https://hdl.handle.net/20.500.12738/2 Publications with full text files / Publikationen mit Volltext(dateien) 2026-09-23T08:50:10Z https://hdl.handle.net/20.500.12738/20062 Title: NOx emissions from the 50 most used engines for passenger aircraft Authors: Scholz, Dieter; Hasanovic, Ahmed; Sarikaya, Muhammed Ali Abstract: Purpose - This study investigates NOx emissions from the 50 most used commercial jet aircraft engines. The primary aim is to derive regression models to estimate NOx emissions based on engine parameters. --- Methodology - The analysis begins by determining the 50 most used engine families in passenger aviation, based on the World Airliner Census 2020 and aircraft delivery data from the major commercial aircraft manufacturers. NOx emissions were obtained using the ICAO Engine Emissions Data bank (EEDB). Emissions were analyzed for different flight phases from the ICAO Landing and Take-Off (LTO) Cycle (taxi, take-off, climb, and approach) and for cruise. For the cruise phase NOx emissions were calculated a) with the Boeing Fuel Flow Method 2 (BFFM2) based on LTO NOx and cruise fuel flow and b) with a method developed by the German Aerospace Center (DLR). Non-linear regression analysis was applied to estimate NOx emissions based on one or two selected engine parameters. Separate models were developed for the full dataset and for 13 specific combustor technology subgroups. --- Findings - NOx emissions from aircraft contribute to local air pollution near airports and to global warming at cruise altitude. Legal limits for NOx emissions are defined for the total LTO emissions per thrust as a function of Overall Pressure Ratio (OPR), with stricter standards introduced since 2004. The 50 selected engine families represent around 95% of the global commercial jet fleet. NOx emissions from the BFFM2 and the DLR method agree well (R² = 0.99). The most predictive engine parameters are OPR, thrust and fuel flow, while Bypass Ratio (BPR) has limited influence. Engine design is a trade-off. Low fuel burn requires higher OPR, which increases NOx emissions. Some combustors can reduce NOx but may lead to more soot emissions, causing denser contrails with more global warming potential. Combustor-specific regression significantly improves prediction accuracy. A model incorporating all combustor types yields a coefficient of determination of only R² = 0.398 and a Mean Absolute Percentage Error (MAPE) of only 62.5%. In contrast, combustor-specific models are much better. E.g. a model for the Twin Annular Premixing Swirler (TAPS) II achieves R² = 0.788 and a MAPE of 12.7%. This underlines the necessity of considering combustor technology in NOx estimation. --- Research Limitations - In this study, regression analysis was limited to a maximum number of two input parameters. However, more parameters seem not to lead to a substantially higher accuracy. --- Practical Implications - The study provides equations for three NOx emission cases: total emissions during the LTO cycle, emission index at take-off, and emission index during cruise. For each of these three cases and for each of the 13 investigated combustor technologies, one equation is proposed based on one engine parameter and a second equation based on the best combination of two engine parameters. This leads overall to 78 equations. --- Social Implications - Easy to use equations make NOx emission from passenger jet aircraft more accessible to a wider community of people to discuss the implications of aviation as a means of transport. --- Originality - No other study seems to be available that offers such a simple way to predict NOx emissions form jet engines for aircraft design or aircraft operation while accounting for different combustor technologies. 2026-09-23T07:23:44Z https://hdl.handle.net/20.500.12738/20060 Title: Preliminary sizing and optimization of propeller aircraft (Part 23) Authors: Scholz, Dieter; Gmelin, Philipp Abstract: Purpose – Preliminary sizing and optimization of propeller aircraft certified under EASA CS-23 Amendment 6 or FAA FAR Part 23. Considering relevant certification constraints and typical propulsion concepts for small aircraft. Integration of the method into a user interface known already from other tools being part of Simple Aircraft Sizing and Optimization (SAS) and PreSTo-Classic at HAW Hamburg. --- Methodology – The tool uses the proven methodology based on the Matching Chart (power-to-mass versus wing loading), the Excel-Solver and Differential Evolution (DE). Conventional propulsion: Piston engines (Otto, Otto with Turbo Compressor, Diesel) and Turboprop engines are considered. Altitude-dependent power modelling for all engines, and extended propeller efficiency calculations for variable-pitch and fixed-pitch propellers are used. The resulting tool is evaluated with the redesign of a Cessna 172. --- Findings – The new optimization tool is "SAS-Part23-Prop". The existing SAS and PreSTo Excel environment known from FAA FAR Part 25 was adapted to ensure continuous user experience. The new tool reproduces the selected Cessna 172 reference parameters almost exactly. The redesign shows that consistent assumptions for propeller efficiency, rotational speed, field-length requirements, and validated statistical parameters are essential for obtaining plausible sizing results. In addition, a simple sizing tool "PreSTo-Classic-Part23-Prop" for use in the Aircraft Design lectures is available. --- Research Limitations – The results are limited by the simplified equations and statistical parameters used in preliminary sizing. Electric propulsion concepts are not yet included. The tool is intended for conceptual design and cannot replace detailed analysis in later design phases. --- Practical Implications – The tool provides a structured environment for students and designers to evaluate CS-23 propeller aircraft concepts, compare manual and solver-based sizing workflows, and investigate the influence of engine and propeller concepts together with matching power-to-mass and wing loading. Highly automated aircraft preliminary sizing and optimization for new and redesign is possible (SAS-Part23-Prop). Alternatively, a simple tool for hand calculations is offered (PreSTo-Classic-Part23-Prop). The tools are designed to give users a steep learning curve. --- Originality – A didactically enhanced design, redesign, and optimization tool (on preliminary sizing level) for small propeller driven aircraft is made openly available. It is especially suited for students and fills a perceived gap. 2026-09-23T06:40:27Z 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