DEGREE PROJECT IN TECHNOLOGY, FIRST CYCLE, 15 CREDITS STOCKHOLM, SWEDEN 2020 Propulsion system for a small unmanned aerial vehicle OSCAR ANDERSSON DENNIS WILKMAN KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF ENGINEERING SCIENCES Propulsion system for a small unmanned aerial vehicle Oscar Andersson [email protected], Dennis Wilkman [email protected] Submitted for the degree of Bachelor School of Engineering Sciences KTH Royal Institute of Technology Sweden June 2020 Propulsion system for a small unmanned aerial vehicle Oscar Andersson [email protected], Dennis Wilkman [email protected] Abstract For unmanned aerial vehicles there is a wide variety of selection for propulsion systems. Depending on the spe- cic choice of system, the characteristics of the aircraft vary signicantly. The choice is also dependent on the size of the UAVitself as well as desired performance and utility. Propulsion systems have made signicant advancements over the last decades in the UAVsector. The Skywalker X8 is a popular small UAVand most commonly own elec- trically. What propulsion would then be tting for the originally 2 m wingspan Skywalker X8 if its size in dimensions were doubled. This study presents an early suggestion of a propulsion system for the double sized Skywalker X8. The nal propulsion system is a hybrid system consisting of a fuel cell and batteries, giving a time of operational ight of 19 hrs. The results show that the method of choice works as an early design solution of selecting a propulsion system and determining performance. However, it may be an inaccurate representation of the physical model and needs to be followed up by more detailed analysis of the UAV. It is concluded that further experimentation should be done in order to verify the data calculated with this model. For¨ obemannade ygfordon nns ett stort urval av framdrivningssystem. Beroende pa˚ det specika valet av system varierar ygplanets egenskaper vasentligt.¨ Valet ar¨ ocksa˚ beroende av storleken pa˚ farkosten sjalv¨ och onskad¨ prestanda och anvandbarhet.¨ Framdrivningssystem har gjort betydande framsteg under de senaste decennierna. Sky- walker X8 ar¨ en popular¨ obemannad luftfarkost och ygs oftast elektriskt. Vilken framdrivning skulle da˚ passa for¨ den ursprungliga Skywalker X8 med 2 m vingspann om dess storlek i dimensioner fordubblats.¨ Denna studie pre- senterar ett tidigt forslag¨ om ett framdrivningssystem for¨ den dubbelt sa˚ stora Skywalker X8. Det slutliga framdrivn- ingssystemet ar¨ ett hybridsystem som bestar˚ av en branslecell¨ och batterier, vilket ger en drifttid pa˚ 19 timmar. Resul- taten visar att valmetoden fungerar som en tidig designlosning¨ for¨ att valja¨ ett framdrivningssystem och bestamma¨ dess prestanda. Det kan dock vara en felaktig representation av den fysiska modellen och maste˚ foljas¨ upp av en mer detaljerad analys av farkosten. Det dras slutsatsen att ytterligare experiment bor¨ goras¨ for¨ att veriera de data som beraknats¨ med denna modell. 1 Contents 1 Foreword 3 1.1 Covid-19 . .3 1.2 Acknowledgements . .3 2 Introduction 3 3 Problem 4 4 Method 4 5 Analysis and Results 4 5.1 Energy Source and Energy Storage . .4 5.1.1 Hydrocarbons . .4 5.1.2 Lithium-Polymer Batteries . .5 5.1.3 Ultra-Capacitors . .5 5.1.4 Solar Cells . .5 5.1.5 Hydrogen . .5 5.1.6 Chemical Storage and reforming of hydrogen . .5 5.1.7 Storage Tank . .6 5.1.8 Hydrogen production . .6 5.2 Mechanical Energy Converter . .6 5.2.1 Internal Combustion Engine . .6 5.2.2 Electrical Engine . .6 5.2.3 Hybrid Alternatives . .6 5.3 Flight conditions . .6 5.4 Modelling/Computation Fluid Dynamics . .7 5.4.1 Angle of Attack . .7 5.4.2 Momentum Theorem . .7 5.5 Component Choices and Placement . .8 5.5.1 Chosen Components . .8 5.5.2 Lift and Drag . .8 5.5.3 Range and Endurance . .8 5.5.4 Velocity . .8 5.5.5 Power Required . .9 5.6 Performance . .9 5.6.1 Stability . .9 5.6.2 Placement . .9 6 Discussion 9 7 Conclusions 10 2 2 Introduction The UAV industry has grown signicantly in the recent Nomenclature years, having a variety of applications in both civilian and military areas such as surveillance, transportation of Pr power required, W goods or simply for fun ying. The choice of the propul- sion system is crucial for the usability, sustainability and T thrust, N ight endurance of the aircraft. A system which is too dicult to manage could lead to unwanted cost as well V1 free stream velocity, m/s as less applicability for civilian usage. Sustainability is im- portant in an environmental sense, the goal is to achieve a CG Center of Gravity net zero carbon footprint and not have any other adverse eect on the environment. The ight endurance dictates CP Center of Pressure the amount of time the UAV can