proposal 1. Erdem chose continue to 4. Erdem gained presentation. starts from large parts logically, previous build on this sample İyi Çalışmalar,

Transcription

1 DEPARTMENT OF MECHANICAL ENGINEERING M MIDDLE EAST TECHNICAL UNIVERSITY ANKARA, TURKEY 05 October 2010 This is a sample thesis proposal completed by Erdem Emre Pınar. Erdem completed this thesis proposal at the end of his 1 st year in the MS program (October 2010). This thesis proposal accomplished several goals: 1. Erdem chose his own topic and through this thesis proposal he was able to clearly define his topic, develop a clear path to graduation, and communicate this information to me. Erdem and I met almost every week throughout the summer. Each week Erdem would critically read several papers in this area (as evidenced by making lots of notes in the margins and being able to discuss the relative strengths and weaknesses of the papers), we would meet to discuss the papers, and Erdem would continue to focus his research goal more and more until he arrived at this thesis proposal. 2. Erdem gained valuable experience in academic writing that will make writing his thesis easier. 3. Erdem is taking ME 590 Thesis Seminar immediately after completing this proposal (Fall 2010), and basically he has already completed the course requirements with this presentation. 4. Erdem gained experiencee completing research and documenting this research in writing by a fixed deadline and in a quality manner. Ultimately this gives me confidence that he will be able to complete his thesis by a desired (or required) date without significant problems. Like many graduate students, Erdem is working. His time line to graduation reflects the time commitments of his job. I specifically asked Emre to backdate his timeline so it starts from the Fall 2009 (his 1 st semester) rather than from today so that new students who are working can see how he balances classes, research, work, and graduation date. I did edit parts of Erdem s proposal, but large parts were not edited by me. Overall Erdem has good English writing skills and academic writing skills (ability to organize information logically, present in a clean manner, and follow basic academic writing conventions). If this was his final thesis I would do a lot of small editing. Also, Erdem wrote this without the benefit of any sample from a previous student (he is my 1 st student to fully complete his thesiss proposal). Future students can build on this sample thesis proposal as follow: 1) Include chapter and section numbering; and, 2) Include a table and list of tables (but both of these are minor points when taken in the larger context of what Erdem accomplished with this proposal). İyi Çalışmalar, Derek Baker Derek K. Baker, Ph.D. Associate Professor Department of Mechanical Engineering Middle East Technical University Ankara /Turkey Room E 105 Tel: +90 (312) Fax: +90 (312) E mail: dbaker@metu.edu.tr Web: /~dbaker

2 ENERGY OPTIMIZATION OF A SOLAR POWERED AIRCRAFT TO DEFINE A THREE DIMENSIONAL FLIGHT PATH A THESIS PROPOSAL SUBMITTED TO STUDENT RESEARCH CONFERENCE ON CLEAN ENERGY OF MIDDLE EAST TECHNICAL UNIVERSITY BY ERDEM EMRE PINAR OCTOBER 2010

3 TABLE OF CO TE TS INTRODUCTION.1 LITERATURE REVIEW..7 MODEL...18 PROPOSED WORK PLAN REFFERENCES..27 ii

4 LIST OF FIGURES FIGURES Figure 1 Gossamer Penguin (1980)....8 Figure 2 Icaré 2 (1996) and Solair II (1998)...9 Figure 3 Sunseeker (1990) Figure 4 Centurion ( ) and Helios ( ) Figure 5 Solong (2005) Figure 6 Zephyr (2005) and Solar Impulse Figure 7 Sky-Sailor Figure 8 Model of the Thesis Figure 9 Proposed Work Plan iii

5 I TRODUCTIO Internal combustion engines and gas turbines have been the main power suppliers of modern aircrafts all over the years. Hydrocarbon fuels consuming power units like internal combustion engines have powered most of the aircrafts since Wright Brother s first flight [1]. Possibility of utilizing unconventional energy in aviation field has been evaluated as an alternative to hydrocarbon consuming aircrafts by several research groups and inventors. As a more systematic approach, National Aeronautics and Space Administration (NASA) have always been concerned with solar energy utilization in space vehicles since early satellite researches had been started. Also interest of NASA has continued by inside atmosphere exploration aircrafts of Mars, Venus and Earth. On the other hand, although several attempts have been done by different research groups, unconventional energy sources have never been perceived as a serious alternative to traditional energy sources of aviation up to early 1990 s. As Nam, Soban and Mavris [1] state that, Only a few attempts have reminded the aerospace community of the obvious but not always apparent fact that aircraft can be powered by different energy sources or different power generation devices. In recent years, as a result of attention on renewable and sustainable energy sources, unconventional energy applications like solar powered aircraft have became an interesting research field for aviation. Revolutionary structural designs have been coupled with solar cells or fuel cells. Pioneer electrical system design and high technology electronic devices have equipped solar powered aircrafts with high capacity batteries. Also, various design, estimation, analysis and simulation methods have been developed which specialize on unconventional energy consuming aircrafts like solar powered aircrafts. These methods generate the scientific base for advanced solar powered aircrafts which has more strength, higher efficiency, longer endurance according to former ones. To sum up, it is very clear to indicate that, solar powered aircrafts have become a strong position on aviation field in last 30 years and promise a bright future. Design and development of the solar powered aircraft has became an interesting issue especially for last 20 years with increasing environmental conscious and improvements in solar powered energy conversion. It is very critical to achieve 1

