MASTER THESIS. Design of a retractable, electric propulsion system for sailplanes. Wojciech Damian Jaron SUPERVISED BY. Dr Antonio Manuel Mateo García - PDF

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MASTER THESIS Design of a retractable, electric propulsion system for sailplanes Wojciech Damian Jaron SUPERVISED BY Dr Antonio Manuel Mateo García Universitat Politècnica de Catalunya Master in Aerospace

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MASTER THESIS Design of a retractable, electric propulsion system for sailplanes Wojciech Damian Jaron SUPERVISED BY Dr Antonio Manuel Mateo García Universitat Politècnica de Catalunya Master in Aerospace Science & Technology May 2012 This Page Intentionally Left Blank Design of a retractable, electric propulsion system for sailplanes BY Wojciech Damian Jaron DIPLOMA THESIS FOR DEGREE Master in Aerospace Science and Technology AT Universitat Politècnica de Catalunya SUPERVISED BY: Dr Antonio Manuel Mateo García Ciència Mat. i Eng. Metal lúrgica This Page Intentionally Left Blank ABSTRACT The aim of this thesis was the design of a retractable, electric propulsion system for sailplanes, which could eliminate the main drawbacks of internal combustion engines. The design process was based on a number of modern sailplanes, within the meter class, with sustainer operation in mind. One of the goals was to create a universal propulsion system that could be fitted to various aircrafts. The first part of the project concerned the selection of the key components of an electric propulsion system. First, the required power and thrust were calculated, and based on the obtained results a suitable electric motor was chosen. For this motor, an electronic controller was selected. Later, the estimation of propeller parameters was performed. Finally, battery basics were discussed and a battery was selected. The second part of the project concerned CAD modeling of the retractable electric propulsion system. The used materials were discussed in the beginning. The design process focused on two main assemblies: the propeller folding mechanism and the retractable structure. The complete result, the individual sub-assemblies and the most important solutions were presented. The use of composite materials was an important point of this thesis. Performance analysis was done after the system had been designed. The retractable electric propulsion system was designed with optimum results. A fullscale CAD model was created. The designed propulsion system can be considered as universal due to its relatively low weight, adequate power and compact size in the retracted position. Custom-made accessories facilitate mounting. A visit to the glider manufacturer Allstar PZL was the source of information about possible mounting solutions and battery placement options. The designed propulsion system can be used as a sustainer for all designated sailplanes. Self-launching proved possible in case of the lightest sailplanes. With similar power and flight duration, the electric propulsion system should be able to compete with petrol powered sustainer systems within the same class. This Page Intentionally Left Blank Table of Contents CHAPTER 1: INTRODUCTION Sailplanes Gliding Motor gliders Modes of operation Electric propulsion The concept of electric propulsion The aim of this project Sailplane size and weight constraints... 7 CHAPTER 2: SELECTION OF THE PROPULSION SYSTEM COMPONENTS Estimation of the required thrust and power Foreword Basic Equations Results and discussion Selection of the electric motor Electric motor types Key parameters of electric motors Electric motor selection Motor control Brushless controller basics Controller choice Controller accessories Wiring Selection of the propeller Foreword Propeller types Propeller estimations Propeller choices Summary Selection of the batteries Battery type consideration Lithium-ion batteries Battery selection Battery charger CHAPTER 3: CAD DESIGN OF THE PROPULSION SYSTEM Design basics Foreword Materials used Design of the folding propeller The propeller blades The folding mechanism Design of the retractable system The geometry CAD design of the retractable structure Servo system Motor cooling... 69 3.4. Results and installation Propulsion system dimensions Structure weight estimation Visit to the Allstar PZL mounting ideas Battery placement and aircraft balance Final performance evaluation CHAPTER 4: CONCLUSIONS Electric propulsion and its key components Advantages of electric propulsion and designated sailplanes Selected components Project accomplishments CAD Model Installation of the propulsion system Achieved performance Enviromental study Designed system features Bibliography... 97 List of Figures Figure 1.1 General sailplane outline... 1 Figure 1.2 Specifications of a 15 meter class competition sailplane... 2 Figure 1.3 Left one-cylinder Solo 210 engine, right two cylinder Solo Figure 1.4 Left Wankel powered system, right a conventional two-stroke engine... 3 Figure 1.5 Silent 2 TARGA and its propulsion system... 4 Figure 1.6 Outline of the retractable propulsion system on the Silent 2 TARGA glider... 