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Materials Aircraft  The material, called GLARE, is made from alternating thin layers of aluminium and resin impregnated with fibreglass, making it more rigid and impact-resistant. GLARE could be combined with large sheets of conducting carbon nanotubes to protect against lightning. The nanotubes would be a lightweight replacement for the metal that lines the fuselage, and would form what's known as a Faraday cage. --------------------------------------- 1 CHAPTER 4 AIRCRAFT BASIC CONSTRUCTION INTRODUCTIONuseless. All materials used to construct an aircraft must be reliable. Reliability minimizes the possibility of Naval aircraft are built to meet certain specified requirements. These requirements must be selected sodangerous and unexpected failures. they can be built into one aircraft. It is not possible forMany forces and structural stresses act on an one aircraft to possess all characteristics; just as it isn'taircraft when it is flying and when it is static. When it is possible for an aircraft to have the comfort of astatic, the force of gravity produces weight, which is passenger transport and the maneuverability of asupported by the landing gear. The landing gear absorbs fighter. The type and class of the aircraft determine howthe forces imposed on the aircraft by takeoffs and strong it must be built. A Navy fighter must be fast,landings. maneuverable, and equipped for attack and defense. To During flight, any maneuver that causes meet these requirements, the aircraft is highly poweredacceleration or deceleration increases the forces and and has a very strong structure. stresses on the wings and fuselage. The airframe of a fixed-wing aircraft consists of theStresses on the wings, fuselage, and landing gear of following five major units: aircraft are tension, compression, shear, bending, and 1. Fuselagetorsion. These stresses are absorbed by each component of the wing structure and transmitted to the fuselage 2. Wings structure. The empennage (tail section) absorbs the 3. Stabilizerssame stresses and transmits them to the fuselage. These stresses are known as loads, and the study of loads is 4. Flight controls surfacescalled a stress analysis. Stresses are analyzed and 5. Landing gearconsidered when an aircraft is designed. The stresses A rotary-wing aircraft consists of the followingacting on an aircraft are shown in figure 4-1. four major units: TENSION 1. Fuselage 2. Landing gearTension (fig. 4-1, view A) is defined as pull.Itisthe stress of stretching an object or pulling at its ends. 3. Main rotor assemblyTension is the resistance to pulling apart or stretching 4. Tail rotor assemblyproduced by two forces pulling in opposite directions along the same straight line. For example, an elevator You need to be familiar with the terms used forcontrol cable is in additional tension when the pilot aircraft construction to work in an aviation rating. moves the control column. COMPRESSION STRUCTURAL STRESS LEARNING OBJECTIVE: Identify the fiveIf forces acting on an aircraft move toward each basic stresses acting on an aircraft.other to squeeze the material, the stress is called compression. Compression (fig. 4-1, view B) is the The primary factors to consider in aircraft structures are strength, weight, and reliability. Theseopposite of tension. Tension is pull, and compression is factors determine the requirements to be met by anypush. Compression is the resistance to crushing material used to construct or repair the aircraft.produced by two forces pushing toward each other in Airframes must be strong and light in weight. Anthe same straight line. For example, when an airplane is aircraft built so heavy that it couldn't support more thanon the ground, the landing gear struts are under a a few hundred pounds of additional weight would beconstant compression stress. 4-1 --------------------------------------- 2 Figure 4-1.Five stresses acting on an aircraft. SHEARcompression one instant and under tension the next. The strength of aircraft materials must be great enough Cutting a piece of paper with scissors is an exampleto withstand maximum force of varying stresses. of a shearing action. In an aircraft structure, shear (fig. 4-1, view D) is a stress exerted when two pieces ofSPECIFIC ACTION OF STRESSES fastened material tend to separate. Shear stress is the outcome of sliding one part over the other in oppositeYou need to understand the stresses encountered on directions. The rivets and bolts of an aircraft experiencethe main parts of an aircraft. A knowledge of the basic both shear and tension stresses.stresses on aircraft structures will help you understand why aircraft are built the way they are. The fuselage of BENDINGan aircraft is subject the fives types of stresstorsion, bending, tension, shear, and compression. Bending (fig. 4-1, view E) is a combination of Torsional stress in a fuselage is created in several tension and compression. For example, when bending aways. For example, torsional stress is encountered in piece of tubing, the upper portion stretches (tension)engine torque on turboprop aircraft. Engine torque and the lower portion crushes together (compression). The wing spars of an aircraft in flight are subject totends to rotate the aircraft in the direction opposite to bending stresses.the direction the propeller is turning. This force creates a torsional stress in the fuselage. Figure 4-2 shows the effect of the rotating propellers. Also, torsional stress TORSIONon the fuselage is created by the action of the ailerons Torsional (fig. 4-1, view C) stresses result from awhen the aircraft is maneuvered. twisting force. When you wring out a chamois skin, youWhen an aircraft is on the ground, there is a are putting it under torsion. Torsion is produced in anbending force on the fuselage. This force occurs engine crankshaft while the engine is running. Forcesbecause of the weight of the aircraft. Bending increases that produce torsional stress also produce torque.when the aircraft makes a carrier landing. This bending action creates a tension stress on the lower skin of the VARYING STRESSfuselage and a compression stress on the top skin. All structural members of an aircraft are subject toBending action is shown in figure 4-3. These stresses are transmitted to the fuselage when the aircraft is in