The present study investigates the deformation of propeller blades in the presence of a wing, specifically analysing the lift-induced upwash effects through experimental measurements conducted in a wind tun- nel. The objective is to quantify the impact of non-uniform inflow on blade bending, with a particular focus on the aerodynamic interactions between the rotor and the wing. Image Pattern Correlation Tech- nique (IPCT) was employed to measure blade deformation, leveraging high-resolution optical methods to capture structural response under varying flight conditions. The experimental campaign was conducted at the Large Low-speed Facility (LLF) of the German- Dutch Wind Tunnels (DNW), a closed-circuit wind tunnel with an open test section measuring 6 × 8 m. The facility provides high flow uniformity, low turbulence levels, and a Mach number range up to 0.2, allowing for detailed aerodynamic and structural measurements. A range of rotor pitch angles and operating conditions were tested to assess how blade deformation varies with changes in aerodynamic loading. Preparatory work was done at DLR in Göttingen to test all the necessary assumptions. Results indicate that inflow incidence angle (αC) corrections, which account for the effective angle of attack due to the lift-induced upwash at the rotor, effectively account for deformation effects, includ- ing in swept-wing configurations. The propwash was found to significantly influence the wing lift and consequently the induced upwash and angle of attack at the rotor. The location of maximum bending, defined as the displacement normal to the plane defined by the rotor span and its root chordline, was verified for both the wing-on and wing-off cases, with the wing sweep being directly responsible for an increase in mean bending and a clockwise rotation in the deformation distribution. Furthermore, mea- surements revealed that the upgoing blade, closer to the wing leading edge, exhibited larger deviations between clean and wing-on setups due to both the rotation of the deformation distribution and to the increase in deformation which were not accounted for by the lift-induced α correction computed for the rotor centre. The effect of the component of lift-induced upwash field due to the wing sweep resulted in a 10% increase in mean bending at the worst case scenario of high angle of attack and advance ratio. These results highlight the importance of wing-rotor integration for aerodynamic efficiency and struc- tural resilience, particularly in higher disk loading configurations, such as open-rotor designs. The find- ings suggest that wing sweep and propwash interactions, identified as the main cause of the non-uniform inflow component, strongly influence blade deformation and could be relevant for future propulsion sys- tem designs. This has implications not only for structural analysis, as the rotor is more stressed, but also for aerodynamics, as the measured displacement can affect the twist distribution. Strain gauges were considered a complementary method to digital image correlation, offering data to correlate IPCT measurements across the rotor disk and reconstruct deformation fields in occluded areas. Furthermore, linking in-plane loads from the RSB with rotor disk deformation could improve the understanding of blade behaviour. The study also underscores the feasibility of using optical measurement techniques for partially occluded stator blades, provided that phase-dependent rotor wake effects on deformation remain negligible. In the investigated configuration with steel stator blades, deformation appeared negligible, falling within the measurement accuracy range. Future work should focus on integrating strain gauge data with IPCT to improve measurement coverage, exploring correlations between vibrational modes and blade deformation. These advancements would refine predictive aerodynamic models, provide insight into rotor-wing interactions and contribute to the development of more efficient propulsion systems for next-generation aircraft

