This study introduces three new proposed mission task elements (MTEs), “Big Air,” “Giant Slalom,” and “Super Combined,” aimed at evaluating handling qualities during low-level and high-speed flight profiles. These MTEs are designed to reflect operational task elements critical in military engagements, particularly where rotorcraft capabilities in evading radar detection and maneuvering at high speeds are paramount. Utilizing piloted simulations with four generic rotorcraft configurations under various flight control laws, the MTEs' effectiveness in exposing aircraft characteristics and handling deficiencies is systematically assessed. The evaluation, conducted with a diverse group of pilots, underscores the MTEs' relevance to real-world scenarios and their robustness in handling qualities assessment across different rotorcraft designs. The study reveals that while some configurations exhibit consistent Level 1 handling qualities ratings, others show varied performance, particularly when integrating additional means of velocity control, such as pusher propellers or velocity hold modes. Findings suggest modifications to current evaluation frameworks to better accommodate the dynamic operational requirements of future vertical lift platforms.

This study investigates the integration of a cycloidal tail rotor as a replacement for the conventional tail rotor in helicopter configurations, focusing on its dual functionality as both an antitorque mechanism and an auxiliary propulsion system. Unlike traditional tail rotors, the cycloidal tail rotor can direct thrust in any direction perpendicular to its axis of rotation, enabling enhanced maneuverability, including the ability to hover at arbitrary pitch attitudes, assist in forward flight, and execute rapid acceleration and deceleration. The cycloidal tail rotor was modeled for flight simulation and incorporated into a generic multi-rotor/wing flight dynamics code to simulate two configurations of a utility helicopter similar to an H-60: one with a conventional tail rotor and the other with a cycloidal tail rotor. A design optimization study defined the geometry of the cycloidal tail rotor, followed by trim, performance, and stability analyses. Results showed that the cycloidal tail rotor configuration exhibited similar trim characteristics to the conventional tail rotor, with minor differences in control inputs and power consumption. The cycloidal tail rotor provided additional propulsive force in forward flight, reducing the pitch-forward requirement and offloading the main rotor, leading to slightly higher power consumption in hover but reduced power requirements at high speeds. Additionally, the cycloidal rotor enabled trimming at arbitrary pitch attitudes. Stability and frequency response analyses revealed minimal differences in flight dynamics, suggesting the feasibility of integrating a cycloidal tail rotor without significantly altering stability or handling qualities. Dynamic inversion control laws adopting pseudo-inverse control allocation demonstrated the ability to reallocate control effort between the main rotor and the cycloidal rotor, with the cycloidal tail rotor acting as a pusher propeller. This reduced the main rotor workload and allowed for a less pronounced nose-down/up pitch attitude during aggressive acceleration/deceleration maneuvers.

This article presents the implementation of an integrated model for rotorcraft flight dynamics, motion perception, and motion sickness. Merfeld's multidimensional sensory conflict model (MSCM), along with its extension to visual–vestibular interaction, is employed to represent motion perception both with and without visual feedback. A recently developed model is then used to predict motion sickness severity based on the neural signal mismatch generated by the MSCM. These models are coupled with a generic multirotor/wing flight dynamics code, which is adapted to represent a multipurpose helicopter configuration representative of the Bo 105. The bare-airframe flight dynamics is validated against flight-test data in the frequency domain. Closed-loop simulations are used to demonstrate the model's application to coordinated turns, the onset of spatial disorientation during a graveyard spiral, and motion sickness during a slalom maneuver. In addition, the approach is validated against motion sickness flight-test data from the German Aerospace Center (DLR). This modeling strategy supports the prediction of ride quality metrics and enables the integration of flight dynamics with human factors considerations.

Despite extensive research on system identification for helicopters in the past, studies characterizing time-periodic dynamics of helicopter rotors using system identification techniques are limited. In this paper, a study is conducted to explore applicability of linear parameter-varying (LPV) system identification techniques in this domain, and the scope is to obtain low-order state-space models for time-periodic helicopter rotor dynamics. The identified models can then be used for LPV controller applications on active rotor control design or envelope cueing. For this work, the LPV subspace identification scheme is employed for the system identification process, together with an optimization step to enhance the fit performance. The method is demonstrated for blade flapping dynamics using a building-block approach progressing from simulations of a rigid blade model to a higher fidelity elastic blade rotor model and, finally, flight-test data. Findings from simulation and flight-test data in this work support that the employed LPV identification scheme is a viable method to capture periodic characteristics of the rotor system.

This article presents the development, implementation, and evaluation of dynamic inversion (DI) flight control laws for compound rotorcraft with auxiliary propulsion systems, with application to a configuration representative of the Airbus Rapid And Cost-Efficient Rotorcraft (RACER). The RACER features a single main rotor, a boxed wing, and two lateral pusher propellers that provide both torque balancing and thrust compounding. The DI control laws are structured using a multiloop architecture and incorporate redundant control allocation to the pusher propellers via a pseudo-inverse (PI) strategy. A primary objective is to investigate control allocation approaches that minimize pitch attitude excursions during acceleration and deceleration maneuvers. A generic multirotor/wing simulation model is adapted to model the flight dynamics of the RACER configuration. The model is trimmed and linearized at discrete speeds from hover to cruise, and control reallocation is used to enable trimming at arbitrary pitch attitudes. Model-order reduction techniques are applied to obtain reduced-order models suitable for control synthesis. Both a baseline DI controller and a PI variant are implemented and tested in closed-loop simulations using the full-order nonlinear model. Three representative maneuvers are considered: (i) a hover-to-cruise transition, (ii) a combined transition, climb, and coordinated turn, and (iii) a cruise-to-hover reverse transition. The PI-based control law reduces pitch attitude variation by reallocating control effort to the auxiliary propulsion system, while achieving comparable tracking accuracy, as well as similar performance and handling-quality metrics relative to the baseline controller.