6 the integration of solar energy in aerospace industry to reduce carbon emissions since aerospace industry has a significant role on global fossil fuel consumption. Not only environmental benefits, but also possibility to accomplish some extreme missions is going to be realized on a large scale use of solar energy in aviation. Solar powered aircrafts have a chance to sustain all day long flight with optimum power system, mission and aircraft design. Also, since non-air breathing solar powered engine has not any exhaust gases, it is very hard to be fixed by thermal sensors and more convenient to work together with measuring systems of atmospheric test airplanes. By this aspect of view, it is convenient to state that, connection of solar power conversion systems with aerospace vehicles is going to be an advanced development subject for aviation on near-term future. As mentioned in the former paragraphs, the most significant advantage of using unconventional energy, like solar energy in aerospace industry is its considerable effect on reducing carbon dioxide emissions. Although it does not seem to be feasible to apply solar energy systems in commercial airplanes in middle-term future, promising development of solar powered aircrafts in last 20 years give hope about long-term future applications. Apart from environmental benefits, utilizing solar power energy in aircrafts is going to present various advantages in near-term future. Especially unmanned solar powered aircrafts are suitable to use in many different commercial and non-commercial applications as well as offering innovations in existing applications. For instance, a high resolution real time imaging system equipped unmanned aero vehicle s use to collect high-spatial resolution; multispectral imagery of the Kauai Coffee Plantation is explained by Herwitz, Johnson, Arvesen, Higgins, Leung and Dunagan [2]. In that project, cameras on imaging pod of solar powered airplane Pathfinder-Plus, gives information to mechanical harvesters by perceiving higher commercial value coffee cherries from their color. Likewise, NASA have designed and tested a series of solar powered aircrafts, in order to use in atmospheric flights in the atmosphere of Mars and Venus. According to Landis, Colozza and LaMarre [3], efficient and low-cost solutions for scientific missions can be supplied by solar-powered aircrafts. An eternal flight theoretically could be achieved by solar powered aircrafts and this factor makes solar 2

7 powered aircrafts a prime choice for long-duration missions. Besides, solar powered aircrafts could be an ideal alternative for military applications which are done by hydrocarbon fueled unmanned aircrafts. Since, an ideal solar powered aircraft can theoretically keep flying all day long; there is no fuel cost, noise limitations of electrical engines are very low and there is no exhaust gas which may be fixed by thermal sensors, it appears as a perfect platform for intelligence missions and some other military applications. Design of a solar powered aircraft is a multi-disciplinary subject which concerns basically aircraft structural design, power-system design, propulsion system design, electrical system design and control system design. In this aspect of view, solar powered aircraft design can be considered as a system engineering issue. Since, configuration details of different aero vehicles should differ according to varied applications, an optimum design should be developed for a successful aircraft. Each of these sub-systems can be evaluated and designed according to mission requirements and harmony with other sub-systems. Although some basic design criteria s are same for all solar powered aircrafts like light-weight, some design criteria s offer validity in definite periods of design history, like large aspect-ratio wings for solar powered aircrafts up to now. It is very clear to indicate that, these design criteria s are constrained by some technological limitations of components. By evaluating a solar powered aircraft, a system which is formed by some sub-systems, it is expected that any improvement on any sub-system affects the general performance of aircraft positively. Obtaining higher efficiency in solar cells or fuel cells of any aircraft, would improve the general efficiency of aircraft directly. Improving a higher efficiency propeller would also returns back with more efficient plane likewise choosing a more suitable aerofoil for a definite aircraft. A long endurance flight can be achieved by only improving battery technology dramatically, as well as improving all sub-systems in a small scale. In addition to these studies on subsystems to accomplish more efficient solar powered aircraft, it is possible to realize mission requirements by not interfering sub- 3

8 system design and/or optimizing the harmony of sub-systems as a system engineering approach. Since solar powered aircraft uses solar energy to sustain flight and charge battery, it is directly affected by changes on utilizing grade of sunlight. Parameters such as; day of the year, panel slope angle, atmospheric conditions, etc. affect the total energy per unit area of the panels directly. So the position of the solar aircraft according to the sun becomes very critical in utilizing solar energy. Major angles of solar aircraft on a definite path determine this crucial position. Also flight path of this solar aircraft is involved directly with major angles like banking angle of a constant altitude aircraft gives turning radius of same airplane. Additionally, other parameters like sky cloudiness, dust concentration, pollutants and altitude are essential for a solar powered aircraft which flies inside the atmosphere [4]. To sum up, other parameters outside the design parameters of solar aircraft and its sub-systems like atmospheric conditions and position of the aircraft have a significant role on solar energy utilization. All aircrafts are designed and used for different mission requirements and scenarios. These mission requirements have a direct effect on flying paths, altitudes, velocities of aero vehicles As an example, while loitering would be crucial for intelligence aimed unmanned small aircraft, level flight occupies the most significant part of the flight period for a commercial plane. So that, it is very important to make an optimization between parameters which affect solar utilization (atmospheric condition, position of the aircraft) and mission requirements which governs flight paths and characteristics in order to obtain the long endurance and high efficiency. It can be useful to emphasize that, design of the aircraft does not have a direct role on this optimization process. On the other hand mission requirements affect the design process of the solar powered aircraft so, design of the aircraft is indirectly related with that optimization. In order to make a realistic and useful energy optimization this gives the optimal path of solar aircraft for given mission, general dimensions and properties of aircraft should be given. Since, mission and design of an unmanned aero vehicle is 4