4 Figure 1.7 The electric propulsion of the Antares 20E, developed by Lange Aviation... 6 Figure 1.8 The IC propulsion with the Solo 2615 engine... 6 Figure 2.1 Effect of altitude on the point of minimum required thrust... 9 Figure 2.2 Variation of the rate of climb with velocity Figure 2.3 Plot of the glide ratio versus the airspeed for Silent Club sailplane Figure 2.4 A simple model for drag estimation Figure 2.5 Classification of electric motors Figure 2.6 A single-phase outer-rotor BLDC motor Figure 2.7 Outer-rotor motor diagram Figure 2.8 A single phase, inner rotor motor Figure 2.9 Components of a three-phase, outer-rotor motor Figure 2.10 Example of a three-phase winding Figure 2.11 Powered paraglider trike with the Paracell motor Figure 2.12 The propulsion system developed by Paracell Figure 2.13 JM2 motor developed by JOBY Motors Figure 2.14 JM2 motor specifications Figure 2.15 E-Spyder powered by the PD 20 motor Figure 2.16 Close-up on the PD 20 motor and the battery packs Figure 2.17 Comparison of the electric E-Spyder and a petrol powered Flightstar Figure 2.18 Specifications of the PD Figure 2.19 Waveforms (Phases U, V, W, commutation steps P1, P2 etc.) Figure 2.20 Hall effect sensor principle Figure 2.21 A Power Block Controller Figure 2.22 Power Block 20 Specifications Figure 2.23 Throttle control for the Yuneec power systems Figure 2.24 Key operated On/Off switch Figure 2.25 Yuneec digital display Figure 2.26 Wiring diagram Figure 2.27 Comparison of a single-blade propeller with a five-blade unit... 33 Figure 2.28 AE-1 Silent glider, both blades are folded parallel to the mast Figure 2.29 Three-blade, electric paraglider propulsion Figure 2.30 The pitch triangle Figure 2.31 Propeller slip Figure 2.32 AeroDesign Propeller Selector Figure 2.33 Ragone plot - practical values of specific power and specific energy Figure 2.34 Specific energy and energy density of various battery systems Figure 2.35 Typical Li-poly discharge curve Figure 2.36 Typical li-poly cycle graph Figure 2.37 Specifications of the 31 Ah lithium polymer battery Figure 2.38 Specifications of the Yuneec E-charger Figure 3.1 An example of CAD design and the machined product Figure 3.2 Various types of screws Figure 3.3 Various types of screws Figure 3.4 Car suspension part, machined from 7075 series aluminum Figure 3.5 Anodized aluminum part Figure 3.6 One-piece CFRP bicycle frame Figure 3.7 View into a composite fiberglass fuselage Figure 3.8 Propeller blade and the view of the airfoil Figure 3.9 The composite blade assembly Figure 3.10 The folding propeller in the folded position Figure 3.11 The folding propeller in the unfolded position Figure 3.12 Close-up of the folding mechanism folded Figure 3.13 Close-up of the folding mechanism unfolded Figure 3.14 The tensile-load-bearing rod exposed Figure 3.15 Parallelogram linkage and the paths of selected nodes Figure 3.16 Propulsion system in the extended position (left) and with folded blades (right) 60 Figure 3.17 Electric propulsion system in the retracted position Figure 3.18 Extended position angles Figure 3.19 Folded position side view Figure 3.20 Motor mount and the foam damper Figure 3.21 Motor mount assembly Figure 3.22 Carbon fiber composite beams and the fuselage mount Figure 3.23 Servo motor position control Figure 3.24 Left servo motor with a planetary gearbox, right servo with a worm drive Figure 3.25 Worm drive Figure 3.26 Details of the main carbon fiber beam and the lock... 66 Figure 3.27 Locking mechanism locked (left) and unlocked (right) Figure 3.28 Locking mechanism and its servo Figure 3.29 Retracting mechanism Figure 3.30 Center of gravity Figure 3.31 Epac a 10 kw electric paraglider propulsion system Figure 3.32 Extended propulsion system general dimensions Figure 3.33 Retracted propulsion system general dimensions Figure 3.34 SZD-55-1 in flight Figure 3.35 Control linkages on the SZD Figure 3.36 Rudder (SZD-55-1) and Elevator (different glider) Figure 3.37 Control linkages in the section behind the wing Figure 2.38 Wing spar and linkages on the SZD Figure 3.39 Bronze bushing in the fiberglass wall Figure 3.40 Mounting location on the SZD Figure 3.41 Example of installation using fiberglass formers and steel alloy profiles Figure 3.42 Shape of the formers that allows clearance for control linkages Figure 3.43 Tail fin of the SZD Figure 3.44 Layout of the DG-808C Figure 3.45 Baggage compartment on the SZD Figure 3.46 Available space in the nose of the SZD Figure 3.47 A new model for drag estimation Figure 4.1 Specifications of the Power Drive 20 electric motor Figure 4.2 Power Drive 20 electric motor Figure 4.3 Power Block 20 Specifications Figure 4.4 Wiring diagram Figure 4.5 Specifications of the 31 Ah lithium polymer battery Figure 4.6 Specifications of the Yuneec E-charger Figure 4.7 Folding mechanism unfolded (left) and folded (right) Figure 4.8 Propulsion system in the extended position (left) and with folded blades (right).. 