Aircraft Landing Gear System Quiz
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Questions and Answers

What is a primary function of the main landing gear in an aircraft?

  • To enhance visibility from the cockpit
  • To provide steering capability during taxiing
  • To prevent ground-looping during landing
  • To absorb download forces during ground operations (correct)

Which of the following is NOT a benefit of tricycle configuration landing gear?

  • Enhances the overall payload capacity (correct)
  • Allows higher landing speeds without nosing over
  • Prevents ground-looping of the aircraft
  • Improves visibility during ground manoeuvring

What role do shimmy dampers play in the landing gear system?

  • They facilitate the steering of the nose landing gear
  • They stabilize the aircraft during ground movements (correct)
  • They aid in the emergency retraction of the landing gear
  • They help absorb shocks during landing

Which landing gear configuration is typically used for rough field operations?

<p>Conventional configuration (A)</p> Signup and view all the answers

How does the nose landing gear typically contribute to aircraft handling?

<p>By allowing the aircraft to steer during ground operations (B)</p> Signup and view all the answers

What is the main advantage of a tricycle landing gear over a tail-wheel configuration regarding braking?

<p>Enables a more forceful application of brakes without nosing over (A)</p> Signup and view all the answers

What is generally required for retracting and extending the landing gear?

<p>Hydraulic or pneumatic power systems (A)</p> Signup and view all the answers

What is the maximum force exerted by the retract actuator for the main landing gear?

<p>53,000 N (B)</p> Signup and view all the answers

What is the flow rate required to retract the three actuators in cubic meters per second?

<p>0.0263 m³/s (A)</p> Signup and view all the answers

What is the power in kilowatts required to drive the pump, assuming an efficiency of 85%?

<p>640 KW (A)</p> Signup and view all the answers

Which component prevents undesired retraction of the landing gear when it is in the ‘DOWN’ position?

<p>Overcenter links (C)</p> Signup and view all the answers

What happens to the uplock mechanism after the landing gear is unlocked?

<p>It extends due to its mass and locks in the down position (C)</p> Signup and view all the answers

What is the primary function of an aircraft wheel?

<p>To support the aircraft's weight during various phases of flight (C)</p> Signup and view all the answers

What role does the trunnion play in the landing gear assembly?

<p>It allows the gear to pivot during retraction and extension (C)</p> Signup and view all the answers

Which component is responsible for locking the landing gear in the down position?

<p>Downlock Mechanism (B)</p> Signup and view all the answers

What is the primary function of the drag link in the landing gear assembly?

<p>To provide support to the shock strut longitudinally (A)</p> Signup and view all the answers

How does the overcenter link contribute to the functionality of the landing gear?

<p>It prevents the link from pivoting during gear retraction (B)</p> Signup and view all the answers

What material are typical aircraft wheels commonly made from?

<p>Aluminum alloy (B)</p> Signup and view all the answers

What is a key function of aircraft tires?

<p>To provide grip with the runway surface (B)</p> Signup and view all the answers

Which component stabilizes the landing gear laterally?

<p>Side Strut or Side Brace Link (D)</p> Signup and view all the answers

What is the main purpose of the axles in the landing gear system?

<p>To support and install the main wheels (C)</p> Signup and view all the answers

What method is NOT used by landing gear to absorb shock during landing?

<p>Transferring force through the airframe at a consistent rate (C)</p> Signup and view all the answers

In a pneumatic/hydraulic shock strut, what is the role of the nitrogen gas?

<p>To maintain pressure in the upper chamber (B)</p> Signup and view all the answers

What happens to the volume of gas in the upper chamber during the compression stroke of the shock strut?

<p>It decreases, leading to increased pressure (C)</p> Signup and view all the answers

What is the immediate effect of the aircraft's wheels touching the ground on the shock strut?

<p>The compression stroke of the shock strut begins (B)</p> Signup and view all the answers

What is a disadvantage of non-shock absorbing landing gear?

<p>It can lead to harmful forces being transferred to the airframe (D)</p> Signup and view all the answers

Which component primarily allows hydraulic fluid to move between the chambers during compression?

<p>Orifice (D)</p> Signup and view all the answers

What effect does increasing pressure in the shock strut have on the aircraft’s vertical motion?

<p>It stops vertical motion (D)</p> Signup and view all the answers

What is a characteristic of flexible spring steel used in non-shock absorbing landing gear?

