Helicopter Structures CASA 12b
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Questions and Answers

What is the primary material used for higher performance helicopter components?

  • Aluminium
  • Wood
  • Composite materials (correct)
  • Steel

    • What does stress refer to in the context of materials?

  • The physical stress experienced during flight
  • The material's elasticity
  • The internal force resisting external forces (correct)
  • The weight of the material

    • Which of the following best describes tension?

  • A force pushing an object together
  • A force that pulls an object apart (correct)
  • A static pressure applied to a material
  • A force that causes twisting

    • What type of load do flexible steel cables in helicopters primarily withstand?

    <p>Tension loads</p> Signup and view all the answers

    How is compression stress characterized?

    <p>By forces pushing against each other</p> Signup and view all the answers

    What happens to a rivet when compressive stress is applied?

    <p>It expands to fill the hole</p> Signup and view all the answers

    Which property primarily distinguishes torsion from other types of stress?

    <p>It involves twisting forces</p> Signup and view all the answers

    What material is typically used for the helicopter’s windscreen and windows?

    <p>Polycarbonate</p> Signup and view all the answers

    What primarily causes torsional stress in an engine crankshaft?

    <p>Rotation caused by the propeller</p> Signup and view all the answers

    What stress is primarily experienced by helicopter blades in flight?

    <p>Bending stress</p> Signup and view all the answers

    What type of stress is caused by forces trying to slice or slide a body apart?

    <p>Shear stress</p> Signup and view all the answers

    Which of the following describes hoop stress?

    <p>Stress in a pipe wall acting circumferentially</p> Signup and view all the answers

    What is strain a result of?

    <p>The deformation caused by stress</p> Signup and view all the answers

    How does fatigue in metal typically occur?

    <p>From a series of stress reversals</p> Signup and view all the answers

    What determines the location of a datum in a helicopter?

    <p>The manufacturer's convenience for measurement</p> Signup and view all the answers

    What do fuselage station numbers identify?

    <p>Locations along the length of the fuselage</p> Signup and view all the answers

    Which line is used to identify vertical measurements in an aircraft?

    <p>Water lines</p> Signup and view all the answers

    What do buttock lines measure?

    <p>Distances to the right or left of the fuselage centerline</p> Signup and view all the answers

    What happens to bending stress when a helicopter blade is on the ground?

    <p>It is reversed</p> Signup and view all the answers

    What aspect does Hooke’s law relate to in materials?

    <p>The relationship between stress and strain</p> Signup and view all the answers

    What type of stress do aircraft clevis bolts experience?

    <p>Shear stress</p> Signup and view all the answers

    What does excessive bending stress cause in materials?

    <p>Significant physical change (strain)</p> Signup and view all the answers

    What certification is required for a helicopter to operate?

    <p>Type Certificate and Certificate of Airworthiness</p> Signup and view all the answers

    Which section relates to the structural strength requirements of rotorcraft?

    <p>CS-29 Section 1 - Subpart C - Structures</p> Signup and view all the answers

    What is the ultimate load requirement for a helicopter structure?

    <p>It must support the ultimate load without failure for at least 3 seconds.</p> Signup and view all the answers

    What must be demonstrated when applying for a certificate under Part 21?

    <p>Compliance with applicable requirements of Part 21</p> Signup and view all the answers

    Which factor represents the Ultimate Factor of Safety (U.F.S.)?

    <p>Ultimate Load divided by Limit Load</p> Signup and view all the answers

    What does a Fail Safe Structural Analysis ensure?

    <p>The helicopter maintains strength if one load path fails.</p> Signup and view all the answers

    What defines a helicopter's Safe Life?

    <p>It is based on the number of loading cycles before failure.</p> Signup and view all the answers

    Which category must a rotorcraft with a maximum weight greater than 20,000 pounds and 10 or more passenger seats be type certificated as?

    <p>Category A Rotorcraft</p> Signup and view all the answers

    Which load type must a helicopter structure support without permanent deformation?

    <p>Limit load</p> Signup and view all the answers

    What led to the need for Damage Tolerance in helicopter design?

    <p>The original safe life philosophy did not account for fatigue cracking</p> Signup and view all the answers

    What is emphasized in the design of a Fail Safe structure?

    <p>Certain redundancy to avoid complete failure</p> Signup and view all the answers

    What is a characteristic of Aircraft Airworthiness standards in different authorities?

    <p>The numbering system remains the same for standardization.</p> Signup and view all the answers

    Which aircraft category pertains specifically to rotorcraft?

    <p>Part 27 - Rotorcraft</p> Signup and view all the answers

    What is the maximum resistance allowed for general electrical bonding across a bonding jumper?

    <p>0.1 ohms</p> Signup and view all the answers

    What material is recommended for jumpers in most cases?

    <p>Aluminium alloy</p> Signup and view all the answers

    Which function do bonding straps serve in aircraft?

    <p>Minimize lightning damage</p> Signup and view all the answers

    What is the purpose of lightning diverter strips?

    <p>Conduct lightning charge away from the radome</p> Signup and view all the answers

    What should be done after an aircraft has experienced a lightning strike?

    <p>Perform an unscheduled inspection for damage</p> Signup and view all the answers

    Which of the following is a requirement for RF bonding?

    <p>Resistance must be a maximum of 0.0025 ohms</p> Signup and view all the answers

    What is NOT a function of bonding straps?

    <p>Increase the structural weight of components</p> Signup and view all the answers

    How should jumpers be installed to facilitate maintenance?

    <p>They should allow easy removal of components</p> Signup and view all the answers

    What is the primary purpose of Damage Tolerance in aircraft design?

    <p>To allow structures to sustain defects until detection</p> Signup and view all the answers

    What characterizes negligible damage in an aircraft?

    <p>Has no adverse effect on airworthiness</p> Signup and view all the answers

    Under which condition is damage considered unrepairable?

    <p>It is deemed too severe to leave unaddressed</p> Signup and view all the answers

    Which of the following factors is NOT involved in the occurrence of corrosion?

    <p>Extreme temperatures</p> Signup and view all the answers

    What does effective drainage in aircraft structures aim to prevent?

    <p>Trapping of fluids that cause corrosion</p> Signup and view all the answers

    What types of tests and inspections are included in the ageing aircraft program?

