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The stress mode shapes are highly sensitive to the local state of the structure, e.g., holes, cracks, and grooves. In this paper, two new defect indices based on stress mode shapes are developed to locate single or multiple local structural defects with different severity levels on the marine propeller blade edge. A stress modal analysis was performed on the intact model of the blade and the different models of the defective blade. The first four stress mode shapes along the propeller blade edge were calculated for every model of the blade. The new defect indices called modal stress flexibility change and defect index based on stress modal energy were calculated for each stress mode shape. Firstly, the ability of the two new defect indices calculated for each mode to locate a single defect was investigated. Secondly, the effectiveness of the defect indices calculated from the combination of the first four stress mode shapes is investigated for single and multiple defect localization considering different severity levels. Through the numerical investigation, the modal stress flexibility and defect index based on stress modal energy are promising to locate single or multiple defects in real structures such as marine propeller blades.

At present, propeller blades are machined single-sided with low efficiency. Thus, a propeller needs to be turned over after completion of the machining of the first side of the blade, which requires second clamping and causes a decline in accuracy. Therefore, a double-sided collaborative machining method for propeller blades is proposed herein. Two XYZ-3RPS hybrid kinematics machines were symmetrically distributed to machine both sides of a propeller blade simultaneously; therefore, the blade could be machined in clamping once, improving the machining efficiency and eliminating the accuracy decline caused by repetitive clamping. Moreover, a supporting device with rigid-flexible switching capability was developed to reduce the cantilever length of the blade, thereby eliminating the substantial deformation and vibration of the blade during the double-sided collaborative machining process to ensure machining accuracy. Additionally, the inverse kinematics formula for XYZ-3RPS hybrid kinematics machines was deduced and the elongation of each drive shaft through the cutter location point and cutter orientation was solved in this study. Thereafter, the decomposition method of the blade shift data was applied to obtain the deformation and vibration amplitude of the blade so that the performance of the double-sided cooperative machining could be quantitatively analyzed. Finally, experiments were conducted on the self-developed prototype, and the results verified the effectiveness of the double-sided collaborative machining method in reducing the deformation and vibration of a blade and improving machining efficiency.

Purpose Modern unmanned air vehicles (UAVs) are usually equipped with rotors connected to electric motors that enable them to hover and fly in all directions. The purpose of the paper is to design optimal composite rotor blades for such small UAVs and investigate their aerodynamic performances both computationally and experimentally. Design/methodology/approach Artificial intelligence method (genetic algorithm) is used to optimize the blade airfoil described by six input parameters. Furthermore, different computational methods, e.g. vortex methods and computational fluid dynamics, blade element momentum theory and finite element method, are used to predict the aerodynamic performances of the optimized airfoil and complete rotor as well the structural behaviour of the blade, respectively. Finally, composite blade is manufactured and the rotor performance is also determined experimentally by thrust and torque measurements. Findings Complete process of blade design (including geometry definition and optimization, estimation of aerodynamic performances, structural analysis and blade manufacturing) is conducted and explained in detail. The correspondence between computed and measured thrust and torque curves of the optimal rotor is satisfactory (differences mostly remain below 15%), which validates and justifies the used design approach formulated specifically for low-cost, small-scale propeller blades. Furthermore, the proposed techniques can easily be applied to any kind of rotating lifting surfaces including helicopter or wind turbine blades. Originality/value Blade design methodology is simplified, shortened and made more flexible thus enabling the fast and economic production of propeller blades optimized for specific working conditions.

In the modern aviation environment, research on unmanned aerial vehicles is attractive in many aspects. Integrating efficient propellers into the unmanned aerial vehicle structure helps to enhance the performance factors such as endurance, range, distance to take-off and payload carrying capacity. This paper numerically investigates the configured propeller blades to enhance aerodynamic efficiency and performance parameters. The design parameters such as diameter, pitch, number of blades, and blade shape were configured with highly efficient propellers. The E62 airfoil opted to configure bi-blade, tri-blade, and modified nozzle-shaped ducted propellers and subjected to a computational fluid dynamic process for the varying rotational velocity. The thrust component, lift, drag and aerodynamic efficiency of the propeller blades were studied for the different operating speeds. The performance of E62 airfoil-based propeller was more efficient whereas the ducted blade profile generates the maximum thrust of 7.07N at the maximum angular velocity.

The objective of this study was to investigate the basic properties of composite materials that were made from epoxidized natural rubber and nanosilica to be used as blades for drones. Nanocomposite samples were prepared with 5% of epoxidized natural rubber and epoxy resin loaded with 3% nanosilica. Their resistance against accelerated weathering conditions as well as mechanical properties, including flexural strength, impact strength, and hardness, were evaluated. Based on the findings of this work, the impact strength of the samples decreased 13.33% and 33.33% as a result of exposing them to weathering by UV radiation for 168 h and 336 h, respectively. However, their tensile strength properties enhanced 35.71% and 19.05% for the above corresponding exposure time spars. Experimental composite samples that were made in this study would have great potential to be used as raw material for propeller blade for drones based on their properties evaluated within the scope of this work.

