The aim of this investigation was to review literature for the most suitable aeroelastic tailoring analysis tools for long slender composite structures, and integrate them into an aeroelastic tailoring process. The JS1C Revelation is a high performance sailplane made from modern composites, mostly carbon fibre. This has the advantage of being more rigid than traditional engineering materials, thereby reducing the effects of the twisting deflections on these long slender structures due to aerodynamic loads. The implementing of aeroelastic tailoring can create bend-twist couples for performance improvements. Composites enable the use of aeroelastic tailoring to improve gliding performance. Flaperon 3 of the JS1C 21 m was used as the design problem for aeroelastic tailoring. Aeroelastic tailoring was done by analysing the flaperon structure at the different layup angles to determine the correct design point to tailor the structure to improve aerodynamic performance at thermalling and cruise, but mostly cruise since it accounts for 70% of the flight time. The composite structure analysis tool has the objective to get results during concept design. This directed the line of research of analysis tools to a solution method of two dimensional cross-section mesh properties projected onto a one dimensional beam. The literature of Hodges had good verification and published data on the analysis tools. The analysis tools comprised of three programs that were not very user friendly. Thus the author compiled a Matlab program as a user interface tool to run the three programs together. The aeroelastic tailoring process systematically works through the known design variables and objectives, which are given as inputs to the analysis tool. The analysis tool plots the coupling data versus layup angle. From this the best layup angles for a sought-after bend-twist couple is used to aeroelastically tailor the wing. The composite structure analysis tool’s accuracy was verified by analysing cantilever beam deflections and comparing the results with hand calculations and SolidWorks Simulation FEM results. The analysis tool’s accuracy was further verified by comparing the aerodynamic torsional load’s twist deflections with thin walled tube theory. The analysis tool was validated by applying a torsional load at the tip of a JS1C production Flaperon 3 in an experimental setup and then comparing this result with the Flaperon 3 modelled in the analysis tool. These comparisons also ensured that the model’s composite material properties and the meshing of the flaperon cross-sectional properties were correct. This aeroelastic tailoring was validated with the advantage of then being used to improve the aerodynamic performance of the JS1C Revelation 21 m tip’s flaperon. This improvement could be made by making use of a tailored bend-twist couple to reduce the effect of the aerodynamic load’s twist deflections. A test sample of the JS1C 21 m flaperon 3 was used to validate aeroelastic tailoring. The test sample was designed to be 1 m in length and have all the specified tailoring coupling characteristics that could improve the aerodynamic performance of the JS1C 21 m flaperon 3. The test sample was manufactured according to Jonker Sailplanes manufacturing standards and experimentally set up with the same applied deflections as in the analysis tool. The calculated bend-twist values and the experimental setup results were similar with a negligible difference, assuming small displacements and an aspect ratio greater than 13; this confirmed that the PreVABS/VABS/GEBT composite structure analysis tool could be used in aeroelastic tailoring to predict and design the bend-twist couple needed to improve the aerodynamic performance of the JS1C 21 m. While the twist behaviour of Flaperon 3 was improved by the tailored bend-twist couple, it was still necessary to add pre-twist as well, to fully address the effects of twisting by aerodynamic forces. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