9 very different from a passenger aircraft, result of optimization should differ. So, it can be easily stated that design parameters of solar aircraft and mission requirements would be the input of energy optimization and resulting path planning. Mission requirements should basically involve initial point of flight, final point of flight and allowed duration for an energy optimal path planning. Aircraft design is a more detailed step which maintains location of solar panels on aircraft, general dimensions of aircraft such as aspect ratio, chord length, etc. As mentioned above, the position of solar panel on the aircraft and consequently position of aircraft according to sun is very essential for solar energy utilization. Position of the sun on the sky and its motion on a given period should be an input of optimization process because this position is crucial as determining the major angles of plane on a path and also the path which are the main outputs of the optimization. Also, atmospheric conditions are important factors which affect solar energy utilization. Air density changes with altitude and clouds have shading effects on solar panels. In addition to this atmospheric occurrences, wind has an effect on drag and consequently on energy loss of the aircraft. Energy optimization for an optimal path-planning of a solar powered aircraft features the interaction between aircraft kinematics, energy collection and energy loss [5]. Aircraft kinematics is related with energy loss, because drag is directly connected with energy loss. Also, design of aircraft is directly determines the drag force, likewise it is one of the main factors on solar energy utilization and consequently energy gain. Similarly, all parameters which have mentioned paragraphs above have a response in energy collection, energy loss and aircraft kinematics. Design optimization of any sub-systems of solar powered aircraft (aircraft structural design, power system design, etc.) is not going to be examined in the scope of this thesis. Scope of thesis is going to be related with three dimensional energyoptimal path planning of a solar powered aircraft. Basic design of aircraft and mission information of the flight are the some inputs of energy optimization process. Additionally, position of the sun on the sky, and motion of the sun are added on the 5

10 inputs list. As mentioned above, atmospheric conditions have an essential effect on solar energy utilization. In the range of this thesis, air density is going to change with altitude. On the other hand, it is going to be assumed that, there is no cloud effect and consequently no shading effect on solar panels of aircraft. Furthermore, wind effect is going to be added into the scope according to development process of thesis. After taking inputs, energy optimization algorithm use energetic equations, flight mechanics equations and mission requirements in order to give an output. Outputs of the optimization are three dimensional paths of solar powered aircraft, change of major angles of aircraft (yaw, pitch, and roll) with time. Additionally, energy optimization algorithm would be capable of comparing results of energy optimal path with some major flight scenarios like direct level flight or simple loitering mission. 6

11 LITERATURE REVIEW Although, there were some studies related with utilizing solar energy in aviation before 1980 s, most of the important researches focus on this subject has been intensified for last thirty years. National Aeronautics and Space Administration (NASA) is one of the major associations which is related with solar energy utilization in aerospace vehicles starting from 1960 s since their satellite project is needed to be get involved with solar energy utilization. After 1990 s solar powered aircraft design projects of NASA continued with in atmosphere solar powered design researches of Venus, Mars and Earth. Additionally NASA has many publications about design, analysis and applications of solar power energy usage in aerospace field. Additionally, many universities mostly from United States, Switzerland and European Union have many significant studies about solar energy applications of aero-space field. Although most of them are related with design of solar powered airplanes, some of them are keen on energy optimal path planning of different various flight scenarios. Furthermore, some studies are related with interesting commercial and non-commercial applications of solar powered aircrafts. Electrical power usage for flight started primitively in France in the year of In this date, electrical system was powered by a steam engine. Development of gasoline engines postponed the use of electrical propulsion system for aero-vehicles for a long time. First officially recorded electric powered radio controlled flight has been done in United Kingdom in June 1957 by Colonel H.J. Taplin. Also, Fred Militky made an electrical powered flight in October 1957 with his uncontrolled model [6]. Although, there had been some electrically powered flight attempts before, use of solar power in model planes was started with the birth of photovoltaic technology in 1954, at Bell Telephone Laboratories. Sunrise I made the first flight of a solar powered aircraft on November 1974 in United States. Sunrise I was kg with power output 450 W, flew 20 minutes in 100 m altitude. The first demonstration continued with Sunrise II, which has 600 W power output with 14% efficiency solar cells and reduced weight of kg. Dream of solar powered flight 7