    <p>A combination of visual and nondestructive testing methods</p> Signup and view all the answers

    What was a significant outcome of the 1988 International Conference on Ageing Aeroplanes?

    <p>Formation of the Airworthiness Assurance Working Group (AAWG)</p> Signup and view all the answers

    What is Widespread Fatigue Damage (WFD) characterized by?

    <p>Multiple structural details showing cracks of significant size and density</p> Signup and view all the answers

    What is the main reason for requiring major structural disassembly in inspections of ageing aircraft?

    <p>To complete visual and structural inspections effectively</p> Signup and view all the answers

    What does the term 'repairable damage' signify in aircraft maintenance?

    <p>Damage that can still be repaired despite its possible effect on airworthiness</p> Signup and view all the answers

    What is the significance of drainage holes in helicopters?

    <p>They allow for moisture and air ventilation</p> Signup and view all the answers

    Which federal body made recommendations to ensure continued safe operations regarding Widespread Fatigue Damage?

    <p>National Transportation Safety Board (NTSB)</p> Signup and view all the answers

    What must occur to maintain airworthiness according to Damage Tolerance standards?

    <p>Defects must be detected before they cause failure</p> Signup and view all the answers

    Which of the following is true about the AAWG's recommendations?

    <p>They addressed shortcomings in the airworthiness system</p> Signup and view all the answers

    What characterizes Multiple Site Damage (MSD)?

    <p>Simultaneous presence of fatigue cracks in the same structural element.</p> Signup and view all the answers

    What is the primary structure of a helicopter?

    <p>Parts whose failure in flight could lead to serious injury.</p> Signup and view all the answers

    What does Design Service Goal (DSG) refer to?

    <p>The time established during which significant cracking is not expected.</p> Signup and view all the answers

    What defines the Point of WFD?

    <p>A lower bound ensuring equivalent protection to fatigue testing.</p> Signup and view all the answers

    What is the monitoring period in the context of fatigue damage?

    <p>The interval when special inspections are mandated due to increased risk.</p> Signup and view all the answers

    What describes the Secondary Structure?

    <p>Features that have reserve strength and can sustain some weakening.</p> Signup and view all the answers

    Why should the term 'Threshold' be used with caution?

    <p>It can mean different things, leading to confusion.</p> Signup and view all the answers

    Which of the following is true regarding the Extended Service Goal (ESG)?

    <p>It is an adjustment based on service experience to avoid significant cracking.</p> Signup and view all the answers

    What action is required if a crack cannot be reliably detected?

    <p>The monitoring period cannot be utilized.</p> Signup and view all the answers

    What is the significance of special inspections during the monitoring period?

    <p>They collect data to reassess WFD parameters.</p> Signup and view all the answers

    What does the Tertiary Structure of a helicopter refer to?

    <p>Elements that pose no risk if they fail.</p> Signup and view all the answers

    What results if the high time aeroplane surpasses the predicted Point of WFD without detecting cracks?

    <p>The predicted Point of WFD could be reevaluated.</p> Signup and view all the answers

    What type of inspections must occur if MSD or MED findings are reported?

    <p>Special inspections must be conducted immediately.</p> Signup and view all the answers

    What is the primary method of fastening materials in helicopter construction?

    <p>Riveting</p> Signup and view all the answers

    Which type of fastener has been historically used since the introduction of sheet metal in aircraft?

    <p>Solid rivets</p> Signup and view all the answers

    What happens to a solid shank rivet during installation?

    <p>It changes in dimension to fit the hole</p> Signup and view all the answers

    Which component of a rivet part number indicates the head style?

    <p>Three-digit number</p> Signup and view all the answers

    What is one of the more modern construction techniques used for helicopter joints?

    <p>Using composite materials held with adhesives</p> Signup and view all the answers

    Which of the following rivet head styles is the most common?

    <p>Universal</p> Signup and view all the answers

    What does the last part of the rivet part code indicate?

    <p>The length</p> Signup and view all the answers

    Which assembly technique is NOT common in helicopter construction?

    <p>Screwing</p> Signup and view all the answers

    What is the purpose of obtaining a fastener manufacturer’s technical information?

    <p>To ensure proper use of the product</p> Signup and view all the answers

    What does the first part of the rivet designation code signify?

    <p>The numbering system used</p> Signup and view all the answers

    Which fasteners are NOT included in the list of common aircraft structural fasteners?

    <p>Threaded rods</p> Signup and view all the answers

    What factor is crucial for the integrity of a helicopter joint?

    <p>Selected fasteners and installation quality</p> Signup and view all the answers

    Which material component is NOT associated with rivets?

    <p>Paper</p> Signup and view all the answers

    What is the primary function of quick disconnect valves in hydraulic lines?

    <p>To prevent fluid loss when units are removed</p> Signup and view all the answers

    What role do bonding straps serve in a helicopter?

    <p>To minimize lightning damage and maintain electrical potential</p> Signup and view all the answers

    How does an external power receptacle facilitate engine starting in helicopters?

    <p>By connecting to a battery cart or external power supply</p> Signup and view all the answers

    What is a critical factor to consider when installing avionics equipment?

    <p>Sufficient air circulation to prevent overheating</p> Signup and view all the answers

    Which fasteners are specifically designed for rapid access to aircraft access panels?

    <p>Turnlock fasteners</p> Signup and view all the answers

    What do anchor nuts simplify in aircraft maintenance?

    <p>Installation and removal of doors and panels</p> Signup and view all the answers

    What is a significant risk when a helicopter is struck by lightning?

    <p>Electrical damage to components and occupants</p> Signup and view all the answers

    Why are larger pins used in aircraft external power receptacles?

    <p>To prevent incorrect connections</p> Signup and view all the answers

    What is one consequence of not using proper bonding in a helicopter's structure?

    <p>Increased likelihood of sparks and electrical failure</p> Signup and view all the answers

    What happens when the coupling nut on a quick disconnect valve is tightened?

    <p>Fluid is allowed to flow through the valve</p> Signup and view all the answers

    Which of the following is NOT a consideration when installing avionics equipment?