<p>It returns to its original shape after flexing (D)</p> Signup and view all the answers

During the landing process, what role does the hydraulic fluid play in the shock strut?

<p>It helps cushion the shock by being forced through a metered opening (C)</p> Signup and view all the answers

What is the role of compressed air in the shock strut of an aircraft during takeoff?

<p>It acts as a shock absorber while the aircraft is taxiing. (C)</p> Signup and view all the answers

What is a disadvantage of having fixed landing gear on an aircraft?

<p>It exposes the gears to airflow, increasing drag. (B)</p> Signup and view all the answers

How does the weight of retractable landing gear compare to its benefits?

<p>The added weight is considered a minor drawback compared to the reduction in drag. (B)</p> Signup and view all the answers

What happens to the landing gear components when the landing gear handle is set to 'OFF'?

<p>They are connected to the return line of the hydraulic system to maintain the 'UP' position. (D)</p> Signup and view all the answers

Which mechanism is responsible for keeping the landing gear in the 'UP' position?

<p>Up-lock mechanism. (A)</p> Signup and view all the answers

What function do the unlatch and door actuators serve in the landing gear system?

<p>They unlock and open the wheel well doors. (C)</p> Signup and view all the answers

What happens when the landing gear handle is set to the 'DOWN' position?

<p>Pressure from the hydraulic system is released to extend the landing gear. (C)</p> Signup and view all the answers

What is the mechanical connection of the landing gear handle in the cockpit responsible for?

<p>Controlling the hydraulic pressure supply for landing gear operation. (C)</p> Signup and view all the answers

During takeoff, which of the following describes the process of shock strut extension?

<p>The shock strut extends until gas pressure can fully support the aircraft's weight. (D)</p> Signup and view all the answers

What mechanism prevents the nose wheel from rotating, ensuring proper wheel alignment?

<p>Torque links (D)</p> Signup and view all the answers

How does the hydraulic pressure affect the nose steering during a right turn?

<p>It directs fluid through the right turn alternating line to cylinder A. (A)</p> Signup and view all the answers

What keeps the nose landing gear aligned when the shock strut is fully extended?

<p>Locating cam assembly (B)</p> Signup and view all the answers

What component adjusts the steering direction based on the nose gear shock strut position?

<p>Tiller (C)</p> Signup and view all the answers

During aircraft taxying, how can the aircraft be steered?

<p>Utilizing nose wheel steering or differential braking. (B)</p> Signup and view all the answers

What happens to the hydraulic fluid in the steering system during a left turn?

<p>It is forced out of steering cylinder B. (C)</p> Signup and view all the answers

What is the result of hydraulic fluid flowing away from the retraction actuator?

<p>It reduces the ‘down’ shock upon retraction. (B)</p> Signup and view all the answers

How does the cam assembly contribute to the landing gear system?

<p>It keeps the wheel aligned once extended. (B)</p> Signup and view all the answers

What is the primary function of a shimmy damper in a nose landing gear system?

<p>To reduce the tendency of the nose gear to oscillate (C)</p> Signup and view all the answers

How does the emergency extension system operate when the main power fails?

<p>It mechanically releases the uplocks via a handle (D)</p> Signup and view all the answers

What role does the squat switch play in the landing gear system?

<p>To indicate the compression or extension of the gear strut (A)</p> Signup and view all the answers

Which statement best describes the function of ground locks in the landing gear system?

<p>They restrict movement of the gear to prevent collapse on the ground (B)</p> Signup and view all the answers

What is the primary mechanism by which a piston-type shimmy damper absorbs oscillations?

<p>Restriction of hydraulic fluid through a bleed hole (C)</p> Signup and view all the answers

What happens when the landing gear safety switch is closed?

<p>Current flows to retract the land gear pin (A)</p> Signup and view all the answers

Which aspect of emergency extension systems can vary between different aircraft?

<p>Method to unlatch the gear (C)</p> Signup and view all the answers

What is the likely consequence of a malfunctioning squat switch during ground operations?

<p>Gear may inadvertently retract while on the ground (C)</p> Signup and view all the answers

What is one of the main advantages of a tricycle landing gear configuration over a tail wheel configuration?

<p>It prevents ground-looping of the aircraft. (A)</p> Signup and view all the answers

Which landing gear configuration is typically associated with older aircraft designed for rough field operations?