12 continued in Europe with 150 seconds flight of Solaris on August Duration of solar powered flights rapidly rise with further solar aircrafts like Solar Solitude and Solar Excel [6]. With proven feasibility of unmanned model aircrafts, researches on manned solar powered aircraft have started to become widespread in aviation field. Larry Mauro flew with Solar Riser on April Solar Riser has flown for ten minutes with its 350 W and nickel-cadmium battery which has needed to charge for 3 hours before flight. Although, Solar Riser achieved a manned flight with solar energy utilization, energy of the sun was not sufficient to manage the flight without help of nickel-cadmium batteries. This stage would have been solved with Gossamer Penguin on May Flight of Gossamer Penguin with its 13 years old pilot Marshall MacCready is accepted as first manned solar energy powered flight. The Dupont Company was the sponsor of the Gossamer Penguin and decided to support the Solar Challenger as a new airplane which could cross the English Channel. Solar Challenger achieved to fly from Paris to London in 5 hours 23 minutes on July 1981 with no onboard energy storage system [6]. Figure 1: Gossamer Penguin (1980) [6] Development of manned solar powered airplanes continued with Sunseeker at the end of the Sun seeker managed to cross the United States in 121 hours 8

13 of total 21 solar powered flights. In European side of the Atlantic, journey of solar powered aircrafts has gone forward with Icaré 2 and Solair II [6]. Figure 2: Icaré 2 (1996) and Solair II (1998) [6] Figure 3: Sunseeker (1990) [6] Apart from manned flight of solar powered aircrafts, high altitude long endurance eternal flights are aimed to get realized by solar powered aircraft designers and especially by NASA. NASA s Pathfinder made its first flight at Dryden in After, Environmental Research Aircraft Sensor Technology (ERAST) program had started in NASA in 1994; Pathfinder joined to this program and exceeded solar powered aircraft altitude record by reaching 15392m in Later, Pathfinder was modified to Pathfinder Plus which was aimed to validate new elements before flight on NASA s new aircraft Centurion. Centurion was capable to fly meters, and could carry over 300 kilograms of payloads. 9

14 Although, Centurion had a lithium battery, it was not sufficient to carry on a flight for all night. Helios was the last plane of NASA solar powered aircraft series, which was made to achieve two essential aims. First was, making a sustained flight in meters ( ft), and second manage to fly non-stop for 24 hours. Helios has been successful in first goal, but unable to success its second mission because of structural failures [6]. Figure 4: Centurion ( ) and Helios ( ) [6] Second goal of Helios, was later achieved by unmanned solar powered aircraft Solong which has made a 24 hour and 11 minutes flight. After this eternal flight, Zephyr aircraft of British Company QinetiQ has broken the longest sustained solar powered aircraft record by flying for 54 hours on September 2007 [6]. Figure 5: Solong (2005) [6] 10

15 The following goal for solar powered aircrafts is achieving a continuous flight for 24 hours with a manned aircraft. Swiss aircraft, Solar-Impulse is very close to achieve this mission by flying over 16 hours with a pilot in the summer of Figure 6: Zephyr (2005) and Solar Impulse [6] Brief history of solar power energy applications in aviation has examined up to now. A significant database has been occurred with this researches and attempts which is going to enlighten the new studies in this field. Most of the publications about solar powered aircrafts are related with their design, analysis, optimizations and different applications. E. Rizzo and A.Frediani [4] from University of Pisa formed a preliminary design model of a solar powered aircraft. This solar powered aircraft was chosen to be suitable for high altitude long endurance missions. They aimed to form a mathematical model for this solar powered aircraft preliminary design. This mathematical model would also be useful to compare four different aircraft configurations such as flying wing, conventional aircraft, twin boom aircraft and biplane aircraft. Solar energy utilization details (available solar energy, scattering, etc.), energy balance (net solar energy, required energy, etc.), photovoltaic panels, aircraft structural design procedures are all evaluated in order to obtain a precise mathematical model. They validated their mathematical model, according to Helios platform of NASA. After validation, they used their validated mathematical model in order to compare four different aircraft configurations. Furthermore, they made a cost analysis and evaluation of critical technologies for this solar powered aircraft. 11

16 Anthony J. Colozza [7] worked on the Effect of Power System Technology and Mission Requirements on High Altitude Long Endurance Aircraft as a part of NASA Lewis Group on November His aim in this study was determining effect of different power system components and mission requirements on the sizing of solar powered long endurance aircraft. Colozza evaluated the energy balance diagram of a solar powered aircraft in order to find the energy gain and energy loss of a 24 hours flight. Scheme of propulsion and power system has been shown clearly and then weight estimation of all components has been done. Changes of wing area and wing span by aspect ratio are given for different fuel cells and photovoltaic cells in different altitudes are given by graphs as a result of this study. This paper is very useful to examine the effect of PV cells and fuel cells on structural parameters of a solar powered aircraft. In October 1998 Anthony J. Colozza, David A. Scheiman and David J. Brinker [8] examined the application of GaAs/Ge space solar cells on solar powered aircrafts. An experimental solar powered aircraft was built in order to see the performance of these solar cells. Authors mentioned about aircraft design, material selection, flight tests (in order to determine flight worthiness) and remote control system of this aircraft in the paper. Furthermore, performance of solar array and power system (which consists of an 11 cell nickel-cadmium battery and solar array) are examined. Authors mentioned about the solutions for condensation problems related with solar arrays. To sum up, this aircraft and related paper formed a technology demonstration for the application of GaAs/Ge solar cells for solar powered aircrafts. Not only the design and analysis of solar powered aircrafts and its subsystems but also some specific issues like the effects of flight types on endurance have examined by researchers and academicians. For instance, David F. Chichka and Jason L. Speyer [9] are investigated the positive effect of formation flight on solar powered aircrafts for sustained endurance. According to them, it is theoretically possible to create a formation flight system that is capable of truly infinite endurance. With this study they mainly indicated the important effect of high aspect 12