    <p>Cost-effectiveness of the equipment</p> Signup and view all the answers

    What type of diode is used to prevent reverse polarity in the external power circuit?

    <p>Reverse-polarity diode</p> Signup and view all the answers

    Which component must be adequately bonded to handle return current flow in helicopters?

    <p>Electrical components using structure as return path</p> Signup and view all the answers

    What is the function of ground locking pins on helicopters?

    <p>To prevent landing gear retraction during ground operations</p> Signup and view all the answers

    Which of the following best describes the operation of a quick-disconnect valve?

    <p>It prevents fluid loss during line disconnection</p> Signup and view all the answers

    What is a disadvantage of using solid rivets?

    <p>They require specialized tools to install.</p> Signup and view all the answers

    Which type of rivet head design is specifically developed to enhance the aerodynamic flow over aircraft surfaces?

    <p>Countersunk rivets.</p> Signup and view all the answers

    What construction method allows for a streamlined shape using the skin as a structural component?

    <p>Monocoque Design</p> Signup and view all the answers

    What process must be done to the metal surface before installing a countersunk rivet?

    <p>Countersinking or dimpling.</p> Signup and view all the answers

    Which construction type is primarily used in modern helicopters due to its successful load distribution?

    <p>Stressed Skin Structure</p> Signup and view all the answers

    What are the disadvantages of tubular construction for helicopter airframes?

    <p>High manufacturing costs and low tolerance</p> Signup and view all the answers

    What is required for the successful installation of Hi-Lok fasteners?

    <p>Access from both sides of the component.</p> Signup and view all the answers

    What type of materials are typically involved in bonded construction methods?

    <p>Fibreglass and Honeycomb</p> Signup and view all the answers

    What is a key difference between pull-type lock bolts and blind-type lock bolts?

    <p>The installation process and visibility requirements.</p> Signup and view all the answers

    What structural element supports the airframe laterally in a semi-monocoque construction?

    <p>Bulkheads</p> Signup and view all the answers

    Which of the following describes a characteristic of countersunk rivet joints?

    <p>They have a lower strength compared to protruding head rivet joints.</p> Signup and view all the answers

    What happens to the protruding rivet head after installation?

    <p>It is shaved flush with the skin.</p> Signup and view all the answers

    What is a primary drawback of using monocoque design in helicopter construction?

    <p>Vulnerability to minor dents or creases</p> Signup and view all the answers

    What is the purpose of the boron patch fitted to the F111 upper wing surface?

    <p>To strengthen the structure and prevent cracking</p> Signup and view all the answers

    What is the primary composite material used in the construction of the Tiger helicopter airframe?

    <p>Carbon and Kevlar laminates</p> Signup and view all the answers

    Which of the following best describes blind rivets?

    <p>They allow for installation with access to only one end.</p> Signup and view all the answers

    What construction technique typically results in close tolerances during the manufacturing process?

    <p>Sheet Metal Construction</p> Signup and view all the answers

    What defines the role of the matrix in a composite material used in helicopter construction?

    <p>Holds reinforcing fibres in place</p> Signup and view all the answers

    Why are the fuel tanks placed in the most protected area of the helicopter's structure?

    <p>To minimize the risk of explosion</p> Signup and view all the answers

    What are lock bolts primarily used for?

    <p>Permanently assembling materials.</p> Signup and view all the answers

    How is the cabin section of the helicopter primarily constructed?

    <p>From polycarbonate and glass fibres</p> Signup and view all the answers

    Which construction type had its advantages in field repairability but faced challenges in tight tolerances?

    <p>Tubular-Truss Construction</p> Signup and view all the answers

    What type of tool is typically needed to install a Hi-Lok fastener?

    <p>A pneumatic installation tool.</p> Signup and view all the answers

    What are 'formers' used for in the fuselage or wing structure?

    <p>To give shape and structural support</p> Signup and view all the answers

    What enables the compatibility of various materials and construction methods in modern airframes?

    <p>Advances in technology</p> Signup and view all the answers

    What is the purpose of the locking collar in Hi-Lok fasteners?

    <p>To provide a permanent connection.</p> Signup and view all the answers

    What is the function of longerons in a helicopter's structure?

    <p>To carry heavy loads longitudinally</p> Signup and view all the answers

    What type of resin is commonly used in earlier matrix systems for composites?

    <p>Polyester resin</p> Signup and view all the answers

    How is a blind-type lock bolt different from conventional bolts?

    <p>Installation is completed by breaking off the pulling stem.</p> Signup and view all the answers

    What type of landing gear is typically less complex and requires less maintenance?

    <p>Skid gear</p> Signup and view all the answers

    What specific property distinguishes tension lock bolts from shear lock bolts?

    <p>Tension lock bolts have thicker heads and more grooves.</p> Signup and view all the answers

    What is the primary purpose of using composite fibre skins in helicopters?

    <p>To provide strength where metal skins are not required</p> Signup and view all the answers

    Which construction technique is characterized by being able to eliminate some riveting and welding due to its method?

    <p>Bonded Construction</p> Signup and view all the answers

    What does the semi-monocoque construction use to distribute loads in helicopter airframes?

    <p>A skeletal framework</p> Signup and view all the answers

    Which section of the helicopter is responsible for supporting landing loads?

    <p>Body Structure</p> Signup and view all the answers

    What factor primarily determines the type of undercarriage fitted to a helicopter?

    <p>The size of the helicopter and its intended role</p> Signup and view all the answers

    Which of the following describes the characteristics of bolting?

    <p>It uses identical tools for different bolt types.</p> Signup and view all the answers

    What advantage do wheeled landing gear have over skid gear?

    <p>Easier ground handling</p> Signup and view all the answers

    What is the role of doubler plates in helicopter structures?

    <p>To strengthen skin structure where components are attached</p> Signup and view all the answers

    What advantage does sheet metal construction typically offer over tubular construction?

    <p>Easier assembly and repair</p> Signup and view all the answers

    Which type of float may be attached to helicopter skids for emergency use?

    <p>Pop-out floats</p> Signup and view all the answers

    How are the frames and beams of the helicopter typically fabricated?

    <p>From Kevlar and carbon laminates</p> Signup and view all the answers

    What role does landing gear perform for helicopters on rough terrain?