<p>Conventional configuration (B)</p> Signup and view all the answers

What primary function does the main landing gear serve during aircraft ground operations?

<p>To absorb large download forces during landing and taxiing. (D)</p> Signup and view all the answers

How does the nose landing gear typically enhance aircraft operation on the ground?

<p>It allows for better visibility and steering capabilities. (D)</p> Signup and view all the answers

What is an important feature of the shock-absorbing element in the landing gear?

<p>It absorbs shock during landing to minimize impact forces. (A)</p> Signup and view all the answers

Which statement about the brake systems on the main landing gear is correct?

<p>Brakes are installed to assist in slowing down or stopping the aircraft during ground operations. (B)</p> Signup and view all the answers

In a hydraulic shock strut, what effect does increasing the pressure in the system generally have?

<p>It increases the aircraft's vertical motion. (C)</p> Signup and view all the answers

What is a key advantage of tricycle landing gear concerning visibility during landing?

<p>It allows pilots to see directly down the runway. (D)</p> Signup and view all the answers

What is the primary role of the hydraulic pressure in the landing gear system?

<p>To unlock and operate the landing gear mechanisms (A)</p> Signup and view all the answers

How much volume is required to retract three actuators of the landing gear?

<p>0.263 m³ (D)</p> Signup and view all the answers

What is the role of the overcenter mechanism in the landing gear system?

<p>To prevent the landing gear from retracting while down (C)</p> Signup and view all the answers

Which factor does NOT influence the calculation of the power required for the pump?

<p>Weight of the aircraft (B)</p> Signup and view all the answers

What is the maximum force exerted by each retract actuator in the landing gear system?

<p>53,000 N (D)</p> Signup and view all the answers

What mechanism converts hydraulic power into mechanical motion in the landing gear system?

<p>Actuators (B)</p> Signup and view all the answers

How does the uplock mechanism secure the landing gear?

<p>Through a physical hook that engages the gear (B)</p> Signup and view all the answers

What is the function of bungee springs in the landing gear system?

<p>To provide a counterforce for gear extension (B)</p> Signup and view all the answers

What is the primary reason for installing retractable landing gear in aircraft?

<p>To reduce drag during flight (C)</p> Signup and view all the answers

Which action occurs when the landing gear handle is placed in the 'UP' position?

<p>Hydraulic pressure supplies energy to unlock and open the wheel well doors (B)</p> Signup and view all the answers

How does the hydraulic power system affect the landing gear when set to the 'OFF' position?

<p>All components are connected to the return line, keeping the landing gear up (D)</p> Signup and view all the answers

What is the role of the up-lock mechanism in the landing gear system?

<p>To automatically lock the landing gear in the up position (B)</p> Signup and view all the answers

In the landing gear system, what is the purpose of the retract actuator?

<p>To apply hydraulic pressure for gear retraction (B)</p> Signup and view all the answers

What occurs to the compressed air in the shock strut during the recoil of the aircraft?

<p>It compresses further, increasing support for the aircraft’s weight (C)</p> Signup and view all the answers

What happens to the hydraulic system's pressure when the landing gear handle is set to 'DOWN'?

<p>Pressure is released, allowing gear extension (B)</p> Signup and view all the answers

During taxiing, what role does the compressed air in the shock strut play?

<p>It absorbs shock and stabilizes the aircraft (A)</p> Signup and view all the answers

What is a consequence of the hydraulic fluid being forced through the metered opening during the compression of a shock strut?

<p>It cushions the initial shock of landing. (B)</p> Signup and view all the answers

Which characteristic of non-shock absorbing landing gear allows it to manage landing impact?

<p>It flexes initially to absorb and dissipate forces. (A)</p> Signup and view all the answers

During the compression stroke, what happens to the gas pressure in the upper chamber of the shock strut?

<p>It increases due to the decrease in gas volume. (B)</p> Signup and view all the answers

What is the primary role of the metering pin within a shock strut during the aircraft's landing?

<p>To adjust the rate of fluid transfer to control damping. (A)</p> Signup and view all the answers

What distinguishes shock absorbing landing gear designs from non-shock absorbing designs?

<p>They incorporate hydraulic and gas mechanisms to dissociate impact forces. (D)</p> Signup and view all the answers

How does the positioning of the aircraft's center of mass affect the operation of shock struts during landing?