one or more stresses. Sometimes a structural memberflight. Bending occurs because of the reaction of the has alternate stresses; for example, it is underairflow against the wings and empennage. When the 4-2 --------------------------------------- 3 TORSIONAL STRESS PROPELLER ROTATION ANfO4O2 Figure 4-2.Engine torque creates torsion stress in aircraft fuselages. aircraft is in flight, lift forces act upward against theQ4-4. Define the term bending. wings, tending to bend them upward. The wings areQ4-5. Define the term torsion. prevented from folding over the fuselage by the resisting strength of the wing structure. The bending action creates a tension stress on the bottom of theCONSTRUCTION MATERIALS wings and a compression stress on the top of the wings. LEARNING OBJECTIVE: Identify the Q4-1. Theresistancetopullingapartorstretchingvarious types of metallic and nonmetallic produced by two forces pulling in oppositematerials used in aircraft construction. directions along the same straight lines isAn aircraft must be constructed of materials that defined by what term?are both light and strong. Early aircraft were made of Q4-2. The resistance to crushing produced by twowood. Lightweight metal alloys with a strength greater forcespushingtowardeachotherinthesamethan wood were developed and used on later aircraft. straight line is defined by what term?Materials currently used in aircraft construction are classified as either metallic materials or nonmetallic Q4-3. Define the term shear as it relates to anmaterials. aircraft structure. COMPRESSION TENSION ANf0403 Figure 4-3.Bending action occurring during carrier landing. 4-3 --------------------------------------- 4 METALLIC MATERIALSforces that occur on today's modern aircraft. These steels contain small percentages of carbon, nickel, The most common metals used in aircraftchromium, vanadium, and molybdenum. High-tensile construction are aluminum, magnesium, titanium,steels will stand stress of 50 to 150 tons per square inch steel, and their alloys.without failing. Such steels are made into tubes, rods, and wires. Alloys Another type of steel used extensively is stainless steel. Stainless steel resists corrosion and is particularly An alloy is composed of two or more metals. The metal present in the alloy in the largest amount is calledvaluable for use in or near water. the basemetal. All other metals added to the base metal NONMETALLIC MATERIALS are called alloying elements. Adding the alloying elements may result in a change in the properties of the In addition to metals, various types of plastic base metal. For example, pure aluminum is relativelymaterials are found in aircraft construction. Some of soft and weak. However, adding small amounts or copper, manganese, and magnesium will increasethese plastics include transparent plastic, reinforced plastic, composite, and carbon-fiber materials. aluminum's strength many times. Heat treatment can increase or decrease an alloy's strength and hardness. Alloys are important to the aircraft industry. TheyTransparent Plastic provide materials with properties that pure metals doTransparent plastic is used in canopies, not possess. windshields, and other transparent enclosures. You need to handle transparent plastic surfaces carefully Aluminum because they are relatively soft and scratch easily. At approximately 225°F, transparent plastic becomes soft Aluminum alloys are widely used in modernand pliable. aircraft construction. Aluminum alloys are valuable because they have a high strength-to-weight ratio. Reinforced Plastic Aluminum alloys are corrosion resistant and comparatively easy to fabricate. The outstanding Reinforced plastic is used in the construction of characteristic of aluminum is its lightweight.radomes, wingtips, stabilizer tips, antenna covers, and flight controls. Reinforced plastic has a high Magnesium strength-to-weight ratio and is resistant to mildew and rot. Because it is easy to fabricate, it is equally suitable Magnesium is the world's lightest structural metal. It is a silvery-white material that weighs two-thirds asfor other parts of the aircraft. much as aluminum. Magnesium is used to makeReinforced plastic is a sandwich-type material (fig. helicopters. Magnesium's low resistance to corrosion4-4). It is made up of two outer facings and a center has limited its use in conventional aircraft.layer. The facings are made up of several layers of glass cloth, bonded together with a liquid resin. The core Titaniummaterial (center layer) consists of a honeycomb HONEYCOMB Titanium is a lightweight, strong, corrosion-CORE 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. Steel Alloys Alloy steels used in aircraft construction have great strength, more so than other fields of engineeringFACINGSAnf0404 would require. These materials must withstand the(MULTIPLE LAYERS OF GLASS CLOTH) Figure 4-4.Reinforced plastic. 4-4 --------------------------------------- 5 structure made of glass cloth. Reinforced plastic isQ4-8. What are the nonmetallic materials used in fabricated into a variety of cell sizes.aircraft construction? Composite and Carbon Fiber FIXED-WING AIRCRAFT Materials LEARNING OBJECTIVE: Identify the High-performance aircraft require an extra highconstruction features of the fixed-wing aircraft strength-to-weight ratio material. Fabrication ofand identify the primary, secondary, and composite materials satisfies this special requirement.auxiliary flight control surfaces. Composite materials are constructed by using several The principal structural units of a fixed-wing layers of bonding materials (graphite epoxy or boron aircraft are the fuselage, wings, stabilizers, flight epoxy). These materials are mechanically fastened to control surfaces, and landing gear. Figure 4-5 shows conventional substructures. Another type of composite these units of a naval aircraft. construction consists of thin graphite epoxy skins bonded to an aluminum honeycomb core. Carbon fiberNOTE: The terms leftor rightused in relation to is extremely strong, thin fiber made by heatingany of the structural units refer to the right or left hand synthetic fibers, such as rayon, until charred, and thenof the pilot seated in the cockpit. layering in cross sections. FUSELAGE Q4-6. Materialscurrentlyusedinaircraftconstruc- tion are classified as what type of materials? The fuselage is the main structure, or body, of the Q4-7. Whatarethemostcommonmetallicmaterialsaircraft. It provides space for personnel, cargo, used in aircraft construction?controls, and most of the accessories. The power plant, wings, stabilizers, and landing gear are attached to it. VERTICAL STABILIZER (FIN) HORIZONTAL AILERONSTABILIZER RUDDER FLAPENGINE EXHAUST LEADING EDGEENGINE OF WINGEXHAUST ELEVATOR CANOPY COCKPIT WING MAIN ENGINEENGINE LANDING RADOMEAIR INLETNACELLE GEAR FAIRING NOSE LANDINGANf0405 GEAR Figure 4-5.Principal structural units on an F-14 aircraft. 