    <p>Absorbs shock and provides ground clearance</p> Signup and view all the answers

    What is the function of bulkheads in a helicopter's fuselage?

    <p>To divide compartments and provide additional strength</p> Signup and view all the answers

    What is the primary function of beams in helicopter structures?

    <p>To transfer load in bending and shear</p> Signup and view all the answers

    Which of the following is NOT a type of undercarriage used on helicopters?

    <p>Fins</p> Signup and view all the answers

    What is used to cure the epoxy resins in structural composites?

    <p>A temperature and humidity controlled environment</p> Signup and view all the answers

    Which of the following describes the landing conditions typically faced by helicopters?

    <p>Very little or no forward motion</p> Signup and view all the answers

    Which material is used in the helicopter blades' construction?

    <p>Carbon composites</p> Signup and view all the answers

    Which of the following components can be part of a helicopter's undercarriage?

    <p>Fixed or retractable wheels</p> Signup and view all the answers

    What is a common feature of both fixed and pop-out floats on helicopters?

    <p>They are always inflated</p> Signup and view all the answers

    What is a primary advantage of using skids over wheeled landing gear in helicopters?

    <p>Lower weight</p> Signup and view all the answers

    In what environment are floats particularly useful for helicopters?

    <p>Water landings</p> Signup and view all the answers

    Which characteristic differentiates helicopter undercarriage from that of fixed-wing aircraft?

    <p>Landing stress due to forward motion</p> Signup and view all the answers

    What is an advantage of using retractable wheels in helicopters?

    <p>Reduced drag during flight</p> Signup and view all the answers

    Which type of undercarriage helps in providing ground handling wheels for movement on the ground?

    <p>Skid gear</p> Signup and view all the answers

    What is a primary advantage of a skid-type undercarriage for helicopters?

    <p>Simplicity of construction</p> Signup and view all the answers

    What is a disadvantage of skids compared to wheeled landing gear?

    <p>Less suitable for running take-offs and landings</p> Signup and view all the answers

    Which factor makes wheeled undercarriages preferred for large helicopters?

    <p>Easier ground handling and taxiing</p> Signup and view all the answers

    What is a common type of shock strut used in wheeled landing gear?

    <p>Oleo-pneumatic strut</p> Signup and view all the answers

    What is a notable disadvantage of a wheeled undercarriage?

    <p>Increased risk of inadvertent movement on slopes</p> Signup and view all the answers

    What component is essential for reducing vibration in skid landing gear?

    <p>Damping devices</p> Signup and view all the answers

    Which type of stabiliser is designed to improve helicopter stability?

    <p>Vertical stabiliser</p> Signup and view all the answers

    What is a function of the horizontal stabiliser?

    <p>To improve pitch stability</p> Signup and view all the answers

    What material is primarily used for skid landing gear construction?

    <p>Tensile steel</p> Signup and view all the answers

    How do retractable landing gears benefit helicopter performance?

    <p>Reduce parasite drag during flight</p> Signup and view all the answers

    What is the function of the tow fitting on a skid?

    <p>To assist in towing the helicopter</p> Signup and view all the answers

    Which type of landing gear allows for easier taxiing prior to takeoff?

    <p>Wheeled landing gear</p> Signup and view all the answers

    What problem does a wheeled undercarriage help to mitigate on heavy helicopters?

    <p>Ground resonance issues</p> Signup and view all the answers

    What is the primary purpose of a horizontal stabiliser in a helicopter?

    <p>To improve stability during forward flight</p> Signup and view all the answers

    How does a horizontal stabiliser affect the helicopter during gusts of wind from straight ahead?

    <p>It helps to prevent follow-through pitching movements</p> Signup and view all the answers

    In what situation can horizontal stabilisers be detrimental?

    <p>When flying at low speeds</p> Signup and view all the answers

    What is a characteristic of synch elevators in helicopters?

    <p>They pitch up and down in response to pilot inputs.</p> Signup and view all the answers

    What should be ensured before heating plastic for molding?

    <p>The protective paper and adhesive are removed</p> Signup and view all the answers

    What does modern electronic stabilization in helicopters utilize?

    <p>Gyro-controlled autopilots and computers.</p> Signup and view all the answers

    What is a characteristic feature of fuel tanks in helicopters?

    <p>They are vented to the atmosphere</p> Signup and view all the answers

    What is the primary function of vertical stabilisers on helicopters?

    <p>To provide lateral stability and counteract torque effects</p> Signup and view all the answers

    What angle is typically associated with the horizontal stabiliser's design?

    <p>Two degrees from the horizontal datum</p> Signup and view all the answers

    What is the purpose of dump valves in fuel tanks?

    <p>To reduce aircraft weight during flight</p> Signup and view all the answers

    What is a defining characteristic of bladder tanks?

    <p>They are made of thin fabric and neoprene</p> Signup and view all the answers

    Why might helicopter stabilators be adjusted during different flight phases?

    <p>To optimize thrust and maintain flight attitude</p> Signup and view all the answers

    What advantage do integral tanks have over rigid tanks?

    <p>They provide significant weight savings</p> Signup and view all the answers

    What construction feature is common in the horizontal stabiliser of a helicopter?

    <p>Aluminium skin ribs and tubular spar</p> Signup and view all the answers

    What impact does a horizontal stabiliser have on the helicopter's drag ratio during cruise?

    <p>Decreases the drag ratio effectively</p> Signup and view all the answers

    Which of the following is a recommended practice for bladder tanks?

    <p>Inspect them for wrinkles that can trap water</p> Signup and view all the answers

    What is a feature commonly found in helicopter fuel tanks?

    <p>Sumps and drains at the lowest point</p> Signup and view all the answers

    What effect does rearward flight have on helicopters equipped with horizontal stabilisers?

    <p>It accentuates longitudinal oscillations.</p> Signup and view all the answers

    In what manner are the vertical stabilisers usually positioned on helicopters?

    <p>Offset at a slight angle or asymmetric</p> Signup and view all the answers

    How should the fuel bay be prepared for a bladder tank installation?

    <p>By covering sharp metal edges with chafe-resisting tape</p> Signup and view all the answers

    During inspection, what must be checked about the bladder in a bladder tank?

