AIRFRAMES NOTES

1. Introduction

INTRODUCTION

Welcome to the fascinating world of aircraft landing gears

These are essential components that enable safe take offs and landings

2. LANDING GEARS

Aircraft landing gear supports the entire weight of an aircraft during landing and ground operations.

 They are attached to primary structural members of the aircraft. The type of gear depends on the aircraft design and its intended use. Most landing gear has wheels to facilitate operation to and from hard surfaces, such as airport runways.

2.1. Importance of Landing Gears

·         Support the aircraft during ground operations

·          Dampens vibrations when the aircraft is being taxied  or towed.

·          Cushion the landing impact.

·          Steering and braking.

3. LANDING GEAR CONFIGURATIONS

A landing gear usually takes the form of two or more main undercarriage units in the wings or fuselage, and an auxiliary undercarriage unit at the nose or tail which carries only a small proportion of the total load and is used steering purposes.

-Aircraft landing-gear can be classified as either;

a.       Tricycle configuration

b.      Convectional Configuration

c.       Tandem Landing Gear Configuration

3.1. TYPES

3.2. Convectional

Tail wheel-type also known as conventional gear because many early aircraft used this type of arrangement. The main gear are located forward of the centre of gravity, causing the tail to require support from a third wheel assembly. -Have two main wheel assemblies, one on each side of the aircraft and a tail wheel

ADVANTTAGES-Reduced drag due to its smaller size.
-Reduced landing gear weight

DISADVANTAGES-Loss of forward visibility for the pilot when maneuvering on the ground due to the aircraft nose-high attitude.

3.3. TriCycle Configuration

The most commonly used landing gear arrangement is the tricycle-type landing gear.

 It is comprised of main gear under the wings and a nose gear. Is characterized by having a nose wheel assembly and two main gear assemblies, one on each side of the aircraft.
-This arrangement places the aircraft fuselage in a level attitude when the aircraft is on the ground

ADVANTAGES-Pilot has a good forward visibility.
-Cabin area is level, making it easier for passengers to move inside the aircraft on ground.
-Makes the aircraft stable during ground operations and easy to control (allows more forceful application of brake for higher landing speed, preventing ground looping)

DISADVANTAGES

The nose gear of a few aircraft with tricycle-type landing gear is not controllable. It simply casters as steering is accomplished with differential braking during taxi.

3.4. Tandem Configuration

Few aircraft are designed with tandem landing gear. As the name implies, this type of landing gear has the main gear and tail gear aligned on the longitudinal axis of the aircraft.

4. LANDING GEAR DESIGN

• 1.      Fixed Landing Gears are designed and fixed permanently and extended throughout the flight. Mostly used for smaller and lighter aircrafts.
• 2.      Retractable-Gears fold into the aircraft structure during flight to reduce drag and extend out during landing. It is common in high speed aircrafts.

4.1. Key Considerations

·         Strength and Stability:

The landing gear must withstand the weight of the aircraft, including during taxiing, takeoff, and landing, as well as side loads. 

·         Ground Clearance:

Sufficient clearance between the landing gear and the ground is crucial to prevent damage to the aircraft or runway. 

·         Energy Absorption:

Landing gear systems are designed to absorb the energy of impact during landing, protecting the aircraft and its occupants. 

·         Retraction and Kinematics:

For retractable landing gear, the design must ensure smooth and reliable retraction and extension. 

·         Tire and Wheel Selection:

The type, size, and spacing of tires and wheels are critical for ground stability and performance. 

·         Braking Systems:

Effective braking systems are essential for controlling the aircraft on the ground. 

·         Steering:

Some landing gear systems include steering capabilities for maneuvering the aircraft on the ground. 

·         Regulatory Compliance:

Landing gear designs must meet stringent airworthiness regulations and safety standards. 

·         Operational Requirements:

The design must consider the specific operational requirements of the aircraft, such as the type of runways it will land on and the types of maneuvers it will perform. 

·         Material Selection:

The choice of materials for the landing gear must consider strength, weight, and resistance to wear and tear. 

·         Weight Reduction:

Engineers constantly strive to reduce the weight of landing gear systems without compromising performance or safety. 

4.2. overview

Landing gear design involves ensuring structural integrity, stability, and energy absorption during ground operations, considering factors like aircraft weight, landing surface conditions, and regulatory requirements. 

5. LANDING GEAR CONSTRUCTION

The tricycle arrangements of landing gear is made up of many assemblies:-

                -Oleo shock struts – Shock absorbers absorb and dissipate landing impact energy. They typically use oleo-pneumatic which is oil and air to absorb landing energy.
                -support units-Hydraulic or Electric actuators and linkages to allow gears raised or lowering.
                -Gear retraction and safety devices.
                -Auxiliary protective devices
                -Nose wheel steering system.-Alows pilot to steer the aircraft on the ground
                -Aircraft wheel assembly-Wheels and tires designed to withstand high loads and speeds. Tires are inflated with nitrogen for stability
                -Brake assemblies.-Used to slow down or stop the aircraft on the ground can be electrically or hydraulically operated.

5.1. Construction