17 ratio wings and formation flight on decreasing the effect of induced drag for aircrafts. As a different example to interesting issues which have been studied by solar powered aircraft researchers, a commercial application of a solar powered unmanned aircraft is examined by a group of academicians from United States. Herwitz, Johnson, Arvesen, Higgins, Leung and Dunagan [2] used NASA aircraft Pathfinder Plus in order to help precision agriculture activities in Kauai Coffee Plantation of United States. Real time imaging system which mounted on a solar powered aircraft, guides mechanical harvesters in this application. Although, telemetry system and image analysis were subjected mostly, some structural issues like payload tests and structural properties examined in some parts of this paper. Another study of NASA in Kauai was related with flight tests of NASA solar powered aircraft fleet. The Pathfinder, Pathfinder Plus and Helios were the issue of these tests. Atmospheric risks like atmospheric turbulence, cloud cover, runway winds and excess wind drift at altitudes aloft are experienced in these flights and analyzed in the paper of Ehernberger, Donohue and Teets [10]. They also gave the record of weather events from June 1997 to June 2003 according to altitudes. According to Authors, results of this tests and analyses, advance in airframe design, solar cell efficiency, batteries and fuel cells are demonstrating new approaches to high-altitude long-endurance aircraft for applications to earth observations, communications and atmospheric sciences. Design of solar powered airplanes for continuous flight was studied by PhD. Thesis of André Noth [6] from ETH Zurich in September First of all, author summarized the history of solar powered aviation very clearly which has also been benefited in the first part of literature survey section in this thesis proposal. Also literature survey section of André Noth s Thesis presents a good guide for many different issues related with solar energy application in aviation. In the second part of his thesis, basics concepts of solar powered aircraft are briefly introduced which are related with flight mechanics, aerodynamics, solar cells, energy storage, maximum power point trackers, electric motors and propellers. Third part, which is defined as 13

18 the theoretical heart of the thesis by author, defines conceptual design methodology of a solar powered aircraft. Mathematical models for requirement of daily electrical energy, obtaining of daily solar energy, mass predictions of components are constituted before summary and resolution of design problem is given in this third part. Application of mathematical model which is formed in third part is done in the fourth part of this thesis. The chosen, aircraft concept is named as Sky-Sailor which is aimed to fly over 24 hours for 3 months in summer. Final configuration is chosen according to the given mathematical model. Also real time simulation environment model of solar flight is done. Realization and Testing of the Sky- Sailor is explained in the fifth part of André Noth s thesis. Transition from preliminary design to detailed design is the general scope of this section with manufacturing and validations by tests. Structure details, airfoil selection, propulsion group (propeller, motor, gearbox and motor controller), control surface actuators, battery, solar generator, control and navigation system and ground control station are all designed comprehensively in this section. Summary of a continuous 27 hours test flight is explained in the end of fifth section which bases as a validation process for theoretical parts of this thesis. Figure 7: Sky-Sailor [6] As researches and publications about solar powered aircrafts have increased rapidly by time, necessity of specialized design, analysis and estimation methods 14

19 have also appeared. Nam, Soban and Mavris [1] from Georgia Institute of technology developed a power based sizing method which is more suitable for unconventional energy consuming aircrafts. Before this study, traditional sizing methods for aircrafts had been more suitable for hydrocarbon fuel consuming aircrafts. One of the major differences between these two methods is weight of the consumable energy (hydrocarbon fuel) changes during the flight despite there is no change in the weight of solar energy. As a result, authors state that Their paper proposes a more generalized formulation which is also applicable for sizing aircraft consuming unconventional types of energy. As a part of NASA researches on solar powered aircrafts Landis, Colozza and LaMarre [11] examined the feasibility of an atmospheric flight on Venus with a solar powered aircraft. Atmospheric properties of Venus and advantages of a solar powered flight for test missions were introduced in the first parts of paper. Then, some design properties which are related with folding inside the Venus atmosphere and aero-shell selection were explained. As a very essential section, critical design parameters of aircraft which are based on power requirement and aero-shell are determined. Mass estimation and brief information about some sub-systems like propeller and electric motor are given. In the final part of this paper, efficiency of aircraft and effect of aspect ratio on solar powered aircrafts were examined. Another study of NASA which is related with solar powered aircrafts has done by a group of students in Worchester Polytechnic Institute. Goal of this study is pertained to confirming the availability of solar utilization in propulsion system of an aircraft. It is planned to sustain a one hour flight in a figure eight flight path at an altitude of 50 meters. Initial altitude of the flight is obtained with a launching catapult system. Configuration of the solar powered aircraft is defined as a nonconventional, high-wing aircraft with two carbon fiber composite support in the paper. Design properties of power system and fuselage, general dimensions and parameters of aircraft and quantitative properties of control surfaces are indicated in the introduction part of the study. Then, aircraft sizing and weight estimation is done by stating the mass of all components. Airfoils of wing and tails, planform type and optimum operational points are chosen according to aerodynamic design and 15