90 Figure 4.9 Electric propulsion system in the retracted position Figure 4.10 Extended propulsion system general dimensions Figure 4.11 Retracted propulsion system general dimensions Figure 4.12 Example of installation using fiberglass formers and steel alloy profiles Figure 4.13 Shape of the formers that allows clearance for control linkages... 93 This Page Intentionally Left Blank List of tables Table 1.1 Specifications of modern sailplanes... 8 Table 2.1 The estimated required thrust and power for a set of m gliders Table 2.2 Effect of speed on the required thrust and power for the Silent Club sailplane Table 2.3 Summary, dark green self-launch capability, light green sustainer operation only Table 2.4 The required input and shaft power of the electric motor ( = 0.85, = 0.8) Table 2.5 Division of the sailplanes into four velocity groups Table 2.6 Calculation of minimum required pitch Table 2.7 Performance data for the four chosen propellers Table 2.8 Approximated parameters of various battery systems Table 2.9 Abuse test results of a lithium-ion cell Table 2.10 Endurance results with the three candidate power sources Table 2.11 Endurance and altitude gain Table 3.1 Propulsion system weight calculation results Table 3.2 Performance data for SZD Table 3.3 Performance summary for various sailplanes Table 4.1 Specifications of modern sailplanes Table 4.2 Propulsion system weight calculation results Table 4.3 Performance data for SZD Table 4.4 Performance summary for various sailplanes... 95 This Page Intentionally Left Blank Introduction 1 Chapter 1 INTRODUCTION 1.1. Sailplanes Gliding Gliding is a recreational activity and a competitive sport. Most sailplanes are used for recreational purposes, however some of them found use in the military sector. Fig. 1.1 describes the general layout of a typical small sailplane. Figure 1.1 General sailplane outline [14] Sailplanes are usually not equipped with an engine, because they can stay in the air for a long time. The gliders gain altitude in columns of rising air. There are three types of natural wind formations that cause the air to rise [8]: Ridge lift created by the wind going upward, following the natural shape of the terrain (hill or a mountain) Wave lift generated at a certain distance from a hill or a mountain by the oscillating air Thermals created when the Sun heats the ground unevenly. The heated ground transfers some of the energy to the air, which in turn rises. To achieve good performance, sailplanes have to be light and have to create minimal drag for the amount of generated lift. On the other hand, sailplanes usually carry water ballast, which increases the gliding speed. This helps the glider reach the next column of rising air faster. The downside is that the aircraft will climb slower. Competition pilots usually start with the ballast and can drop it immediately after the start, depending on the weather conditions. Ballast has to be dropped before landing. 2 Title of the Master Thesis There are many types of gliders: single person, two people, designed for training or competition, and made from a variety of materials. This thesis will focus on smaller, single person gliders. The particular design features applied to these gliders are: Lack of engine (motor gliders are discussed in the next paragraph) High aspect ratio (long, narrow wings allow to achieve lower drag and better glide angle) [2] Streamlined fuselage Tight cockpit for one person Minimum instruments on board Use of lightweight composite materials Single, retractable wheel for landing All of these requirements lead to a high Lift-to-Drag ratio, which is an indicator of glider performance [14]. The L/D is simply the glide ratio it describes how far the glider can fly for a given amount of lost altitude. Fig. 1.2 contains the specifications of a typical high performance glider. Figure 1.2 Specifications of a 15 meter class competition sailplane [14] Motor gliders Glider aircrafts have to be kept as light as possible to achieve good gliding capabilities, and for this reason they usually have no engine. They are launched by other aircrafts or winches. However, some are equipped with an engine petrol or electric. The benefit is substantial: the pilot can stay longer in the air and climb using engine power. They extend range allow pilots to fly further away from the landing zone. They provide a safety value the aircraft can fly to a suitable landing location and is not forced to land if it loses too much altitude. Some of them can launch themselves using the engine. However, these installations are quite heavy and impact the gliding performance significantly when they are not used. Introduction 3 Generally, the propeller is mounted on a retractable mast. When the propulsion system is not used, the mast is retracted into the fuselage, to reduce the drag. With the system retracted, there is virtually no drag added over a non-motorized version of the glider. The power is transmitted from the engine, mounted at the bottom of the mast, through a belt drive. The belt drive adapts the rotational speed of the engine to the requirements of the propeller. The relatively large propeller operates at lower RPM (Revolutions Per Minute) than the petrol engine delivers. Usually, the power source is a petrol, two-stroke, one- or two-cylinder engine, such as the 16 horse-power (approx. 