<p>A downward movement assists in the fluid transfer during compression. (B)</p> Signup and view all the answers

What happens to the temperature within the shock strut as the pressure increases during compression?

<p>It increases because of hydraulic fluid going through compression. (B)</p> Signup and view all the answers

What is the function of the orifice in the shock strut mechanism during the compression stroke?

<p>To regulate the transfer of hydraulic fluid from the lower to the upper chamber. (B)</p> Signup and view all the answers

Flashcards

Main Landing Gear

The main landing gear is responsible for supporting the aircraft's weight during landing and taxiing, absorbing large forces during these operations. It also houses the brakes used for slowing down or stopping.

Nose Landing Gear

The nose landing gear supports the aircraft's weight and provides steering capability for ground maneuvers. Its steering mechanism allows the aircraft to be directed on the ground.

Tail Wheel/Conventional Landing Gear

Tail wheel or conventional landing gear is found on older aircraft and is designed for landings on rough terrain. It has a single wheel at the tail of the aircraft for support.

Tandem Landing Gear Configuration

Tandem configuration utilizes two sets of landing gear, one in front of the other, for greater stability and weight distribution.

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Tricycle Landing Gear Configuration

Tricycle configuration has a nose wheel and two main wheels, providing increased stability and maneuverability compared to traditional tail-wheel configurations.

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Benefits of Tricycle Landing Gear

The tricycle landing gear configuration is preferred over conventional landing gear due to its ability to handle higher landing speeds, improve visibility for the pilot, and prevent ground-looping accidents.

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Ground-Looping

A ground-loop is an incident where an aircraft becomes uncontrollable due to the rear wheel lifting off the ground during a turn. This is most prevalent in conventional landing gear configurations.

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Aircraft Wheels

The primary component of a landing gear, crucial for supporting the aircraft's weight during taxiing, takeoff, and landing, minimizing impact forces.

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Trunnion

A vital part of the landing gear that connects to the airframe, allowing the gear to retract and extend smoothly. It provides a pivot point for the gear.

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Strut

A crucial structural element of the landing gear that supports the entire assembly, absorbing shock forces during landing and taxiing.

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Drag Link or Drag Strut

A support component that reinforces the landing gear's shock strut longitudinally, enhancing its stability and resistance to forces.

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Side Strut or Side Brace Link

A lateral support component for the landing gear, ensuring its stability against sideways forces.

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Overcenter Link

A safety component that locks the main landing gear in the down position during ground operations, preventing accidental retraction.

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Lock Mechanism

This mechanism safely locks the landing gear in both the down position (for ground contact) and the up position (for flight).

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Axles

The central element of the landing gear that supports and houses the main wheels. It provides a solid base for the entire landing gear assembly.

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Uplock Mechanism

A critical safety feature on aircraft, ensuring that the main landing gear is securely locked in the up position during flight, preventing accidental extension.

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Landing Gear Shock Absorption

Landing gear systems are designed to absorb the shock of landing, preventing damage to the aircraft.

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Non-Shock Absorbing Landing Gear

Non-shock absorbing landing gear uses flexible materials like steel or aluminum to absorb shock, slowly releasing energy back into the airframe.

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Pneumatic/Hydraulic Shock Strut

Pneumatic/hydraulic shock struts combine nitrogen gas and hydraulic fluid to absorb and dissipate shock loads.

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Shock Strut Components

The upper cylinder of a shock strut is fixed to the aircraft, while the lower cylinder, called the piston, is free to move inside the upper cylinder.

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Shock Strut Compression

The shock strut compresses as the aircraft touches down, forcing the piston upwards.

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Shock Strut Orifice

The orifice regulates the flow of hydraulic fluid between the chambers, controlling the rate of shock absorption.

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Shock Strut Gas Compression

As the shock strut compresses, the gas chamber volume decreases, increasing pressure and slowing the aircraft's vertical descent.

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Hydraulic Fluid Shock Absorption

The initial shock is absorbed by the hydraulic fluid as it is forced through the metered opening, reducing impact force.

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Shock Strut Pressure and Temperature

Increased pressure and temperature in the cylinder slow down the aircraft's vertical speed until the pressure is sufficient to stop the motion.

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Shock Energy Dissipation

The shock strut effectively converts the shock energy into heat energy, dissipating it through the system and protecting the aircraft.

