11.4 Landing Gear Systems

Landing gear systems are crucial for aircraft safety and performance. They absorb landing impacts, enable ground movement, and affect aerodynamics. This section covers gear types, shock absorption, steering, and braking, highlighting how these components work together to support aircraft operations.

From tricycle setups to advanced carbon brakes, landing gear design balances weight, efficiency, and functionality. Understanding these systems is key to grasping how aircraft transition between air and ground, impacting everything from fuel economy to passenger comfort.

Landing Gear Configurations

Main Types of Landing Gear

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• Tricycle landing gear consists of two main wheels behind the center of gravity and a nose wheel
  • Provides better visibility during ground operations
  • Improves stability during takeoff and landing
  • Reduces the risk of ground looping
• Tailwheel landing gear features two main wheels forward of the center of gravity and a small wheel under the tail
  • Offers better performance on unpaved runways
  • Allows for shorter takeoff distances
  • Requires more skill to handle during ground operations
• Retractable landing gear can be withdrawn into the aircraft during flight
  • Reduces aerodynamic drag, increasing aircraft speed and fuel efficiency
  • Adds complexity and weight to the aircraft design
  • Typically used in high-performance and commercial aircraft
• Fixed landing gear remains extended throughout the flight
  • Simpler and lighter than retractable systems
  • Requires less maintenance
  • Commonly used in small general aviation aircraft and some military transports

Design Considerations and Performance Impact

• Weight distribution affects the choice between tricycle and tailwheel configurations
• Runway surface conditions influence the selection of fixed vs. retractable gear
• Aerodynamic efficiency plays a crucial role in determining gear type for different aircraft speeds
• Maintenance requirements vary significantly between fixed and retractable systems
• Operating costs increase with more complex landing gear configurations
• Aircraft mission profiles (short-field operations, long-range flights) impact landing gear design choices

Shock Absorption Systems

Types and Functions of Shock Absorbers

• Shock absorbers dissipate landing impact energy to protect the aircraft structure
  • Reduce vertical loads transmitted to the airframe during touchdown
  • Improve passenger comfort by minimizing abrupt movements
  • Extend the lifespan of landing gear components and aircraft structure
• Oleo struts function as hydraulic shock absorbers in aircraft landing gear
  • Consist of a cylinder filled with oil and compressed gas (typically nitrogen)
  • Utilize a piston that compresses the fluid and gas mixture upon impact
  • Provide progressive damping as the strut compresses
  • Offer excellent energy absorption capabilities for their weight

Shock Absorption Mechanisms and Materials

• Rubber disc shock absorbers use stacked rubber discs to absorb impact
  • Simple and lightweight design
  • Suitable for smaller aircraft with lower landing speeds
• Steel spring shock absorbers employ coiled springs for energy absorption
  • Reliable and low-maintenance option
  • Limited in their ability to handle high-energy impacts
• Liquid spring shock absorbers combine hydraulic fluid and gas for energy dissipation
  • Offer adjustable damping characteristics
  • Provide consistent performance across various temperatures
• Carbon fiber composites increasingly used in modern shock absorption systems
  • Offer high strength-to-weight ratios
  • Allow for innovative designs that optimize energy absorption

Steering and Braking

Aircraft Steering Systems

• Nose wheel steering enables directional control during ground operations
  • Hydraulic or electrical systems control nose wheel movement
  • Steering angle typically limited to 30-60 degrees in each direction
  • Some aircraft use differential braking for steering at low speeds
• Rudder pedals often interconnected with nose wheel steering for improved control
  • Allows pilots to steer using familiar flight controls
  • Enhances coordination between air and ground maneuvering
• Tiller steering wheel provides precise control in larger aircraft
  • Located in the cockpit, usually on the side panel
  • Allows for tighter turns and better maneuverability in confined spaces

Braking Systems and Technologies

• Braking systems slow and stop aircraft on the ground
  • Disc brakes most common in modern aircraft
  • Multiple discs stacked together for increased braking power
  • Hydraulic pressure applies force to brake pads, creating friction
• Anti-skid systems prevent wheel lock-up during heavy braking
  • Sensors monitor wheel speed and detect impending skids
  • Automatically modulate brake pressure to maintain optimal braking efficiency
  • Improve stopping performance and reduce tire wear
• Carbon brakes offer advantages over traditional steel brakes
  • Lighter weight, improving fuel efficiency
  • Better heat dissipation, allowing for shorter cooling times between landings
  • Longer service life, reducing maintenance costs
• Autobrake systems automatically apply brakes upon landing or rejected takeoff
  • Ensure consistent deceleration regardless of pilot input
  • Reduce pilot workload during critical phases of flight
  • Can be preset to different levels of braking intensity