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

2. 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

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

4. 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)

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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)

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

13. 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

14. 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

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

16. 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

17. 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)

18. 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

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

20. 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

21. 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

22. 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

23. 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

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

25. 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

26. Introduction to the course
Fuselage and tail boom
Apache structure

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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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)

37. 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

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

39. 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

40. 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

41. 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

42. 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)

43. 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

44. 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

45. 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.

46. 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

47. 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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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