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Hydraulic Power for Landing Gear

Hydraulic pressure used to extend and retract landing gear, unlock wheels, and operate other vital components of an aircraft's landing gear system.

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Retract Actuator

The primary force that drives the extension and retraction of an aircraft's landing gear, usually generated by a hydraulic pump.

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Downlock Mechanism

A safety mechanism that prevents the landing gear from retracting while it's in the down position, ensuring the aircraft stays grounded.

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Bungee Springs

Spring-loaded parts that help to ensure smooth and controlled extension of the landing gear when it is unlocked.

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Retractible Landing Gear

A mechanical system that allows the aircraft's landing gear to be retracted into the fuselage during flight for reduced drag, but extended for landing and taxiing. This reduces aerodynamic resistance and improves fuel efficiency during flight.

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Fixed Landing Gear

Fixed landing gear remains constantly extended during flight, increasing drag compared to retractable systems. It is often found on smaller, slower aircraft where the additional complexity and weight of retractable systems are not beneficial.

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Landing Gear Handle

The landing gear handle in the cockpit controls the extension and retraction of the landing gear by adjusting the flow of hydraulic pressure to actuators. These actuators manipulate the landing gear and wheel well doors.

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Selector Valve

A crucial part of landing gear systems that uses hydraulic pressure to move the landing gear up or down. It connects to the landing gear handle and distributes hydraulic power accordingly.

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Actuators

Hydraulic actuators are powered by pressurized fluid to unlock, retract, extend, and lock the landing gear in position. They are essential for the smooth operation of the landing gear system.

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Landing Gear 'UP' Position

The 'UP' position on the landing gear handle initiates the retraction sequence. Hydraulic pressure unlocks the landing gear, opens wheel well doors, and retracts the landing gear.

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Landing Gear 'DOWN' Position

The 'DOWN' position on the landing gear handle triggers the extension sequence. Hydraulic pressure releases the lock, allowing the gear to extend, and the doors to close.

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Landing Gear 'OFF' Position

The 'OFF' (neutral) position on the landing gear handle disengages the landing gear retraction and extension systems. It effectively isolates the actuators from hydraulic pressure, preventing unintentional movement of the gear.

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Shock Strut - Upper Cylinder

The upper cylinder of a shock strut, fixed to the aircraft.

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Shock Strut - Lower Cylinder (Piston)

The lower cylinder of a shock strut, free to move inside the upper cylinder.

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Tricycle Landing Gear

A tricycle landing gear configuration has a nose wheel for steering and two main wheels for stability.

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Shock Strut

The shock strut is a crucial part of the landing gear that absorbs the shock forces during landing and taxiing.

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Landing Gear Control

The main landing gear can be extended or retracted using a control handle in the flight deck. This handle is connected to a selector valve, which directs hydraulic pressure to actuators responsible for unlocking, extending, and locking the landing gear.

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Selector Valve Function

The selector valve acts as a central control point, distributing hydraulic pressure to various actuators depending on the position of the handle. It moves hydraulic fluid through internal circuits, ensuring smooth operation of locking, unlocking, extending, and retracting the landing gear.

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Landing Gear Actuators

Actuators are powered hydraulic components responsible for extending or retracting the landing gear. They use hydraulic pressure supplied by the system to move the gear and doors, ensuring safe and reliable operation.

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Nose Landing Gear Alignment

A mechanism that helps align the nose wheel with the aircraft's longitudinal axis, preventing damage during retraction and aligning for landing.

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Torque Links/Arms

Torque links or torque arms connect the upper and lower cylinders of a shock strut, preventing rotation and keeping the wheels aligned.

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Nose Landing Gear Steering System

The system used to steer an aircraft during taxiing, controlled from the flight deck using a wheel, tiller or joystick.

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Hydraulic Steering Mechanism

The pressure from the aircraft hydraulic system is routed through a metering valve to the steering cylinder, causing the nose wheel to turn.

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Metering Valve

A key component of the steering system that directs hydraulic fluid to the appropriate steering cylinder based on the desired direction of turning.

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Steering Cylinders (A & B)

Steering cylinder A and B are attached to the nose steering spindle, their extension turning the spindle towards the right or left respectively.

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Fluid Return System

Fluid from the steering cylinders is routed to a compensator that returns it to the aircraft hydraulic system.