This article presents an in-depth flight dynamics analysis of a quadrotor biplane tailsitter and proposes novel dynamic inversion (DI) flight control laws for autonomous hover-to-cruise transition. As the basis for the synthesis and demonstration of such control laws, a flight dynamics model is developed that also accounts for rotor dynamics and rotor-on-wing interactions. The flight dynamics model is trimmed and linearized at discrete increments in flight speed, from hover to cruise flight. The order of the linearized models is reduced by means of residualization, a subset of singular perturbation theory, to enable stability analysis and control design. The stability and response properties are analyzed both at hover and in cruise flight in terms of eigenvalues, motion modes, and frequency responses. A multiloop DI control law is developed, where an outer velocity loop tracks commanded longitudinal, lateral, and vertical ground velocities in the heading frame and computes the desired pitch and roll attitudes for the inner loop to follow. The inner attitude loop ensures stability, disturbance rejection, and appropriate dynamic response about the roll, pitch, and yaw axes. To demonstrate the proposed control strategy and investigate performance limits, two distinct trim and closed-loop transition trajectories are considered: one in which the vehicle performs the transition with a vertical climb component, and another in which it performs a level, forward-only translation. Closed-loop simulations based on the full nonlinear dynamics are used to demonstrate autonomous hover-to-cruise transitions and to assess the minimum feasible transition time before the onset of rotor stall.

A low-fidelity model for modeling ice accretion phenomena over two-bladed teetering rotors has been developed. In this approach, the blades are assumed to be rigid, and the flapping motion is caused by the inertial, centrifugal, and aerodynamic forces acting on the blade section. The aerodynamic forces are computed using a table look-up of precomputed airfoil lift and drag coefficients as a function of effective angle of attack. Following the analysis of the rotor without icing effects, ice shapes at selected radial locations on the rotor are computed. The impact of ice shapes on the two-dimensional (2D) lift and drag characteristics is estimated using a 2D computational fluid dynamics analysis. Finally, the rotor is reanalyzed using the low-fidelity model with the iced airfoil lift and drag characteristics. Comparisons with test data and a higher fidelity model are also presented.

Composite rotor blade planform design focuses on optimizing blade shape to achieve higher performance. However, structure failure is rarely considered concurrently with outer mold line design. The traditional rotor blade strength analysis is typically conducted through a multilevel analysis. This process becomes inefficient in optimization frameworks due to the vast number of load cases encountered in blade design optimization. Ignoring strength analysis may result in a blade designed solely based on aerodynamic considerations being infeasible from a strength point of view. Furthermore, composite materials are anisotropic and susceptible to various failure mechanisms. In this paper, we propose to optimize the composite rotor blade design with strength consideration. To overcome the rotor blade multilevel analysis inefficiency issue, we introduced a novel approach using machine learning. Specifically, we proposed a beam-level failure criterion surrogate model, constructed using artificial neural networks, based on the Timoshenko beam model. This model directly correlates blade loads with the strength ratios of the cross section, which significantly reduces the computational cost of cross-sectional failure analysis. For demonstration, we constructed a beam-level failure criterion of a UH60 composite rotor blade. The beam-level failure criterion was then integrated into the planform optimization process. The result showed that while the optimization with the beam-level failure criterion reduced the computational time significantly, it can also achieve the same accuracy level as the physics-based optimization.

The installation effects of the Volocopter-2X beam structures are studied by performing high-fidelity simulations of singleand three-rotor configurations in hover. To verify the installation effects, the studied cases are compared with simulations without an airframe. In addition, the noise emission of the configurations is simulated using a Ffowcs Williams-Hawkings-based computational aeroacoustic code. Scattering effects are also included by using a boundary element method code as well as a permeable integration surface surrounding the entire configuration. The rotors are simulated at identical rotational speeds and in their respective mounting positions. An additional setup with individual rotational speeds is simulated for the three-rotor configuration. The installation mainly affects the rotor wake, thrust, and pressure fluctuations on the rotor, while the integral aerodynamic quantities remain almost unchanged. This results in additional oscillations in the acoustic pressure signal. Overall, the installation increases the overall sound pressure level by about 1.5 dB. However, it has a larger effect on the 3rd ‐ 20th harmonics. The simulation data were compared with measurements performed by Volocopter and showed good agreement. For the three-rotor configurations, the rotor???rotor interactions were found to be dominant for the aerodynamic and acoustic performance, while the installation effects only locally affected the noise emission by 3‐4 dB.

Applications of unmanned aerial vehicles are on the rise. Particularly within the healthcare sector, the potential is huge as it is cited as the most accepted application. This paper introduces an agent-based simulation to evaluate the network performance of UAV-based logistics networks in healthcare. The simulation is applied to a hypothetical real-world network. During a simulated day, the UAV fleet performs 212 flights, including 97 delivery flights, amounting to 4,264 min en route and covering a distance of 5,941 km. The analysis reveals average non-idle and mission utilization of 66% and 33%, respectively. The study also calculates the annual network costs of EUR 2.23 Mn, with a majority of it being direct costs (54.5%). Further sensitivity analysis identifies the biggest influences of battery capacity, C-rate, and operator-to-UAV ratio on network performance and costs, highlighting these factors as critical for future optimization. Additionally, the benefit of incorporating various different UAV types into the network is only given if each UAV provides a unique value proposition to enhance the network performance.