Aircraft structure


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Brief description on Aircraft structure

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Aircraft structure

  1. 1. A Project by Darshak BhuptaniEnrolment no: 093574710 Roll no: Aep-2009-S12 1
  2. 2. Major components : Although airplanes are designed for a variety of purposes, most of them have the same major components. The overall characteristics are largely determined by the original design objectives. Most airplane structures include a fuselage, wings, an empennage, landing gear, and a power plant. 2
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  4. 4. The fuselage includes the cabin and/or cockpit,which contains seats for the occupants and thecontrols for the airplane. In addition, the fuselagemay also provide room for cargo and attachmentpoints for the other major airplane components.Some aircraft utilize an open truss structure. Thetruss-type fuselage is constructed of steel oraluminium tubing. Strength and rigidity isachieved by welding the tubing together into aseries of triangular shapes, called trusses. 4
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  6. 6. Construction of the Warren truss features longerons, as well as diagonaland vertical web members. To reduce weight, small airplanes generallyutilize aluminium alloy tubing, which may be riveted or bolted into onepiece with cross-bracing members.As technology progressed, aircraft designers began to enclose the trussmembers to streamline the airplane and improve performance. This wasoriginally accomplished with cloth fabric, which eventually gave way tolightweight metals such as aluminium. In some cases, the outside skin cansupport all or a major portion of the flight loads. Most modern aircraft usea form of this stressed skin structure known as monocoque orsemimonocoque construction. The monocoque design uses stressed skin to support almost all imposedloads. This structure can be very strong but cannot tolerate dents ordeformation of the surface. This characteristic is easily demonstrated by athin aluminium beverage can. You can exert considerable force to the endsof the can without causing any damage.However, if the side of the can is dented only slightly, the can willcollapse easily. The true monocoque construction mainly consists ofthe skin, formers, and bulkheads. The formers and bulkheadsprovide shape for the fuselage. 6
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  8. 8. Since no bracing members are present, the skin mustbe strong enough to keep the fuselage rigid. Thus, asignificant problem involved in monocoqueconstruction is maintaining enough strength whilekeeping the weight within allowable limits. Due tothe limitations of the monocoque design, a semi-monocoque structure is used on many of today´saircraft.The semi-monocoque system uses a substructure towhich the airplane´s skin is attached. Thesubstructure, which consists of bulkheads and/orformers of various sizes and stringers, reinforces thestressed skin by taking some of the bending stressfrom the fuselage. 8
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  10. 10. The principal structural parts of the wing arespars, ribs, and stringers. 10
  11. 11. The correct name for the tail section of anairplane is empennage. The empennageincludes the entire tail group, consisting offixed surfaces such as the vertical stabilizer andthe horizontal stabilizer. The movable surfacesinclude the rudder, the elevator, and one ormore trim tabs. 11
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  13. 13. Analyses introduce cyclic loads from ground-air-ground cycle and from power spectraldensity descriptions of continuous turbulence.Component fatigue test results are fed into theprogram and the cumulative fatigue damage iscalculated. Stress levels are adjusted to achieverequired structural fatigue design life. 13
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  15. 15. Fatigue failure life of a structural member is usually defined as thetime to initiate a crack which would tend to reduce the ultimatestrength of the member.Fatigue design life implies the average life to be expected underaverage aircraft utilization and loads environment.Scatter factors of 2 to 4 have been used to account for statisticalvariation in component fatigue tests and unknowns in loads. Loadunknowns involve both methods of calculation and type of serviceactually experienced.Primary structure for present transport aircraft is designed, basedon average expected operational conditions and average fatigue testresults, for 120,000 hrs. For the best current methods of design, ascatter factor of 2 is typically used, so that the expected crack-freestructural life is 60,000 hrs, and the probability of attaining a crack-free structural life of 60,000 hrs is 94 percent as shown in thefollowing figure and table. 15
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  17. 17. Np (Flight Np (Years) Probability of Hours)s.f. = N / Np (3,000 flight Survival (%) (N = 120,000 hrs / year) hrs)2.0 94.0 60,000 202.5 97.5 48,000 163.0 98.8 40,000 13.33.5 99.3 34,300 11.4 174.0 99.54 30,000 10.0
  18. 18. Choice of materials emphasizes not onlystrength/weight ratio but also:Fracture toughnessCrack propagation rateNotch sensitivityStress corrosion resistanceExfoliation corrosion resistance 18
  19. 19. The main alloy used is the aluminum alloy.The alloy must have high strength to weightratio.The thickness of the sheet must be such that itshould bear the shear stress.For high shear stress, the thickness of the sheetmust be high, which also increase the deadweight of an aircraft which cannot be afforded. 19
