Air Structure and Design, the Three Types of Aircraft Loads - Assignment Example

Air Structure and Design Question 1 The three types of aircraft loads include the quasi-static load, dynamic loads, and fatigue load. The quasi-static loads are designed in flight loads, ground handling, and in local and internal loads. To prevent damage the flight loads have symmetric manoeuvres, asymmetric manoeuvres, gust loads, and deep and flat spin. For ground handling, they are designed for takeoff, landing, repaired runway, taxiing, towing, and pivoting. The local and internal loads have the maximum and minimum aerodynamic pressures on the outer surface. In addition, the bay pressures are confined on the pressurized area, hydrostatic pressures on the fuel tanks and the engine thrust. The dynamic loads have buffet on the outer wing, and on the vertical fin buffet. Consequently, the loads have dynamic gust, vibrations, shimmy undercarriage, acoustic noise, and Engine hammershock conditions designed to provide alerts in case of damage. The aircraft is designed to support the ground and the air loads. The fatigue loads are gotten from the dynamic and quasi-static conditions when the frequency of load cycle is high during the set usage. The fatigue loads the loads combination especially when the flight loads are combinations of the internal, local, or acoustic noise. The loads have dynamic buffet that are difficult in predicting due to the high potential in damage. The load may further be categorized as surface loads and body forces. The surface loads acts over the structures surface like the hydrostatic loads and aerodynamic. The body forces act over the structure volume and are developed by the inertia effects and gravitational effects. The structure is designed using the concept of semi- monocoque reinforced by the longerons and frames in the body and skin-stringer that is supported by the ribs and spars on the surfaces. The stress levels are computed with the help of the computer matrix techniques to solve the detailed internal load. The fail-safe design is achieved through the selection of material, proper stress levels, and many load path structural plan that maintains the higher strength during damage. Question 2 According to Griffith theory, the strength of a material is E/10. E in this case is the Young’s modulus for a given material. The theory only considered elastic and brittle material without plastic deformation. However, the correct value for a critical strength was higher than the predicted value. The theory believes that there are variety of microscopic crack is each material that present. The theory hypothesizes that the cracks normally reduced the material’s overall strength. According to Irwin, determined that there was energy form deformation of plastics that has to be added to the energy under strain that were originally considered in Griffith theory in order for the literature to operate for the ductile materials. Irwin theory develops the strain energy’ release rate concept. The Griffith equation is  while the Irwin equation is  a) In expected component life, the theory is applicable to aircraft to determine the life of the aircraft component by including works of the plastic into the elastic energy needed to extend the life of a crack wall. b) In tolerable crack length, considering a thickness crack having a length of 2a subjected to a certain tensile stress at infinity. The length of the crack will occur when the elastic strain energy is releases and equal to the energy needed to come up with a new crack surface. This has helped aircraft in determining the time taken for a crack in aircrafts to be detected. c) In inspection intervals, the theory has helped the engineers to find out the stress needed to create a new crack surface. This is depends on the size of the crack and tend to satisfy only the brittle materials used in constructing the aircraft. Question 3 Flight loads The flight loads for the airborne and aircraft are expensive and not easy to get, since the resources are not available to fly the various combination of mission types, aircraft and stores. The loads found on the stores of aircrafts are different from the ones found on the center of gravity. Aero elastic loads A load model for the stationary part of a flight has to involve both loads because of turbulence in the wind field and aero elastic loads that are undisturbed. The aero elastic loads occur because of structure motions in the wind. In the aircraft, the loads are conventionally described through the flutter derivatives. Fatigue Loads This is a load that is caused by an increasing life of a store, which has made the aircraft to experience mechanical wear out. This has led to a crucial consideration of the concern during the design of aircraft. The methods of developing the store loading spectra is characterized by the economy and realism in collection of data, and therefore, in the testing of fatigues themselves. Question 4 The five Non Destructive Testing methods include Liquid Penetrant, Magnetic Particle, Eddy Current, Ultrasonic, and Radiography. Liquid penetrant is applicable in detecting the structural