ac structure reviewer (1).pdf

George Cayley - pioneered directional control of aircraft by including the earliest form of a rudder on his gliders. 1800s - Otto Lilienthal built upon Cayley's discoveries. He manufactured and flew his own gliders on over 2,000 flights. Above all, Lilienthal proved that man could fly 1890s - Oc...

George Cayley - pioneered directional control of aircraft by including the earliest form of a rudder on his gliders. 1800s - Otto Lilienthal built upon Cayley's discoveries. He manufactured and flew his own gliders on over 2,000 flights. Above all, Lilienthal proved that man could fly 1890s - Octave Chanute, a retired railroad and bridge engineer, published 'Progress in Flying Machines 1903 - Wright Brothers built their successful, powered airplane. The first of its kind to carry a man aloft, the Wright Flyer had thin, cloth-covered wings attached to what was primarilyly truss structures made of wood. The wings contained forward and rear spars and were supported with both struts and wires Stacked wings 1909 - Frenchman Louis Bleriot produced an aircraft with notable design differences. He built a successful mono- wing aircraft. The wings were still supported by wires, but a mast extending above the fuselage enabled the wings to be supported from above, as well as underneath. This made possible the extended wing length needed to lift an aircraft with a single set of wings. 1910 - German Hugo Junkers was able to build an aircraft with metal truss construction and metal skin due to the availability of stronger powerplants to thrust the plane forward and into the sky. The use of metal instead of wood for the primary structure eliminated the need for external wing braces and wires His J-1 also had a single set of wings (a monoplane) instead of a stacked set World War I (WWI) - stronger engines also allowed designers to develop thicker wings with stronger spars. Wire wing bracing was no longer needed. Flatter, lower wing surfaces on high-camber wings created more lift 1920s - the use of metal in aircraft construction increased Fuselages able to carry cargo and passengers were developed 1930s-all-metal aircraft accompanied new lighter and more powerful engines. World War II (WWII) brought about a myriad of aircraft designs using all metal technology. Deep fuel-carrying wings were the norm, but the desire for higher light speeds prompted the development of thin-winged aircraft in which fuel was carried in the fuselage. De Havilland Mosquito -the first composite structure aircraft, used a balsa wood sandwich material in the construction of the fuselage. The fiberglass radome was also developed during this period A steady increase in the use of honeycomb and foam core sandwich components and a wide variety of composite materials characterizes the state of aviation structures from the 1970s to the present. Advanced techniques and material combinations have resulted in a gradual shift from aluminum to carbon fiber and other strong, lightweight materials. These new materials are engineered to meet specific performance requirements for various components on the aircraft. Many airframe structures are made of more than 50 percent advanced composites, with some airframes approaching 100 percent. The term "very light jet" (VLJ) has come to describe a new generation of jet aircraft made almost entirely of advanced composite materials. An aircraft is a device that is used for, or is intended to be used for, Major categories of aircraft are airplane, rotorcraft, glider, and lighter-than air vehicles. The most common aircraft is the fixed-wing aircraft. As the name implies the wings on this type of flying machine are attached to the fuselage and are not intended to move independently in a fashion that results in the creation of lift Glider airframes are very similar to fixed-wing aircraft. Unless otherwise noted maintenance practices described for fixed-wing aircraft also apply to gliders Wing spar – main structural member in a wing Stress – an applied force or system of forces that tends to strain or deform a body Strain – is the resistance to pulling, drawing or stretching of an aircraft part Tension – ability of metal to withstand being pulled apart Compression – strength that resists the stress of a crushing force Torsion – applied to an object being twisted Shear – forces that tends to produce shearing strain Bending – combination of stress and tension Fuselage – main structure of fixed wing aircraft - provides space for cargo, controls, accessories, passengers and other equipment - in single-engine aircraft, the fuselage houses the powerplant. - In multi engine aircraft, the engines may be either in the fuselage, attached to the fuselage, or suspended from the wing structure. 2 types of fuselage construction - Truss - Monocoque Truss type - A truss is a rigid framework made up of members, such as beams, struts, and bars to resist deformation by applied loads. - The truss-type fuselage frame is usually constructed of steel tubing welded together in such a manner that all members of the truss can carry both tension and compression loads.  - In some aircraft, principally the light, single engine models, truss fuselage frames may be constructed of aluminum alloy and may be riveted or bolted into one piece, with cross-bracing achieved by using solid rods or tubes Monocoque type - The monocoque (single (single shell) fuselage relies largely on the strength of the skin or covering to carry the primary loads. - uses formers, frame assemblies, and bulkhead to give shape to the fuselage. - The heaviest of these structural members are located at intervals to carry - concentrated loads and at points where fittings are used to attach other units such as wings, powerplants, and stabilizers. - Since no other bracing members are present, the skin must carry the primary stresses and keep the fuselage rigid. - Thus, the biggest problem involved. - in monocoque construction is maintaining enough strength while keeping the weight within allowable Semi monocoque type - It also consists of frame assemblies, bulkheads, and formers as used in the monocoque design. - additionally, the skin is reinforced by longitudinal members called longerons - Longerons usually extend across several frame members and help the skin support primary bending loads. - Stringers - longitudinal members are typically more numerous and lighter in weight than the longerons - web members - these additional support pieces may be installed vertically or diagonally. - It must be noted that manufacturers use different nomenclature to describe structural members.  - The semi monocoque fuselage is constructed primarily of alloys of aluminum and magnesium, although steel and titanium are sometimes found in areas of high temperatures. - Individually, no one of the aforementioned components is strong enough to carry the loads imposed during light and landing. - But, when combined, those components form a strong, rigid framework. - This is accomplished with gussets, rivets, nuts and bolts, screws, and even friction stir welding. - A gusset is a type of connection bracket that adds strength. Longerons - typically made of aluminum alloy either of a single piece or a built-up construction. Stringers - usually made from single piece aluminum alloy extrusions or formed aluminum. - have some rigidity but are chiefly used for giving shape and for attachment of the skin. - Stringers and longerons together prevent tension and compression from bending the fuselage Wings - are airfoils that, when moved rapidly through the air, create lift. - They are built in many shapes and sizes. - Wing design can vary to provide certain desirable - Chord is The distance from the leading to trailing edge of the wing The wings of an aircraft can be attached to the fuselage at the top, mid-fuselage, or at the bottom - They may extend perpendicular to the horizontal plain of the fuselage or can angle up or down slightly. - This angle is known as the wing dihedral. - The dihedral angle affects the lateral stability of the aircraft Low wing Dihedral wing Mid wing High wing Gull wing Inverted gull wing strongest wing structure is the full cantilever which is attached directly to the fuselage and does not have any type of external, stress bearing structures. The semi-cantilever usually has one, or perhaps two, supporting wires or struts attached to each wing and the fuselage. The externally braced wing is typical of the biplane (two wings placed one above the other) with its struts and flying and landing wires - Wing position lights are located at the center of the tip and are not directly visible from the cockpit - As an indication that the wing tip light is operating, some wing tips are equipped with a Lucite rod to transmit the light to the leading edge. The internal structures of most wings are made up of spars and stringers running spanwise and ribs and formers or bulkheads running chordwise (leading edge to trailing edge). Spars - Spars are the principal structural members of a wing. - They support all distributed loads, as well as concentrated weights such as the fuselage, landing gear, and engines. - The skin, which is attached to the wing structure, carries part t of the loads imposed during light. - It also transfers the stresses to the wing ribs. - The ribs, in turn, transfer the loads to the wing spars In general, wing construction is based on one of three fundamental designs 1. The monospar wing incorporates only one main spanwise or longitudinal member in its construction. Ribs or bulkheads supply the necessary contour or shape to the airfoil. 2. The multispar wing incorporates more than one main longitudinal member in its construction. To give the wing contour, ribs or bulkheads are often included. 3. The box beam type of wing construction uses two main longitudinal members with connecting bulkheads to furnish additional strength and to give contour to the wing. Air transport category aircraft often utilize box beam wing construction. - They correspond to the longerons of the fuselage. - They run parallel to the lateral axis of the aircraft from the fuselage toward the tip of the wing, and are usually attached to the fuselage by wing fittings, plain beams, or a truss. - Spars may be made of metal, wood, or composite materials depending on the design criteria of a specific aircraft. - Wooden spars are usually made from spruce - They can be generally classified into four different types by their cross-sectional configuration. They may be solid. box shaped, partly hollow, or in the form of an I- beam. - Lamination of solid wood spars is often used to increase strength. - The spar in Figure E has had material removed to reduce weight but retains the strength of a rectangular spar. Ribs - Ribs are the structural cross pieces that combine with spars and stringers to make up the framework of the wing. - They usually extend from the wing leading edge to the rear spar or to the trailing edge of the wing. - The ribs give the wing its cambered shape and transmit the load from the skin and stringers to the spars. - Similar ribs are also used in ailerons, elevators, rudders, and stabilizers. - Wing ribs are usually manufactured from either wood or metal - while most aircraft with metal spars have metal ribs  - Wood ribs are usually manufactured from spruce - The three most common types of wooden ribs are the plywood web, the lightened plywood web, and the truss types. Of these three, the truss type is the most efficient because it is strong and lightweight, but it is also the most complex to construct - Wing ribs may also be referred to as a