INTRODUCTION TO THE COURSE AEROSPACE STRUCTURES Prof. Alessandro Airoldi INTRODUCTION TO THE COURSE

Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course

Introduction to the course Objectives of the course Approaches to the analysis of structures in aerospace constructions

Introduction to the course Objectives of the course Aerospace constructions Aerospace structures AERODYNAMIC LOADS AERODYNAMIC LOADS Structure works to transfer the applied loads THRUST INERTIAL LOAD Force equilibrium (D’Alembert principle) INERTIAL LOAD Such considerations apply to all type of structures (not only aerospace structure)

Introduction to the course Objectives of the course Aerospace constructions Aerospace structures Structure works to transfer the applied loads THRUST AERODYNAMIC LOADS ROTOR THRUST Force equilibrium (D’Alembert principle) INERTIAL LOAD Such considerations apply to all type of structures (not only aerospace structure)

Introduction to the course Objectives of the course Requirements: Stiffness Limitation to the relative displacements due to functional requirements (e.g. aerodynamics) Avoid frequency coupling (resonance) AERODYNAMIC LOADS AERODYNAMIC LOADS Strength Avoid permanent deformation and the collapse of the structures under operative load INERTIAL LOAD Shape Constraints INERTIAL LOAD AERODYNAMICS, INTERNAL VOLUMES FOR PAYLOADS OBJECTIVE: perform structural functions, fullfilling requirements, respect constraints with MINIMUM WEIGHT THRUST

Introduction to the course Objectives of the course Why analysis ? 1 Analysis of existing structures helps understanding the functions of structural elements, critical issues in design, the available solution for design (synthesis) 2 Design is an iterative process, which involve analysis of design hypothesis at different level of detail

Introduction to the course Objectives of the course Enhance the capability to apply the approaches of structural mechanics to the structural types that are employed in aerospace structure. Given the applied loads: methods for the evaluation of internal stress and strain states methods for the evaluation of stiffness, displacements, natural frequencies Learn the main features of aerospace structures: comprehension of structural roles, capability to critically analyse a structure Achieve the bases for a proper use of structural calculation software (Finite Element Method): knowledge of principles, technologies, limitations

Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course

Introduction to the course Stressed skin constructions in aircraft structures Truss Structures were used at the beginning of flight history Vickers Wellington (1943) They consist of slender members connected at the ends They are a very efficient structural concept, which is still widely used in aerospace engineering PA-18 welded tubes structure Engine Mounts Integrated Truss Structure Section in ISS

Introduction to the course Stressed skin constructions in aircraft structures However, the peculiar and severe requirements for aircraft structures led to the development of another very effective structural typology: Thin load bearing skin (stressed skin), reinforced by longitudinal stringers and internal frames SEMI-MONOCOQUE STRUCTURES They still represent the basic structural concept in all aerospace structures (toghether with truss structures)

Introduction to the course Stressed skin constructions in aircraft structures STRESS SKIN STRUCTURES Longitudinal stringers Airbus A340 Thin load bearing skin Transverse Frames

Introduction to the course Stressed skin constructions in aircraft structures FABRIC COVER TRUSS STRUCTURE Biplane (1916) INTERNAL FRAMES (RIBS) AND LONGITUDINAL REINFORCEMENT (SPARS) Motivations for the development of stressed skin constructions can be traced to the beginning of flight

Introduction to the course Stressed skin constructions in aircraft structures Torsional stiffness: critical issue in wing design High pitch angle Low pitch angle WING TORSION

Introduction to the course Stressed skin constructions in aircraft structures Torsional stiffness of biplane wings

Introduction to the course Stressed skin constructions in aircraft structures Hurricane had originally a fabric cover (1935) All metal stressed skin provided in 1939 Load bearing skin provides a closed high-stiffness path for shear stress, contribute to bending stress and stiffness

Introduction to the course Stressed skin constructions in aircraft structures Thin load bearing skin (stressed skin), reinforced by longitudinal stringers and internal frames Semi-monocoque structure (1943)