  20. 20. For this reason there is an air gap between thetwo sheets of less thicknessDue to sudden decompression if one sheet failsthere is another sheet to prevent the aircraft forsome from the decompression.If there is a bird hit, due to the air gap, there isno severe damage to the aircraft body. 20
  21. 21. IF PRESSURE IS SET AT 1 IF PRESSURE IS SET BELOW 1ATMOSPHERIC ATMOSPHERIC If the pressure of an If the pressure of an aircraft aircraft is set at 1 atm, is set equal to the pressure than at an altitude of at 8000 feet, than at an 36,000 feet, the altitude of 36,000 feet, the differential pressure is 50 psi. differential pressure is only 7 psi. Thus due to this the structure must be able to Thus due to this the withstand such huge structure has to withstand amount of stress, less amount of stress, resulting in high cost in resulting in low cost in production. production. 21
  22. 22. Aircraft tires, tubeless or tube type, provide acushion of air that helps absorb the shocks androughness of landings and takeoffs: they supportthe weight of the aircraft while on the groundand provide the necessary traction for braking andstopping aircraft on landing. Thus, aircrafttires must be carefully maintained to meet therigorous demands of their basic job to accept avariety of static and dynamic stresses dependably--in a wide range of operating conditions. 22
  23. 23. Dissect an aircraft tire and youll find that itsone of the strongest and toughest pneumatictires made. It must withstand high speeds andvery heavy static and dynamic loads. Forexample, the main gear tires of a four-engine jettransport are required to withstand landingspeeds up to 250 mph, as well as static anddynamic loads as high as 22 and 33 tonsrespectively. 23
  24. 24. It is made of rubber compound for toughnessand durability, the tread is patterned inaccordance with aircraft operationalrequirements. The circumferential ribbedpattern is widely used today because itprovides good traction under widely varyingrunway conditions. 24
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  26. 26. Example of the structure failureAccident summaryDate : April 28, 1988Type: Explosivedecompression causedby fatigue failure Fuselage of Aloha Airlines Flight 243 afterAircraft type: explosive decompression.Boeing 737-200Operator:Aloha Airlines 26
  27. 27. A small section on the left side of the roofruptured.The resulting explosive decompression tore off alarge section of the roof, consisting of the entiretop half of the aircraft skin extending from justbehind the cockpit to the fore-wing area.Investigation by the United States NationalTransportation Safety Board (NTSB) concludedthat the accident was caused by metal fatigueexacerbated by crevice corrosion (the planeoperated in a coastal environment, with exposureto salt and humidity) 27
  28. 28. The root cause of the problem was failure of an epoxyadhesive used to bond the aluminium sheets of the fuselagetogether when the B737 was manufactured. Water was able to enter the gap where the epoxy failed tobond the two surfaces together properly, and started thecorrosion process. The age of the aircraft became a key issue (itwas 19 years old at the time of the accident and had sustaineda remarkable number of takeoff-landing cycles — 89,090, thesecond most cycles for a plane in the world at the time — wellbeyond the 75,000 trips it was designed to sustain).The crack was located aft of the front port side passenger door.The crack was probably due to metal fatigue related to the89,090 compression and decompression cycles experienced inthe short hop flights by Aloha. 28
  29. 29. Major disaster due tostructure failurewhich changed the aviationhistory. Accident summary: Date: 25 July 2000 Type: Foreign object damage Aircraft type: Air France Flight 4590 on fire moments Aérospatiale-BAC after takeoff. Concorde Operator: Air France 29
  30. 30. Five minutes before the takeoff of Flight 4590, a ContinentalAirlines McDonnell Douglas DC-10 destined to Newark (US), lost atitanium alloy strip, 435 millimetres (17.1 in) long and about29 millimetres (1.1 in) to 34 millimetres (1.3 in) wide, during takeofffrom the same runway of Charles de Gaulle Airport.During the Concordes subsequent take-off run, this piece ofdebris, still lying on the runway, cut a tyre causing ruptureand tyre debris to be hurled by centrifugal force.A large chunk of this debris (4.5 kilograms or 9.9 lb) struck theunderside of the aircrafts wing structure at an estimatedspeed of 500 kilometres per hourIt sent out a pressure shockwave that eventually ruptured thenumber five fuel tank at the weakest point, just above thelanding gear. Leaking fuel rushing over the top of the wingwas ignited by an electric arc in the landing gear bay orthrough contact with severed electrical cables. 30
  31. 31. the crash was caused by a titanium strip, part of a thrustreverser, that fell from a Continental Airlines DC-10(Continental Flight 55)This metal fragment punctured the Concordes tyres, whichthen disintegrated. A piece of rubber hit the fuel tank andbroke an electrical cable. The impact caused a shock-wave thatfractured the fuel tank some distance from the point of impact.This caused a major fuel leak from the tank, which thenignited. The crew shut down engine number two in responseto a fire warning but were unable to retract the landing gear,which hampered the aircrafts ability to climb.With engine number one surging and producing little power,the aircraft was unable to gain altitude or airspeed, entering arapid pitch-up then a violent descent, rolling left.The impact occurred with the stricken aircraft tail-low,crashing into the Hotelissimo Hotel in Gonesse. 31
  32. 32. AnyQuestion ??? 32