The aim of this investigation was to review literature for the most suitable aeroelastic tailoring analysis tools for long slender composite structures, and integrate them into an aeroelastic tailoring process. The JS1C Revelation is a high performance sailplane made from modern composites, mostly carbon fibre. This has the advantage of being more rigid than traditional engineering materials, thereby reducing the effects of the twisting deflections on these long slender structures due to aerodynamic loads. The implementing of aeroelastic tailoring can create bend-twist couples for performance improvements. Composites enable the use of aeroelastic tailoring to improve gliding performance. Flaperon 3 of the JS1C 21 m was used as the design problem for aeroelastic tailoring. Aeroelastic tailoring was done by analysing the flaperon structure at the different layup angles to determine the correct design point to tailor the structure to improve aerodynamic performance at thermalling and cruise, but mostly cruise since it accounts for 70% of the flight time. The composite structure analysis tool has the objective to get results during concept design. This directed the line of research of analysis tools to a solution method of two dimensional cross-section mesh properties projected onto a one dimensional beam. The literature of Hodges had good verification and published data on the analysis tools. The analysis tools comprised of three programs that were not very user friendly. Thus the author compiled a Matlab program as a user interface tool to run the three programs together. The aeroelastic tailoring process systematically works through the known design variables and objectives, which are given as inputs to the analysis tool. The analysis tool plots the coupling data versus layup angle. From this the best layup angles for a sought-after bend-twist couple is used to aeroelastically tailor the wing. The composite structure analysis tool’s accuracy was verified by analysing cantilever beam deflections and comparing the results with hand calculations and SolidWorks Simulation FEM results. The analysis tool’s accuracy was further verified by comparing the aerodynamic torsional load’s twist deflections with thin walled tube theory. The analysis tool was validated by applying a torsional load at the tip of a JS1C production Flaperon 3 in an experimental setup and then comparing this result with the Flaperon 3 modelled in the analysis tool. These comparisons also ensured that the model’s composite material properties and the meshing of the flaperon cross-sectional properties were correct. This aeroelastic tailoring was validated with the advantage of then being used to improve the aerodynamic performance of the JS1C Revelation 21 m tip’s flaperon. This improvement could be made by making use of a tailored bend-twist couple to reduce the effect of the aerodynamic load’s twist deflections. A test sample of the JS1C 21 m flaperon 3 was used to validate aeroelastic tailoring. The test sample was designed to be 1 m in length and have all the specified tailoring coupling characteristics that could improve the aerodynamic performance of the JS1C 21 m flaperon 3. The test sample was manufactured according to Jonker Sailplanes manufacturing standards and experimentally set up with the same applied deflections as in the analysis tool. The calculated bend-twist values and the experimental setup results were similar with a negligible difference, assuming small displacements and an aspect ratio greater than 13; this confirmed that the PreVABS/VABS/GEBT composite structure analysis tool could be used in aeroelastic tailoring to predict and design the bend-twist couple needed to improve the aerodynamic performance of the JS1C 21 m. While the twist behaviour of Flaperon 3 was improved by the tailored bend-twist couple, it was still necessary to add pre-twist as well, to fully address the effects of twisting by aerodynamic forces. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

A criação racional de abelhas sem ferrão, conhecida como meliponicultura, é uma atividade crescente no Brasil e sua demanda abriu o campo para pesquisas que favorecem esse mercado. Além disso, o papel essencial desempenhado por esses insetos na polinização tem chamado atenção para o seu uso sustentável na prática agrícola. Nesses aspectos, alguns trabalhos são direcionados à aquisição de conhecimento básico sobre a biologia dessas abelhas que embasem técnicas de manejo e aprimoramento da sua criação. Um fator crucial é a multiplicação de colmeias em um intervalo de tempo menor a partir da obtenção artificial de rainhas, que foi o foco deste trabalho. A espécie aqui envolvida, Tetragona clavipes, tem distribuição ampla em território brasileiro e um potencial relevante no fornecimento de produtos como mel, pólen, cera e resinas, apesar dos poucos dados sobre seu manejo na literatura afim. Sua diferenciação de castas depende da quantidade de alimento ingerido durante a fase larval. A primeira parte da pesquisa envolveu a criação de larvas in vitro, onde foi caracterizada a quantidade limiar de alimento larval para diferenciação de castas: entre 45 e 50 µL. Nessas condições emergiram operárias e rainhas; entre 20 e 40 µL, apenas operárias e a partir de 60 até 110 µL, apenas rainhas. Houve mortalidade alta das larvas, com média de 40%, sendo o controle de umidade relativa o ponto crítico. A segunda parte do trabalho envolveu a formação de minicolônias, em que grupos de operárias jovens (aproximadamente 50) foram mantidos com rainhas virgens em caixas pequenas. 