built the way they are. For immediate action, hints are given: In case of smoke in the cockpit pilots should read the carbon monoxide (CO) concentration from a personal CO detector as an objective indicator in addition to their human senses. The present CO concentration should be compared with values obtained under normal conditions. If pilots are alerted and it is suitable (fuel reserves, terrain clearance), pilots should consider to descend to 10000 ft, reduce speed and ventilate the aircraft by means of the ram air inlet. This is the only source of fresh air in flight, independent of engines or APU. If smoke is present, checklists tell pilots to put on their oxygen mask. Cabin crew should consider wearing a personal breathing mask in such cases. Technically the easiest way to install carbon filters to filter VOCs in existing aircraft is in the recirculation path, where HEPA filters are already in use. Unfortunately, the physics are such that filters in the recirculation path cannot remove substances fully. It is only possible to reduce the concentration down to a value depending on filtration rate and recirculation rate. With typical values the incoming VOC concentration can be reduced to about 60%. In case of full filtration (including ducts from the bleed air sources) incoming VOC concentration can be reduced to about 18%. Aircraft from the beginning of the jet age (B707, DC-8) used turbocompressors keeping bleed air and outside air compressed for cabin ventilation separate. Based on past experience, turbocompressors cannot be considered a solution for future aircraft. A final solution to the problem of contaminated cabin air is seen in electric (bleed free) cabin air supply architectures. Here, outside air for cabin ventilation is compressed separately in dedicated clean compressors. Bleed free cabin air architectures have the additional advantage of much improved fuel economy. So far, the Boeing 787 is the only passenger aircraft in service with a bleed free cabin air architecture. Airbus could follow with related technology already available and checked in test flights. 2026-09-16T13:03:25Z https://hdl.handle.net/20.500.12738/20048 Title: Themenkongress Mobilität 2026 2026-09-16T11:53:03Z https://hdl.handle.net/20.500.12738/20027 Title: Umweltsimulationsprüfstand als Multi-Exciter zur gezielten Strukturverformung der Traktionsbatterien Authors: Hein, Eugen; Plaumann, Benedikt 2026-09-14T14:45:47Z