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Retraction Shock Reduction

The reduction in speed of retraction caused by the hydraulic fluid flowing away from the retraction actuator, lessening the shock.

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Nose Wheel Shimmy Damper

A device that dampens the rapid oscillation (shimmy) of the nose wheel at certain speeds, using hydraulic fluid flow.

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Emergency Landing Gear Extension System

A system that deploys the landing gear in case of a primary hydraulic system failure, typically using gravity or pneumatic power.

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Landing Gear Squat Switch

A switch that senses the position of the main landing gear, preventing retraction while the aircraft is on the ground. It activates a solenoid to release the lock-pin and allow gear retraction.

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Ground Locks

A safety device that prevents the collapse of the landing gear while the aircraft is on the ground, usually a pin inserted into pre-drilled holes, locking the gear.

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How Nose Wheel Shimmy Dampers Work

Hydraulic fluid is forced through a restricted bleed hole in the piston as the lower strut cylinder shimmies, effectively damping the oscillation.

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Emergency Landing Gear Release Handle

When the emergency release handle is operated, it unlocks the gear uplocks, allowing gravity to pull the gear down to the extended position.

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Squat Switch Function

The squat switch is wired to various systems, ensuring the gear stays down while on the ground. Once the gear is extended during takeoff, the switch closes, allowing the solenoid to retract the lock-pin and permit gear retraction.

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Importance of Ground Locks

Ground locks are essential safety features for aircraft, preventing accidental collapse of the gear when on the ground. They provide an added layer of protection.

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Study Notes

Aircraft Systems - Hydraulic and Pneumatic Power Systems

  • ME3531 is the course code for Aircraft Systems at Singapore Polytechnic.
  • The course content covers Hydraulic and Pneumatic Power Systems.
  • The course includes a detailed study of the Landing Gear System with specific topics to be covered.

Landing Gear System

  • Configurations: Different configurations of aircraft landing gear will be stated and described.
  • Operating Principles: The operating principles of main and nose-landing gear will be discussed.
  • Components: The functions of various landing gear components (struts, torque links, drag links, side struts, shimmy dampers, axles, wheels, and tires) will be described.
  • Shock Absorbing Element: The construction and function of the shock absorbing element in the landing gears will be explained.
  • Aircraft Steering: Aircraft steering systems will be discussed.
  • Extension/Retraction Systems: The normal and emergency extension/retraction systems of the landing gear will be described.
  • Safety Devices: The safety devices, indications, and warning systems of the landing gear will be discussed.

Hydraulic Power - Landing Gear System

  • Main Landing Gears: Main landing gears provide primary support, absorbing high download forces during ground operations like landing and taxiing. Brakes are installed for slowing down or stopping as required. The number of landing gears, wheels, and brakes vary based on the initial aircraft design considering weight and load capacities.
  • Nose Landing Gears: Nose landing gears also provide aircraft support, carrying load. The gears normally include steering mechanisms for manoeuvring on the ground.

Types of Landing Gear Arrangement

  • Tail or Conventional Configuration: This is used on older aircraft for landing in rough field operations.
  • Tandem Configuration: Aircraft configuration details are not provided.
  • Tricycle Configuration: This is used in contemporary aircraft, offering advantages over conventional landing gears: forceful braking without stability loss; improved flight deck visibility (especially during landing and ground maneuvers); and prevention of ground-looping due to the aircraft's center of gravity position.

Sub-components of the Main and Nose Landing Gear

  • Aircraft Wheels: Crucial for a landing gear system, they support the entire aircraft weight during taxiing, takeoff, and landing. Typical wheels are lightweight, strong and constructed from aluminum alloy.
  • Aircraft Tyres: Support aircraft weight, absorb shock from landing/taxiing, provide grip with runway, and discharge static electricity.
  • Trunnion: Part of the landing gear assembly, fixed to the airframe. Trunnion uses bearing assemblies for retraction/extension pivot.
  • Strut: The vertical member of the landing gear system; a diagram or complete description of the important parts involved is not given.
  • Drag Link or Drag Strut: Supports and stabilizes the strut longitudinally.
  • Side Strut or Side Brace Link: Stabilizes the landing gear laterally.
  • Overcenter Link: Prevents movement at joints during landing gear retraction, prevents collapse during ground operations. Locks main gear in down position (also called 'Downlock'), allowing hydraulic retraction.
  • Lock Mechanism: A "downlock" locks the landing gear in the down position. The main landing gear is held in the UP position by the uplock mechanism.
  • Axles: Supports and installs the main wheels on the aircraft.