4-5 --------------------------------------- 6 There are two general types of fuselageconsidered to be of semimonocoque-type constructionwelded steel truss and monocoqueconstruction. designs. The welded steel truss was used in smaller Navy aircraft, and it is still being used in someThe semimonocoque fuselage is constructed helicopters.primarily of aluminum alloy, although steel and titanium are found in high-temperature areas. Primary The monocoque design relies largely on thebending loads are taken by the longerons, which strength of the skin, or covering, to carry various loads.usually extend across several points of support. The The monocoque design may be divided into threelongerons are supplemented by other longitudinal classesmonocoque, semimonocoque, and reinforcedmembers known as stringers. Stringers are more shell.numerous and lightweight than longerons. The true monocoque construction usesThe vertical structural members are referred to as formers, frame assemblies, and bulkheads tobulkheads, frames, and formers. The heavier vertical give shape to the fuselage. However, the skinmembers are located at intervals to allow for carries the primary stresses. Since no bracingconcentrated loads. These members are also found at members are present, the skin must be strongpoints where fittings are used to attach other units, such enough to keep the fuselage rigid. The biggestas the wings and stabilizers. problem in monocoque construction is maintaining enough strength while keeping theThe stringers are smaller and lighter than longerons weight within limits.and serve as fill-ins. They have some rigidity but are chiefly used for giving shape and for attachment of Semimonocoque design overcomes theskin. The strong, heavy longerons hold the bulkheads strength-to-weight problem of monocoqueand formers. The bulkheads and formers hold the construction. See figure 4-6. In addition tostringers. All of these join together to form a rigid having formers, frame assemblies, andfuselage framework. Stringers and longerons prevent bulkheads, the semimonocoque constructiontension and compression stresses from bending the has the skin reinforced by longitudinalfuselage. members.The skin is attached to the longerons, bulkheads, and other structural members and carries part of the The reinforced shell has the skin reinforced byload. The fuselage skin thickness varies with the load a complete framework of structural members.carried and the stresses sustained at particular loca- Different portions of the same fuselage maytion. belong to any one of the three classes. Most are ANf0406 Figure 4-6.Semimonocoque fuselage construction. 4-6 --------------------------------------- 7 There are a number of advantages in using thesemimonocoque fuselage can withstand semimonocoque fuselage.damage and still be strong enough to hold together. The bulkhead, frames, stringers, and longerons aid in the design and construction of aPoints on the fuselage are located by station streamlined fuselage. They add to the strengthnumbers. Station 0 is usually located at or near the nose and rigidity of the structure.of the aircraft. The other stations are located at measured distances (in inches) aft of station 0. A The main advantage of the semimonocoque typical station diagram is shown in figure 4-7. On this construction is that it depends on many particular aircraft, fuselage station (FS) 0 is located structural members for strength and rigidity. 93.0 inches forward of the nose. Because of its stressed skin construction, a WS 400 AIRCRAFT STATIONS380 360 340 320 300oo FS - FUSELAGE20 WING75 WING 280STATIONUNSWEPTOVERSWEPT 26068o 240WS - WINGWING STATION 220SWEPT 200 180 160 140 120 100 80 60 40 20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 STATIC GROUNDARRESTING HOOK LINEFULLY EXTENDED 050100150200250300350400450500550600650700750800850ANfO407 Figure 4-7.Fuselage station diagram of an F-14 aircraft. 4-7 --------------------------------------- 8 WINGSthat is constructed so it can be used as a fuel cell. The wet wing is sealed with a fuel-resistant compound as it Wings develop the major portion of the lift of ais built. The wing holds fuel without the usual rubber heavier-than-air aircraft. Wing structures carry some ofcells or tanks. the heavier loads found in the aircraft structure. The particular design of a wing depends on many factors,The wings of most naval aircraft are of all metal, such as the size, weight, speed, rate of climb, and use offull cantilever construction. Often, they may be folded for carrier use. A full cantilever wing structure is very the aircraft. The wing must be constructed so that itstrong. The wing can be fastened to the fuselage holds its aerodynamics shape under the extremewithout the use of external bracing, such as wires or stresses of combat maneuvers or wing loading.struts. Wing construction is similar in most modernA complete wing assembly consists of the surface aircraft. In its simplest form, the wing is a frameworkproviding lift for the support of the aircraft. It also made up of spars and ribs and covered with metal. Theprovides the necessary flight control surfaces. construction of an aircraft wing is shown in figure 4-8. NOTE: The flight control surfaces on a simple Spars are the main structural members of the wing.wing may include only ailerons and trailing edge flaps. They extend from the fuselage to the tip of the wing. AllThe more complex aircraft may have a variety of the load carried by the wing is taken up by the spars.devices, such as leading edge flaps, slats, spoilers, and The spars are designed to have great bending strength. Ribs give the wing section its shape, and they transmitspeed brakes. the air load from the wing covering to the spars. RibsVarious points on the wing are located by wing extend from the leading edge to the trailing edge of thestation numbers (fig. 4-7). Wing station (WS) 0 is wing.located at the centerline of the fuselage, and all wing In addition to the main spars, some wings have astations are measured (right or left) from this point (in false spar to support the ailerons and flaps. Mostinches). aircraft wings have a removable tip, which streamlines the outer end of the wing.STABILIZERS Most Navy aircraft are designed with a wingThe stabilizing surfaces of an aircraft consist of referred to as a wetwing. This term describes the wingvertical and horizontal airfoils. They are called the TRAILING EDGE LEADING EDGE RIBS SPARS ANf0408 Figure 4-8.Two-spar wing construction. 