Purpose This paper aims to present a methodology of designing a custom propeller for specified needs. The example of propeller design for large unmanned air vehicle (UAV) is considered. Design/methodology/approach Starting from low fidelity Blade Element (BE) methods, the design is obtained using evolutionary algorithm-driven process. Realistic constraints are used, including minimum thickness required for stiffness, as well as manufacturing ones – including leading and trailing edge limits. Hence, the interactions between propellers in hex-rotor configuration, and their influence on structural integrity of the UAV are investigated. Unsteady Reynolds-Averaged Navier–Stokes (URANS) are used to obtain loading on the propeller blades in hover. Optimization of the propeller by designing a problem-specific airfoil using surrogate modeling-driven optimization process is performed. Findings The methodology described in the current paper proved to deliver an efficient blade. The optimization approach allowed to further improve the blade efficiency, with power consumption at hover reduced by around 7%. Practical implications The methodology can be generalized to any blade design problem. Depending on the requirements and constraints the result will be different. Originality/value Current work deals with the relatively new class of design problems, where very specific requirements are put on the propellers. Depending on these requirements, the optimum blade geometry may vary significantly.

Purpose Development or upgradation of airplanes requires many different analyses, e.g. thermal, aerodynamic, structural and safety. Similar studies were performed during configuration change design of commuter category aircraft equipped with pusher turboprop engines. In this paper, thermo-fluid analyses of interactions of the new propulsion system in tractor configuration with selected elements of airplane skin are carried out. This study aims to check the airplane skin material, and its geometry, including the Plexiglas passenger window material degradation, due to hot exhaust gas plume impingement. The impact of change in exhaust stub angle and asymmetric inboard-outboard stubs on the jet thrust at various flight operating conditions like minimum off-route altitude and cruise performance is assessed. Design/methodology/approach Commercial software-based numerical models were developed. In the first stage, heat and fluid flow analysis was performed over a twin-engine airplane’s nacelle, wing and center fuselage with its powerplant mounted in the high wing configuration. Subsequently, numerical simulations of thermal interactions between the hot exhaust gases, which leave the exhaust system close to the nacelle, flaps and the center fuselage, were estimated for various combinations of exhaust stub angles with asymmetry between inboard-outboard stubs at different airplane configurations and operating conditions. Findings The results of the simulations are used to recommend modifications to the design of the considered airplane in terms of material selection and/or special coatings. The importance and impact of exhaust jet thrust on the overall aircraft performance are investigated. Originality/value The advanced numerical model for the exhaust jet-airplane skin thermal interaction was developed to estimate the temperature effects on the propeller blades and aircraft fuselage surfaces during different flight operating conditions with multiple combinations of stub orientations.

This paper studies application of the method of projected fringes on measurement of the surface topography of double-curved propeller blades, produced in liquid metal, i.e. NiAl-bronze, with surface areas of about one square meter. The measurements are performed inside a grinding hall of a propeller factory. To meet the challenges encountered in such a demanding environment, it is important to keep the equipment as simple and robust as possible. Therefore, a method is developed for locating the fringe positions with sub-pixel accuracy. To avoid the need for a physical reference plane of sufficient area, a method of extrapolating the fringes projected on a small reference plane is applied. The method has been tested on a grinded propeller blade and the results agree very well compared to a standard manual measurement method.

An experimental investigation was conducted to determine the dynamic strain characteristics of marine propellers under non-uniform inflow. Two 7-bladed highly skewed model propellers of identical geometries, but different elastic characteristics were tested at various rotational speeds and free stream velocities in the water tunnel. Two kinds of wire mesh wake screens located 400mm upstream of the propeller plane were used to generate four-cycle and six-cycle inflows. A laser doppler velocimetry (LDV) system located 100mm downstream of the wake screen plane was used to measure the axial velocity distributions produced by the wake screens. Strain gauges were bonded onto the propeller blades in different positions. A customized underwater data acquisition system which can record data off-line was used to record the dynamic strain. The results show that the frequency properties of the blade dynamic strain are determined by the harmonics of the inflow and that the stiffness of the propeller has an essential effect on the dynamic strain amplitudes.

Aluminum is the light weight metal used in various applications of Civil construction, Mechanical & Aeronautical machines etc. next to steels. The banana fibres are having various applications like natural absorbent remediation agent, in making paper cards, tea bags, fabric materials and rope. Also the ash of banana leaf sheath having pozzolanic property and used in green concrete. In aluminum matrix composite(AMC) aluminum is the matrix which forms network and other non-metallic material embedded into the matrix(Banana leaf sheath). Stir casting technique is the most promising and economical technique for processing MMC. In this aluminium alloy is made by using banana leaf sheath ash with aluminium 8011, it provides desirable material properties as the Particulate composite offer several advantages like strengthening the material and also provides specific material properties.