In recent years, the civil aviation sector has increasingly focused on optimizing propulsion designs to improve efficiency and reduce CO₂ emissions. Propellers have regained attention for their superior efficiency, particularly in applications like full-electric aircraft, though high noise emissions remain a significant challenge. This thesis investigates the aerodynamic and acoustic performance of a Boundary Layer Ingesting (BLI) propeller installed at the end of the fuselage of a transport plane, behind the vertical tail. The study focuses on the impact of unsteady blade loading on performance and explores whether increasing blade count or modifying blade sweep can mitigate drawbacks in a BLI configuration.
The development of numerical tools was the first step in this investigation. The aerodynamic tool, an enhanced Unsteady Non-Linear Vortex Lattice Method, accounts for viscosity and flow separation, while the acoustic solver uses Hanson's Helicoidal Surface Theory to model noise emissions from propellers in both isolated and installed conditions. Simulations were conducted on a modified 6-bladed XPROP-S. The velocity profiles at the propeller disk, used as inflow for the installed BLI analysis, were taken from CFD results of the fuselage with the vertical tail installed.
The complex inflow field led to periodic increases in blade loading, especially behind the vertical tail, causing oscillations in thrust and power. Increasing the blade count from two to six resulted in steadier performance and reduced force oscillations. In the installed configuration, the propellers exhibited a thrust-to-power ratio increase of 2% to 5%, with in-plane forces scaling with thrust and remaining within 3% of it. Noise emissions rose significantly after installation, with peak emissions shifting from the rotational plane to the propeller axis, where unsteady loading noise sources became more prominent. The noise level increase reached up to 46 dB during cruise for the 6-bladed baseline. While increasing the blade count reduced noise levels in isolated conditions due to lower propagation efficiency of steady loading noise, in installed conditions, unsteady loading noise sources counterbalanced this, leading to overall increased noise. Maximum noise emissions ranged from 32 dB (isolated, six blades) to 78 dB (installed, six blades). Sweeping the baseline blade backward at the tip and forward near the hub increased loading and thrust by up to 20%, particularly at the tips. In installed conditions, backward sweep reduced overall blade loading changes, while forward sweep increased them. Noise levels varied, with isolated conditions showing a slight increase and installed conditions experiencing up to a 4.7 dB reduction with backward sweep.
The analysis underscores the importance of accounting for unsteady blade loading and how the dominance of unsteady loading noise sources is influenced by loading oscillation amplitude, propeller geometry, and operating conditions.

An unintended yaw is a persistent accident characterised by an unexpected helicopter rotation around the yaw axis without the pilot’s intention and any technical malfunctions. Unintended yaw accidents are one of the top operational causes of helicopter accidents, causing serious damages and fatalities each year. This thesis in collaboration with Airbus Helicopters and the FAA does a numerical investigation of unintended yaw to provide a characterisation of the phenomena for different helicopter configurations with an open tail rotor and find an optimal recovery method. The simulations include trimmed flights and time domain flights to assess the yaw trim capabilities of the helicopter. Specific attention is placed on the tail rotor aerodynamics and demands. An uncontrollable unintended yaw did not appear for any of the evaluated flight cases and helicopter configurations, showing that the pilot always could trim the helicopter with sufficient pedal margin. In case of unintended yaw, applying immediate and maximum opposite pedal to the rotation of the helicopter could always recover the yaw rate to zero.

The effect of excluding the nacelle in tip-mounted propeller research can be modelled with Computational Fluid Dynamics (CFD) to quantify this effect on the wing performance and flow measurements. For this, the performance parameters of the wing in terms of lift and drag are analysed. Also, swirl angle and total pressure in the wake is investigated to understand the vortex behaviour. This is all done for a configuration set without a propeller, and also with a propeller installed in the form of a disk model.

Propeller-based propulsion technology is experiencing renewed interest owing to its superior propulsive efficiency in comparison to conventional jet engines. This phenomenon is attributed to the capacity to generate thrust by accelerating a significant volume of air through a small velocity differential. Additionally, owing to its compatibility with electrical power systems, propeller-based propulsion offers an opportunity to utilize more environmentally friendly energy sources and configurations like the distributed propulsion systems. To optimize the integration between the propeller-based propulsion system and the airframe, it is imperative to thoroughly understand the interactive aerodynamics of the propeller-wing system.

This thesis presents a comprehensive study on the aerodynamics of propeller-wing interactions, with a specific focus on leading-edge distributed propeller configurations.
The research was conducted through a comparative analysis, employing a single propeller-wing system, modeled based on the ATR 42/300 as the baseline. This involved comparing a conventional single tractor propeller configuration with a three-propeller leading edge distributed configuration. The methodology used is an unsteady panel method
solver, FlightStream, which is a commercially available software, allowing for an in-depth
examination of the two-way interactions between the propeller and wing (Full interaction mode), and allowing for a force-free wake.

The findings of the study highlighted significant aerodynamic benefits of the leading-edge distributed propeller configuration over the traditional single propeller setup. Notably, there was a 2.5% increase in wing efficiency and a 6.1% reduction in induced drag. Additionally, the propeller efficiency in the distributed system saw a 3% increase compared to the single propeller system. However, it’s crucial to note that these propellers operated at different, non-optimal points, which influences their comparative performance. A key result was the reduced power consumption of the three-propeller system, which required 8.1% less power to maintain steady level-flight conditions than the baseline single-propeller model. This finding suggests potential for increased efficiency in aircraft designs incorporating such configurations.