4-8 --------------------------------------- 9 vertical stabilizer (or fin) and horizontal stabilizer.FLIGHT CONTROL SURFACES These two airfoils, along with the rudder and elevators, form the tail section. For inspection and maintenanceFlight control surfaces are hinged (movable) purposes, the entire tail section is considered a singleairfoils designed to change the attitude of the aircraft unit called the empennage.during flight. These surfaces are divided into three The main purpose of stabilizers is to keep thegroupsprimary, secondary, and auxiliary. aircraft in straight-and-level flight. The vertical stabilizer maintains the stability of he aircraft about itsPrimary Group vertical axis (fig. 4-9). This is known as directionalThe primary group of flight control surfaces stability. The vertical stabilizer usually serves as theincludes ailerons, elevators, and rudders. The ailerons base to which the rudder is attached. The horizontalattach to the trailing edge of the wings. They control the stabilizer provides stability of the aircraft about itsrolling (or banking) motion of the aircraft. This action lateral axis. This is known as longitudinalstability. Theis known as longitudinal control. horizontal stabilizer usually serves as the base to which the elevators are attached. On many newer,The elevators are attached to the horizontal high-performance aircraft, the entire vertical and/orstabilizer and control the climb or descent (pitching horizontal stabilizer is a movable airfoil. Without themotion) of the aircraft. This action is known as lateral movable airfoil, the flight control surfaces would losecontrol. their effectiveness at extremely high altitudes.The rudder is attached to the vertical stabilizer. It determines the horizontal flight (turning or yawing Stabilizer construction is similar to wing construction. For greater strength, especially in themotion) of the aircraft. This action is known as thinner airfoil sections typical of trailing edges, adirectional control. honeycomb-type construction is used. Some largerThe ailerons and elevators are operated from the carrier-type aircraft have vertical stabilizers that arecockpit by a control stick on single-engine aircraft. A folded hydraulically to aid aircraft movement aboardyoke and wheel assembly operates the ailerons and aircraft carriers.elevators on multiengine aircraft, such as transport and VERTICAL AXIS ROLLLATERAL AXIS YAWLONGITUDINAL AXIS PITCH ANf0409 Figure 4-9.Axes and fundamental movements of the aircraft. 4-9 --------------------------------------- 10 patrol aircraft. The rudder is operated by foot pedals on all types of aircraft. PLAIN FLAP Secondary Group The secondary group includes the trim tabs and spring tabs. Trim tabs are small airfoils recessed into the trailing edges of the primary control surface. EachSPLIT FLAP trim tab hinges to its parent primary control surface, but operates by an independent control. Trim tabs let the pilot trim out an unbalanced condition without exertingLEADING EDGE FLAP pressure on the primary controls. Spring tabs are similar in appearance to trim tabs but serve an entirely different purpose. Spring tabs are used for the same purpose as hydraulic actuators. TheyFOWLER FLAP aid the pilot in moving a larger control surface, such as the ailerons and elevators.ANf0410 Figure 4-10.Types of flaps. Auxiliary Group The auxiliary group includes the wing flaps, spoilers, speed brakes, and slats.they are flush with the wing skin. In the raised position, they greatly reduce wing lift by destroying the smooth WING FLAPS.Wing flaps give the aircraft extra lift. Their purpose is to reduce the landing speed.flow of air over the wing surface. Reducing the landing speed shortens the length of theSPEED BRAKES.Speed brakes are movable landing rollout. Flaps help the pilot land in small or control surfaces used for reducing the speed of the obstructed areas by increasing the glide angle withoutaircraft. Some manufacturers refer to them as dive greatly increasing the approach speed. The use of flapsbrakes; others refer to them as dive flaps. On some during takeoff serves to reduce the length of the takeoff aircraft, they're hinged to the sides or bottom of the run.fuselage. Regardless of their location, speed brakes serve the same purposeto keep the airspeed from Some flaps hinge to the lower trailing edges of thebuilding too high when the aircraft dives. Speed brakes wings inboard of the ailerons. Leading edge flaps are used on the F-14 Tomcat and F/A-18 Hornet. Fourslow the aircraft's speed before it lands. types of flaps are shown in figure 4-10. The plain flap SLATS.Slats are movable control surfaces that forms the trailing edge of the airfoil when the flap is inattach to the leading edge of the wing. When the slat is the up position. In the split flap, the trailing edge of theretracted, it forms the leading edge of the wing. When airfoil is split, and the lower half is hinged and lowers to the slat is open (extended forward), a slot is created form the flap. The fowler flap operates on rollers andbetween the slat and the wing leading edge. tracks, causing the lower surface of the wing to roll outHigh-energy air is introduced into the boundary layer and then extend downward. The leading edge flapover the top of the wing. At low airspeeds, this action operates like the plain flap. It is hinged on the bottomimproves the lateral control handling characteristics. side. When actuated, the leading edge of the wingThis allows the aircraft to be controlled at airspeeds actually extends in a downward direction to increasebelow normal landing speed. The high-energy air that