26 minicolônias foram montadas, dentre estas, 5 com rainhas naturais. Somente duas rainhas naturais foram fecundadas e tiveram sucesso na fundação dos ninhos. Nesses dois casos o número de operárias utilizado foi maior (em torno de 200) e com idades diferentes. O principal fator que limitou essa etapa foi a agressividade das operárias durante a fase para aceitação das rainhas virgens. Nesse ponto, a estratégia mais eficiente foi a introdução de rainhas, ainda em fase de pupa, dentro de cápsulas de cerume da própria minicolônia, apesar de não terem permanecido nas caixas mesmo depois de terem sido aceitas. Uma análise por morfometria geométrica, com os programas de computador tpsDig e MorphoJ, mostrou a diferença no padrão de venação entre as asas de operárias e rainhas obtidas em laboratório. Em todas as colônias observadas foi constatada a presença de um fungo que se desenvolve naturalmente no interior das células de cria, cujas hifas são ingeridas pela larva. Entretanto, não foi possível o seu isolamento em meio de cultivo. Apesar do número pequeno de ninhos novos formados, o estudo desta espécie possibilitou a aquisição de dados importantes para a continuidade das pesquisas e também para conduzir seu manejo mais eficiente, acrescentando informações até então desconhecidas sobre sua biologia e seu comportamento. / The rational creation of stingless bees, known as meliponiculture in Brazil, is a growing activity and its demand opened the field for research and many works that favor this market. Moreover, the essential role played by these insects as pollinators has drawn attention for its sustainable use in crop pollination. In these respects, some studies are directed to the acquisition of basic knowledge about the biology of these bees which to base management techniques and improvement on its creation. A crucial factor is the multiplication of hives in a shorter interval of time by the artificial obtainment of queens, which is the focus of present work. The species involved here was Tetragona clavipes, which has a wide distribution in Brazil and a significant potential to supply products such as honey, pollen, wax and resins, despite the few data about its management in the related literature. Its caste differentiation depends only on the amount of larval food ingested at the larval stage. The first step of the research involved the development of larvae in vitro, when was characterized the amount of larval food that is the threshold for its caste differentiation: between 45 and 50 µL. In these conditions workers and queens emerge; between 20 and 40 µL, only workers and from 60 to 110 µL, only queens. There was a high mortality of larvae with an average of 40%, where the control of relative humidity was the critical point. The second part of the work involved the attempted to form mini colonies, where groups of young workers (aroud 50) with virgin queens were kept in small boxes. 26 mini colonies were assembled, among these, five with virgins natural queens. Only two natural queens were fertilized and founded nests with success. In these cases the number of workers put inside box was higher (around 200) and with different ages. The main factor that had limited this step was the aggressiveness of the workers during the acceptance of the virgin queens. At this point, the most effective strategy was the introduction of queens still in the pupal stage, inside capsules of cerumen from the own mini colonies, despite not having stayed in the boxes probably by other reasons, even when already were accepted. Additional analysis using geometric morphometrics, with the computer programs tpsDig and MorphoJ, showed a difference in the pattern of wing venation between workers and queens obtained in laboratory. In all colonies observed also was found the presence of a fungus that grows naturally inside of brood cells, whose hyphae are ingested by the larvae. However, it could not be isolated in culture medium. Despite the small number of new nests acquired, the study of this species allowed the acquisition of important data for further research and also to conduct its management more efficient, adding previously unknown details about its biology and behavior.