Ammonia shows great potential for decarbonizing the road transportation sector because it does not produce CO₂ emissions during combustion. On the other hand, ammonia-fueled engines emit gases such as (unburned) ammonia (NH₃), and nitrogen oxides (NO)_x, which contribute to air pollution and adversely impact human health, among other environmental effects. The aim of this work is to investigate the air quality impacts and human health trade-offs associated with potential emissions from an ammonia-fueled road transportation fleet of different vehicle categories. Specifically, we create a simplified emissions tool to quantify the NH₃ and NO_x spatial emissions from state-of-the-art ammonia engine developments. Next, the emissions are combined with spatial sensitivities, obtained from the adjoint of GEOS-Chem, to estimate the corresponding air quality impacts in terms of PM_2.5 formation and human health impacts with respect to premature mortalities.
The research findings indicate that the ammonia-fueled sector generally exhibits higher air quality and human health impacts compared to conventional transport. We estimate that the implementation of various ammonia engine configurations into the road transportation fleet in the USA in 2011 could lead to approximately 23 000 to 250 000 premature mortalities.
However, there is potential for mitigating air quality impacts of ammonia emissions through the use of post-combustion treatment methods or the adoption of ammonia-fueled heavy-duty vehicles. These approaches could help achieve air pollution levels comparable to those of fossil fuel vehicles while reducing the carbon footprint, offering future possibilities for an ammonia-fueled road transportation sector.

In recent years, there has been renewed interest in propeller research due to environmental concerns. Propellers are known for their low-speed efficiency and compatibility with electric motors. The utilization of regenerative energy during deceleration has been demonstrated to be beneficial for automobiles and has the potential to be applied to propeller-driven aircraft. This technology allows for the recharging of batteries and could increase the overall efficiency of the propulsion system by utilizing the regenerated energy in other flight maneuvers. The negative thrust mode of propellers has several additional advantages, including weight reduction, improved safety, and increased maneuverability. However, when operated in reverse thrust conditions, the performance of conventional propellers is suboptimal because they are designed for forward thrust. This suboptimal operation can lead to boundary layer separation on the blades, increasing broadband noise and potentially making it more dominant over tonal noise. To assess the relative importance between an isolated propeller's tonal and broadband noise sources under positive and negative thrust conditions, an experimental study was conducted using a scaled propeller setup in a low-turbulence wind tunnel (LTT). Aeroacoustic measurements were taken using a microphone array with 63 microphones placed in the floor and wall of the test section. The advance ratio was varied across different wind speeds at Reynolds numbers ranging from Re_c^0.7R = 0.8·10⁵ to Re_c^0.7R = 1.9·10⁵. Signal processing methods were used to analyze the data and quantify tonal and broadband noise sources, including fast Fourier transformation (FFT), phase averaging, beamforming, and blade element momentum (BEM) analysis. The results showed that the broadband noise component of the propeller significantly increased in negative thrust mode compared to positive thrust mode due to fully separated boundary layers. The tonal propeller components were often masked by interference from wind tunnel and motor noise, suggesting the need for further research to validate propellers in regenerative mode.

From the desire to reduce the impact of traveling on the environment and the increase in fuel prices over the past years, the propeller has regained interest as a propulsion mechanism in the aviation industry. Two main reasons can be found in their high propulsive efficiency and ability to combine with electric motors. The scaling of the motors is rather insensitive to the efficiency, allowing the propeller to be placed around the aircraft, resulting in new design freedoms.

