Fixed Gear & Shock Absorption - Landing Gear - Airframes & Aircraft Systems #14

Summary

This educational series delves into the intricacies of aircraft landing gear design and construction, focusing on both fixed and retractable systems. It covers retraction mechanisms powered by hydraulics, steering systems, and landing gear indicators. The first lesson emphasizes the gear's functions, such as ground maneuverability, weight support, and energy absorption during landing. It distinguishes between tricycle and tailwheel layouts, highlighting the tricycle's advantages. The discussion then shifts to various shock absorption systems, with a detailed look at the olio pneumatic strut, which uses gas to support the aircraft and fluid to dampen oscillations. The lesson concludes with different methods of wheel attachment to the undercarriage.

Takeaways

• 🛫 The landing gear serves multiple functions including maneuvering on the ground, supporting the aircraft, providing clearance for engines and propellers, facilitating loading, and absorbing landing impact.
• 🔧 Landing gear is designed to be lightweight and compact, with extensive research dedicated to its design to minimize its impact on aircraft performance.
• 🔄 There are two main types of landing gear layouts: tricycle, with a nose wheel and two main gear units, and taildragger, with a tail wheel and main wheels.
• 👍 The tricycle gear layout is preferred for its stability, improved visibility for pilots, and level loading platform, and is used in most modern aircraft.
• ⚖️ The main gear units in tricycle gear layouts are positioned near the aircraft's center of gravity to support most of the aircraft's weight and absorb landing shocks.
• 🚫 Fixed non-retractable landing gear is used in some aircraft for its simplicity, low maintenance, and cost-effectiveness, despite the drag it creates during flight.
• ✈️ High-performance aircraft often feature retractable landing gear to reduce drag, although this increases weight, complexity, and maintenance requirements.
• 🔩 There are three common types of fixed landing gear shock absorption systems: spring steel legs, rubber cord, and oleo pneumatic struts.
• 💡 The oleo pneumatic strut is a key component in landing gear, using a combination of hydraulic fluid and compressed gas to absorb shocks and support the aircraft's weight.
• 🔧 The design of the oleo pneumatic strut includes a separator piston to keep fluid and gas apart, with a flutter valve to control the rate of fluid flow and dampen oscillations.
• 🔗 Various methods are used to connect wheels to the landing gear legs, including fork and half-fork, cantilever, dual wheel, and multi-wheel using a bogie or truck.

Q & A

What are the primary functions of an aircraft's landing gear?

The primary functions of an aircraft's landing gear are to provide a means of maneuvering the aircraft on the ground, support the aircraft at a convenient height, give clearance for engines, propellers, and flaps, facilitate loading, absorb the kinetic energy of landing, and provide a means of controlling deceleration through the brakes.

Why is the landing gear considered dead weight once airborne?

Once airborne, the landing gear serves no useful purpose and is effectively dead weight because it does not contribute to the flight and only adds to the aircraft's overall weight, which can increase fuel consumption and decrease performance.

What are the two types of landing gear layout mentioned in the script?

The two types of landing gear layout are the tricycle layout, which has a nose wheel unit forward of two main gear units, and the tailwheel or taildragger type, which has a tail wheel behind the main wheels.

What are the advantages of tricycle gear over tailwheel type?

The advantages of tricycle gear over tailwheel type include no danger of tipping over onto its nose in a strong tailwind, an improved forward view on the ground for the pilot, and a more level platform for loading.

What is the purpose of the nosewheel unit in an aircraft with tricycle gear?

The nosewheel unit in an aircraft with tricycle gear keeps the aircraft level and in most cases also provides a means of steering.

Why are fixed non-retractable landing gears often fitted in slow light aircraft?

Fixed non-retractable landing gears are often fitted in slow light aircraft due to the simplicity, reduced maintenance, and low initial cost, even though they cause reduced performance due to drag during flight.

What are the three types of fixed landing gear shock absorption systems mentioned in the script?

The three types of fixed landing gear shock absorption systems mentioned are spring steel legs, rubber cord, and oleo pneumatic struts.

How does the oleo pneumatic strut absorb shocks during landing?

The oleo pneumatic strut absorbs shocks during landing by using the compressed gas to cushion bumps and support the aircraft's weight. The hydraulic fluid dampens oscillations and controls the rate of compression and extension of the cylinders.

What is the function of the flutter valve in an oleo pneumatic strut?

The flutter valve in an oleo pneumatic strut limits the rate of movement more when the strut is extending than when it is contracting, which helps to control the speed of compression and extension and prevent a bounce on landing.

What are the common methods used for connecting wheels to the landing gear legs?

The common methods used for connecting wheels to the landing gear legs are fork half, fork cantilever, dual wheel, and multi-wheel using a bogie or truck.