Introduction to the course Stressed skin constructions in aircraft structures Modern airliner structure CLOSELY SPACED FRAME AND RIBS (internal diaphragm in fuselage and wing COMPOSITE VERTICAL TAIL WITH SEMI-MONOCOQUE MORPHOLOGY

Introduction to the course Stressed skin constructions in aircraft structures Wing box and ribs REAR SPAR FWD SPAR Integrally stiffened composite skin

Introduction to the course Stressed skin constructions in aircraft structures TRUSS STRUCTURES Type of diaphragms and instability C – SHAPED BEAMS WITH VARIABLE SECTION AND CUTOUTS CLOSED LOOP OF BEAMS WITH L, C, Z or other shape SECTIONS

Introduction to the course Stressed skin constructions in aircraft structures Tail structure and bulkheads AIRBUS A 300 TAIL BULKHEAD WORKING UNDER PRESSURE LOADS A380 COMPOSITE BULKHEAD

Introduction to the course Stressed skin constructions in aircraft structures Supersonic fighters FUSELAGE FRAMES ARE MORE SPACED DUE TO NEED OF LARGE CUT-OUTS (Cockpit, cut-out inspections of engines, air inlets) WINGS BECOME VERY THIN AND STRINGERS ARE MERGED IN A SERIES OF SPARS

Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course

Introduction to the course Helicopter anatomy Different structural parts can be distinguished for the static design: fuselage; tail boom; tail planes; rotor blades.

Introduction to the course Stressed-skin and helicopter structure FEW SPACED FUSELAGE FRAMES LARGE CUT-OUTS TAIL BOOM AND PLANES FOLLOW A MORE CONVENTIONAL STRESSED-SKIN CONSTRUCTION SCHEME EH 101 structure

Introduction to the course Fuselage and tail boom Apache structure

Introduction to the course Application of beam schemes BEAM AXES A 109 structure

Introduction to the course Fuselage, floor and subfloor FUSELAGE STRUCTURE WITH LARGE CUTOUTS REAR FRAME ROTOR THRUST CUTOUT FOR DOORS FORWARD FRAME INERTIAL LOAD FLOOR AND SUBFLOOR

Introduction to the course Importance of crashworthiness SOIL OCCUPANTS Seats Subfloor Landing Gear Fuselage Energy Absrober Structural part the influences occupant survivability Controlled failure of the tail boom to reduce the mass to be decelerated Fuel tank response Subfloor Fuselage structure must withstand to avoid occupants injuries Crashworthy seats Roof response Landing gears Crashworthy seats

Introduction to the course Rotor Blades VERY LARGE CENTRIFUGAL LOADS ORIGINAL DESIGN FOLLOWED THE PRINCIPLES OF STRESSED SKIN CONSTRUCTION APPLICATION OF COMPOSITES: D SPAR (UD FIBRE REINFORCEMENT) TORSIONAL STIFFNESS PROVIDED BY +/-45 BOXES FOAM AND HONEYCOMB FILLERS

Damage tolerance and helicopter composite components Rotor Blades: section D-spar: 0° UD bulk core wrapped by +/- 45° anti-torsion box Carbon +/-45° trailing edge skin Metallic wear strap Nomex honeycomb

UD material of D-spar arranged in ribbons wrapped around lug bushes Damage tolerance and helicopter composite components Rotor Blades: root Centrifugal load is reacted at two lugs connecting the blade to the hub UD material of D-spar arranged in ribbons wrapped around lug bushes Blade root

Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course

Introduction to the course Examples of space structures: SPACE SHUTTLE Unique combination of semi-monocoque, pressure vessels, truss structures structural concepts Orbiter Many different materials used: Aluminium alloy high strength steel Titanium Boron/aluminium composite Carbon/epoxy composites Fibreglass Ceramics SRB External tank

Introduction to the course Examples of space structures: SPACE SHUTTLE Solid busters MAIN STRUCTURE: SEGMENTED STRUCTURE (11 SEGMENT) HIGH STRENGTH STEEL 13 mm THICK JOINED BY STEEL PINS JUNCTIONS WRAPPED BY FIBERGLASS SEALED WITH RUBBER BANDS SUCH MAIN STRUCTURE IS CLOSED BY THE FWD AND AFT SEGMENT DOMES IT IS THE EXTERNAL STRUCTURE BETWEEN THE FORWARD AND THE AFT SKIRT EXTERNAL COVER, SUCH AS NOSE CAP AND SKIRTS ARE MADE OF WELDED ALUMINUN