Hydraulic Power - Landing Gear System

  • Shock Absorbing and Non-Shock Absorbing Landing Gear: Landing gear absorbs forces on landing and taxiing. Absorption methods include heat conversion ("damping") or altered transfer through the airframe.
  • Non-Shock Absorbing Landing Gear: Many aircraft use flexible spring steel, aluminium, or composite struts which absorb landing impact and redistribute force to the airframe at safe rates.
  • Shock Absorbing: Common design uses nitrogen gas and hydraulic fluid in telescoping cylinders. The upper cylinder is fixed to the aircraft, and the lower-piston moves inside the upper cylinder. Two chambers are formed; the lower chamber is always full of hydraulic fluid, while the upper contains nitrogen gas. The orifice between cylinders allows fluid to move.
  • Shock Strut Operation: During landing, as the aircraft touches down, the strut compresses. The lower cylinder/piston goes up into the upper cylinder. This increases pressure within the chamber. During recoil, the strut extends until the air pressure supports the aircraft's weight, cushioning the aircraft during taxiing.

Fixed and Retractable Landing Gear

  • Fixed Landing Gear: Exposed to airflow during flight, leading to increased drag with increasing speed.
  • Retractable Landing Gear: Mechanisms retract/stow landing gear to reduce drag, but they have some weight addition.

Retraction and Extension of Main Landing Gear

  • Manual Operations: The main landing gear is extended/retracted using a handle on the flight deck.
  • Hydraulic Systems: The control is connected to an internal circuit in the selector valve, supplying pressure for mechanisms like unlocking wheel well doors and actuators for gear retraction and extension.
  • "UP", "OFF" (Neutral), "DOWN" Positions: Different actions occur based on handle position.
  • Up-lock Mechanism: The landing gear stays in an up position due to the uplock mechanism.
  • Down Position: Release of hydraulic pressure from internal selector valve circuit (following handle change) allows unlocking of uplock mechanism and wheel well doors, and trigger extension of the gear.

Nose Landing Gear Steering System

  • The steering system allows aircraft maneuverability during taxying. Control is from the pilot’s station through small wheels, tillers, or joysticks. Methods include nose-wheel steer, or differential braking.

Nose Landing Gear Alignment

  • Shock struts feature torque links/torque arms. These connect to the upper cylinder and are non-rotating, aligning the wheels.
  • Locating cam assemblies keep the landing gear in alignment. This ensures wheel/axle assembly alignment when the landing gear is extended fully. It avoids possible structural damage by aligning the wheels/axles in a straight position ahead.

Nose Landing Gear Shimmy Dampers

  • Shimmy dampers control nose landing gear oscillations (shimmy), especially at high speeds. Reduced oscillations happen due to the proper directed flow of hydraulic fluid.
  • Piston-type dampers resist shimmy by directing hydraulic fluid flow in a controlled way through restricted openings (in a piston within the damper). This reduces any oscillations that may occur because of the structure/mechanisms.

Emergency Extension System

  • The emergency system provides gear lowering in case of primary power failure.
  • Emergency handles in flight decks allow the landing gear to drop if the primary hydraulic system fails, using uplock release mechanism and gravity pull to the down position.
  • Some systems might use pneumatic power for unlatching the gear.

Landing Gear Safety Devices

  • Safety Switch (Landing Gear Safety Device): Monitored the landing gear position (extended / retracted); prevents ground gear retraction.
  • Ground Locks (Landing Gear Safety Device): Prevent any collapse of landing gear while aircraft is stationary. Pins in pre-drilled holes are used.
  • Gear Indicator: Displays micro/proximity switch data (gear status) on the instrument panel. Green light shows gear is down/locked, red light shows it is in transit, and a lack of illumination signifies the gear is in the up/locked position.
  • Warning Horn: Indicates when landing gears are not down and locked (during landing).

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Aircraft Landing Gear Systems PDF

Description

Test your knowledge on the various functions and configurations of aircraft landing gear systems. This quiz covers topics like tricycle configurations, shimmy dampers, and the mechanics behind landing gear operation. Perfect for aviation enthusiasts and students in aerospace engineering.

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