Nehru Institute of Technology Department of Aeronautical Engineering AE3301 Elements of Aeronautical Engineering Anna university Question Bank UNIT IV PART A UNIT IV INTRODUCTION TO AIRPLANE STRUCTURES AND MATERIALS 12 General types of construction Monocoque semi monocoque Typical wing and fuselage structure Metallic and non metallic materials Use of aluminum alloy titanium stainless steel and composite materials 1 What is the use of stiffness Ans The use of stiffness is the structural efficiency of the materials This is more useful for the selection of aircraft materials for constructing an aircraft 2 Why is titanium suitable as airframe material for supersonic aircraft Ans Titanium is a lightweight strong corrosion resistant metal Recent developments make titanium ideal for applications where aluminum alloys are too weak and stainless steel is too heavy Additionally titanium is unaffected by long exposure to seawater and marine atmosphere 3 Enumerate the stiffener shapes used in aircraft fuselage shell Ans There are two general types of fuselage construction welded steel truss and monocoque The welded steel truss was used in smaller aircraft and it is still being used in some helicopters The monocoque design relies largely on the strength of the skin or covering to carry various The monocoque design may be divided into three classes monocoque semi monocoque and 4 What are the main advantages and disadvantages of composite materials for aircraft designs loads reinforced shell structures Ans Advantages 1 Weight reduction is the greatest advantage 2 High corrosion resistance and 3 Resistance to damage from cyclic loading fatigue Disadvantage Relatively high cost of the materials NB for understanding Advanced composite materials consist of new high strength fibers embedded in an epoxy matrix These composites provide for major weight savings in airplane structures since they have high strength to weight ratios When replacing aluminum structure with graphite epoxy composite weight reductions of 20 or better are possible Weight reduction is the greatest advantage of composite material and is one of the key items in decisions regarding its selection Other advantages over conventional structure include its high corrosion resistance and its resistance to damage from cyclic loading fatigue The major disadvantage of using advanced composite materials in airplane construction is the relatively high cost of the materials 5 What are the components of a modern airplane name any four for which aluminum alloy is used Ans The following are the components of a modern airplane for which aluminum alloy is used Fuselage Emphanage Wings Stabilizers horizontal and vertical stabilizers Fin Flight control surfaces Also internal parts such as longerons wing spars and stiffeners 6 What are the main structural components of an aircraft wing Ans The main structural components of a wing 1 Spars 2 Ribs 3 Ailerons and trailing edge flaps 4 Leading edge flaps slats spoilers and speed brakes 5 Struts 6 Stringers 7 Internal braces NB for understanding NB for understanding Wing construction is similar in most modern aircraft In its simplest form the wing is a framework made up of spars and ribs and covered with metal The construction of an aircraft wing is shown in figure 4 8 Spars are the main structural members of the wing They extend from the fuselage to the tip of the wing The entire load carried by the wing is taken up by the spars The spars are designed to have great bending strength Ribs give the wing section its shape and they transmit the air load from the wing covering to the spars Ribs extend from the leading edge to the trailing edge of the wing In addition to the main spars some wings have a false spar to support the ailerons and flaps Most aircraft wings have a removable tip which streamlines the outer end of the wing NOTE The flight control surfaces on a simple wing may include only ailerons and trailing edge flaps The more complex aircraft may have a variety of devices such as leading edge flaps slats spoilers and speed brakes 7 What are the new types of alloys used now a days for airframe construction of modern aircraft Ans The following are the new types of alloys used now a days for airframe construction of modern aircraft Aluminum alloys Magnesium beryllium alloys Titanium alloys Medium carbon and low alloys steels Super alloys iron nickel based super alloys cobalt based super alloys nickel based super alloys 8 What are the general considerations for the fuselage design of an airplane Name any two Ans The fuselage of an aircraft is subject the five types of stress torsion bending tension shear and compression The general considerations for the fuselage design of an airplane Design relies largely on the strength of the skin or covering to carry various loads Skin must be strong enough to keep the fuselage rigid To be maintaining enough strength while keeping the weight within limits Design overcomes the strength to weight problem 9 What are the most common maneuvers usually classed under the heading of aerobatics Ans The most common maneuvers usually classed under the heading of aerobatics Rolling banking pitching yawing 10 What are the general types of construction of a fuselage structure Or What are the general types of construction of an airplane structure Ans There are two general types of fuselage construction welded steel truss and monocoque designs The welded steel truss was used in smaller aircraft and it is still being used in some helicopters The monocoque design relies largely on the strength of the skin or covering to carry various loads The monocoque design may be divided into three classes monocoque semi monocoque and reinforced shell 11 What are the factors that influence the selection of the structural materials for an aircraft Ans The primary factors to consider in aircraft structures are strength weight and reliability These factors determine the requirements to be met by any material used to construct or repair the aircraft Airframes must be strong and light in weight An aircraft built so heavy that it couldn t support more than a few hundred pounds of additional weight would be useless All materials used to construct an aircraft must be reliable Reliability minimizes the possibility of dangerous and unexpected failures Many forces and structural stresses act on an aircraft when it is flying and when it is static When it is static the force of gravity produces weight which is