    <p>The bladder must not have pulled away from attachment points</p> Signup and view all the answers

    What is a potential drawback of having horizontal stabilisers at odd angles?

    <p>They might not perform well at cruise speeds.</p> Signup and view all the answers

    What angle should a twist drill ideally have?

    <p>150°</p> Signup and view all the answers

    What is the primary purpose of a pylon in aircraft?

    <p>To support external equipment like fuel tanks or landing gear</p> Signup and view all the answers

    Which characteristic is NOT an integrity check for crew seats?

    <p>Monitoring seat adjustment mechanisms</p> Signup and view all the answers

    What material is primarily used in the construction of passenger seats in Bell helicopters?

    <p>Aluminium honeycomb panels</p> Signup and view all the answers

    How are the doors of a helicopter primarily constructed?

    <p>Aluminum alloy with a formed sheet-metal structure</p> Signup and view all the answers

    What is a significant characteristic of acrylic compared to cellulose acetate?

    <p>Maintains clarity and stability over time</p> Signup and view all the answers

    Why are damaged windows usually replaced instead of repaired in helicopters?

    <p>Repairs can be quite labor intensive</p> Signup and view all the answers

    What should NOT be done when sanding scratches on acrylic plastics?

    <p>Sand down to a minimal thickness</p> Signup and view all the answers

    What is the appropriate method for trimming acrylic windows?

    <p>Use a hack saw, band saw, or jig saw with precision</p> Signup and view all the answers

    What is a primary identification feature of cellulose acetate when applying acetone?

    <p>It softens and changes color</p> Signup and view all the answers

    Which of the following statements about the door mechanisms in helicopters is true?

    <p>Clamshell doors allow for easier cargo handling.</p> Signup and view all the answers

    What signifies the minimum allowable material thickness for aircraft windows?

    <p>Maintenance Manual specifications</p> Signup and view all the answers

    Which condition is an indicator to replace the seatback cushions in pilot or co-pilot seats?

    <p>Loss of comfort for the user</p> Signup and view all the answers

    What characteristic does not apply to the construction of helicopter doors?

    <p>They are often made of solid wood.</p> Signup and view all the answers

    Study Notes

    Airframe Structures

    • Airframe structures can be made of metal, composites, or a combination of both.
    • High-performance aircraft often use composites like epoxy with glass, aramid, or carbon fiber for their higher strength-to-weight ratio.
    • Tubular and sheet metal substructures are typically made of aluminum, but stainless steel or titanium are used in high-stress or high-heat areas.
    • Helicopter rotor blades are usually made of fiber-reinforced resin with a sheet metal layer for edge protection.
    • Helicopter windshields and windows are made of polycarbonate sheeting.

    Stress

    • Stress is a force or load acting on a unit area of material.
    • It represents the internal force resisting external forces trying to change a body's shape.
    • Tension: force pulling an object apart.
    • Compression: force pushing an object together.
    • Torsion: force twisting an object.
    • Bending: force causing a material to bend.
    • Shear: force trying to slice or slide an object apart.
    • Hoop Stress: stress in a pipe wall from internal pressure acting perpendicular to the pipe's axis.

    Strain

    • Strain is the deformation or physical change in a material caused by stress.
    • Hooke's Law states that strain is proportional to stress within the elastic limit of a material.
    • Excessive bending stress causes significant strain.

    Fatigue

    • Fatigue is the loss of strength in a material caused by repeated stress reversals.
    • Helicopter blades are susceptible to fatigue due to varying bending stresses in flight and on the ground.

    Identification Systems

    • Fuselage station numbers identify locations along the fuselage, measured from a reference point called datum.
    • Water lines identify structure by vertical measurement, with zero water line at the base reference plane.
    • Buttock lines measure distances to the right or left of the fuselage centerline.
    • Clock positions are used to report faults on aircraft or engine.

    Aircraft Airworthiness

    • Helicopters must have a Type Certificate and a Certificate of Airworthiness to fly.
    • Certification requirements are outlined in Part 21 of relevant regulatory authorities.
    • Structural strength requirements are addressed in the initial design phase to ensure the aircraft can withstand operational stresses.
    • Five aircraft categories exist: sailplanes, small aeroplanes, transport category aeroplanes, primary/intermediate category aeroplanes, and rotorcraft.
    • Transport category rotorcraft are further categorized into Category A and Category B based on weight and passenger capacity.

    Structural Strength Requirements

    • Aircraft structural strength requirements are defined by limit load, ultimate load, and Ultimate Factor of Safety (U.F.S.).
    • Limit load is the maximum expected load in service.
    • Ultimate load is the limit load multiplied by a factor of safety.
    • Structures must withstand the limit load without permanent deformation and the ultimate load without failure for at least 3 seconds.

    Fail Safe

    • Fail-safe structural design ensures the helicopter has sufficient strength to prevent complete structural failure even if a component fails.
    • Structures are designed with multiple load paths to ensure redundancy.

    Safe Life

    • Safe Life measures the useful life of a material by the number of load cycles it can withstand before failure.
    • Used for critical systems that are difficult to repair and may cause severe damage.
    • Safe life is determined through fatigue testing.

    Damage Tolerance

    • Damage Tolerance accounts for fatigue cracking arising from manufacturing defects or in-service maintenance.
    • Structures are designed to sustain a defect until it is detected through Non-Destructive Inspection (NDI).
    • NDI schedules are determined based on Damage Tolerance philosophies.

    Ageing Aircraft Inspection Requirements

    • Ageing aircraft program requires regular inspections and tests after a specified number of years or flight cycles.
    • Inspections often involve visual and non-destructive testing methods, like ultrasound, eddy current, and X-rays.
    • Corrosion control and structural repairs are made as needed.
    • Major disassembly may be required after a certain number of flight hours as specified by the manufacturer.

    Ageing Aircraft Background

    • The need for ageing aircraft inspection programs arose from the Aloha Airlines 737 accident in 1988, which was attributed to widespread fatigue damage.
    • The Airworthiness Assurance Working Group (AAWG) was formed to address the issue and developed an alternative approach to the FAA's "strawman" SFAR regarding fatigue testing for older aeroplanes.

