The effect of twist distribution on rotor performance and its applications on rotor blades

Abstract

The long-established industry of aviation has been evolving inexhaustedly throughout the history and the story has to be continued from now on with the new developments. From the fixed-wing aircraft model developed in earlier times in history of the industry, numerous advancements have been investigated. Each investigation had its own reason to improve. Then vertical flight technology came to mind for enabling hovering, vertical takeoff and manoeuvrability. Helicopter rotorcrafts are essential for both military and civilian applications to operate in confined or remote areas. In order to complete missions such as search and rescue and medical evacuation and aerial firefighting, the biggest advantage for helicopters are vertical takeoff, versatility and ability to reach out areas that neither the fixed-wing aircraft nor ground vehicles can go through. The main motivation for improvements in aviation is about lowering the operational cost and maximizing the capacity in every sense. In order to lower the cost, generaly the power consumption of aircraft must be reduced or in a similar way the efficiency must be enhanced. These improvements can occur in structural meaning, in aerodynamic or in propulsive systems. A major contributor to the overall power consumption of rotorcraft is the rotor system, particularly the aerodynamic characteristics of the blades. It is important to say that the aerodynamical efficiency is a key factor to improve a performance for all aircraft types. The aerodynamic loading, lift distribution, and eventually the thrust and power consumption properties of the rotor are directly influenced by the phenomena called twist distribution. A key factor in rotor design is blade twist distribution, which shows the pitch angle variation over the blade span. Understanding and optimising blade twist can help to increase hover efficiency, enhance forward flight performance, and lower overall energy requirements. Twist distribution thus becomes a strategic aerodynamic instrument for performance improvement as well as a geometric issue. In rotorcraft engineering, the importance of customised twist designs grows more as mission profiles get more varied and demanding. This thesis examines the impact of various twist distributions on rotor performance during hover and forward flight using theoretical and computational techniques. Afterwards, It also developes a radical opinion about passive and active twist implementations in contemporary rotorcraft design. The agreeable rotor topologies may be determined by having a solid understanding of twist mechanics and how it affects the power coefficient and induced flow. This work is supported by a solid basis in MATLAB computer modelling and helicopter theory. The results of this study seek not just to increase energy efficiency but also to help create more adaptive, intelligent rotor systems. This thesis hopes to provide significant insights for future rotorcraft innovation by combining classical aerodynamic theory with contemporary technical solutions. In order to understand the idea beehind the performance improvements in rotorcrafts, the theory of helicopter has to be examined deeply. There are three main principles for helicopter motions. First and the most primary is the Momentum Theory, and it basically defines a relation around the actuator disk with the airflow going downwards in order to create a thrust. Momentum Theory treats the rotor as an actuator disc and uses the ideas of mass, momentum, and energy conservation to explore thrust and power generation. Next theory is called Blade Element Theory (BET) and this theory considers the rotating blades individually to derivate the aerodynamic forces such as lift and drag forces. So overcoming the problem, Blade Element Theory divides the blade into tiny radial parts to compute local lift and drag forces depending on relative velocity and angle of attack. By integrating these two methodologies, BEMT provides a more comprehensive and pragmatic framework for assessing the influence of blade twist, especially when the pitch angle is represented as a function of the non-dimensional radial location. Since the theories are now understood, the effect of twist distributions can be demonstrated. Types of distributions are, untwisted (uniform pitch), linearly twisted, quadratically twisted and the ideally twisted blades. Mathematical models of these distributions must be obtained for analyzing the performance values. The major concern is the achieve a homogeneous inflow ratio (λ) distribution in order to reduce losses and increse the rotor efficiency. A key non-dimensional value in rotorcraft aerodynamics, the inflow ratio measures the axial flow velocity across the rotor disc in relation to the rotor tip speed. Fundamental in both momentum theory and blade element momentum theory (BEMT), it is also huge for understanding induced velocity and overall rotor efficiency. Using real rotorcraft attributes especially those from the UH-60A Black Hawk main rotor, MATLAB does calculations. Power coefficients are calculated for various negative twist angles (e.g., 