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Under which scenario is Urban Air Mobility more sustainable than ground-based mobility? To answer this question, we provide a Life Cycle Assessment of three electric Vertical TakeOff and Landing concept aircraft, including a quantification of uncertainties in the concept's material composition. We conduct a Cradle-to-Gate analysis of the concepts and extend it by a Wellto-Shaft analysis of Urban Air Mobility operation, including all relevant upstream greenhouse gas emissions due to battery use, again including input uncertainties. As for aviation systems in general, we show that the impact of power demand in operation is most significant and exceeds emissions from production by orders of magnitude. We thus provide sensitivity analyses of the results for each of the most influential quantities. We report an optimum flight speed for minimum greenhouse gas emissions and a quantification of the impact of hover flight. Finally, we compare and quantify the impact's sensitivities on influential factors like the region of operation, and mission design within reasonable ranges. From the sensitivity analyses, we conclude that only very lightweight vehicles for Urban Air Mobility can be more sustainable than traditional, fossil-fueled ground-based transportation, given a maximum seat utilization, clean power grid, low hover share and an effective reduction in travel distance. We further conclude that, with a combination of the most optimistic assumptions, Urban Air Mobility concepts may environmentally compete with battery-powered cars.

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This publication shows advantages and possible applications for variable transmission drivetrains within rotorcraft. The power requirement of a generic helicopter with constant and variable rotor speed was calculated. Various drive train technologies that support a variable transmission were described. The prospects of this technology, its influence on the dynamic behaviour of a rotor and further areas that need to be investigated extensively are presented. This technology is applicable to some rotorcraft architecture. Requests from the rotorcraft industry underline the necessity for future rotorcraft using variable rotational speeds. However, the A160 or the EC145 and Mi-8 already show the potential of this technique. Reduction of required power of the rotor should be possible and also an extension of the flight envelope towards higher flight speeds, higher altitudes, better manoeuvrability, etc. By using a variable transmission gearbox, turbine and auxiliary units can still be driven at their design point, independent of the current rotor speed. Excessive loads may occur when discrete speed transmission are used. Frictional or fluid transmissions with continuous variable ratio may fail due to overheating. Other continuous concepts are favoured. The design of a variable speed rotor focuses specifically on its dynamic behaviours and on structural and geometrical optimisation to avoid operation at rotational speed resonance frequencies. Morphing structures may support this. Some rotorcraft architectures can benefit from a variable speed rotor technology. It probably will increase efficiency, decrease noise levels, fuel consumption and CO 2 production, and the flight envelope may be extended.

Turbine blade dampers are small elements of a parabolic configuration usually fabricated from sheet steel. They are positioned loosely between the roots of turbine blades improving the damping of blade vibrations by generating dry friction from the relative motion of blades and damper. This paper presents a theoretical approach to these stick-slip vibrations and compares theory with measurements. Additionally, some design aspects of such dampers are discussed by considering the damping behaviour in relation to important design parameters.