There is currently a great deal of interest within the aviation community in the design of small, slow-flying but manoeuvrable uninhabited vehicles for reconnaissance, surveillance, and search and rescue operations in urban environments. Inspired by observation of birds, insects, fish and cetaceans, flapping wings are being actively studied in the hope that they may provide greater propulsive efficiencies than propellers and rotors at low Reynolds numbers for such Micro-Air Vehicles (MAVs). Researchers have posited the Strouhal number (combining flapping frequency, amplitude and forward speed) as the parameter controlling flapping wing aerodynamics in cruising flight, although there is conflicting evidence. This thesis explores the effect of flapping frequency and amplitude on forces and wake structures, as well as physical mechanisms leading to optimum propulsive efficiency. Two-dimensional rigid airfoils are considered at Reynolds number 2,000 ??? 40,000. A compressible Navier-Stokes simulation is combined with numerical and analytical potential flow techniques to isolate and evaluate the effect of viscosity, leading and trailing edge vortex separation, and wake vortex dynamics. The wake structures of a plunging airfoil are shown to be sensitive to the flapping frequency independent of the Strouhal number. For a given frequency, the wake of the airfoil exhibits ???vortex lock-in??? as the amplitude of motion is increased, in a manner analogous to an oscillating circular cylinder. This is caused by interaction between the flapping frequency and the ???bluff-body??? vortex shedding frequency apparent even for streamlined airfoils at low Reynolds number. The thrust and propulsive efficiency of a plunging airfoil are also shown to be sensitive to the flapping frequency independent of Strouhal number. This dependence is the result of vortex shedding from the leading edge, and an interaction between the flapping frequency and the time for vortex formation, separation and convection over the airfoil surface. The observed propulsive efficiency peak for a pitching and plunging airfoil is shown to be the result of leading edge vortex shedding at low flapping frequencies (low Strouhal numbers), and high power requirements at large flapping amplitudes (high Strouhal numbers). The efficiency peak is governed by flapping frequency and amplitude separately, rather than the Strouhal number directly.

The conventional Mini and Large scale Unmanned Aerial Vehicle systems span anywhere from approximately 12 inches to 12 feet; endowing them with larger propulsion systems, batteries/fuel-tanks, which in turn provide ample power reserves for long-endurance flights, powerful actuators, on-board avionics, wireless telemetry etc. The limitations thus imposed become apparent when shifting to Micro Aerial Vehicles (MAVs) and trying to equip them with equal or near-equal flight endurance, processing, sensing and communication capabilities, as their larger scale cousins. The conventional MAV as outlined by The Defense Advanced Research Projects Agency (DARPA) is a vehicle that can have a maximum dimension of 6 inches and weighs no more than 100 grams. Under these tight constraints, the footprint, weight and power reserves available to on-board avionics and actuators is drastically reduced; the flight time and payload capability of MAVs take a massive plummet in keeping with these stringent size constraints. However, the demand for micro flying robots is increasing rapidly. The applications that have emerged over the years for MAVs include search&rescue operations for trapped victims in natural disaster succumbed urban areas; search&reconnaissance in biological, radiation, natural disaster/hazard succumbed/prone areas; patrolling&securing home/office/building premises/urban areas. VTOL capable rotary and fixed wing flying vehicles do not scale down to micro sized levels, owing to the severe loss in aerodynamic efficiency associated with low Reynolds number physics on conventional airfoils; whereas, present state of the art in flapping wing designs lack in one or more of the minimum qualities required from an MAV: Appreciable flight time, appreciable payload capacity for on-board sensors/telemetry and 6DoF hovering/VTOL performance. This PhD. work is directed towards overcoming these limitations. Firstly, this PhD thesis presents the advent of a novel Quad-Wing MAV configuration (called the QV). The Four-Wing configuration is capable of performing all 6DoF flight maneuvers including VTOL. The thesis presents the design, conception, simulation study and finally hardware design/development of the MAV. Secondly, this PhD thesis proves and demonstrates significant improvement in on-board Energy-Harvesting resulting in increased flight times and payload capacities of the order of even 200%-400% and more. Thirdly, this PhD thesis defines a new actuation principle called, Fixed Frequency, Variable Amplitude (FiFVA). It is demonstrated that by the use of passive elastic members on wing joints, a further significant increase in energy efficiency and consequently reduction in input power requirements is observed. An actuation efficiency increase of over 100% in many cases is possible. The natural evolution of actuation development led to invention of two novel actuation systems to illustrate the FiFVA actuation principle and consequently show energy savings and flapping efficiency improvement. Lastly, but not in the least, the PhD thesis presents supplementary work in the design, development of two novel Micro Architecture and Control (MARC) avionics platforms (autopilots) for the application of demonstrating flight control and communication capability on-board the Four-Wing Flapping prototype. The design of a novel passive feathering mechanism aimed to improve lift/thrust performance of flapping motion is also presented.