The influence of the propeller slipstream can increase the aerodynamic performance of a propeller-wing system. Propellers with inboard-up rotational configuration are found to reduce the induced drag of the wing in propeller-wing systems compared to isolated wings. To increase the aerodynamic performance of propeller-wing systems and certify design choices, a detailed understanding of the relative contribution of the lift-induced drag and swirl recovery to the induced drag of propeller-wing systems is desired. A low-order numerical model has been used for a parametric study on propeller-wing systems. From the results follow that the gradient of the spanwise wing lift distribution is of influence on the amount of net swirl recovery that the wing can obtain. It is shown that when a propeller is placed in front of a wing section where the gradient of the isolated spanwise wing lift distribution is positive from root to tip, more swirl recovery can be obtained by the inboard-down rotating configuration. In this case, the difference in lift between the wing sections behind the two propeller sides is increased. The increase of the difference in the lift also increases the lift-induced drag of the wing. With low disk loadings, the contribution of the swirl recovery is found to be higher than the increase in lift-induced drag. Increasing the disk loading results in more significant differences in lift between the wing sections behind the propeller sides, such that the gradient of the spanwise wing lift distribution increases. From this increase, the contribution of the lift-induced drag can become more significant than the contribution of the swirl recovery of the wing, increasing the induced drag of the system.

The angular momentum or swirl in the propeller slipstream is an energy loss. An effective method to recover the swirl and increase the propulsive efficiency is to use Swirl Recovery Vanes (SRVs). Former research showed an over-prediction in SRV thrust by a lifting line theory (LLT) model compared to wind tunnel experiments. The LLT model assumes an unbounded flow field from minus infinity to plus infinity, while in reality the SRV flow field is bounded due to a small axial spacing between the SRVs and the propeller plane. Using a 2D correction method, based on the application of the Kutta–Joukowski theorem in an axially confined domain combined with the thin airfoil approximation, a correction in the angle of attack can be computed for each blade element of the SRV. The LLT model including the correction method could match the SRV thrust of the experiments. Additionally, the original LLT thrust prediction was met with a corrected pitch angle of the SRVS. An SRV in off-design conditions would result in different correction angles. For a smaller thrust setting of the propeller, the thrust of the SRV will also be lower, hence the correction angle will be smaller. To make the correction method also applicable in off-design conditions, a fixed correction angle would be more practical since the whole vane can be rotated with a variable pitch to match the appropriate correction angle for the corresponding thrust setting. The fixed correction angle was determined by taking an average of all correction angles along the blade radius and the thrust prediction showed good agreement, with a negligible thrust loss of the SRV compared to correcting the pitch angle for each blade element separately. Finally, in the airfoil profile optimization, it was found that the profile drag of the profile is of less influence on the SRV thrust, hence more design freedom can be used to select the appropriate airfoil profile for the SRV.

This thesis investigates the aerodynamics of a propeller-wing-flap system, spurred by the growing interest in propeller-driven aircraft and the potential introduction of distributed electric propulsion. The research focuses on the complex flowfield involving the interaction of the propeller slipstream with the main wing and flap at high-lift conditions. Using unsteady RANS simulations at a chord based Reynolds number of 2 million, the study explores the impact of a propeller slipstream on flap time-dependent boundary layer variations. The computational results are validated against experimental data, showing good agreement. The analysis reveals intricate details of the flow field, including propeller slipstream shifts and complex vortex systems contributing to flap stall mechanics. The study highlights the influence of these phenomena on the spanwise lift distribution and flap flow separation areas. The findings contribute valuable insights into the understanding of propeller-wing-flap interactions, yet emphasizing the need for further research to confirm and expand upon the current discoveries.

The ever-growing aerospace industry's urgent need to reduce greenhouse gas emissions has ignited a surge of interest in hybrid or fully electric propulsion systems. The electrification of aircraft introduces the possibility for energy to be recovered during phases of flight where no power input is required, and previous research has demonstrated the potential for small energy balance enhancements using dual role propellers. The design and operation of dual-role propellers involves considering two opposing load cases: positive thrust and torque during propulsive operation, and negative thrust and torque in regenerative operation. Thus, the ideal blade shape for maximizing performance in each opposing operating condition will be very different. Structural tailoring of the composite blades may be an effective approach for reducing energy consumption during operation in both regimes. Accordingly, the primary objective of this research is to determine the extent of dual-role propeller performance improvements that may be obtained through the application of aeroelastic tailoring. Sensitivity studies were conducted to convey an understanding of how dual-role propeller performance is affected through variations in structural designs (ply orientations and thicknesses). Optimization studies were subsequently performed to identify the extent of performance enhancements yielded solely through aeroelastic tailoring for flexible constant- and variable-pitch propellers of fixed geometry, assuming installation on a reference aircraft, and evaluated over multiple cruise distances for a climb-cruise-descent mission.