Introduction to the course Examples of space structures: SPACE SHUTTLE External Tank TWO TANKS: OXYGEN AND HYDROGEN PRE-FORMED ALUMINUM ELEMENTS (PANELS, MACHINED THICK ELEMENTS) PRESENCE OF INTEGRALLY MACHINED STRINGERS AND RING FRAMES RING FRAMES STABILIZE THE TANK AT HIGH COMPRESSIVE LOADS INTERTANK STRUCTURE IS A MORE CONVENTIONAL SEMIMONOCOQUE STRUCTURE (PANELS-SKIN-FRAMES MECHANICALLY JOINTED)

Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter BASED ON SEMIMONOCOQUE PRINCIPLES LARGE PARTS MADE OF ALUMINUM ALLOY PECULIAR ASPECTS CONVENTIONAL FORWARD FUSELAGE STRUCTURE HOSTS WELDED PRESSURISED CREW MODULE CENTRAL SECTION FRAMES MADE OF BORON/ALUMINUM TRUSS STRUCTURE THRUST BEARING TRUSS STRUCTURE WITH BORON/EPOXY REINFORCEMENTS WINGS WITH HONEYCOMB SKIN COVER

Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter FORWARD FUSELAGE: EXTERNAL SHELL STRUCTURE (SEMIMONOCOQUE CONCEPT) INTERNAL PRESSURIZED VESSEL

Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter CENTRAL SECTION LONGHERON CARRY BENDING LOADS HIGH STIFFNESS- STRENGTH REQUIRMENT FOR FRAMES: TRUSS WITH BORON/ALUMINUM TUBES CONCEPTS OF STRESSED SKIN CONSTRUCTION LARGELY EMPLOYED

Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter GRAPHITE\EPOXY PAYLOAD BAY DOORS REINFORCED BY FRAMES AND END TORQUE BOXES HIGH STRENGTH 3D TRUSS STRUCTURE TO SUSTAIN THE THRUST LOAD OF MAIN ENGINES

Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter CONVENTIONAL ALUMINUM STRUCTURE WITH MULTI SPAR AND RIB ARRANGEMENT HONEYCOMB SKIN REINFORCED BY ALUMINUM HAT-SHAPED STRINGERS

Introduction to the course Examples of space structures: SATURN V First Stage Separate serial tanks within semimonocque structure SEMI-MONOCOQUE AL 7075 INTERTANKS AND SKIRTS AL 2219 – T87 TANK WITH ANTI-SLOSH BAFFLES (diaphragms that reduces fuel movements)

Introduction to the course Examples of space structures: SATURN V Second Stage Integral serial tanks with common bulkhead INTEGRALLY STIFFENED TANKS MADE OF DIFFUSION-WELDED AL 2014 PARTS COMMON BULKHEAD: AL 2014 SHEET + FIBERGLASS/ PHENOLIC HONEYCOMB CORE SKIRTS, INTERSTAGES, THRUST STRUCTURE: AL7075 SEMIMONOCOQUE

Introduction to the course Examples of space structures: SATURN V Third Stage Serial tanks with common bulkhead VERY SIMILAR TO 2° STAGE STRUCTURE INTEGRALLY STIFFENED TANKS AND SEMIMONOCOQUE STRUCTURES

Introduction to the course Examples of space structures: SPACECRAFTS Experimental spacecraft designed at John Hopkins University: multisensor platform including a Spatial Infrared Telescope IN SPACECRAFTS THE DISTINCTION BETWEEN PRIMARY AND SECONDARY STRUCTURES IS IMPORTANT: PRIMARY STRUCTURES TRANSMIT LOADS TO THE BASE OF THE SATELLITE THROUGH SPECIFICALLY DESIGN COMPONENTS (CENTRAL TUBE, HONEYCOMB PLATFORM, BAR TRUSS, ETC.). PROVIDE THE ATTACHEMENT POINTS FOR THE PAYLOAD AND THE ASSOCIATED EQUIPMENTS. FAILURE OF THE PRIMARY STRUCTURE LEADS TO COLLAPSE OF SATELLITE SECONDARY STRUCTURES BAFFLE, THERMAL BLANKET SUPPORT AND SOLAR PANELS MUST ONLY SUPPORT THEMSELVES AND ARE ATTACHED TO THE PRIMARY STRUCTURE WHICH GUARANTEE THE OVERALL STRUCTURAL INTEGRITY.