There is currently a great deal of interest within the aviation community in the design of small, slow-flying but manoeuvrable uninhabited vehicles for reconnaissance, surveillance, and search and rescue operations in urban environments. Inspired by observation of birds, insects, fish and cetaceans, flapping wings are being actively studied in the hope that they may provide greater propulsive efficiencies than propellers and rotors at low Reynolds numbers for such Micro-Air Vehicles (MAVs). Researchers have posited the Strouhal number (combining flapping frequency, amplitude and forward speed) as the parameter controlling flapping wing aerodynamics in cruising flight, although there is conflicting evidence. This thesis explores the effect of flapping frequency and amplitude on forces and wake structures, as well as physical mechanisms leading to optimum propulsive efficiency. Two-dimensional rigid airfoils are considered at Reynolds number 2,000 ??? 40,000. A compressible Navier-Stokes simulation is combined with numerical and analytical potential flow techniques to isolate and evaluate the effect of viscosity, leading and trailing edge vortex separation, and wake vortex dynamics. The wake structures of a plunging airfoil are shown to be sensitive to the flapping frequency independent of the Strouhal number. For a given frequency, the wake of the airfoil exhibits ???vortex lock-in??? as the amplitude of motion is increased, in a manner analogous to an oscillating circular cylinder. This is caused by interaction between the flapping frequency and the ???bluff-body??? vortex shedding frequency apparent even for streamlined airfoils at low Reynolds number. The thrust and propulsive efficiency of a plunging airfoil are also shown to be sensitive to the flapping frequency independent of Strouhal number. This dependence is the result of vortex shedding from the leading edge, and an interaction between the flapping frequency and the time for vortex formation, separation and convection over the airfoil surface. The observed propulsive efficiency peak for a pitching and plunging airfoil is shown to be the result of leading edge vortex shedding at low flapping frequencies (low Strouhal numbers), and high power requirements at large flapping amplitudes (high Strouhal numbers). The efficiency peak is governed by flapping frequency and amplitude separately, rather than the Strouhal number directly.

A criação racional de abelhas sem ferrão, conhecida como meliponicultura, é uma atividade crescente no Brasil e sua demanda abriu o campo para pesquisas que favorecem esse mercado. Além disso, o papel essencial desempenhado por esses insetos na polinização tem chamado atenção para o seu uso sustentável na prática agrícola. Nesses aspectos, alguns trabalhos são direcionados à aquisição de conhecimento básico sobre a biologia dessas abelhas que embasem técnicas de manejo e aprimoramento da sua criação. Um fator crucial é a multiplicação de colmeias em um intervalo de tempo menor a partir da obtenção artificial de rainhas, que foi o foco deste trabalho. A espécie aqui envolvida, Tetragona clavipes, tem distribuição ampla em território brasileiro e um potencial relevante no fornecimento de produtos como mel, pólen, cera e resinas, apesar dos poucos dados sobre seu manejo na literatura afim. Sua diferenciação de castas depende da quantidade de alimento ingerido durante a fase larval. A primeira parte da pesquisa envolveu a criação de larvas in vitro, onde foi caracterizada a quantidade limiar de alimento larval para diferenciação de castas: entre 45 e 50 µL. Nessas condições emergiram operárias e rainhas; entre 20 e 40 µL, apenas operárias e a partir de 60 até 110 µL, apenas rainhas. Houve mortalidade alta das larvas, com média de 40%, sendo o controle de umidade relativa o ponto crítico. A segunda parte do trabalho envolveu a formação de minicolônias, em que grupos de operárias jovens (aproximadamente 50) foram mantidos com rainhas virgens em caixas pequenas. 