plain rib or a main rib - False ribs are ribs that do not span the entire wing chord, leading edge to the trailing edge of the wing. - Wing butt ribs may be found at the inboard edge of the wing where the wing attaches to the fuselage - A butt rib may also be called a bulkhead rib or a compression rib Wing tips - Wing tips at the inboard end of the wing spars is some form of wing attach fitting - These provide a strong and secure method for attaching the wing to the fuselage. - The interface between the wing and fuselage is often covered with a fairing to achieve smooth airflow in this area. - The fairing(s) can be removed for access to the wing attach fittings - internal structures of most wings are made up of spars and stringers running spanwise and ribs and formers or bulkheads running chordwise (leading edge to trailing edge). - skin, which is attached to the wing structure, carries part of the loads imposed during light. - The ribs, in turn, transfer the loads to the wing spars. - wing tip is often a removable unit, bolted to the outboard end of the wing panel One reason for this is the vulnerability of the wing tips to damage, especially during ground handling and taxiing. The wing tip assembly is of aluminum alloy construction. The wing tip cap is secured to the tip with countersunk screws and is secured to the interspar structure at four points with 1/4-inch diameter bolts. To prevent ice from forming on the leading edge of the wings of large aircraft, hot air from an engine is often channeled through the leading edge from wing root to wing tip. A louver on the top surface of the wingtip allows this warm air to be exhausted overboard Wing position lights are located at the center of the tip and are not directly visible from the cockpit. As an indication that the wing tip light is operating some wing tips are equipped with a Lucite rod to transmit the light to the leading edge. Wing skin - Wing skin is designed to carry part of the light and ground loads in combination with the spars and ribs. - This is known as a stressed-skin design. -The all-metal, full cantilever wing section illustrated below shows the structure of one such design. - The lack of extra internal or external bracing requires that the skin share some of the load. - Fuel is often carried inside the wings of a stressed-skin aircraft. - The joints in the wing can be sealed with a special fuel resistant sealant enabling fuel to be stored directly inside the structure. - This is known as wet wing design. - Alternately, a fuel-carrying bladder or tank can be fitted inside a wing. - On aircraft with stressed-skin wing design, honeycomb structured wing panels are often used as skin. - A honeycomb structure is built up from a core material resembling a bee hive's honeycomb. Which is laminated or sandwiched between outer skin sheets. Nacelles - nacelles (sometimes called "pods") are streamlined enclosures used primarily to house the engine and its components. - They usually present a round or elliptical profile to the wind thus reducing aerodynamic drag. - On most single-engine aircraft, the engine and nacelle are at the forward end of the fuselage. - On multiengine aircraft, engine nacelles are built into the wings or attached to the fuselage at the empennage (tail section). - Occasionally, a multiengine aircraft is designed with a nacelle in line with the fuselage aft of the passenger compartment. - Nacelle contains the engine and accessories, engine mounts, structural members, a firewall, and skin and cowling on the exterior to fare the nacelle to the wind. - Some aircraft have nacelles that are designed to house the landing gear when retracted. - Retracting the gear to reduce wind resistance is standard procedure on high- performance/high-speed aircraft. - The wheel well is the area where the landing gear is attached and stowed when retracted. - Wheel wells can be located in the wings and/or fuselage when not part of the nacelle. - The framework of a nacelle usually consists of structural members similar to those of the fuselage. - Lengthwise members, such as longerons and stringers, combine with horizontal/vertical members, such as rings, formers, and bulkheads, to give the nacelle its shape and structural integrity. - A firewall is incorporated to isolate the engine compartment from the rest of the aircraft. - Engine mounts are also found in the nacelle. - These are the structural assemblies to which the engine is fastened. - The exterior of a nacelle is covered with a skin or fitted with a cowling which can be opened to access the engine and components inside. - Both are usually made of sheet aluminum or magnesium alloy with stainless steel or titanium alloys being used in high-temperature areas, such as around the exhaust exit. - The skin is typically attached to the framework with rivets Cowling - Cowling refers to the detachable panels covering those areas into which access must be gained regularly - It is designed to provide a smooth airflow over the nacelle and to protect the engine from damage. - Cowl panels are generally made of aluminum alloy construction. - However, stainless steel is often used as the inner skin aft of the power section and for cowl flaps and near cowl flap openings. It is also used for oil cooler ducts. - Cowl flaps are moveable parts of the nacelle cowling that open and close to regulate engine temperature. - There are many engine cowl designs. - Figure below shows an exploded view of the pieces of cowling for a horizontally opposed engine on a light aircraft. - It is attached to the nacelle by means of screws and/or quick release fasteners. - Some large reciprocating engines are enclosed by "orange peel cowlings” which provide excellent access to components inside the nacelle. - Cowling on a transport category turbine engine nacelle