The thesis objectives were achieved through the development and application of an aeroelastic analysis and optimization framework. Blade element momentum (BEM) theory was used for the aerodynamic model with engineering corrections for compressibility, effects of rotation, root- and tip-losses, and the turbulent wake state. Excellent agreement was obtained from comparisons with a previous BEM code, and reasonable agreement in performance trends was observed through comparisons with experimental data during verification and validation. A modified version of PROTEUS, an aeroelastic tailoring code that was developed at the TU Delft, was used for the structural model. The aerodynamic analysis routine of PROTEUS was modified to instead use the developed BEM code for the evaluation of loads, sensitivities, and performance. The structural model of PROTEUS was modified to feature centrifugal forces and different input structures that are more conducive to the analysis of rotor blades. The structural model implemented during this project accounts for geometric nonlinearities, as well as nonlinear loads through the application of a corotational framework, and it is capable of accurately representing the detailed 3D blade as a reduced-order Timoshenko beam element mesh through its use of a cross-sectional modeller. Finally, a tightly coupled aeroelastic analysis procedure was developed and applied, which ensures convergence through the minimization of a residual vector using Newton's method, and analytical sensitivities for all loads were included in the analysis. Excellent agreement was obtained during verification studies for both the structural and aeroelastic analyses.

Results from the optimization and sensitivity studies indicate that the flexible blades constructed out of symmetric-unbalanced laminates yield a significant variation in thrust and power through the presence of bend-twist and extension-shear coupling, which results in an increasing change in twist distribution with increasing deflection or elongation. Only small variations in performance were observed from symmetric-balanced laminates, as the minimal amount of coupling resulted in negligible twist deformations, which confirms that the presence of bend-twist and extension-shear coupling drives variations in performance obtained through aeroelastic tailoring. Furthermore, it was found that the presence of an aerodynamic wash-out effect augments the range of advance ratio values corresponding to high-efficiency operation during both propulsive and regenerative modes. An opposite trend was observed in the presence of a wash-in effect. Lastly, due to the significantly decreased loading in descent, combined with its small contribution towards the total mission energy consumption, effects of aeroelastic tailoring are significantly greater in propulsive conditions (climb and cruise) in comparison to regenerative conditions.

From optimization, it was found that the flexible constant-pitch propeller features an energy consumption that is between 0.7% and 1.5% lower than the energy consumption of the rigid propellers. Despite this consistent decrease in energy consumption, all optimal flexible constant-pitch propellers were found to regenerate between 3% and 25% less energy than the rigid variable-pitch propeller, and between 3% and 10% less energy than the rigid constant-pitch propeller. This further suggests that the application of aeroelastic tailoring is most-suitable for improving performance in propulsive mode, as the enhanced performance yielded in propulsive mode outweighs the degraded performance in descent by a significant enough margin to enable the flexible constant-pitch propeller to outperform all rigid propellers. Moreover, the flexible variable-pitch propeller naturally yielded an even better performance than the constant-pitch propeller, with a total mission energy consumption that is between 1.5% and 2.0% less than the energy consumption of the rigid propellers. It has thus been shown that aeroelastic tailoring can yield noticeable improvements in propeller performance, at least for the fixed mission profile and reference aircraft that was studied.

Propeller propulsion systems combined with Boundary layer ingestion (BLI) have been proposed as a propulsive system to reduce the CO2 emissions of aircraft by 50% by 2050. BLI leads to increased disturbances at the propeller disk and causes more noise due to the fluctuating blade loading. Using the APPU project as a test case, unsteady inflow is used to determine whether a metric to lower the blade loading fluctuation on an airfoil level is possible. Therefore, an optimisation was created using an Euler solver reliant on the harmonic balance method and the adjoint method to lower the computing time of the simulation. The combination of these methods has proven successful in turbomachinery applications. The optimisation scheme uses the modelled APPU inflow conditions to optimise for the drag coefficient while lowering the Root Mean Squared Error of the lift coefficient during the simulations by applying a constraint in various optimisation runs.