26 minicolônias foram montadas, dentre estas, 5 com rainhas naturais. Somente duas rainhas naturais foram fecundadas e tiveram sucesso na fundação dos ninhos. Nesses dois casos o número de operárias utilizado foi maior (em torno de 200) e com idades diferentes. O principal fator que limitou essa etapa foi a agressividade das operárias durante a fase para aceitação das rainhas virgens. Nesse ponto, a estratégia mais eficiente foi a introdução de rainhas, ainda em fase de pupa, dentro de cápsulas de cerume da própria minicolônia, apesar de não terem permanecido nas caixas mesmo depois de terem sido aceitas. Uma análise por morfometria geométrica, com os programas de computador tpsDig e MorphoJ, mostrou a diferença no padrão de venação entre as asas de operárias e rainhas obtidas em laboratório. Em todas as colônias observadas foi constatada a presença de um fungo que se desenvolve naturalmente no interior das células de cria, cujas hifas são ingeridas pela larva. Entretanto, não foi possível o seu isolamento em meio de cultivo. Apesar do número pequeno de ninhos novos formados, o estudo desta espécie possibilitou a aquisição de dados importantes para a continuidade das pesquisas e também para conduzir seu manejo mais eficiente, acrescentando informações até então desconhecidas sobre sua biologia e seu comportamento. / The rational creation of stingless bees, known as meliponiculture in Brazil, is a growing activity and its demand opened the field for research and many works that favor this market. Moreover, the essential role played by these insects as pollinators has drawn attention for its sustainable use in crop pollination. In these respects, some studies are directed to the acquisition of basic knowledge about the biology of these bees which to base management techniques and improvement on its creation. A crucial factor is the multiplication of hives in a shorter interval of time by the artificial obtainment of queens, which is the focus of present work. The species involved here was Tetragona clavipes, which has a wide distribution in Brazil and a significant potential to supply products such as honey, pollen, wax and resins, despite the few data about its management in the related literature. Its caste differentiation depends only on the amount of larval food ingested at the larval stage. The first step of the research involved the development of larvae in vitro, when was characterized the amount of larval food that is the threshold for its caste differentiation: between 45 and 50 µL. In these conditions workers and queens emerge; between 20 and 40 µL, only workers and from 60 to 110 µL, only queens. There was a high mortality of larvae with an average of 40%, where the control of relative humidity was the critical point. The second part of the work involved the attempted to form mini colonies, where groups of young workers (aroud 50) with virgin queens were kept in small boxes. 26 mini colonies were assembled, among these, five with virgins natural queens. Only two natural queens were fertilized and founded nests with success. In these cases the number of workers put inside box was higher (around 200) and with different ages. The main factor that had limited this step was the aggressiveness of the workers during the acceptance of the virgin queens. At this point, the most effective strategy was the introduction of queens still in the pupal stage, inside capsules of cerumen from the own mini colonies, despite not having stayed in the boxes probably by other reasons, even when already were accepted. Additional analysis using geometric morphometrics, with the computer programs tpsDig and MorphoJ, showed a difference in the pattern of wing venation between workers and queens obtained in laboratory. In all colonies observed also was found the presence of a fungus that grows naturally inside of brood cells, whose hyphae are ingested by the larvae. However, it could not be isolated in culture medium. Despite the small number of new nests acquired, the study of this species allowed the acquisition of important data for further research and also to conduct its management more efficient, adding previously unknown details about its biology and behavior.

