Novel Model-Based Control Mixing Strategy for a Coaxial Push-Pull Multirotor

A Coaxial push-pull multirotor is a Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) having 2n (n ∈ IN*) rotors arranged in n blocks of two coaxial contrarotating rotors. A model-based control allocation algorithm (mixer) for this architecture is proposed. The novelty of the approach lies in the fact that the coaxial aerodynamic interference occurring between the pairs of superimposed rotors is not neglected but rather nonlinear empiric models of the coaxial aerodynamic thrust and torque are used to build the mixer. Real flight experiments were conducted and the new approach showed promising results

Experimental Study of Aerodynamic Disturbance Rejection On Multirotor Unmanned Aerial Vehicles

PID (Proportional-Integral-Derivative) controllers are the most widely used control algorithms in different industrial applications. Multirotor Unmanned Aerial Vehicles (UAVs) are not an exception in this regard. This success is due to the efficiency of this type of algorithms. In fact, they are easy to understand, to tune and to implement. Added to that, PID controllers perform surprisingly well in most operational cases, even when those start to become challenging. But this effectiveness becomes questionable when the conditions are far fro

Robust active disturbance rejection control for systems with internal uncertainties: Multirotor UAV application

Abstract Active Disturbance Rejection Control (ADRC) has recently stood out as a viable alternative to the proportional–integral–derivative controllers. An interesting field of application of this approach is the control of multirotor unmanned aerial vehicles (UAVs) which are inevitably subject to various force and torque disturbances. What makes ADRC attractive is the enhanced trajectory tracking and disturbance rejection capabilities that it allows while requiring minimal knowledge about the system. Although in theory, larg

12th EASN International Conference on "Innovation in Aviation & Space for opening New Horizons"

Epoxy resins show a combination of thermal stability, good mechanical performance, and durability, which make these materials suitable for many applications in the Aerospace industry. Different types of curing agents can be utilized for curing epoxy systems. The use of aliphatic amines as curing agent is preferable over the toxic aromatic ones, though their incorporation increases the flammability of the resin. Recently, we have developed different hybrid strategies, where the sol-gel technique has been exploited in combination with two DOPO-based flame retardants and other synergists or the use of humic acid and ammonium polyphosphate to achieve non-dripping V-0 classification in UL 94 vertical flame spread tests, with low phosphorous loadings (e.g., 1-2 wt%). These strategies improved the flame retardancy of the epoxy matrix, without any detrimental impact on the mechanical and thermal properties of the composites. Finally, the formation of a hybrid silica-epoxy network accounted for the establishment of tailored interphases, due to a better dispersion of more polar additives in the hydrophobic resin

Towards a better understanding of the flight mechanics of compound helicopter configurations

The compound helicopter is a high speed design concept that is once again being explored due to the emerging requirements for rotorcraft to obtain speeds that significantly surpass the conventional helicopter. The speed of the conventional helicopter is limited by retreating blade stall, however the introduction of compounding delays the onset of this aerodynamic limitation until greater flight speeds. There are two common types of compounding known as lift and thrust compounding. Lift compounding, provided by the addition of a wing offloads the main rotor of its lifting responsibilities in high speed flight. Thrust compounding, provided by the addition of a propulsive source such as a propeller, provides additional axial force divorcing the main rotor of its propulsive duties at high speeds. The addition of compounding to the helicopter design can therefore increase the maximum speed of the aircraft. This increase in speed, provided that efficient hover capability is maintained, would make the compound helicopter suitable for various roles and missions in both military and civil markets. The compound helicopter is not a novel idea with many compound helicopter configurations flight tested in the 1960's. Due to these test programmes, as well as other studies, there is some material relating to the compound helicopter in the literature. However, the majority of the compound helicopter work describes flight tests of experimental aircraft or focuses on the design of the aircraft configuration. There are no systematic studies of the flight dynamics of compound helicopters which have been published. This Thesis targets this gap in the literature. Consequently, the aim of this Thesis is to investigate the effects of compounding on the conventional helicopter and how this addition to the helicopter design influences the flight mechanics of this aircraft class. With the renewed interest in the compound helicopter design this work is both original and timely. To investigate the flight dynamics of this aircraft class, two mathematical models of compound helicopter configurations are developed and compared with a conventional helicopter. The first compound helicopter configuration features a coaxial rotor with a pusher propeller providing additional axial thrust, and is referred to as the coaxial compound helicopter. The second configuration, known as the hybrid compound helicopter, features two wings each with a tip mounted propeller providing thrust compounding. The conventional helicopter features a standard helicopter design with a main rotor providing the propulsive and lifting forces, whereas a tail rotor, mounted at the rear of the aircraft, provides the yaw control. Other authors have focused on design considerations and have quantified all of the benefits of compounding but to date, a comprehensive study of the effect of compounding on the flight dynamics of a helicopter has not been published. The strategy of the work is to take the three aircraft configurations, the two compound helicopter configurations and the conventional helicopter, and determine their flight mechanics characteristics. Subsequently, the compound helicopter results can be compared with the baseline configuration, thereby isolating the effects of compounding. The flight mechanics characteristics that are determined in this Thesis include: trim, performance, stability and manoeuvrability attributes of the three helicopter configurations. These attributes are assessed by calculating the control angles which result in a steady flight condition and by the use of numerical linearisation and inverse simulation algorithms. All of these flight mechanics characteristics were assessed with the results, in some aspects, reinforcing the potential of the compound helicopter as well as highlighting some possible difficulties that will have to be addressed in the design of a compound helicopter