    Damage Tolerance (Defined)

    • Damage tolerance is the ability of a structure to retain its required residual strength without significant deformation after experiencing fatigue, corrosion, accidental, or discrete source damage.

    Corrosion Control

    • Corrosion requires an anode, a cathode, a metallic connector, and an electrolyte.
    • Effective drainage of all structures is crucial to prevent fluids from becoming trapped and causing corrosion.
    • Drain holes and paths prevent galvanic corrosion.

    Widespread Fatigue Damage (WFD)

    • Characterized by multiple cracks in structural details, impacting damage tolerance and residual strength.
    • Multiple Site Damage (MSD): Fatigue cracks in the same structural element, potentially coalescing and leading to strength loss.
    • Multiple Element Damage (MED): Fatigue cracks in similar adjacent structural elements, impacting strength.

    Key Terminology for Structural Integrity

    • Fatigue Crack Initiation: The point in time when a fatigue crack is first expected to form.
    • Point of WFD: A lower bound on expected behavior, operating up to this point equals the protection of a two-lifetime fatigue test.
    • Monitoring Period: Period of time during which special inspections are conducted due to increased MSD/MED risk, ending when the Point of WFD is established.
    • Design Service Goal (DSG): The period of time (flight cycles/hours) during which the principal structure is expected to be free from significant cracking and WFD.
    • Extended Service Goal (ESG): An adjustment to the DSG based on service experience, analysis, or testing, also ensuring the structure's integrity.

    Misinterpreted Terminology

    • Threshold: Avoid using this term as it can be interpreted as "Fatigue Threshold" (first crack) or "Inspection Threshold" (start of supplemental inspections).
    • Onset: An alternative to "Threshold," but using both terms can create confusion.
    • Sub-Critical: Requires clarification of "critical fatigue cracks" in relation to WFD.

    Conditions for Monitoring Period Implementation

    • No aircraft can operate beyond the Point of WFD without modifications or replacements.
    • Special inspections during the monitoring period should align with estimated fatigue crack initiation.
    • Reliable crack detection is essential before cracks become critical to implement a monitoring period.
    • Inspection requirements are defined using empirical analysis, test evidence, and in-service data.
    • The purpose of inspections is to collect data for WFD reassessment and maintaining structural integrity.
    • Inspections are mandatory for every aircraft, and results must be reported.
    • MSD/MED findings lead to Point of WFD re-establishment, repair of affected areas, and a revised monitoring program.
    • If no cracks are found by the time the high-time aircraft reaches the predicted Point of WFD, the Point of WFD can be reevaluated and the inspection program continued.
    • The monitoring period ends when sufficient MSD/MED evidence exists or the Point of WFD is reached.

    Structural Classifications

    • Primary Structure: Failure can cause structural collapse, loss of control, power failure, or serious injury. Examples: engine mounts and landing gear.
    • Secondary Structure: Possesses reserve strength, but weakening may be permitted without significant risk. Failure may cause damage but not severe danger. Example: fairings.
    • Tertiary Structure: Failure won't endanger the helicopter or cause significant damage. Examples: loom and piping attachment brackets.

    Aircraft Installations

    • Quick Disconnect Valves: Prevent fluid loss during unit removal and enable connections to hydraulic test stands.
    • External Power Receptacles: Provide power for starting from external sources using a battery cart or rectifier.
    • Avionics Racks: House and secure avionics equipment, ensuring safe operation and ease of installation/removal, while considering ventilation, temperature, protection, and interference prevention.
    • Ground Locking Pins: Prevent landing gear retraction during ground and maintenance operations.
    • Anchor Nuts: Simplify installation/removal of doors and panels by eliminating the need for a spanner to hold the nut.
    • Turnlock Fasteners: Enable quick access panel removal for inspection and maintenance, including Camloc, Dzus, and Airloc fasteners.
    • Electrical Connectors: Provide flexibility for attaching electrical wiring, used in frequently disconnected wiring.

    Bonding and Lightning Protection

    • Bonding Straps: Connect structural components to minimize lightning damage and ensure equal electrical potential throughout the airframe.
    • Lightning Diverter Strips: Conduct lightning strikes away from fibreglass nose radomes into the aircraft structure.
    • Lightning Strike Inspection: Required after lightning strikes to check for structural, engine, and/or avionics damage.
    • Conditional Inspection: Conducted after specific over-limits or abnormal events.

    Bonding Straps Key Functions

    • Minimizing lightning damage at structure joins or hinges.
    • Supplying ground path for electrical equipment.
    • Reducing radio interference.
    • Allowing static charge equalization between airframe parts, reducing fire hazards.

    Bonding Straps Positioning

    • Insulating passenger cabin, fuel tanks, cargo areas, and cockpits from sparks or electric shock.
    • Diverting charge around electronic equipment.
    • Providing low resistance path for electrical charge exit.

    Bonding Resistance Tests

    • Resistance across a bonding jumper is required to be 0.1 ohms (100 milliohms) or less for general electrical bonding.
    • For RF components, the resistance should be a maximum 0.0025 ohms (2.5 milliohms).
    • Tests are conducted after mechanical connection using a milliohmmeter.
    • Aluminum alloy jumpers are recommended, while copper jumpers are used for stainless steel, cadmium plated steel, copper, brass, or bronze components.

    Aircraft Special Inspections

    • Special Inspections (SI) are required for events that compromise an aircraft's structural integrity
    • Examples: Hard landings, Overstress, Severe turbulence, Volcanic ash encounter, Overheating, Overweight landings, Exceeding flap/landing gear speed limits, Bird strike, Lightning strike and Foreign Object Damage (FOD).

    Primary Airframe Construction

    • Structural Assembly Techniques used to join different components of an aircraft structure:

      • Riveting
      • Bolting
      • Bonding

    • Riveting involves using various types of fasteners:

      • Solid rivets
      • Lockbolt fasteners
      • Hi-Lok fasteners
      • Cherry fasteners
      • Jo-bolt fasteners

    • Rivet Codes provide information about the size, head style, and alloy material of a rivet. Two systems are used:

      • Air Force - Navy (AN)
      • Military Standards 20 (MS20)

    • Rivet Head Design is crucial for functionality:

      • Universal head (AN470) for general applications
      • Countersunk head (AN426) for a flush, aerodynamic finish require countersinking or dimpling

    • Blind Rivets offer the advantage of installation from one side only, but are more expensive.

