Design Synthesis of Advanced Technology, Flying Wing Seaplanes Uninhabited Aircraft Design Optimised forby Close Formation Air-Refuelling Flight Errikos Levis Supervisor: Dr.by V.C. Serghides Sma ilsuwan Department of Aeronautics Imperial College London A thesis submitted for the degree of A Thesis Submitted for the degree of Doctor of Philosophy Doctor of Philosophy 2011 2010 Department of Aeronautics Imperial College of Science, Technology and Medicine Prince Consort Road London SW7 2BY Declaration I hereby certify that the research presented in this thesis has been carried out at Imperial College London, and has not been previously submitted to any other university for any degree or award. The thesis comprises only my original work. Due acknowledgments are made where appropriate. Errikos Levis i Abstract Over the past decades there has been increasing pressure for ever more efficient and environmen- tally friendly aircraft to be designed. The use of waterborne aircraft could be a means of satisfying those requirements in the future. The aim of the PhD research program presented in this thesis was to develop the methodologies necessary for the preliminary design of large passenger seaplanes and evaluate the performance of such an aircraft compared to the current state of the art. The ma- jor technological and operational constraints in designing large waterborne aircraft were identified through an extensive feasibility study. A number of subject areas necessitating further investigation were also identified. To ensure that waterborne takeoff distance requirements are met, a novel initial sizing methodology was generated, relating the aircraft's thrust and lifting characteristics to the take- off Balanced Field Length. To allow the design of a broad family of aircraft based on a predefined baseline configuration, the seaplane geometry was fully parameterized. The aerodynamic properties of the entire aircraft were determined using a vortex-lattice potential flow solver, written specifically for the configuration being investigated, combined with other commonly used empirical methods. Novel methodologies for estimating the hydrodynamic characteristics of a broad range of parametric hulls were developed using the wealth of experimental hydrodynamic test data available. These methods can be used not only to predict the resistance and trim characteristics of a seaplane throughout the entire takeoff and landing manoeuvre but also give an initial estimate of the attitudes where hydrody- namic instabilities may be encountered. The airborne and waterborne performance characteristics of each resulting aircraft design were estimated using the aforementioned methods. The resulting design synthesis has been integrated into a single algorithm, written in FORTRAN, intended to allow the easy and prompt analysis of any parametric variant of the baseline configuration. ii Contents Abstract i Contents iii List of Figures ix List of Tables xiv Nomenclature xvi 1 Introduction 1 1.1 Motivation..........................................1 1.2 Objectives...........................................2 1.3 Background..........................................2 1.3.1 Seaplanes.......................................2 1.3.2 The Flying Wing...................................5 2 Feasibility Study 6 2.1 Possible Uses of Large Seaplanes..............................6 2.1.1 Passenger and Cargo Transport...........................6 2.1.2 Maritime Search and Rescue............................7 2.1.3 Firefighting......................................8 2.1.4 Troop and Cargo Transport.............................8 2.1.5 Electronic and Anti-Submarine Warfare......................9 2.1.6 Aerial Refueling...................................9 2.2 Technological Feasibility...................................9 2.2.1 Fluid Dynamics....................................9 iii 2.2.1.1 Wing Design................................9 2.2.1.2 Hull Design................................. 10 2.2.1.3 Extreme Ground Effect.......................... 11 2.2.2 Propulsion...................................... 12 2.2.3 Stability and Control................................. 13 2.2.3.1 Airborne.................................. 13 2.2.3.2 Waterborne................................. 14 2.2.3.3 Rough Water Performance........................ 15 2.2.4 Configuration Layout................................ 16 2.2.5 Structural Design................................... 16 2.3 Seaplane Operations..................................... 17 2.3.1 Implications of Seaborne Operation........................ 17 2.3.1.1 Effect Of Sea State on Operations.................... 17 2.3.1.2 Icing.................................... 18 2.3.1.3 Attachment of Sedentary Marine Organisms.............. 20 2.3.1.4 Interaction with other Vessels...................... 