the camber of the wing. Landing flaps are used inflows over the top of the wing is known as boundary conjunction with other types of flaps.layer control air. Boundary layer control is intended primarily for use during operations from carriers. SPOILERS.Spoilers are used to decrease wingBoundary layer control air aids in catapult takeoffs and lift. The specific design, function, and use vary with different aircraft. On some aircraft, the spoilers are longarrested landings. Boundary control air can also be accomplished by directing high-pressure engine bleed narrow surfaces, hinged at their leading edge to theair across the top of the wing or flap surface. upper surfaces of the wings. In the retracted position, 4-10 --------------------------------------- 11 On all high-performance aircraft, the control surfaces have great pressure exerted on them. At high airspeed, it is physically impossible for the pilot to ANf0411move the controls manually. As a result, power-operated control mechanisms are used. In a Figure 4-11.Push-pull tube assembly.power-operated system, a hydraulic actuator (cylinder) is located within the linkage to assist the pilot in moving the control surface. A typical flight control mechanism is shown in FLIGHT CONTROL MECHANISMSfigure 4-12. This is the elevator control of a lightweight The term flight control refers to the linkage thattrainer-type aircraft. It consists of a combination of connects the control(s) in the cockpit with the flightpush-pull tubes and cables. control surfaces. There are several types of flightThe control sticks in the system shown in figure controls in naval aircraft; some are manually operated4-12 are connected to the forward sector by push-pull while others are power operated.tubes. The forward sector is connected to the aft (rear ) Manually operated flight control mechanisms aresector by means of cable assemblies. The aft sector is further divided into three groupscable operated,connected to the flight control by another push-pull push-pull tube operated, and torque tube operated.tube assembly. Some systems may combine two or more of these types.LANDING GEAR In the manually operated cable system, cables are connected from the control in the cockpit to a bell crankBefore World War II, aircraft were made with their or sector. The bell crank is connected to the controlmain landing gear located behind the center of gravity. surface. Movement of the cockpit controls transfersAn auxiliary gear under the fuselage nose was added. force through the cable to the bell crank, which movesThis arrangement became known as the tricycletypeof the control surface.landinggear. Nearly all present-day Navy aircraft are equipped with tricycle landing gear. The tricycle gear In a push-pull tube system, metal push-pull tubeshas the following advantages over older landing gear: (or rods) are used as a substitute for the cables (fig. 4-11). Push-pull tubes get their name from the way they More stable in motion on the ground transmit force. Maintains the fuselage in a level position In the torque tube system, metal tubes (rods) with Increases the pilot's visibility and control gears at the ends of the tubes are used. Motion is transmitted by rotating the tubes and gears. Makes landing easier, especially in cross winds ANf0412 Figure 4-12.Typical flight control mechanism. 4-11 --------------------------------------- 12 TO LEFT ACTUATING MAIN GEAR CYLINDER DOOR CYLINDER DOWNLOCK CYLINDER RETRACTING FROMCYLINDER COMBINED SYSTEM LANDING GEARDOORAND SELECTORDOORLATCHUPLOCK VALVECYLINDERSCYLINDER MAIN GEAR DOWNLOCK NOSE GEARCYLINDER NOTE TIMER VALVESARE USED IN MAIN GEAR SYSTEM TO CONTROL PROPER SEQUENCE. Anf0413 Figure 4-13.Typical landing gear system. The landing gear system (fig. 4-13) consists ofThe hook hinges from the structure under the rear three retractable landing gear assemblies. Each mainof the aircraft. A snubber meters hydraulic fluid and landing gear has a conventional air-oil shock strut, aworks in conjunction with nitrogen pressure. The wheel brake assembly, and a wheel and tire assembly. The nose landing gear has a conventional air-oil shock strut, a shimmy damper, and a wheel and tire assembly. AIR VALVE The shock strut is designed to absorb the shock that would otherwise be transmitted to the airframe during landing, taxiing, and takeoff. The air-oil strut is used on all naval aircraft. This type of strut has two telescopingOUTER CYLINDER cylinders filled with hydraulic fluid and compressed air or nitrogen. Figure 4-14 shows the internal constructionMETERING PIN of one type of air-oil shock strut. ORIFICE PLATE The main landing gear is equipped with brakes for stopping the aircraft and assisting the pilot in steering the aircraft on the ground. The nose gear of most aircraft can be steered fromORIFICETORQUE ARMS the cockpit. This provides greater ease and safety on the runway when landing and taking off and on the taxiway in taxiing. INNER ARRESTING GEARWHEEL AXLECYLINDER (PISTON) TOWING EYE A carrier-type aircraft is equipped with an arresting hook for stopping the aircraft when it lands on the carrier. The arresting gear has an extendible hook and the mechanical, hydraulic, and pneumatic equipment ANf0414 necessary for hook operation. See figure 4-15. The arresting hook on most aircraft releases mechanically, lowers pneumatically, and raises hydraulically. Figure 4-14.Internal construction of a shock strut. 