To make propellers more viable as a greener alternative to jet engines, the issue of propeller noise needs to be addressed. Previous propeller design optimization studies rarely take into account the effects on aerodynamic and aeroacoustic performance due to non-uniform inflow, the type of flow the propeller would experience if it was installed on an aircraft. This study compares propeller designs optimized in uniform flow with propeller designs optimized in an inflow under an angle of attack of 5 degrees, and compares their aerodynamic and aeroacoustic performance when both propellers operate under an angle of attack of 5 degrees. The objective was to investigate whether it makes a difference in terms of performance if the non-uniform inflow is included and accounted for in the optimization routine. It was found that for the non-uniform inflow studied in this work, there was no significant improvement in aerodynamic and aeroacoustic performance when comparing the design optimized in the non-uniform flow with the design optimized in uniform flow.

Aviation is responsible for a large part of the emissions due to transportation, which is why, in recent years, a trend towards implementing sustainability in aviation has emerged. In small aircraft, the concept of Leading-Edge Distributed Propulsion (LEDP) can provide aerodynamic advantages to reduce fuel consumption thanks to the ability to increase lift due to the interaction between the slipstream of the propellers and the wing.

Therefore, a wind tunnel experiment is performed to study the aerodynamic interaction in propeller-wing-flap systems when Leading-Edge Distributed Propulsion is used. The objective of this research is to gain insight into the difference in wing loading distribution between the distributed-propeller and single-propeller configurations in the flap retracted case, about the effect of flap position on the lift enhancement in LEDP and about the effect of flap deflection on the wake downstream of the system...

To cater to the increasing demand in short-range passenger air transport and the research in electric and hybrid aircraft, there is a renewed interest in the research of propellers. Propellers are known to have high aerodynamic efficiency, which translates to lower fuel burn in comparison to other jet engines, making it an attractive option for airlines to operate it in regional transport. With such a heightened interest in the research of propellers for future applications, it is crucial to study the effect of the shape-design of the blades on its aerodynamic performance parameters. The combination of advanced numerical methods with computational fluid dynamics allows determining the sensitivity of cost function to variations of the design parameters. In this thesis, a RANS-based CFD methodology incorporating the adjoint method is developed to perform the sensitivity analysis of the propeller's aerodynamic performance to the variation in the shape design of the blade. This methodology is applied to two propeller test cases- straight and swept blade. The propeller aerodynamic analysis is performed with SU2 for a range of advance ratios and compared against ANSYS Fluent's. Based on the verification and validation of SU2's flow solver, a larger discretization error was obtained with SU2 in comparison with ANSYS Fluent, for the simulations on the same computational mesh. Once SU2's flow solver is verified and validated using the two propeller cases, it is used to draw a comparison between the aerodynamic performance of the two blades. the swept blade operated with higher aerodynamic efficiency at high advance ratios with the largest gain of 0.47% at J=1.2. While it experiences a marginal loss in the efficiency at lower advance ratios with the largest decrement being 0.37% at J=0.6.

SU2’s adjoint solver is used to perform discrete adjoint-based sensitivity analysis of the propellers at multiple design points with thrust coefficient and torque coefficient as the objective functions. The sensitivity analysis of the thrust coefficient suggested that the regions of high sensitivity are located along the leading-edge and outboard portions of the blade's suction side. The concentration of the regions of high sensitivity varied with the advance ratio. For a given blade, similar trends were seen for the surface sensitivities of the torque coefficient. Both blades exhibit similar trends for surface sensitivities of both objective functions. Whereas based on the gradient information, the highest gradients of thrust coefficient are attained for the design variables located near the trailing edge of the straight blade, at a given radial position. Swept blade shows a chordwise gradient trend similar to the straight blade at most radial positions, except the tip region. It was inferred that the introduction of sweep at the tip results in the shift of the dominant design variable from trailing edge to mid-chord. Similar to surface sensitivities, trends of the chordwise gradient of two objective functions were alike for a given blade. Based on this study, the resulting understanding of the sensitivity of the propeller’s performance parameters to the variation in blade shape design can be used as an input for future design studies aimed at designing efficient propellers. Likewise, the RANS-based CFD methodology incorporating the adjoint method used in this work can be aimed at developing adjoint-based multidisciplinary design capabilities for propellers.