Cyber-Human Systems, Space Technologies, and Threats

CYBER-HUMAN SYSTEMS, SPACE TECHNOLOGIES, AND THREATS is our eighth textbook in a series covering the world of UASs / CUAS/ UUVs / SPACE. Other textbooks in our series are Space Systems Emerging Technologies and Operations; Drone Delivery of CBNRECy – DEW Weapons: Emerging Threats of Mini-Weapons of Mass Destruction and Disruption (WMDD); Disruptive Technologies with applications in Airline, Marine, Defense Industries; Unmanned Vehicle Systems & Operations On Air, Sea, Land; Counter Unmanned Aircraft Systems Technologies and Operations; Unmanned Aircraft Systems in the Cyber Domain: Protecting USA’s Advanced Air Assets, 2nd edition; and Unmanned Aircraft Systems (UAS) in the Cyber Domain Protecting USA’s Advanced Air Assets, 1st edition. Our previous seven titles have received considerable global recognition in the field. (Nichols & Carter, 2022) (Nichols, et al., 2021) (Nichols R. K., et al., 2020) (Nichols R. , et al., 2020) (Nichols R. , et al., 2019) (Nichols R. K., 2018) (Nichols R. K., et al., 2022)https://newprairiepress.org/ebooks/1052/thumbnail.jp

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction

Rotor Fatigue Life Prediction and Design for Revolutionary Vertical Lift Concepts