20 analysis. Structural design details are explained in structural design and analysis (ANSYS analysis tool is used) part by mainly giving the details about material selection. NiCad batteries are selected to serve as a secondary power source which can help to solar cells in critical maneuvers. Several motor-propeller combinations were tested in wind tunnels and most suitable configuration is selected according to the test results. In the end section of this paper, construction procedure of the aircraft is explained [12]. As a more relevant subject to the scope of this thesis proposal, several papers about energy optimal path planning for solar powered aircrafts are published by some academicians from University of Michigan. A.T. Klesh and Pierre T. Kabamba [13] from University of Michigan published a forerunner paper about Energy-Optimal Path Planning for Solar- Powered Aircraft in Level Flight in This study is mainly indicated the role of banking angle on energy balance of a solar powered aircraft. So that, effect of bank angle on aircraft kinematics and energetics is examined mainly to reach the optimal path of a solar powered aircraft. Aircraft kinematic model, energy collection model and energy loss model are examined in the modeling section. Then, mission is described and dynamic optimization problem is presented in problem formulation section. In the optimal path planning section, required equations in order to provide the optimal paths are derived. Then, the problem is divided into small parts to get a numerical approximation and graph of the energy optimal path is drawn in the discretization procedure section. At the end of the paper, experimental connection of power-ratio with energy-ratio and summary of extreme paths are given by authors. According to the authors, most essential activity of this paper is showing the increase of energy collection by both efficient design and optimal path planning for a solar powered aircraft. Another study of Klesh and Kabamba [14] is related with Energy-Optimal Path Planning and Perpetual Endurance. Selected solar powered aircraft design concept is same as the plane in the former paper. It is an unmanned solar powered aircraft which has solar cells on the wings. As a difference from the former study, 16

21 this paper is interested in two different missions. First is traveling between two different points within allowed duration by maximizing the final energy and second is loiter perpetually from a given position. Again, relation with energy balance and aircraft kinematics is used for optimization. Although general sections of paper which form the optimization process are very similar with former study, some modifications are done in order to enable the optimization of two different missions. Also, difference in total energy between optimal flight trajectory and direct flight is figured in this paper. As a major addition, comparison of design requirements between Earth and Mars is done by the authors for this paper. Spangelo, Gilbert and Girard joined to Kabamba and Klesh [15], in their last paper which has searched in this literature survey about energy optimal path planning for solar powered aircrafts. As an important difference with other two papers, altitude is taken into account with this paper. In former two studies altitude is constant so flight path is on a plane without ascending and descending. In this study, solar powered aircraft fly along the surface of a vertical cylinder. Up to this study, authors have not study for pitching maneuvers of aircraft. So, main addition of this paper is developing a new spline-based optimization process in periodic and cylindrical constraints. Another important contribution to the literature is giving the change of flight angles, velocity, forces and power by time as an output of analysis. On the other hand, air-density and position of the sun assumed to be constant in this paper although air-density changes with altitude and position of sun changes continuously on the sky with time. An important common point about all of these three papers which are related with energy optimal path planning is presenting a very useful literature survey. This literature survey sheds light on the history of energy related studies on solar powered aircrafts. 17

22 MODEL Scope of the thesis is mainly related with the energy optimal path planning of a solar powered aircraft instead of concentrating the possible improvements on solar powered aircraft design or any sub-system design. Energy optimization on a route of the solar powered aircraft includes mainly flight mechanics and solar energy conversion subjects. Flight mechanics comprises mostly drag, thrust, weight and lift forces. Aerodynamic properties, general dimensions, structural properties and power system of the aircraft affect these forces directly. Solar energy conversion subject contains energetic equations which are established firmly by solar radiation and energy balance. Additionally mission requirements are the other constraints which have effects on optimization process. Other researches and studies related with same subject use these flight mechanics and solar energy conversion concepts to determine an optimal path for a given mission. Since these main concepts establish the mathematical model which states optimum flight path, it is important for these main concepts to correspond physical conditions on a large scale. For instance, it is important to take into account air density change with altitude for a three dimensional flight path optimization. Similarly, change in the position of the sun on sky with time is very critical for optimization process of a long endurance aircraft. To sum up, although most of the studies related with energy optimal path planning use same subjects (flight mechanics and energetics) to obtain a model, success of the model on reflecting the real conditions (for a given flight mission) shows the achievement of an optimization study. General structure of the model consists four main parts; inputs, obtaining mathematical model, developing computer codes and outputs. Additionally, results of the model which are given in output part are checked and verified by comparison and validation part in the end. Required model structure to make a successful energy optimal path planning is shown in Figure.8 clearly. 18

23 Figure 8: Model of the Thesis Input section is involved with obtaining required data that is needed in forming mathematical model to have a realistic optimization results in the end of the thesis. Model aircraft, mission requirements, geographical position and atmospheric conditions selections are the main subject headings that are going to be searched in this section. First step of the obtaining inputs section is mission requirements selection. A long endurance flight is corresponding with the spirit of the solar powered aircraft as well as being an accommodating model for many popular commercial and noncommercial applications of this aircraft. Also, it is very available to choose a high altitude flight for a solar powered aircraft to maximize solar energy utilization. More concretely, it is required to specify a starting point and a finishing point to obtain a path. Additionally, type of the flight according to the application is important. Mainly, level flight and loitering generate the main type of flights in popular solar powered aircraft applications. At the same time, it should be required to give the periods of flight parts (take off, level flight, loitering, etc.). 19

