Aircraft Construction Lecture Notes PDF

ME2511 Aircraft Structures Aircraft Construction 1st powered flight - Wright Flyer First flight – 17 December 1903  Structural Design Considerations 1: Understanding the Truss three fuselage Monocoque design concepts Semi-...

ME2511 Aircraft Structures Aircraft Construction 1st powered flight - Wright Flyer First flight – 17 December 1903  Structural Design Considerations 1: Understanding the Truss three fuselage Monocoque design concepts Semi-monocoque 2: Identify the internal structural members of the wing and Objectives flight control surfaces Learning 3: Understanding the Primary Structures three levels of Secondary Structures structural Tertiary Structures classifications Fuselage Design Concepts Truss Monocoque Semi-monocoque Fuselage Design Truss type Most early aircraft used this technique with wood and wire trusses. The truss type fuselage frame is assembled with members forming a rigid frame comprising beams, bars, tubes, etc. Primary members of the truss are four longitudinal members (longerons). There are two types of truss structures: Pratt truss Warren truss  Pratt Truss This design uses vertical members for compression and horizontal members to respond to tension. Configuration of the members result in vertical members being in compression while the longer diagonal members are usually only in tension. Pratt Truss 2 Diagonal members slant towards the centre allowing them to be used more efficiently, as slenderness effects are related to buckling under compression loads. Longeron are principal longitudinal members of the framing of an aircraft fuselage. Longerons are connected with rigid vertical and lateral members also called struts. Diagonal members made of tubing or solid rods to carry tension/compression loads. Pratt Truss 3 Warren Truss A truss consisting of horizontal top and bottom chords, separated by sloping members. Has no vertical pieces (except at the two ends). Longerons are connected only to diagonal members. All members are capable of carrying both tensile and compressive loads.  Warren Truss 2 MM3521 – Revision 1.0 Monocoque Design Fuselage skin carries all structural stresses Formed by construction of a cone or tube with no reinforcement from internal structural members Only effective for small diameter fuselage Inefficient for large diameter fuselage due to decrease in strength in weight ratio as significantly thicker skins are required to withstand the structural stresses Monocoque Design To maintain thin skin for weight savings, larger large aircraft fuselage are supported by additional structural members principally frames, bulkheads and longerons leading to a semi-monocoque type of fuselage design Semi-Monocoque Design Most transport-category aircraft fuselages adopt the semi-monocoque construction A typical semi-monocoque fuselage comprises: o outer skin o Frames o Stringers o Longerons o Bulkheads o Keel beam o Floor beams o Shear ties Monocoque and Semi-Monocoque fuselage designs Outer skin Covers the rigid fuselage framework Attached to the bulkheads, frames, longerons and stringers Stressed-Skin – primary load-carrying structure Usually made of aluminium alloy materials (e.g. T2024) Frames Circumferential members longitudinally spaced at regular intervals along the fuselage Provide the fuselage its cross-sectional shape and prevent it from buckling under bending loads Stringers Are longitudinal members spaced around the fuselage circumference, extending the full length of the fuselage Smaller and lighter than the longerons Serve as fill-ins between longerons Support the skin under compression and/or torsion loads Semi-monocoque fuselage construction (typical) Longerons Main lengthwise members of the fuselage structural construction Heavy structural members that usually extend the entire length of the fuselage Hold the bulkheads and frames and form a rigid fuselage frame work together with the stringers Bulkheads Heavy frames reinforced by beams attached to webs Usually located at the two ends of the fuselage Various body pressure bulkheads may also be located at different fuselage stations Bulkheads Keel Beam Major longitudinal member in the wing centre section and wheel well areas Carries bulk of the loads travelling forward and aft of aircraft Floor Beams The fuselage is usually divided vertically into two areas known as the upper and lower lobes, separated by the floor beams Floor beams are the structural members that are attached to the frames and run laterally across the fuselage Provides support for the cabin floor and cabin loads Floor Beams Shear ties Structures that transfer the payloads/dead weight applied to the frames or floor beams to the skin Fuselage internal structure Wings Primary lifting surfaces of aircraft Major contributor to lateral stability Two types of wing design: Semi-cantilever  Externally reinforced by struts and wires  Found on light aircraft design Full cantilever  No external support required  Made from stronger materials - metal Wings Typical stressed-skin wing Wing structure Wing Spar Principal span-wise member of wing structure Transport aircraft wings normally consist of 2 or more main spars (front & rear), with intermediate spars in-between in some designs Main