Due to the rising demand for short-range air travel and the desire for aircraft driven by electric propulsion, there has been a renewed interest in propeller research. Despite the high potential aerodynamic efficiency of propellers, their excessive noise emissions prevent a widespread use on aircraft. A gradient based optimization study is performed to assess the trade-off between aerodynamic and aeroacoustic performance of propellers. A blade-element-momentum theory(BEMT) approach with a dependence to the effects of blade sweep is used. The BEMT-model is combined with a frequency domain approach for tonal noise prediction. The optimization study shows that the advance ratio and pitch are important operational parameters during the climb phase to induce a noise reduction. The application of blade sweep proves useful as a design measure to reduce noise, given that the propeller operates in high speed conditions.

Propellers were the first means of powered propulsion for aircraft. However the development of propellers stalled due to the growing interest in jet propulsion. Due to the growing interest in more fuel efficient and environmentally responsible aviation, propeller research is currently seeing a resurgence.

Wingtip-mounted propellers are seen as an attractive option for increasing the efficiency of aircraft. Indeed, due to the favorable interaction between the propeller slipstream and wingtip vortex, the performance of the integrated propeller-wing system is improved compared to the same elements in isolation.

Propellers installed at the wingtip have a considerable moment arm. When a thrust imbalance occurs, a fairly large moment about the aircraft yaw axis can negatively affect the aircraft trim. As a result, the aircraft directional static stability requirements are more stringent compared to the conventional layout. It is known, that a propeller at an angle with regards to the flow direction develops a considerable side force. The change in thrust and the side force that develops in this case could potentially be used to aid in the aircraft stability, instead of adversely affecting it, if the tip-mounted propeller were installed at a so-called "toe-out" angle. This configuration would take advantage of the benefits of the Wingtip-mounted propeller configuration, while also potentially enhancing the aircraft directional stability as well, thus reducing the adverse effects on aircraft trim of the wingtip propeller configuration.

With the aim of understanding the possible impacts of modifying the propeller installation angle, RANS CFD simulations were used to compute the flowfields of various configurations. First an isolated NACA-series wing and small diameter propeller were simulated at steady-state, in order to validate the methods used in this investigation. Following this, an isolated wing based on the experimental NASA aircraft X-57 was simulated, as this aircraft uses wingtip-mounted propellers. Then, the previously simulated propeller was scaled up to the operational size of the X-57, and simulated in transient conditions at zero and a non-zero sideslip angle of 10 degrees, since the inflow angle is non-uniform for this case, leading to unsteady blade loading. Finally the propeller was installed on the wing and power-off and power-on transient simulations were performed at installation angles of -10, 0 and +10 degrees. For each of the computational domains, grid convergence studies were performed to assess the numerical error associated with the chosen element sizes. The domain used for the isolated wing was calculated to have an uncertainty of 2% and 6% respectively when it comes to C_L and C_D. The domain used for the propeller simulations was calculated to have an uncertainty in C_T and C_P of almost 4% and 6%, respectively. These domains were combined for the investigation of the installed propeller cases and, to reduce computational costs, no grid convergence study was performed.

The results obtained from the simulation of the wing installed with the nacelle and spinner only, showed that there is a significant blockage effect due to the presence of the nacelle, which reduced lift over the wing, and increased drag. The presence of the propeller in power-on cases were observed to reduce the negative effects of the nacelle.

It was observed for the -10 degrees installed propeller, that the lift and drag performance of the wing was increased in this configuration compared to the 0 degree case, while the +10 degrees installed propeller showed decreased wing lift and drag performance. This was due to the orientation of the propellers. At $\epsilon_{TMP} = -10^\circ$, a larger portion of the wing is washed by the propeller slipstream, and thus affected by the interaction. This effect reduces with increasing toe-out angle as less of the wing is washed by the propeller slipstream. Additionally, due to the toe-out angle, the loading over the propeller disc is not distributed uniformly. Because of this, also the propeller slipstream is not uniform and thus the trailing wing is affected differently by the interaction for varying toe-out angles. The +10 degrees installed propeller was estimated to have an efficiency $.2%$ lower than its counterpart and $1.3%$ lower than the 0 degree installed case.