24 Model aircraft selection is done by scanning the aircraft database very detailed. A high altitude long endurance aircraft is selected by also considering mission requirements. Some major designs which have essential effect on solar powered aviation history are examined in literature survey section of this thesis proposal. By examining these designs also evaluating mission requirements and availability on access to the critical data, an ideal aircraft design is selected. It very important to reach some critical dimensions and properties of design such as; wing aspect ratio, chord length, lift and drag coefficients, weight, solar panel area, etc. Model aircraft properties can be easily divided into two main groups: aircraft structural properties and power system properties. It can be practical to add propulsion system properties into power system properties section. Although solar powered aircraft is comprised some other sub-systems, those two are mainly related with the subject of this thesis study. The other step is atmospheric conditions selection. Since atmospheric conditions have a direct effect on solar energy utilization it is important to identify these conditions in the start of optimization process. As a major issue in this part, airdensity change with altitude should be taken into account. Also, scattering effect of clouds should be considered carefully according to the flight mission scenarios. Since a high altitude long endurance aircraft maintains most of its flight time above clouds, it can be available to consider no scattering effect for level flight or high altitude loiter. Moreover, although wing does not have a considerable effect on solar utilization thrust and lift forces are influenced directly from this atmospheric fact. To sum up, it can be unnecessary to take into account all of those atmospheric events for short endurance aircrafts but it is very critical to choose appropriate conditions for a given flight mission for a realistic simulation and optimization. Finally, geographical position selection has a direct effect on energy utilization also having indirect effect on major forces and consequently on flight mechanics. Geographical position is connected with the position of the sun on the sky. It is an obligation to know the position of the sun in order to determine the major angles of aircraft on account of this flight path of aircraft. For a long endurance aircraft, position of the sun should not be assumed to stay constant in a 20

25 particular point on the sky. Since position of the sun changes continuously and slowly on a path on the sky, major angles and flight path are directly affected from this change. Some mathematical manipulations should be done in order to make calculations easier when motion of the sun is taken into account. Apart from being necessary for an accurate optimization process, data accessibility of the route of the sun on the sky for a given date should be considered. It is a very essential milestone of geographical position selection to reach a reliable path of sun motion at an available date. Obtaining mathematical model is the theoretical heart of this thesis. Required mathematical equations are derived from basic flight mechanic equations and solar radiation equations. Some series of critical manipulations and derivations should be done to obtain these final equations. According to the mathematical model of Spangelo, Elmer, Gilbert, Klesh, Kabamba and Girard [15], velocity and acceleration vectors are expressed in terms of moving coordinate system in the start of model. Then, aerodynamic forces and thrust vectors are defined to get the equations of motion. Then, lift and drag forces and coefficients are expressed in aerodynamic model part in the usual way. Authors need these forces to use in the equations of motion. Also, major dimensions of selected aircraft (aspect ratio, wing span, etc.) are used in this aerodynamic model. After defining all of these concepts and equations in Aircraft Model and Kinematics section, Energy Model is constituted. Solar incidence angle and angle between sun and aircraft are the main components of this model. According to the authors, solar incidence angle (κ) is defined as a function of sun s elevation (e), azimuth (ã), aircraft heading angle (Ψ) and pitch angle (θ) as: cos(κ) = -cos(e)sin(θ)sin(ã-ψ) + sin(e)cos(θ) (1) In the next step, it is available to calculate the power collected as a function of solar cell efficiency (η), solar spectral density (SD), total wing area (S) and solar incidence angle (κ) as shown in Equation 2. Power in = η.sd.s.cos (κ) (2) 21

26 Then, it is available to find total energy inlet by integrating power in (Equation.2) for all over the flight period. Finally, in the Computational Maximization of Total Energy section, conditions which satisfy the mission requirements are added to optimization equations and results are obtained. Similar to the given study in literature, flight mechanics and energetic equations are used to obtain required mathematical model for optimization process. Additionally, required attachments and modifications are made to satisfy extra conditions in the scope of this thesis. Also, it is possible to use new methods and solutions to obtain three dimensional paths which include altitude of the aircraft. After obtaining mathematical model, it is appropriate to develop an energy optimization algorithm. An advanced programming knowledge is required to develop a useful and practical code in addition to being trustworthy and realistic. In the inputs level, some mission requirements are given by users such as initial point, final point and flight period. Besides, some mission requirements are going to be decided to select by users manually or accepted to lie inside algorithm, in the development process of codes like major aircraft dimensions and orientation of solar panels. On the other hand, some inputs like geographical position selection are accepted to lie inside algorithm. This means a particular geographical position is accepted for optimization. So, geographical position of the airplane could not be available to select by users because of limited data. Finally, outputs are taken after the process of computer codes. Energy optimal three dimensional paths and change of major angles by time are the main outputs of this thesis. Additionally, it is optional to make a comparison and validation process. Similar studies of related people can be used for this comparison process. For instance, two dimensional projections of three dimensional paths may be useful to check with the results of dimensional optimization studies also by neglecting some inputs. 22

