Analytical investigation of quasi-aeroservoelastic behaviour of an aircraft spoiler

Abstract

The application of science and mathematics to solve problems is called as engineering. In most of engineering process, accuracy is directly dependent on cost which can be defined as function of time and money. In the problem solving processes, there are a lot of assumptions in exchange for accuracy in order to reduce cost and find more solutions in a short time. Reducing solution time provides ability to enhance problem solving capabilities by increasing number of ways to solve problems, finding different sources of problems or optimizing solution methods. At the end, exact solution may not be reached, but more related problems can be solved with approximate solutions in limited time. With advanced technology in aviation industry, accurate designs are more important than before due to desire for better performance. In order to increase accuracy, research and development studies are performed, such as analytical formulizations and tests. Owing to high cost and long durations of test operations, analytical solutions are preferred to be supported if possible. Especially for aircraft design, due to safety consideration and aim for lightweight designs, designers have to balance time, weight and cost without any penalty for safety. In this condition, analytical solutions helps to reduce solution time for lightweight designs and create extra time for optimization studies. In this study, behavior of spoiler structures are investigated for desired deflection angle under external loads by means of analytical solutions. Spoiler is a control surface which can create drag and lift for aircraft. Spoiler structures have been implemented to aircrafts in order to improve control, especially while rolling, landing and braking. One of the main objectives of a spoiler structure is to increase drag for landing and braking applications. Additionally, spoilers can be used to increase roll rate for acrobatic or trainer aircrafts. Under aerodynamic load, as all structures deform, spoiler structures show a deformation. It affects spoiler deflection mechanism because points of mechanism changes when spoiler deformation occurs. In this case, spoiler rotates back towards to its original position where back rotation angle is usually not able to be considered in mechanism design. This condition creates dwindle for effectivity of spoiler surface which means reducing performance of aircraft. In this thesis, an analytical formulation study is performed in order to foresee back rotation angles of spoiler structures and gain ability to design mechanism for more convenient deflection angles for spoilers under aerodynamic loads. Result curves are created by curve fitting method in order to monitor and compare behavior of both analytical method analyses and finite element method analyses. Error functions are defined and calculated to find out tendency difference between analytical method and finite element method analyses under changing variables. For realistic deflection angles, the aim of this study is to accomplish accurate analytical results with error percentage below ±15% for back rotation angles and ±2% for final deflection angle compared to finite element method analyses. In the introduction section, engineering approaches for development studies are explained. Importance of accuracy for engineering application is tried to be stated by support of relations between accuracy and other engineering concerns. These concerns can be expressed with time, cost and other concerns, such as health issues, ethic concerns and safety. Also, scope and purpose of thesis are determined in this section. In the literature review section, spoiler structures and their duties on aircraft are stated. Dimensions are shown with examples and figures from aircraft industry. Grid stiffened spoiler concepts are explained in addition to commonly used structural architectures, such as composite and metal builtup structures.