20 2.3.1.5 Floating Debris.............................. 21 2.3.1.6 Bird Hazards................................ 21 2.3.1.7 Safety Equipment............................. 22 2.3.2 Maintenance..................................... 22 2.3.2.1 Inspection of Submerged Parts...................... 22 2.3.2.2 Beaching.................................. 23 2.3.3 Seaplane Base Design................................ 24 2.3.3.1 Requirements for Water Area....................... 24 2.3.3.2 Marking and Lighting........................... 25 2.3.3.3 Airport Boundaries............................ 26 2.3.3.4 Mooring and Docking........................... 27 2.4 Environmental Impact.................................... 28 2.4.1 Wildlife........................................ 28 2.4.2 Noise......................................... 29 2.4.3 Fuel Consumption and Emissions.......................... 29 iv 3 Literature Review 31 3.1 Introduction.......................................... 31 3.2 Aircraft Design........................................ 31 3.3 Aerodynamic Design..................................... 33 3.4 Hull Design.......................................... 34 4 Baseline Configuration & Initial Sizing 37 4.1 Baseline Configuration.................................... 37 4.1.1 Baseline Design Justification............................ 37 4.1.2 General Arrangement................................ 39 4.2 Initial Sizing......................................... 41 4.2.1 Mission Profile.................................... 41 4.2.2 Initial Weight Estimation.............................. 42 4.2.2.1 Empty Weight............................... 44 4.2.3 Thrust-to-Weight and Wing Loading........................ 45 4.2.3.1 Design to Requirements.......................... 45 4.2.3.2 Takeoff & Landing Distance....................... 46 4.2.4 The Carpet Plot................................... 57 5 Geometrical Modelling 59 5.1 Hull Parametrization..................................... 59 5.2 Planform Parametrization.................................. 62 5.3 Airfoil Parametrization.................................... 64 5.4 3D Modelling......................................... 67 5.4.1 Hull Section & Seawing............................... 68 5.4.2 Outer Wing Section................................. 72 6 Systems Packaging 74 6.1 Pressurised hull sizing.................................... 74 6.1.1 Passenger Cabin................................... 74 6.1.2 Cargo bays...................................... 76 6.1.3 Cabin placement & centreline thickness estimation................ 78 6.2 Fuel System.......................................... 79 6.3 Propulsion System...................................... 80 v 6.4 Fins.............................................. 81 7 Aerodynamics 84 7.1 Pressure loads......................................... 84 7.2 Lift Distribution & Optimum Twist............................ 88 7.3 Viscous Effects........................................ 90 7.4 Transonic Effects....................................... 91 7.5 Control Surfaces & High Lift Devices............................ 93 7.6 Maximum Lift........................................ 93 7.7 Step Effects.......................................... 95 8 Hydrostatics & dynamics 103 8.1 Hull Sizing.......................................... 103 8.2 Hydrostatic Analysis..................................... 106 8.3 Hydrodynamic Analysis................................... 107 8.3.1 Parameter Choice.................................. 109 8.3.2 Resistance....................................... 111 8.3.3 Pitching Moment................................... 113 8.3.3.1 Centre of Pressure............................. 113 8.3.3.2 Equilibrium Trim Angle.......................... 116 8.4 Validation........................................... 118 9 Weight, Balance & Stability 126 9.1 Weight & Balance...................................... 126 9.1.1 Empty Aircraft.................................... 126 9.1.2 Fuel & Payload.................................... 130 9.2 Static Stability........................................ 131 9.2.1 Aerodynamic..................................... 131 9.2.2 Hydrostatic...................................... 134 9.3 Dynamic Stability...................................... 136 9.3.1 Aerodynamic..................................... 136 9.3.2 Hydrodynamic.................................... 138 9.3.2.1 Lower Trim Limit............................. 142 9.3.2.2 Upper Trim Limit - Increasing Trim................... 143 vi 9.3.2.3 Upper Trim Limit - Decreasing Trim.................. 145 10 Performance 147 10.1 Engine Performance..................................... 147 10.2 Specific Excess Power.................................... 149 10.3 Mission Analysis......................................