spars provide supporting structure fittings for attachment to fuselage, pylons, flight control surfaces etc Wing Ribs Chord-wise member of wing structure placed at intervals along wing span Provide the airfoil shape of wing Stabilize the spars against twisting under torsion loads May act as fuel bulkheads in the integral fuel tank design Wing structure Wing Stringers Spanwise members attached to wing skins placed at chord-wise intervals Assist in maintaining the shape of wing Reinforce and stiffen the wing skins that are subjected to bending and twisting loads Wing Skin Attached to the ribs and stringers Serves as a cover and also primary load carrying structure Auxiliary Wing Structures Winglet  Other wing design features Centre-Wing Section In many transport- category aircraft, the wing is constructed in three or more assemblies, e.g. the left and right outer wing sections and centre-wing section The various sections are joined together to form a single-piece wing that is attached to the fuselage Other wing design features Integral Fuel Tank When the wings also serve as fuel tanks Achieved by incorporating fuel tanks in the basic wing structure Also known as “wet wing” Integral fuel tanks are sealed with special compounds (fuel tank sealant) to prevent fuel leakages Wing areas not holding fuel are called “dry bays” Centre-Wing Tank Other wing design features Flight Control Surfaces Primary Control Surfaces Include the ailerons, rudder and elevators Secondary Control Surfaces Include the flaps, slats (or leading edge flaps), spoilers and trim tabs Construction similar to the stabilizers Wing flight control surfaces Ailerons Controls aircraft movement about the longitudinal axis (rolling) Attached on the trailing edge of wing near the wing tip Large transport aircraft usually has an additional set of ailerons mounted at the mid- wing area, closer to the wing root Flaps Are primarily lift augmentation devices Designed as a hinged, pivoted, or sliding airfoil Normally mounted near the trailing edge of the wing Flap deployment changes the camber or increases the wing area and thus increases the lift Enables aircraft to operate at lower flight speeds for landing and takeoff Slats Forms the leading edge of wing when retracted and creates a slot at the leading edge when extended Slot allows air from high-pressure area under the leading edge to flow up through the leading edge and directed along the top of the wing Used to increase lift at low speeds Some aircraft type have leading edge flaps instead of slats, which perform the same function as the trailing edge flaps Slats  Spoilers Installed on the upper surface of the wings Uses to reduce, or “spoil” the lift on a wing Common type of spoiler on large jet aircraft is a flat panel lying flush with the wing upper surface during cruising flight Spoilers are hinged at the forward edge and rise up to reduce the lift when deployed MM3521 – Revision 1.0  Spoilers MM3521 – Revision 1.0 Empennage Tail section that provides directional stability of an aircraft in-flight Vertical Stabilizer  To which the rudder is attached rudders controls the directional or movement about the vertical axis of aircraft Horizontal Stabilizers  To which the elevators are attached elevators control pitch or movement about the lateral axis of aircraft Empennage Structural Classification In the construction of aircraft structures, aircraft components can generally be grouped into Structural and Non-structural components Structural Components Components that carry or transfer the forces exerted on the aircraft during its operation. They are usually the primary or secondary structures. Examples include skin, ribs, bulkheads and stringers. Non-structural Components Components that do not absorb or transmit forces of flight. They include providing aerodynamic functions to aid aircraft performance during flight. Examples include aircraft fairings and engine cowlings.  Structural Classification Aircraft structural members may be classified as Primary, Secondary or Tertiary structures depending on the loads they support and their respective effect on the integrity of aircraft in the event of their failure: Primary Structures These are aircraft structural members/parts that significantly contribute to the carrying of the ground, flight, pressure or control loads on their aircraft. And whose failure may affect the structural integrity and/or safety of the aircraft Structural Classification Secondary Structures Aircraft structural members that are designed to achieve safe separation or loss of function such that it would not affect the operations of the aircraft and can continue to fly safely. Tertiary Structure Failure would not significantly affect operation of the aircraft. (Note: Aircraft manufacturer’s structural repair manuals will state the category a particular part of aircraft falls under.) Other Aircraft Structural Members Airframe and Power-plant Structures Undercarriage and Landing Gear Common Aircraft Materials Others Airframe and Power-plant Structures Aircraft power plants (engine) are enclosed in a housing called the Nacelle and attached to the aircraft (at wing, fuselage, etc.) by means of engine mounts The Nacelle Houses and protects the engine and its components