27 PROPOSED WORK PLA Proposed work plan for Energy Optimization of a Solar Powered Aircraft to Define a Three Dimensional Flight Path thesis subject is formed from four main periods. First period is related with the Master of Science courses. Second period is an entrance for thesis workout which is concentrating on summing up input data. Third period is the theoretical heart of thesis which is dealing with obtaining mathematical model and developing computer codes. Final period of the thesis workout is comparing and validating results. Additionally error correction and writing thesis text are included in this period. First period is named as Focus on Courses in the given Gantt chart (Figure. 9). The main goal of this period is being successful on courses simply. Also, it is an important issue to take courses that are related with thesis subject. Since, flight mechanics and energetics are the main fields which are directly related with thesis subject, it is convenient to take courses in these subjects. Solar energy utilization, solar radiation, thermodynamics, kinematics, flight kinematics& mechanics (and related other courses) are all available subjects to use directly in the thesis. Also it is extremely needed to develop programming knowledge in this first period by concentrating on programming projects. Since, it is a long period to be capable of using programming languages skillfully, perceiving programming missions seriously provides a great simplicity for the thesis period. Second period of the thesis is a time interval that is related with providing and selecting useful data for energy optimization process. Model aircraft selection, aircraft mission selection, geographic position selection and atmospheric condition selection are main goals of this timeline. Model aircraft selection is primarily related with accessibility to the design parameters and main dimensions of aircraft. Model aircraft selection and aircraft mission selection are interconnected with each other because all aircrafts are designed according to a particular mission. So that, it is crucial to be consistent on mission and aircraft design harmony. It can be advantageous to find several aircraft designs for a selected particular mission in case of facing problems with selected model in later stages. After deciding aircraft model 23

28 and mission, the next step is geographical position selection. Geographical position is the operational point of the aircraft in the earth atmosphere. It is essential to reach the path of sun in the sky for a given date in geographical position selection level. Also, it is required to select an operational date to get the path of sun. Generally longest day time is selected as the operational date in the energy analysis studies about solar powered aircrafts. Atmospheric condition selection has an important effect on mathematical model and computer code. Without any doubt, more realistic results are taken by taking atmospheric condition account more accurately. In the scope of atmospheric condition selection, air density change by altitude should be searched. Also effect of clouds should be assumed for different missions (take off, level flight, loitering, etc.). Optionally, in the case of taking wind effect into account, change of wind speed averages for given altitude and geometric position should be learned. Additionally it is important to know that, both effect of clouds and wind effect are both related with operational date. As the theoretical heart of the thesis, third period is formed from two main sections. First is obtaining mathematical model and second is developing computer codes (see Figure.8). A series of straight forward flight mechanics equations and energetic equations about solar energy utilization are taken from literature first. Some mathematical manipulations should be done to express the energy optimization model from these equations. It is possible to use any mathematical methods that are used in similar studies as well as making additions to these methods for new needs. It is critical to reflect inputs accurately to the basic equations and choosing correct manipulation methods in this section. Secondly, a programming code is developed to compute the mathematical model. Results are taken in the end of this programming process. It is important to develop a flexible routine which means that it should be easy to interfere to any part of the code in any time. Of course, main mission of this second section is developing a computer code which shows the accurate results of mathematical model simply. The final period is involved with getting outputs and evaluating them precisely. As the main output, three dimensional path of solar powered aircraft is given clearly in the end of optimization process. Additionally change of major 24

29 angles, velocity and important forces by time should be indicated. Giving the graphs of these parameters can be advantageous on visualizing the results. As a comparison section, energy balance parameters of a solar powered aircraft which flies on an energy optimal path can be compared with a direct level flight basically. Moreover, two dimensional reflection of three dimensional flight can be compared with former similar studies on two dimensional paths. As indicated clearly in the Gantt chart (Figure. 9), period of the study includes a three years timeline. The study has already started with focusing on courses in the September of 2009, this period continues up to the end of the June After finishing the courses, inputs searching period starts with model aircraft selection and aircraft mission selection by the July of 2011 and takes two months up to the end of the August. After those two steps, input searching period continues with geometric position selection and atmospheric condition selection parts. These two parts need a month of workout which takes all of the September. After completing searching inputs period, it is needed to start obtaining mathematical model in the starting of October. This essential part continues for two months and finishes by the end of the November of After obtaining the mathematical model same period continues with developing the computer codes. This programming part starts in early December of 2011 and finishes in the end of the January of After finishing this third period, last period of the study starts and occupies the left six months up to the end of the thesis workout. The final period mainly includes two important tasks. First of them is comparison and validation part which starts in the early January and ends in the start of the March of It is important to emphasize that developing computer codes section shares a month timeline with comparison and validation section in the January of The second part of last period includes thesis writing and error correction. This last part has a four months timeline from early March to the end of the June of Four months period is evaluated to be suitable for this task because a significant timeline can be required for the correction process of a possible error. Apart from these thesis development processes, a literature survey timeline starts with the July of the 2011 and continues up to the end of the June of

30 Figure 9: Proposed Work Plan 26