The generated side force of the installed propellers varied in sign, which depended on the sign of the installation angle. The side force for non-zero installation angle was estimated to be at least 13% of the zero installation angle thrust, for a representative cruise thrust setting and flight conditions. The side force imbalance for an aircraft experiencing sideslip, with non-zero angle wingtip-installed propellers with an aft center of gravity (CG), was investigated with regards to the directional stability. The thrust imbalance was estimated to be a slightly stabilizing factor when the propellers are installed at +10 degrees and, when combined with the destabilizing nature of the resulting side force imbalance, a slight improvement to the aircraft directional stability was found, though not sufficient to greatly affect the aircraft. At 10 degrees of sideslip, the resulting stabilizing moment due to the force imbalance in this case was found to constitute 1% of the magnitude of the aircraft restoring yawing moment caused by the vertical tailplane. This effect was a destabilizing factor when installed at -10 degrees, with the resulting destabilizing moment due to the force imbalance at 10 degrees of sideslip found to constitute 13% of the magnitude of the aircraft restoring yawing moment caused by the vertical tailplane. Since these calculations were done for a configuration where the propeller forces act ahead of the aircraft CG, it was noted, that the side force imbalance would be stabilizing in both cases for a forward CG. The contribution to the moment is largely determined by the location of the propellers, and the moment contribution of the thrust imbalance of the non-zero installed wingtip mounted propellers is estimated to be 20% larger than that of the side force imbalance, on the X-57.

The present study has contributed towards a better understanding of the interaction effects and performance of wingtip-mounted propellers installed at a nonzero toe-out/toe-in angle. The results indicate that both inboard- and outboard-directed propellers have benefits and drawbacks with respect to the zero installation angle configuration. Nevertheless, future studies should still be performed on this topic. At higher Mach numbers, actively controlled propeller installation angles or tailplane-mounted propellers at an incidence angle could take advantage of the unique characteristics of this configuration.

As electric vehicles are quickly taking over the automotive industry, electric airplanes are also starting their upswing. With air travel and transport in general being a large polluter of CO2 gases, the transition to electric flight becomes more prominent every year. This transition is starting small with non-commercial airplanes. Several companies are starting with development of eVTOLs, electric Vertical Take-Off and Landing vehicles. The idea behind them is that they can easily move into and out of the city through the air, speeding up transport and travel in urban areas while keeping CO2 emissions at the vehicle level at zero.
This thesis, together with two other theses, will elaborate on the design of such an eVTOL. Its design is created by looking at the layout of the propellers, the wings and the fuselage and the internal layout is composed by working out the electric drivetrain from the energy storage to the electric motors and by drafting up the control systems. In specific, this thesis dives into the external design and the internal electric energy storage. It does this by settling on a design and calculating certain specifications, like wing area and propeller and fuselage size. From there the necessary powers and energies are calculated. With these powers and energies, a battery pack is designed together with a battery management system and a charging system. The other two theses will design the propulsion system and the control system of the eVTOL.
The result of the thesis is a theoretical design that states the possibilities of Lithium-Sulfur cells inside an eVTOL. An efficient tandem wing design with fixed wings and fixed rotors makes sure there is a healthy balance between the maximum power and total energy needed to take off vertically and fly 125 kilometers. With the Lithium-Sulfur cells a battery pack is made with its accompanying battery management system that monitors and manages the cells' characteristics. Next to the battery pack, theory on charging and a simplified charging simulation has been done to show that charging in 15 minutes should be possible by the time the eVTOL enters into service.

In the global search to more sustainable developments, research in the field of propeller propulsion systems is experiencing a renewed interest. The combination of efficiency and noise production is not studied as extensively as propeller efficiency alone in past studies. In this study, the relation between propeller noise and efficiency is investigated. Adjusted parameters are sweep, advance ratio and the collective pitch angle. The performance of randomly generated blades is evaluated using both RANS and BEM methods first, after which the noise is evaluated using Hanson’s frequency formulation. All results are combined in a multi-fidelity kriging surrogate model. The results suggest that maximum efficiency and minimum noise cannot be obtained at the same operating conditions. Adjusting advance ratio and pitch of a given propeller during flight may reduce the noise emissions at the cost of efficiency. Sweep is also shown to have a considerable effect on both efficiency and noise.