remain in the air. The greater the endurance, the less amount of times the UAV is required to land and refuel during an extended mis- EE Electrical Engine sion. Subsequently reducing the cost in addition to in- creasing operability. ICE Internal Combustion Engine The propulsion system can be split into four parts: LiPo Lithium Polymer The energy source, the storage media, the mechanical energy converter and nally the lift/thrust converter [1]. When choosing the specic options for the dierent PEMFC Polymer Electrolyte/Proton Exchange Mem- parts, the main things to consider from a purely per- brane Fuel Cell formance standpoint are: the specic energy and the amount of stored energy per weight of the energy source. UAV Unmanned Aerial Vehicle The fuel storage weight percentage is the percentage of weight that is fuel in the energy storage module. The spe- cic power, the power output per unit of weight for the 1 Foreword mechanical energy converter. The eciency per module is the energy losses at each specic point of the propul- 1.1 Covid-19 sion system and what percentage amount of energy is lost for the entire system altogether, from the energy storage This project was started and went on during the Covid- to converter. 19 outbreak. Due to this occurrence the scope of this re- port had to be changed. Variousresources were no longer One common type of UAVon the market is the Sky- available and so the extent of what the study would con- walker X8. This airplane is characterized by its ying tain has been altered since what was initially planned for wing design. There are only two main wings attached to could not be done, such as wind tunnel experiments that the fuselage as seen in gure 1. would have provided improvement of some of the re- sults. With this mentioned, in any further reading of this article the reader is asked to keep these circumstances in mind. 1.2 Acknowledgements Special thanks to our supervisor Raello Mariani for helping us to carry out this project during these excep- tional times. Figure 1: CAD model of the Skywalker X8 3 The aim of this report is to give insight in the pro- powered aircraft cannot be calculated using the Breguet cess of choosing a propulsion system for the Skywalker equations [2]. X8 with the properties of a 4 meter wingspan and a body The propeller eciency is expected to be around weight of 10 kg (not including the propulsion system), 70%. However, given the ight conditions and the pro- scaled up twice from the original model. peller diameter the ideal propeller eciency can be calcu- lated with the momentum theorem [3]. 3 Problem 5 Analysis and Results What is a suitable propulsion system for the Skywalker X8 with a wingspan of 4 meters and a body weight of 10 5.1 Energy Source and Energy Storage kg that satises a moderate ease of use, is sustainable in an environmental sense, as well as having a ight endurance The purpose of the energy source is to provide energy to of at least 4 hours in cruise ight. It should also be able to the relevant systems in the plane. Properties that are rele- provide enough thrust to y at an airspeed of 100 km/h. vant to the energy sources are: the specic energy, density and sustainability. The specic energy is the amount of energy per 4 Method weight of the energy source, in units J/kg: the higher the specic energy the more fuel can be supplied before A comparison of the four dierent modules (energy reaching the maximum take-o weight. source, energy storage, mechanical energy converter, thrust converter) of the propulsion system will be made, The density of the fuel is the amount of mass per vol- kg/m3 in respect to specic power/energy, power/energy den- ume of the energy source, in units and higher den- sity, eciency, operability, sustainability and ight en- sity enables the fuel to occupy less space. In small UAVs durance. A suitable propulsion system will then be cho- this property is very relevant since there is often a very sen specically for the upscaled Skywalker X8. limited amount of space on board. In order to determine the required properties of the Sustainability is determined by the environmental propulsion system, one must assess the operating con- impact of the fuel. Both the production and the fuel con- ditions such as: cruise speed, cruise altitude, the total sumption are to be considered during the analysis of the amount of drag and lift aecting the aircraft and the max- fuels sustainability. Specically to the fuel, the greatest imum power output required during the ight (e.g. dur- environmental impact is the release of greenhouse gases ing takeo/landing). such as carbon dioxide or large amounts of non recy- In order to determine the lift and drag aecting the clable waste products.