Streamlined shape enhancing the aerodynamics of aircraft Structure similar to that of the fuselage. Depending of aircraft, built from a combination of sheet metal and/or composite materials and assembled through permanent/removable fasteners or bonding Split into several engine cowling sections: fixed and hinged cowls to enable access to engine for maintenance Hinged cowls are hinged on the pylon and latched at the bottom (fan, thrust reverser and core cowls) Engine nacelle The Pylon A structure that attaches the engine nacelle to a wing or fuselage Is also known as a Strut Pylons transmit engine loads to the wing/fuselage through the engine mounts  Firewalls High temperature and fire generating components of the engine, e.g. the combustion, turbine and exhaust sections, must be isolated from other aircraft structures Accomplished through means of firewall installations to protect other parts of the aircraft structures from high temperature and possible damage by fire Fabricated from fireproof materials e.g. stainless steel, titanium, etc. for both heat and corrosion protection MM3521 – Revision 1.0 Firewall Engine mounts An engine mount is a frame that supports the engine and attaches it to the nacelle/pylon Forged-metal mounts are normally found in turbine engine aircraft Bolted to the engine and airframe attachment points, e.g. the mounting bulkheads of pylon Engine mounts and Shock absorbers Structural fuses Permits the loss of an engine without sacrificing the wing in situations of engine damage and consequent high vibrational and drag forces Accomplished through the shearing of fuse pins at various linkage points Landing Gear - Undercarriage Landing gears are designed to soften the impact of landing. The shock of impact may be divided into vertical and horizontal components. The energy of the vertical component is absorbed by some form of resilient springing provided by shock absorber and the tyres. The horizontal component is absorbed the drag struts and support members. Most modern aircraft designs use the nose wheel type landing gear. This arrangement proportions the load more evenly, gives better ground handling, enables easier and safer take-off and landing. Nose and Main Landing Gear Landing gear arrangements Wing landing gear attachment fittings comprise:  forward and aft trunnion bearing support fittings,  walking beam support fittings  side strut fittings Trunnion bearing support fittings that supports the landing gear strut are installed on the rear wing spar and landing gear support beam Main landing gear Aircraft structural materials Modern aircraft are constructed from different types of metal alloys. Most commonly used metal alloys are:  Aluminium alloy - fuselage skin, wing skin, bulkheads, etc.  Titanium alloy - Thrust reverser fittings, main landing gear beams, etc.  Stainless steel - engine mounts, firewalls, etc.  Monel, a nickel alloy - mechanical parts of landing gear, etc. Aircraft also use non-metallic materials e.g. composites such as carbon fibre reinforced plastics (CFRP) on areas e.g. control surface skins, cabin floor beams, etc. Aircraft assembly “Aircraft Assembly refers to the joining of parts or sub-assemblies by various means until the entire aircraft is in a ready condition for operation” Aircraft manufacturing begins with the construction of major sub-assemblies, e.g. fuselage, wings, nacelles, landing gears, etc. These major sub-assemblies are inspected to ensure airworthiness and applicable specifications are complied with The inspected and approved sub-assemblies are transported to the assembly line for final assembly Aircraft assembly After the assembly of major aircraft structural parts and components, other miscellaneous components are then installed, depending on the aircraft type and desired operations The following are commonly found in the passenger aircraft:  flight, passenger and cargo compartment  cabin furnishing installations e.g. the passenger seats, overhead stowage bins, wall partitions, etc.  cabin entertainment equipment e.g. seat video monitors, in flight entertainment (IFE) systems, etc.  buffet and galley installations – booths where the meals are prepared The cargo loading system (CLS) is installed on the aircraft to load/unload the goods/passengers’ luggage, etc. CLS is located on the lower lobe of a passenger aircraft and the entire main deck on freighter aircraft Further reading Text Book - “Aircraft Maintenance & Repair” Sections: Pages Chapter 2 Fuselages 23 - 26 Transport Aircraft Fuselages 27 - 34 Wings 44, 45 Transport Aircraft Wings 49 - 52 Tail & Control Surfaces 52 - 55 Power Plant Structures 56 - 61 Landing Gear 56 Chapter 12 Ailerons, Rudder, Elevators 297, 299, 300 Tabs 303 (1st to 4th para) Flaps, Slats, Spoilers 306 - 308 Assembly Procedures 285 (1st para), 286 Aircraft doors All Airbus aircraft have the "translating" doors where the doors slide right open and the exterior side is always facing the exterior side. All Boeing NARROWBODY aircraft (717/727/737/747/757) have the "plug" type which rotate so that the interior side is facing out when open. Boeing 777 has Airbus-like "translating" doors as described above MD11/DC10/L1011/B767 have hydraulic doors that move up above the doorway when open.