damage or surface detects in the material of aircrafts, the fluorescent penetrants are applicable in critical regions for the sensitive evaluation. The key points for the method are easily transportable, inexpensive, simple and fast to use. The magnetic principle is a method that is very sensitive used in breaking surface and discontinuation of sub-surface in materials that are Ferro magnetic. Here, it is assumed that the magnetic flux is domestically distorted by the discontinuity presence. The distortion catalyzed the magnetic field to re-enter the test object. The method applies the magnetic particles in a dry power for the liquid suspension. Eddy current is induced in electricity conductor by reacting with the alternate magnetic field. The currents are oriented perpendicularly and also circular to the magnetic field direction. The current comprises of five operation; oscillator, bridge circuit, display, and signal processing circuit. The ultrasonic allows small flaws detection with one surface accessible and has the ability of estimating the size and location of the detect. The detection equipment has the following elements timing, cathode ray oscilloscope, RF pulser, and Transducer. The method is used in detecting the subsurface and surface I forging, welds, and cast crucial structural fittings. The radiography is a record formed by passing of the electromagnetic radiation like gamma rays or x-ray via the object onto the film. Considering the absorption and penetration ability of the x-radiation, the radiography is helpful in inspecting the various nonmetallic parts for water entrapment, porosity, cracks, and crushed core. Question 5 The fail-safe approach is one of the techniques used in achieving the damage tolerance. The goal of the approach is to apply the multiple load paths and crack arrest tools so that one component failure do not result to immediate loss of the whole structure. The carried load is picked up immediately by adjacent structures and the total fracture of the aircraft is avoided. It is important, that the previous failure is detected and repaired promptly since the load carried as extra will shorten the fatigue life of the components. Conversely, the safe-life approach the structure is designed to have a lower life, which is commonly referred to that no catastrophic damage will happen. At the life terminal the structure will be replaced despite no signs for detecting fatigue is seen. The approach encourages the likelihood to replace the components liker the undercarriage legs and techniques to have a life that is safe than that of the entire craft because It will more economical to use it. The safe-life is encouraged because the fail-safe approached has to be accompanied by inspections that locate the previous members’ failure which is seen to be time wasting. Question 6 Physical Advantages 1) The large monolithic structures are incredibly strong and efficient structure; they handle the hurricane earthquakes and winds along their strides. 2) Additionally, the construction speed is a crucial features. In addition, the structures can take various shapes including overlapping various units. 3) The outside shell material can be finished in any form, making it more flexible. Economic Advantage 1) Someone can take an insurance cover for the structure; fire policy. The structures can be insured under fire policy; therefore, the cost incurred in building the coverage is experienced to be slightly lower of the cost of a conventional structure. 2) It is cost effective; the shell can be built for a cheaper amount per square foot. Cumulatively this is cheaper than the small monolithic domes 3) In terms of safety, the shell of the building cannot be burned. The contents, which are flammable, cannot be damaged thereby saving repair costs and other expenses that come along with fire. The physical properties of monolithic that need to be enhanced include their strength in case of high temperature, their resistance to abrasion, and their thermal conductivity. Question 7 Skin This are the fuselage or wing skin used in carrying the loads. The small metal strips include the stringers, longerons, and stiffeners attached in preventing buckling. Ribs The rib tends to maintain the airfoil shape and shifts the loads to the spar. Spar These are the beams that extend from the wing root to the tip. It is made of the spar cap and the spar web. The spar caps carries the bending loads while the spar web carries the shear load. Stringers The stringers are fuselage frames that are used in maintaining the fuselage shape and transferring load. Question 8 The crack will be detected during the routine inspection even before, it could develop to this length. In the event of comet, the cracks propagated from the rivet holes near cabin windows. When the cracks reached at the window, the window opening size was added to the length of the crack. The modern aircraft are designed using the same failure mode and they have the tear strips that are able to reduce any growing attack. Question 9 Reference Yun, Liang, and Alan Bliault. Theory and design of air cushion craft. London: Arnold ;, 2000. Print. Read More