Despite recent technological advancements, rotorcraft still lag behind their fixed-wing counterparts in the areas of flight safety and operating cost. Competition with fixed-wing aircraft is difficult for applications where vertical takeoff and landing (VTOL) capabilities are not required. Both must be addressed to ensure the continued competitiveness of vertical lift aircraft, especially in the context of new military and civilian rotorcraft programs such as Future Vertical Lift and urban air mobility, which will require orders-of-magnitude improvements in reliability, availability, maintainability, and cost (RAM-C) metrics. Lifecycle costs and accident rates are strongly driven by scheduled replacement or failure of flight-critical components. Rotor blades are life-limited to ensure that they are replaced before fatigue damage exceeds critical levels, but purchasing new blades is extremely costly. Despite aggressive component replacement times, fatigue failure of rotor blades continues to account for a significant proportion of inflight accidents. Fatigue damage in rotorcraft is unavoidable due to the physics of rotary-wing flight, but new engineering solutions to improve fatigue life in the rotor system could improve rotorcraft operating costs and flight safety simultaneously. Existing rotorcraft design methods treat fatigue life as a consequence, rather than a driver, of design. A literature review of rotorcraft design and fatigue design methods is conducted to identify the relevant strengths and weaknesses of traditional processes. In rotorcraft design, physics-based rotor design frameworks are focused primarily on fundamental performance analysis and do not consider secondary characteristics such as reliability or fatigue life. There is a missing link between comprehensive rotor design frameworks and conceptual design tools that prevents physics-based assessment of RAM-C metrics in the early design stages. Traditional fatigue design methods, such as the safe life methodology, which applies the Miner's rule fatigue life prediction model to rotorcraft components, are hindered by a lack of physics-based capabilities in the early design stages. An accurate fatigue life quantification may not be available until the design is frozen and prototypes are flying. These methods are strongly dependent on extrapolations built on historical fatigue data, and make use of deterministic safety factors based on organizational experience to ensure fatigue reliability, which can lead to over-engineering or unreliable predictions when applied to revolutionary vertical lift aircraft. A new preliminary fatigue design methodology is designed to address these concerns. This methodology is based on the traditional safe life methodology, but replaces several key elements with modern tools, techniques, and models. Three research questions are proposed to investigate, refine, and validate different elements of the methodology. The first research question addresses the need to derive physics-based fatigue load spectra more rapidly than modern comprehensive analysis tools allow. The second investigates the application of different probabilistic reliability solution methods to the fatigue life substantiation problem. The third question tests the ability of the preliminary fatigue design methodology to evaluate the relative impact of common preliminary fatigue design variables on the probability of fatigue failure of a conceptual helicopter's rotor blade. Hypotheses are formulated in response to each research question, and a series of experiments are designed to test those hypotheses. In the first experiment, a multi-disciplinary analysis (MDA) environment combining the rotorcraft performance code NDARC, the comprehensive code RCAS, and the beam analysis program VABS, is developed to provide accurate physics-based predictions of rotor blade stress in arbitrary flight conditions. A conceptual single main rotor transport helicopter based on the UH-60A Black Hawk is implemented within the MDA to serve as a test case. To account for the computational expense of the MDA, surrogate modeling techniques, such as response surface equations, artificial neural networks, and Gaussian process models are used to approximate the stress response across the flight envelope of the transport helicopter. The predictive power and learning rates of various surrogate modeling techniques are compared to determine which is the most suitable for predicting fatigue stress. Ultimately, shallow artificial neural networks are found the provide the best compromise between accuracy, training expense, and uncertainty quantification capabilities. Next, structural reliability solution methods are investigated as a means to produce high-reliability fatigue life estimates without requiring deterministic safety factors. The Miner's sum fatigue life prediction model is reformulated as a structural reliability problem. Analytical solutions (FORM and SORM), sampling solutions (Monte Carlo, quasi-Monte Carlo, Latin hypercube sampling, and directional simulation), and hybrid solutions importance sampling) are compared using a notional fatigue life problem. These results are validated using a realistic helicopter fatigue life problem \jnr{which incorporates the fatigue stress surrogate model and is based on a probabilistic definition of the mission spectrum to account for fleet-wide usage variations. Monte Carlo simulation is found to provide the best performance and accuracy when compared to the exact solution. Finally, the capabilities of the preliminary fatigue design methodology are demonstrated using a series of hypothetical fatigue design exercises. First, the methodology is used to predict the impact of rotor blade box spar web thickness on probability of fatigue failure. Modest increases in web thickness are found to reduce probability of failure, but larger increases cause structural instability of the rotor blade in certain flight regimes which increases the fatigue damage rate. Next, a similar study tests the impact of tail rotor cant angle. Positive tail rotor cant is found to improve fatigue life in cases where the center of gravity (CG) of the vehicle is strongly biased towards the tail, but is detrimental if the CG is closer to the main rotor hub station line. Last, the effect of design mission requirements like rate of climb and cruising airspeed is studied. The methodology is not sensitive enough to predict the subtle impact of changes to rate of climb, but does prove that a slower cruising airspeed will decrease probability of fatigue failure of the main rotor blade. The methodology is proven to be capable of quantifying the influence of \jnr{rotor blade design variables, vehicle layout and configuration, and certain design mission requirements}, paving the way for implementation in a rotorcraft design framework. This thesis ends with suggestions for future work to address the most significant limitations of this research, as well as descriptions of the tasks required to apply the methodology to conventional rotorcraft or conceptual revolutionary vertical lift aircraft.Ph.D