      • This is because installation requires special tools.

    • Hi-Lok Fasteners are used in high-strength applications due to their ability to withstand bearing and shearing loads.

      • Available in various materials (Titanium, Stainless Steel, Steel, Aluminum).

    • Bolting is a common method that utilizes different bolt types, requiring a common set of tools for installation.

      • Torque wrench may be required to set the correct tension.
      • Safetying mechanisms like lock nuts, lock washers, split pins, and lock wire are used to prevent loosening.

    • Lock Bolts are designed for permanent assembly and come in three types:

      • Pull-type
      • Blind-type
      • Stump-type

    • Lock Bolts can be classified based on application:

      • Shear lock bolts (thin head)
      • Tension lock bolts (thicker head)

    Airframe Construction

    • Helicopter Structures consist of:

      • Doors
      • Fuselage
      • Vertical stabilizer
      • Fairings
      • Tail cone
      • Windows

    • Helicopter Fuselage Framework employs a semi-monocoque construction with:

      • Longitudinal beams
      • Longerons
      • Stringers (supported by bulkheads, frames, and formers)

    • Tubular Construction was used in early helicopters but has limitations:

      • High manufacturing cost
      • Difficulty in achieving close tolerances
      • Advantage - easier field repair

    • Sheet Metal Construction is commonly used in modern helicopters:

      • Higher strength-to-weight ratio compared to tubular construction
      • Faster manufacturing with stamping and compound curves
      • Easier field repair (generally) but may require jigs for larger repairs

    • Combined Sheet Metal and Tubular Construction is used in some helicopters, leveraging the advantages of both techniques.

    Airframes - Secondary Construction

    • Airframes are constructed using different techniques, including stressed-skin, monocoque, semi-monocoque, and bonded construction.
    • Stressed-skin structures are lightweight and durable, but can fail due to minor dents or creases.
    • Semi-monocoque structures distribute loads between the skin and a sub-structure or skeletal framework.
    • Bonded construction utilizes fibreglass, honeycomb, and adhesives for high strength-to-weight ratios and reduced construction costs.
    • Composite materials, like Kevlar and carbon laminates, are used in modern helicopters for their strength, weight, and heat resistance. These materials require specific environmental conditions for curing.
    • The body structure, or main structural member of the fuselage, carries lift, thrust, and landing loads and supports other fuselage members.
    • The body structure is a reinforced box with X-members, housing fuel tanks for protection.
    • The bottom structure and cabin floor consist of two cantilevered beams connected to the body structure, supporting the cabin weight.
    • The cabin section is primarily made from synthetic materials like polycarbonate reinforced with glass fibers.
    • The rear section connects to the body section and houses the engine, baggage area, and the tail boom.
    • Formers provide the fuselage or wing with shape and are attached to a skin of sheet aluminium.
    • Bulkheads act as structural partitions dividing the fuselage or wings into bays or compartments, providing additional strength and shape definition.
    • Longerons provide the helicopter with longitudinal load carrying capacity, connecting frames for strength.
    • Stringers provide longitudinal strength in the fuselage, connecting formers and the sheet metal skin.
    • Doublers are pieces of metal used to strengthen skin structure where components are attached or as repair plates.
    • Beams are long structural members that support loads in bending and shear.
    • The floor structure is composed of a network of longerons and floor beams, incorporating seat tracks within the passenger cabin. Flooring panels are made from composite sandwich materials, and the underfloor structure accomodates control cable runs and fluid lines.
    • Helicopters utilize formed metal skins for extra strength and weight reduction.
    • Composite fibre skins offer a lighter-weight alternative and are manufactured by impregnating fibre with a resin and curing.
    • Sandwich core skinning involves bonding thinner fibre or metal skins to honeycomb core for high strength and low weight.
    • Struts are compression resistant members that prevent crushing. They resist both compression and tension loads.

    Undercarriage

    • Undercarriage, also referred to as landing gear, provides a safe and controlled landing.
    • Skids are the simplest form of landing gear used in helicopters.
    • Wheeled landing gear provides greater stability and is preferred for tarmac operations.
    • Retractable landing gear reduces drag and is essential for high-performance helicopters.
    • Fixed wheeled landing gear is less complex and more durable, but increases drag.

    Stabilisers

    • Stabilisers, or horizontal stabilisers, help maintain longitudinal stability, preventing nose-up or nose-down pitch.
    • Pitch control is achieved by adjusting the angle of the horizontal stabiliser.
    • Synch elevators are commonly found in civil helicopters, where two halves of the tailplane are connected and work together.
    • A moveable horizontal stabiliser, or stabilator, acts as an elevator and functions independently of the vertical stabiliser.

    Vertical Stabiliser

    • The vertical stabiliser contributes to directional stability and prevents yawing.

    Pylons

    • Pylons are structures mounted to the fuselage supporting external equipment, such as fuel tanks or weapons.

    Seats

    • Crew seats are designed for safety and comfort, with specialized features to prevent strain.
    • 5-point harnesses secure the pilots in case of an emergency.
    • Passenger seats are typically designed for comfort and durability, adapting to different aircraft configurations.

    Doors

    • Helicopter doors are designed for safe and efficient entry and exit, as well as escape in emergencies.
    • Doors can be designed for jettisoning, allowing quick removal in emergency situations.
    • Two-piece doors enable partial opening for ventilation or cargo loading.
    • Clamshell doors offer a wide opening for easy access.
    • Rear cargo doors provide access to the cargo bay.

    Windows

    • Helicopter windows are constructed from materials like cellulose acetate or acrylic glass, offering transparency and strength.
    • Windows are often designed for emergency escape and are often fitted with escape hatches.

    Fuel Storage

    • Fuel storage systems vary depending on the helicopter type and missions.
    • Bladder tanks are flexible containers within fuel tanks, allowing for increased storage capacity.
    • Integral fuel tanks are built into the fuselage structure, providing a more integrated and efficient design.
    • External fuel tanks, or drop tanks, can be attached to the fuselage to increase fuel capacity.