Introduction to the course Examples of space structures: SPACECRAFTS SEVERAL DIFFERENT STRUCTURAL TYPES: TRUSS (ALSO IN HIGH STIFFNESS/STRENGTH COMPOSITE MATERIAL) HONEYCOMB PANELS (OFTEN USED FOR ELECTRONIC SUPPORT AND SOLAR CELL SUPPORT) MACHINED BEAMS AND PLATES

Introduction to the course Examples of space structures: SPACECRAFTS MANNED SPACECRAF INCLUDES TRUSS STRUCTURES SEMI-MONOCOQUE CONCEPTS (THIN WALLED STRUCTURES WITH STIFFENERS AND FRAMES) STIFFENED PRESSURE VESSELS

Composite structures requires additional tools for analysis and design Introduction to the course What have we learned ? Structural concepts: truss and semi-monocoque Central role of two different but very effective structural types: semi-monocoque and truss structures Basic structural elements: beams and plates Beam models can be applied at level of the vehicle structure, for the analyses of truss systems, for the analyses of ribs and frames Plate theory is required to understand the behavior of panels and covers Different materials: metals, fiber reinforced composites, sandwich plates Composite materials are used to increase structural efficiency: lower weight, higher stiffness (and strength ?) Composite structures requires additional tools for analysis and design

Course Content and Organisation: Introductory lessons Course Content and Organisation: Lectures (theory) CONTINUUM MECHANICS BEAM MODELS AND BEAM SYSTEMS SEMI-MONOCOQUE STRUCTURES DISPLACEMENT BASED APPROACHES PLATES AND COMPOSITES INSTABILITY FE METHOD

Slides of the lectures will be provided during the course Introductory lessons Course Content and Organisation: Course Material & Textbooks Slides of the lectures will be provided during the course MALVERN, MECHANICS OF CONTINUOUS MEDIUM Continuum mechanics, general principles T.H. MEGSON, AIRCRAFT STRUCTURES FOR ENGINEERING STUDENTS, BUTTERWORTH-HEINEMANN, 1972 Semi-monocoque structures, force and displacement approach to beam systems J.N. REDDY, ENERGY PRINCIPLES AND VARIATIONAL METHODS IN APPLIED MECHANICS, WILEY 2002 Energy methods, Ritz Method, Plate Theory K.J. BATHE, FINITE ELEMENT PROCEDURES, PRENTICE HALL 1982 Finite elements V. GIAVOTTO, STRUTTURE AERONATICHE CITTA’ STUDI Covers several parts of the course

Course Content and Organisation: Introductory lessons Course Content and Organisation: Exercise Classes (for written test) CONTINUUM MECHANICS BEAM MODELS AND BEAM SYSTEMS SEMI-MONOCOQUE STRUCTURES DISPLACEMENT BASED APPROACHES PLATES AND COMPOSITES INSTABILITY FE METHOD

Course Content and Organisation: Introductory lessons Course Content and Organisation: Computer Labs CONTINUUM MECHANICS BEAM MODELS AND BEAM SYSTEMS SEMI-MONOCOQUE STRUCTURES DISPLACEMENT BASED APPROACHES PLATES AND COMPOSITES INSTABILITY FE METHOD

Will include proofs of main theorems and formulation development Introductory lessons Course Content and Organisation: Written Examination Based on the same type of exercises that have been presented, solved and discussed during classes Capability to critically apply concepts as well as to organize and carry out calculations Admission to oral examination is possible only if the written text will obtain a positive mark Oral Examination Comprehension of structural concepts, analytical and numerical approach Will include proofs of main theorems and formulation development