4-12 --------------------------------------- 13 Q4-11. In an aircraft, what are the main structural members of the wing? Q4-12. What does the term wet wing mean? Q4-13. Thestabilizingsurfacesofanaircraftconsist of what two airfoils? Q4-14. What are the three groups of flight control surfaces? Q4-15. What is the purpose of speed brakes on an aircraft? Q4-16. Mostpresent-dayNavyaircraftareequipped with what type of landing gear? ROTARY-WING AIRCRAFT LEARNING OBJECTIVE: Identify the construction features of the rotary-wing aircraft and recognize the fundamental differencesbetweenrotary-wingand ANf0415 fixed-wing aircraft. Within the past 20 years, helicopters have become aFigure 4-15.Arresting gear installation. reality, and are found throughout the world. They perform countless tasks suited to their unique snubber holds the hook down and prevents it fromcapabilities. bouncing when it strikes the carrier deck.A helicopter has one or more power-driven horizontal airscrews (rotors) to develop lift and CATAPULT EQUIPMENT propulsion. If a single main rotor is used, it is necessary Carrier aircraft have built-in equipment forto employ a means to counteract torque. If more than catapulting off the aircraft carrier. Older aircraft hadone main rotor (or tandem) is used, torque is eliminated hooks on the airframe that attached to the cable bridle.by turning each main rotor in opposite directions. The bridle hooks the aircraft to the ship's catapult.The fundamental advantage the helicopter has over Newer aircraft have a launch bar built into the nosefixed-wing aircraft is that lift and control are landing gear assembly. See figure 4-16. The holdbackindependent of forward speed. A helicopter can fly assembly allows the aircraft to be secured to the carrierforward, backward, or sideways, or it can remain in deck for full-power turnup of the engine prior tostationary flight (hover) above the ground. No runway takeoff. For nose gear equipment, a track attaches to theis required for a helicopter to take off or land. For deck to guide the nosewheel into position. The track hasexample, the roof of an office building is an adequate provisions for attaching the nose gear to the catapultlanding area. The helicopter is considered a safe aircraft shuttle and for holdback.because the takeoff and landing speed is zero, and it has NOTE: The holdback tension bar separates whenautorotational capabilities. This allows a controlled the catapult is fired, allowing the aircraft to be launcheddescent with rotors turning in case of engine failure in with the engine at full power.flight. FUSELAGE Q4-9. In fuselage construction, what are the threeLike the fuselage of a fixed-wing aircraft, the classes of monocoque design?helicopter fuselage may be welded truss or some form Q4-10. Points on the fuselage are located by whatof monocoque construction. Many Navy helicopters are method?of the monocoque design. 4-13 --------------------------------------- 14 FUSELAGE AIRCRAFT CATAPULT (A)BRIDLE HOOKS CATAPULT BRIDLE BRIDLE ARRESTER LANYARD CABLE CATAPULT GUIDE SHUTTLE CATAPULT TRACK SLIDE LANYARD BLAST SCREEN (B) CATAPULTCATAPULTCATAPULT SHUTTLEBRIDLEHOLDBACKBRIDLECATAPULT ARRESTER PENDANT PENDANT SLIDELANYARD ARRESTER LANYARDBUNGEE CLEAT LINK TENSION BAR AIRCRAFT CATAPULT HOLDBACK FITTING DECK CLEAT CATAPULT HOLDBACK PENDANT ANf0416 Figure 4-16.Aircraft catapult equipment. 4-14 --------------------------------------- 15 A typical Navy helicopter, the H-60, is shown inrings, drag braces, and safety switches. They are part of figure 4-17. Some of its features include a single mainthe lower end of the shock strut piston. rotor, twin engine, tractor-type canted tail rotor, controllable stabilizer, fixed landing gear, rescue hoist,Tail Landing Gear external cargo hook, and weapons pylons. The fuselage consists of the entire airframe, sometimes known as theThe H-60's tail landing gear is a nonretracting, dual body group.wheel, 360-degree swiveling type. It is equipped with The body group is an all-metal semimonocoquetubeless tires, tie-down ring, shimmy damper, construction. It consists of an aluminum and titaniumtail-wheel lock, and an air/oil shock-strut, which serves skin over a reinforced aluminum frame.as an aft touchdown point for the pilots to cushion the landing shock. LANDING GEAR GROUPMAIN ROTOR ASSEMBLY The landing gear group includes all the equipmentThe main rotor (rotor wing) and rotor head (hub necessary to support the helicopter when it is not inassembly) are identical in theory of flight but differ in flight. There are several types of landing gear onengineering or design. They are covered here because helicoptersconventionalfixed(skidtype), retractable, and nonretractable.their functions are closely related. The power plant, transmission, drive-train, hydraulic flight control, and Main Landing Gearrotor systems all work together. Neither has a function without the other. The H-60's nonretracting main landing gearRotary Wing consists of two single axle, air/oil type of shock-strut assemblies that mount to the fuselage. Each is equippedThe main rotor on the H-60 (fig. 4-17) has four with tubeless tires, hydraulic disc brakes, tie-downidentical wing blades. Other types of helicopters may Anf0417 Figure 4-17.H-60 helicopter. 4-15 --------------------------------------- 16 have two, four, five, six, or seven blades. Figure 4-18main gearbox or transmission. The flight controls and shows some typical rotor blades.hydraulic servos transmit movements to the rotor blades. The principal components of the rotor head are Rotary-wing blades are made of titanium, the hub and swashplate assemblies (fig. 4-19). The hub aluminum alloys, fiber glass, graphite, honeycomb is one piece, made of titanium and sits on top of the core, nickel, and steel. Each has a nitrogen-filled, rotor mast. Attaching components are the sleeve and pressurized, hollow internal spar, which runs the length spindles, blade fold components, vibration absorber, of the blade. The cuff provides the attachment of the bearings, blade dampers, pitch change horns, blade to the rotor hub. A titanium abrasion strip covers adjustable pitch control rods, blade fold hinges, balance the entire leading edge of the spar from the cuff end to weights, antiflapping and droop stops, and faring. the removable blade tip faring. This extends the life of the rotor blade.The swashplate consists of a rotating disc (upper), stationary (lower) portion with a scissors and sleeve The examples shown in figure 4-18 show other assembly separated by a bearing. The swashplate is featurestrim tabs, deicing protection, balance permitted to slide on the main rotor vertical driveshaft markings, and construction. and mounts on top the main transmission. The entire assembly can tilt in any direction following the motion Main Rotor Head/Hub Assembly of the flight controls. The rotor head is fully articulating and is rotated by The hydraulic servo cylinders, swashplate, and torque from the engines through the drive train and adjustable pitch control rods permit movement of the DEICEANTI-CHAFE CONNECTIONSTRIPABRASION STRIP TIP CAP BLADE INSPECTION INDICATOR BALANCE STRIP BLADE CUFF TRIM TABS TIP CAP 1 2 SPARABRASION3 STRIP4 ICE GUARD5 6 7 SPAR8 9 10 11 ROOT POCKET1213 14POCKET IDENTIFICATION 15 16 17 CUFF18 19 20 21 22 23 ANf0418 Figure 4-18.Types of main rotor blades. 