0°, -4°, -8°, -10°, -12°), and the results show that negatively twisted blades significantly lower power requirements during hover. The findings confirm the aerodynamic advantage of include twist, particularly when tailored for specific flight circumstances. The thesis looks at twist effects in forward flight, when the inflow model turns unequal owing to advancing and retreating blades. The twist distribution helps to balance lift and reduce vibratory loads. Simulations conducted under forward flight conditions show that twist improves efficiency and stabilises rotor dynamics. One of the numerous design components that regulate rotor behaviour is the twist ratio, which is the variation in pitch angle along the rotor blade. The ability to passively or actively adjust the twist ratio allows for improved flying qualities in a variety of operating regimes. The goal of the thesis is to comprehend how twist affects performance characteristics in order to lower the power required for rotorcrafts to hover and fly forward. Moreover, the subsequent aim is to discover how the active twist ratio concepts are implemented. Apart from traditional (passive) twist, the paper investigates active twist systems for real-time modification of blade twist during flight. Morphing rotor blades that use smart materials to change blade geometry without requiring mechanical hinges or joints are thereby produced. There are 2 main types of active twist technologis that investigated throughout this paper. First one is called Active Fiber Composites (AFC) basically consists of embedded electrodes and piezoceramic materials and they are capable to be used in high-force applications due to its significant in-plane deformation. Likewise, the other type is called Macro Fiber Composites (MFC) is based on multiple layers (including piezoelectric fibers, kapton film, and epoxy) and provide better energy conversion efficiency and better flexibility than monolithic ceramics. Active Twist Rotor (ATR) systems include these actuators either attached to or incorporated into the composite blade structure. Electrical activation causes them to produce torsional strain, hence dynamically changing the pitch angle of the blade. Dispersed actuation allows for precise twist control over the span. Benefits include reduced noise, vibration damping, and improved aerodynamic loading performance. There are many important factors that affect how well Active Twist Rotor (ATR) systems work. These include the location and orientation of the actuators, the anisotropic behaviour of composite blade materials, the distribution of structural stiffness along the blade, and the dynamic responsiveness of the control system. Of all the actuation technologies that have been looked into, Macro Fibre Composite (MFC)-based solutions stand out as the most promising. This is mostly because they are light, can withstand a lot of wear and tear, and work well with the fiber-reinforced composite materials that are often used to make current rotor blades. MFC actuators are a good choice for advanced rotorcraft applications because they strike a good compromise between mechanical efficiency and structural adaptability, even if ATR systems can be hard to integrate. This study focusses on the aerodynamic importance of blade twist and starts with a detailed theoretical look at how helicopter rotors work. It helps to create and compare mathematical models that show how different twist distributions work in both hover and forward flight modes. The study uses simulation-based assessments to figure out how the UH-60A Black Hawk rotor settings affect performance. In addition to passive configurations, it also looks into morphing blade technologies and evaluates the practicality of active twist mechanisms from both an engineering and a theoretical point of view. The findings contribute valuable insights for aerospace engineers and designers striving to optimize aerodynamic performance and extend operational range in future helicopter platforms. Ultimately, this work bridges classical rotorcraft theory with modern smart material innovations, paving the way for continued advancements in adaptive blade technologies. Focussing particularly on the relevance of blade twist, the paper starts with a thorough theoretical investigation of helicopter rotor aerodynamics. It promotes the evolution and comparison of mathematical models for several twist distributions in both hover and forward flight conditions. Performance impacts are assessed by means of simulations using the UH-60A Black Hawk rotor settings. The paper also offers morphing blade technologies and evaluates the viability of active twist systems from theoretical and technological perspectives. Examining passive and active twist methods concurrently reveals their unique and relative benefits in enhancing rotorcraft performance. The results offer important new information for engineers and designers trying to improve aerodynamic efficiency and increase the flight range of next-generation helicopters. Advancing the subject of rotorcraft morphing systems and enabling future research in flexible blade design, this work combines traditional aerodynamic theory with modern smart material technologies.