12 kw) Solo 210 manufactured by SOLO Kleinmotoren GmbH [19]. A bigger, more powerful engine from SOLO Kleinmotoren GmbH is the Solo that develops 38 kw. It can be used for self-launching motor gliders up to 600 kg of gross weight [25]. Both engines are shown in Fig 1.3. Some sailplanes are equipped with a Wankel engine. These engines have higher power-to-weight ratio than piston engines with the same displacement (capacity). Yet, they are not popular because of the high maintenance and shorter service life. Fig. 1.4 is a comparison of the Wankel-powered system and a two-stroke installation. Figure 1.3 Left one-cylinder Solo 210 engine [60], right two cylinder Solo [25] Figure 1.4 Left Wankel powered system [50], right a conventional two-stroke engine [25] 4 Title of the Master Thesis There exists a variety of designs but for the purpose of this project only the standard retractable system with a rigid mast will be presented. Fig. 1.5 shows the propulsion system of the Silent 2 TARGA manufactured by Alisport [22]. It is a 13.3 m sailplane equipped with a 28 hp (ca. 21 kw), single-cylinder, air-cooled engine [22]. Fig. 1.6 presents the general layout of the retractable system installed in this glider. It features an unusual one-blade propeller, which allows for a much smaller opening in the fuselage than a conventional propeller. This solution, however, is not common. The propeller choice is covered in another chapter. Figure 1.5 Silent 2 TARGA and its propulsion system [22] Figure 1.6 Outline of the retractable propulsion system on the Silent 2 TARGA glider [22] Introduction Modes of operation The propulsion system installed on a glider can operate in two modes: Sustainer these systems are used to gain altitude while the aircraft is already in the air. Because of their low power, they are not used for take-off. The technique used by motor glider pilots is called saw-tooth [15]. The engine is activated to gain altitude, at a typical rate of feet per minute (ca m/s). When the desired altitude is reached, the propulsion system is turned off and retracted. The aircraft continues flight as a regular glider. When a minimum altitude is reached the pilot can engage the propulsion again and climb under power the cycle continues. Self-launch these propulsion systems are more powerful than sustainers and are able to launch the aircraft without external assistance. During flight they are operated in the same way as sustainers. The disadvantage of selflaunching systems is the higher weight and complexity. The rate of climb for self-launch gliders normally varies from 200 to as much as 800 feet per minute (ca. 1 4 m/s) or more [6] Electric propulsion The concept of electric propulsion Despite all the advantages that a propulsion system can provide, an internal combustion engine has a number of disadvantages. Two-stroke engines are loud and the motor is located behind the head of the pilot. It is also inherent for engines with low number of cylinders to produce a lot of vibrations. Another drawback of the petrol engine is that on occasions the engine does not start immediately. When the mast with the wind-milling propeller is deployed, the glide ratio decreases dramatically due to the extra drag (mainly because of the spinning propeller). The strategy normally adopted by motor glider pilots is to position the aircraft close to a possible landing field below (within easy gliding range), before extending and trying to start the engine [6]. This is done for safety reasons, since accidents are not uncommon. If the engine did not start, the aircraft would quickly lose altitude. For the above reason, some sailplane pilots are not fond of motor gliders, despite all the benefits they provide. In the recent years, a new idea has been spreading: electric propulsion. Electric propulsion solves most of the problems related to operating an internal combustion engine. The main advantages of electric propulsion are the following: Very quiet No vibrations Low maintenance Simplicity of operation Confidence that the motor will start everytime No pollution Obviously, no solution is perfect and an electric propulsion system has also its disadvantages, which are the following: 6 Title of the Master Thesis Higher initial cost of the system (although lower operating cost) Higher total weight of the system for the same duration of powered flight (energy density for petrol is much higher than for rechargeable batteries, the advantage belongs to the internal combustion engine even when taking into account its low efficiency) The majority of sailplanes still utilize internal combustion engines, however electric propulsion is entering the market. Electric propulsion systems are less complex many components related to petrol engines can be eliminated (e.g. vibration dampening mounts, radiator, electric starter, exhaust system, fuel tank, fuel pump). In some cases, it is also possible to
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