In this study the potential for fuel savings through electric taxiing is investigated. Therefore simple models are used to investigate the difference of fuel consumption during the ground phase and the flight phase of a gate-to-gate mission. By using these models the fuel savings can be estimated, which are the sum of the fuel saved during ground operations and the additional fuel required during the flight phase due to an increased Operating Empty Weight. The models are applied to actual data of flights conducted by domestic carriers within the United States National Airspace System. Results show that electric taxiing offers the potential for fuel savings depending on the flight mission, i.e. the ratio of time an aircraft spends on ground and the flight distance. A parametric analysis is conducted to investigate the sensitivity of the results for different constraints. The study concludes with a comparison of the concept compared to other operational or technological measures aiming to reduce fuel consumption on ground. NomenclatureATU = Autonomous Taxiing Unit APU = Auxiliary Power Unit BTS = Bureau of Transportation Statistics DOC = Direct Operating Costs ESUT = Engine Start Up Time ECDT = Engine Cool Down Time F Blockfuel = Fuel for a flight mission F Ground = Fuel for ground operations F Airborne = Tripfuel FF Idle = Fuel flow of the main engines in idle mode FF APU = Fuel flow of the APU FAA = Federal Aviation Administration FCOM = Flight Crew Operating Manual ICAO = International Civil Aviation Organisation ISA = International Standard Atmosphere n eng = Number of engines NAS = National Airspace System NO x = Nitrogene Oxide OEW = Operating Empty Weight t Ground = Ground Time t Taxi-in = Taxi-in Time t Taxi-out = Taxi-out Time

The current push in automation, communication, and electrical energy storage technologies has the potential to lift urban mobility into the sky. As several urban air mobility (UAM) concepts are conceivable, all relevant physical effects as well as mutual interrelations of the UAM system have to be addressed and evaluated at a sufficient level of fidelity before implementation. Therefore, a collaborative system of systems modeling approach for UAM is presented. To quickly identify physical effects and cross-disciplinary influences of UAM, a pool of low-fidelity physical analysis components is developed and integrated into the Remote Component Environment (RCE) workflow engine. This includes, i. a., the disciplines of demand forecast, trajectory, vertiport, and cost modeling as well as air traffic flow and capacity management. The definition and clarification of technical interfaces require intensive cooperation between specialists with different areas of expertise. To reduce this communication effort, the Common Parametric Aircraft Configuration Schema (CPACS) is adapted and used as central data exchange format. The UAM system module is initially applied for a 24-hour simulation of three generic networks in Hamburg City. After understanding the basic system-level behavior, higher level analysis components and feedback loops must be integrated in the UAM system module for evaluation and optimization of explicit operating concepts.

Various technologies and concepts have been developed recently in order to reduce fuel consumption and emissions of aircraft during taxi. In this study four innovative concepts are investigated regarding their potential fuel savings: electric taxiing, operational towing, single-engine taxiing, and minimization of taxi times through improved operations (e.g. by using planning tools). For this purpose models are introduced to estimate future development of taxi times, to forecast traffic growth and the associated fleet rollover, as well as to calculate fuel consumption during taxiing for the aforementioned concepts. By defining operational scenarios for each of the concepts, the potential of fuel savings is determined compared to a reference scenario. Results show that the potential benefit of the different approaches mainly depends on the respective airport and its future traffic development.

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Green liquid hydrogen (LH2) could play an essential role as a zero-carbon aircraft fuel to reach long-term sustainable aviation. Excluding challenges such as electrolysis, transportation and use of renewable energy in setting up hydrogen (H2) fuel infrastructure, this paper investigates the interface between refueling systems and aircraft, and the impacts on fuel distribution at the airport. Furthermore, it provides an overview of key technology design decisions for LH2 refueling procedures and their effects on the turnaround times as well as on aircraft design. Based on a comparison to Jet A-1 refueling, new LH2 refueling procedures are described and evaluated. Process steps under consideration are connecting/disconnecting, purging, chill-down, and refueling. The actual refueling flow of LH2 is limited to a simplified Reynolds term of v·d=2.35 m2/s. A mass flow rate of 20 kg/s is reached with an inner hose diameter of 152.4 mm. The previous and subsequent processes (without refueling) require 9 min with purging and 6 min without purging. For the assessment of impacts on LH2 aircraft operation, process changes on the level of ground support equipment are compared to current procedures with Jet A-1. The technical challenges at the airport for refueling trucks as well as pipeline systems and dispensers are presented. In addition to the technological solutions, explosion protection as applicable safety regulations are analyzed, and the overall refueling process is validated. The thermodynamic properties of LH2 as a real, compressible fluid are considered to derive implications for airport-side infrastructure. The advantages and disadvantages of a subcooled liquid are evaluated, and cost impacts are elaborated. Behind the airport storage tank, LH2 must be cooled to at least 19K to prevent two-phase phenomena and a mass flow reduction during distribution. Implications on LH2 aircraft design are investigated by understanding the thermodynamic properties, including calculation methods for the aircraft tank volume, and problems such as cavitation and two-phase flows. In conclusion, the work presented shows that LH2 refueling procedure is feasible, compliant with the applicable explosion protection standards and hence does not impact the turnaround procedure. A turnaround time comparison shows that refueling with LH2 in most cases takes less time than with Jet A-1. The turnaround at the airport can be performed by a fuel truck or a pipeline dispenser system without generating direct losses, i.e., venting to the atmosphere.