4-16 --------------------------------------- 17 SPINDLE ASSEMBLY FAIRINGBIFILAR FOLD HINGE ROTOR HUB PITCH LOCK ACTUATOR DAMPER BLADE FOLD ACTUATORBLADE LOCKPIN PULLERS ROTOR HEAD BALANCE WEIGHTS LOWER PRESSURE PLATE PITCH CHANGEROTATING SCISSORS HORN PITCH CONTROLSWASHPLATEANf0119 ROD Figure 4-19.Main rotor head/hub assembly. flight controls to be transmitted to the rotary-wing Flap is the tendency of the blade to rise with blades. The sleeve and spindle and blade dampers allowhigh-lift demands as it tries to screw itself limited movement of the blades in relation to the hub.upward into the air. These movements are known as lead, lag, and flap. Antiflapping stops and droop stops restrict flapping Lead occurs during slowing of the driveand conning motion of the rotary-wing head and blades mechanism when the blades have a tendency toat low rotor rpm when slowing or stopping. remain in motion. TAIL ROTOR GROUP Lag is the opposite of lead and occurs during acceleration when the blade has been at rest The directional control and antitorque action of the and tends to remain at rest.helicopter is provided by the tail rotor group. See 4-17 --------------------------------------- 18 figure 4-20. These components are similar in functionsuch items as the hub, spindle, pitch control beam, pitch to the main rotor.change links, bearings, and tail rotor blades. Change in blade pitch is accomplished through the Pylon pitch change shaft that moves through the horizontal shaft of the tail gearbox, which drives the rotary rudder The pylon, shown in figure 4-20, attaches on theassembly. As the shaft moves inward toward the tail aircraft to the main fuselage by hinge fittings. These hinge fittings serve as the pivot point for the pylon togearbox, pitch of the blade is decreased. As the shaft moves outward from the tail gearbox, pitch of the blade fold along the fuselage. Folding the pylon reduces the overall length of the helicopter, which helps foris increased. The pitch control beam is connected by confined shipboard handling.links to the forked brackets on the blade sleeves. The pylon houses the intermediate and tail rotorRotary Rudder Blades gearboxes, tail rotor drive shaft, cover, tail bumper,Like the blades on a main rotor head, the blades position/anticollision lights, hydraulic servos, flightfound on a rotary rudder head may differ, depending on control push-pull tubes/cables/bell cranks, stabilizer/the type of aircraft. Tail rotor blades may consist of the elevator flight control surface, some antennas, andfollowing components: rotary rudder assembly. Aluminum alloy, graphite composite, or Rotary Rudder Headtitanium spar Aluminum pocket and skin with honeycomb The rudder head can be located on either side of thecore or cross-ply fiber glass exterior pylon, depending on the type of aircraft, and includes Aluminum or graphite composite tip cap ROTARY RUDDER BLADE PITCH CHANGE LINK SPINDLE ROTARY RUDDER HUB TAIL ROTOR GEAR BOXPYLON PITCH CONTROL BEAM ANf0420 Figure 4-20.Tail rotor group. 4-18 --------------------------------------- 19 Aluminum trailing edge cap A reservoir to hold a supply of hydraulic fluid Aluminum or polyurethane and nickel abrasion A pump to provide a flow of fluid leading edge strip Tubing to transmit the fluid Additionally, rotary rudder blades may have A selector valve to direct the flow of fluid deicing provisions, such as electrothermal blankets that are bonded into the blade's leading edge. or a neoprene An actuating unit to convert the fluid pressure anti-icing guard embedded with electrical heatinginto useful work elements. A simple system using these essential units is Q4-17. What is the main advantage of rotary-wing shown in figure 4-21. aircraft over fixed-wing aircraft? You can trace the flow of fluid from the reservoir Q4-18. Whatarethethreetypesoflandinggearused on helicopters?through the pump to the selector valve. In figure 4-21, the flow of fluid created by the pump flows through the Q4-19. Thedirectionalcontrolandantitorqueactionvalve to the right end of the actuating cylinder. Fluid of the helicopter is provided by what group?pressure forces the piston to the left. At the same time, the fluid that is on the left of the piston is forced out. It AIRCRAFT HYDRAULIC SYSTEMSgoes up through the selector valve and back to the reservoir through the return line. LEARNING OBJECTIVE: Identify the components of aircraft hydraulic systems andWhen the selector valve is moved to the position recognize their functions.indicated by the dotted lines, the fluid from the pump flows to the left side of the actuating cylinder. The aircraft hydraulic systems found on most navalMovement of the piston can be stopped at any time aircraft perform many functions. Some systems simply by moving the selector valve to neutral. When operated by hydraulics are flight controls, landing gear, the selector valve is in this position, all four ports are speed brakes, fixed-wing and rotary-wing folding closed, and pressure is trapped in both working lines. mechanisms, auxiliary systems, and wheel brakes. Hydraulics has many advantages as a power source for operating these units on aircraft. RESERVOIR Hydraulics combine the advantages of lightweight, ease of installation, simplification of inspection, and minimum maintenance requirements. PRESSURE LINE Hydraulics operation is almost 100-percent efficient, with only a negligible loss due to fluid friction. HAND However, there are some disadvantages to usingPUMP hydraulics.RETURN LINE SELECTOR VALVE The possibility of leakage, both internal andIN "DOWN" external, may cause the complete system toPOSITION become inoperative.SELECTOR VALVE IN "UP" POSITION Contamination by foreign matter in the system can cause malfunction of any unit. Cleanliness WORKING in hydraulics cannot be overemphasized.LINES COMPONENTS OF A BASIC HYDRAULICANF0421ACTUATING UNIT SYSTEM Basically, any hydraulic system contains the Figure 4-21.Basic hydraulic system, hand pump operated. following units: 4-19 --------------------------------------- 20 Figure 4-22 shows a basic system with the additionautomatically adjusts to supply the proper volume of of a power-driven pump and other essentialfluid as needed. components. These components are the filter, pressure regulator, accumulator, pressure