<p>The use of drones, also called unmanned aerial vehicles (UAVs), is increasing every day. These aircraft are piloted either remotely by a human pilot or completely autonomously by an on-board computer. UAVs are typically equipped with a video camera providing a live video feed to the operator. While they were originally developed mainly for military purposes, many civil applications start to emerge as they become more affordable.<p><p><p>Micro air vehicles are a subgroup of UAVs with a size and weight limitation; many are designed also for indoor use. Designs with rotary wings are generally preferred over fixed wings as they can take off vertically and operate at low speeds or even hover. At small scales, designs with flapping wings are being explored to try to mimic the exceptional flight capabilities of birds and insects. <p><p><p>The objective of this thesis is to develop a control mechanism for a robotic hummingbird, a bio-inspired tail-less hovering flapping wing MAV. The mechanism should generate moments necessary for flight stabilization and steering by an independent control of flapping motion of each wing.<p><p><p>The theoretical part of this work uses a quasi-steady modelling approach to approximate the flapping wing aerodynamics. The model is linearised and further reduced to study the flight stability near hovering, identify the wing motion parameters suitable for control and finally design a flight controller. Validity of this approach is demonstrated by simulations with the original, non-linear mathematical model.<p><p><p>A robotic hummingbird prototype is developed in the second, practical part. Details are given on the flapping linkage mechanism and wing design, together with tests performed on a custom built force balance and with a high speed camera. Finally, two possible control mechanisms are proposed: the first one is based on wing twist modulation via wing root bars flexing; the second modulates the flapping amplitude and offset via flapping mechanism joint displacements. The performance of the control mechanism prototypes is demonstrated experimentally. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Highly-loaded turbomachine blades can stall under off-design conditions. In this regime, the flow can separate close to the leading edge of the blade in a periodic manner that can lead to blade vibrations, commonly referred to as stall flutter. Prior experimental studies on stall flutter have been at large Re (Re ~ 106). In the present work, motivated by applications in Unmanned Air Vehicles (UAV) and Micro Air Vehicles (MAV), we study experimentally the forces and flow fields around an oscillating blade at low Re (Re ~ 3 x 104). At these low Re, the flow even over the stationary blade can be quite different. We experimentally study the propensity of an isolated symmetric and cambered blade (with chord c) to undergo self-excited oscillations at high angles of attack and at low Reynolds numbers (Re ~ 30, 000). We force the blade, placed at large mean angle of attack, to undergo small amplitude pitch oscillations and measure the unsteady loads on the blade. From the measured loads, the direction and magnitude of energy transfer to/from the blade is calculated. Systematic measurements have been made for varying mean blade incidence angles and for different excitation amplitudes and frequencies (f). These measurements indicate that post stall there is a possibility of excitation of the blade over a range of Strouhal Numbers (St = fc/U) with the magnitude of the exciting energy varying with amplitude, frequency and mean incidence angles. In particular, the curves for the magnitude of the exciting energy against Strouhal number (St) are found to shift to higher St values as the mean angle of attack is increased. We perform the same set of experiments on two different blade shapes, namely NACA 0012 and a compressor blade profile, SC10. Both blade profiles show qualitatively similar phenomena. The flow around both the stationary and oscillating blades is studied through Particle Image Velocimetry (PIV). PIV measurements on the stationary blade show the gradual shift of the flow separation point towards the leading edge with increasing angle of attack, which occurs at these low Re. From PIV measurements on an oscillating blade near stall, we present the flow field around the blade at different phases of the blade oscillation. These show that the boundary layer separates from the leading edge forming a shear layer, which flaps with respect to the blade. As the Strouhal number is varied, the phase between the flapping shear layer and the blade appears to change. This is likely to be the reason for the observed change in the sign of the energy transfer between the flow and the blade that is responsible for stall flutter.

This master's thesis discusses the possibilities of safe-life extension program for ZLIN Z 126 and 226 airplanes, which despite their age and long-end production are still widespread and popular not only in the Czech Republic. The age of these aircraft is also related to the fact, that some aircraft are already approaching its border life, so there is an interest for the longest possible technical and legislative airworthiness. As mentioned in my bachelor's thesis, during the existence of this model series, there was no major damage occurred, except for sporadic exfoliation corrosion of wing flanges. Experience with maintenance of this aircraft points to certain underestimation of the current 5500hrs lifetime and it is obvious to suggest possible steps to increase the current limit. The thesis is therefore considered in this context the possibility of producing new wing flanges made of another material, performed the calculation for wing fatigue exchanged with flanges and designed technological process of this exchange, so that ZLIN Z 126 and 226 airplanes can be safely operated in the future.