    Nacelles

    • Nacelles are streamlined enclosures that house the engines and other components.
    • Nacelles can be designed with features such as sand filters for operations in dusty environments.

    Firewalls

    • Firewalls are structural barriers between the engine compartment and the cabin, preventing the spread of fire in case of an engine fire.

    Engine Mounts

    • Engine mounts secure the engine to the fuselage and are designed to absorb vibrations and shock loads during operation.

    Helicopter Undercarriages

    • Helicopters have unique landing gear due to their limited forward motion during landing, requiring different load handling capabilities.

    • Skid gear is simpler and requires less maintenance than wheeled gear.

    • Wheel gear offers better ground handling, especially useful for larger helicopters and ship-borne operations.

    • Floats can be fixed or pop-out, inflated for water landings or emergencies.

    Skids

    • Skids are a non-absorbing landing gear, made of steel with damping devices depending on the helicopter and rotor type.

    • Advantages:

      • Simple construction
      • Resistance to movement on slopes
      • Suitability for external cargo attachments

    • Disadvantages:

      • Less ideal for running take-offs and landings
      • Ground handling can be more difficult

    Wheeled Landing Gear

    • Advantages:

      • Easier ground handling, allowing taxiing away from busy areas
      • Improved lift-off performance, reducing hover out-of-ground-effect (OGE) issues
      • Retractible options for reduced drag

    • Disadvantages:

      • Increased risk of movement on slopes
      • Complexity and weight of brake and hydraulic systems
      • Added maintenance requirements

    Oleo-Pneumatic Shock Struts

    • Often called "oleo legs," struts use compressed air and hydraulic fluid to absorb landing shocks.

    • They consist of a telescoping cylinder and plunger tube, with the wheel axle attached to the plunger tube.

    Retractable Landing Gear

    • Retracts to minimize drag and improve efficiency.

    • Typically attached to the fuselage with trunnions.

    • Sikorsky S-76 is an example of a helicopter with retractable gear.

    Fixed Wheeled Landing Gear

    • Advantages:

      • Less weight than retractable gear
      • Allows taxiing (skids don't)
      • Easier ground handling

    • Disadvantages:

      • Increased drag due to fixed undercarriage

    Stabilisers

    • Horizontal Stabilizer

      • Improves stability and prevents pitching down during forward flight.
      • Increases drag but improves controllability.
      • Can be detrimental to rearward flight as it can accentuate oscillations.

    • Vertical Stabilizer

      • Also known as fins, they counter the torque effect from the main rotor during forward flight.
      • Unloads the tail rotor, improving efficiency.
      • Generally asymmetric airfoils for improved performance.

    • Stabilator

      • Used to electronically manage stability, especially important for longitudinal control.
      • Connected to the cyclic linkage of the main rotor to pitch the tail up or down, adjusting lift and drag.

    Seats

    • Crew Seats

      • Tubular metal construction or composite material.
      • Include back cushions, lap and shoulder harnesses, and inertia reels.

    • Passenger Seats

      • Aluminium honeycomb panels form the seat structure in many helicopters.
      • Provide harnesses, cushions, and may be removable for cargo space.

    Doors

    • One-piece Doors

      • Typically hinged at the leading edge and swing outward and forward for access.
      • May include emergency release mechanisms.

    • Two-piece Doors

      • Top half hinges and locks in place.
      • Bottom half lowers to act as stairs for entry.

    • Clamshell Doors

      • Large, rear-mounted doors for easy loading and unloading of passengers or cargo on stretchers.

    • Cargo Platform Doors

      • Large rear doors allowing for loading/unloading of cargo, including pallets, vehicles, and even dropping stores while flying.

    Windows

    • Acrylic

      • Most commonly used due to its lightweight and moldable nature.
      • Can be scratched easily, requiring careful maintenance.

    • Cellulose Acetate

      • Less common due to its tendency to yellow and become dimensionally unstable.

    Window Repairs

    • Damaged windows are usually replaced rather than repaired.

    • Scratches can be removed by sanding with progressively finer grit sandpaper

    • Important:

      • Avoid exceeding minimum allowable material thickness.
      • Do not sand windshields excessively to avoid distorting the pilot's vision.
      • Use appropriate tools like hack saws, band saws, and jig saws for proper cutting.
      • Use water-soluble cutting oil to keep drill bits cool and lubricated when drilling acrylic.

    Plastic Moulding

    • Plastic is available in various sizes, from 1/8 inch to 7/8 inch
    • Plastic must be clean and dry before heating for moulding
    • Remove protective paper and its adhesive before heating
    • Holes are stress crack free

    Fuel Storage

    • Fuel tanks vary in size and shape depending on the helicopter type and intended use.
    • Tanks are made from fuel-resistant materials
    • Tanks have a sump and drain at the lowest point
    • Tanks are vented to the atmosphere
    • Baffles are installed in most tanks to prevent fuel surging
    • Tanks have expansion space for fuel volume increase due to temperature changes
    • Dump valves allow for fuel jettison during flight for weight reduction
    • Dump valves are installed for safe, rapid fuel discharge

    Bladder Tanks

    • Bladder tanks are made from a thin fabric impregnated with neoprene or a similar fuel-impervious material
    • Bladder tanks are an alternative to welded fuel tanks
    • They are installed by snapping or lacing into the fuel cell cavity in the aircraft wing
    • Sharp edges in fuel bays must be covered with chafe-resistant tape for bladder installation
    • Secure the bladder opening with an inspection plate
    • Inspect for bladder detachment from the attachment points, which can affect fuel volume and gauge accuracy
    • Inspect for wrinkles that can trap water
    • Do not leave bladder tanks empty for extended periods
    • Wipe the inside of the bladder with an oily rag if it must be left empty for an extended period

    Integral Tanks

    • Integral tanks are referred to as wet tanks
    • Integral tanks save weight compared to rigid tanks
    • Sealants are used to seal parts of the helicopter structure during assembly
    • Integral tanks are part of the helicopter structure, not separate tanks
    • Sikorsky S76 helicopters use integral tanks in the fuel system

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    Test your knowledge on the materials and stresses involved in helicopter engineering. This quiz covers topics such as tension, compression, and the types of materials used for various components. Perfect for students and professionals in aerospace engineering.

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