gauge, relief valve,The accumulator serves a twofold purpose. and two check valves. The function of these1. It serves as a cushion or shock absorber by components is described below.maintaining an even pressure in the system. The filter (fig. 4-22) removes foreign particles2. It stores enough fluid under pressure to provide from the fluid, preventing moisture, dust, grit, and otherfor emergency operation of certain actuating undesirable matter from entering the system.units. The pressure regulator (fig. 4-22) unloads orThe accumulator is designed with a compressed-air relieves the power-driven pump when the desiredchamber separated from the fluid by a flexible pressure in the system is reached. Therefore, it is oftendiaphragm, or a removable piston. referred to as an unloading valve. With none of the actuating units operating, the pressure in the lineThe pressure gauge indicates the amount of pressure in the system. between the pump and selector valve builds up to the desired point. A valve in the pressure regulatorThe relief valve is a safety valve installed in the automatically opens and fluid is bypassed back to thesystem. When fluid is bypassed through the valve to the reservoir. (The bypass line is shown in figure 4-22,return line, it returns to the reservoir. This action leading from the pressure regulator to the return line.)prevents excessive pressure in the system. NOTE: Many aircraft hydraulic systems do notCheck valves allow the flow of fluid in one use a pressure regulator. These systems use a pump thatdirection only. There are numerous check valves installed at various points in the lines of all aircraft hydraulic systems. A careful study of figure 4-22 shows why the two check valves are necessary in this system. One check valve prevents power pump pressure from entering the hand-pump line. The other valve prevents hand-pump pressure from being directed to the accumulator. HYDRAULIC CONTAMINATION Hydraulic contamination is defined as foreign materialinthehydraulicsystemofanaircraft. Foreign material might be grit, sand, dirt, dust, rust, water, or any other substance that is not soluble in the hydraulic fluid. There are two basic ways to contaminate a hydraulic system. One is to inject particles, and the other is to intermix fluids, including water. Particle contamination in a system may be self-generated through normal wear of system components. It is the injection of contaminants from ANf0422outside that usually causes the most trouble. Regardless of its origin, any form of contamination in the hydraulic 1. Reservoir7. Hand pumpsystem will slow performance. In extreme cases, it 2. Power pump8. Pressure gaugeseriously affects safety. 3. Filter9. Relief valve 4. Pressure regulator10. Selector valveA single grain of sand or grit can cause internal 5. Accumulator11. Actuating unitfailure of a hydraulic component. Usually, this type of 6. Check valves contamination comes from poor servicing andFigure 4-22.Basic hydraulic system with addition of power fluid-handling procedures. For this reason, the highestpump. 4-20 --------------------------------------- 21 level of cleanliness must be maintained when workingbrakes, emergency landing gear extension, emergency on hydraulic components.flap extension, and for canopy release mechanisms. Only approved fill stand units are used to serviceWhen the control valve is properly positioned, the naval aircraft hydraulic systems. By following a fewcompressed air in the storage bottle is routed through basic rules, you can service hydraulic systems safelythe shuttle valve to the actuating cylinder. and keep contamination to a minimum. NOTE: The shuttle valve is a pressure-operated Never use fluid that has been left open for anvalve that separates the normal hydraulic system from undetermined period of time. Hydraulic fluidthe emergency pneumatic system. When the control that is exposed to air will absorb dust and dirt.handle is returned to the normal position, the air pressure in the lines is vented overboard through the Never pour fluid from one container intovent port of the control valve. another. Use only approved servicing units for theThe other type of pneumatic system in use has its specific aircraft.own air compressor. It also has other equipment necessary to maintain an adequate supply of Maintain hydraulic fluid-handling equipmentcompressed air during flight. Most systems of this type in a high state of cleanliness.must be serviced on the ground prior to flight. The air Always make sure you use the correct hydraulic fluid. Contamination of the hydraulic system may be caused by wear or failure of hydraulic components and seals. This type of contamination is usually found through filter inspection and fluid analysis. Continued operation of a contaminated system may cause malfunctioning or early failure of hydraulic components. Q4-20. What are two disadvantages of a hydraulic system? Q4-21. On a basic hydraulic system, what is the purpose of the selector valve? Q4-22. On a basic hydraulic system, what is the purpose of the actuating unit? Q4-23. Define hydraulic contamination. PNEUMATIC SYSTEMS LEARNING OBJECTIVE: Identify the components of aircraft pneumatic systems and recognize their functions. There are two types of pneumatic systems currently used in naval aircraft. One type uses storage bottles for an air source, and the other has its own air compressor. Generally, the storage bottle system is used only for emergency operation. See figure 4-23. This system has an air bottle, a control valve in the cockpit for releasing the contents of the cylinders, and a ground chargeANf0423 (filler) valve. The storage bottle must be filled with compressed air or nitrogen prior to flight. Air storage cylinder pneumatic systems are in use for emergencyFigure 4-23.Emergency pneumatic system. 4-21 --------------------------------------- 22 compressor used in most aircraft is driven by aSUMMARY hydraulic motor. Aircraft that have an air compressor use the compressed air for normal and emergencyIn this chapter, you have learned about aircraft system operation.construction and the materials used in construction. You have also learned about the features and materials Q4-24. Whatarethetwotypesofpneumaticsystemsused to absorb stress on both fixed-wing and currently used in naval aircraft?rotary-wing aircraft. 4-22 |