A Look at Landing Gear Mechanism of Aircraft
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A Look at Landing Gear Mechanism of Aircraft

No aircraft can be complete without a landing gear system. Thus studying a landing gear gear of an aircraft is of great importance

Ever since the Wright brothers launched the first manned flight, the air plane has developed by leaps and bounds. Over the last 100+ years the aircraft has reached levels of sophistication that are hard to imagine just a few decades back.

The aircraft is a heavier than air machine and making it land and take off from a surface is of paramount importance. This is facilitated by what is termed a Landing Gear mechanism. The word gear can sometimes be a misnomer, but it refers to the Landing apparatus in its entirety and involves no gears.

The landing gear of a modern aircraft is a complex piece of engineering and is part of the aircraft design. It is something worked out on the design table itself and integrated with the other systems of the aircraft. It is peculiar to each class and model of aircraft. There can be no generalizations.

The landing gear in most aircraft consists of a tricycle configuration. This has a landing wheel that retracts into the nose (forward fuselage) of the aircraft and a set of two wheels that normally retract into the wings of the aircraft. All landing gears have a brake assembly and anti skid mechanism, which are centered on rubberized tires or wheels. Generally all landing gear systems retract into the aircraft body, except in the case of very small aircraft like the Cessna or the earlier Tiger Moth. The retraction into the body is basically to cut down on air resistance and affects the drag coefficient. The National advisory Committee for Aeronautics (NACA) by testing in a wind tunnel in 1927 came to the conclusion that the aircraft landing gear made a significant contribution to the drag of an airplane. The retractable landing gears thus became a priority.

However earlier aircraft had what is known as the conventional landing gear which consisted of two wheels forward of the aircraft’s centre of gravity and a third wheel at the aircrafts tail. This type of landing gear does not help when brakes are applied and the aircraft tends to pitch forward. There is another type of landing gear referred to as tandem landing gear and is used for very heavy aircraft like the B-52 bomber. In this the main landing gear is in two sets that are located one behind the other on the fuselage. It makes use of flexible wings and may need small wheels at the tip of the wings to avoid them touching the ground.

Modern aircraft design incorporates the Landing gear system with the aircraft. This is an entire process of engineering and parameters like weights, runaway design, structures and economics come into play. This is referred to as Multi Disciplinary Optimization (MDO). Landing gear is a part of MDO and incorporates flight mechanics, stability, control and performance. The center of Gravity (cg) of the aircraft assumes great importance in the design of a landing gear. Correctly gauging the cg of the aircraft is thus a vital parameter. The operation of the landing gears is hydraulic, but smaller aircraft landing gear may be operated electronically.

An aircraft approaching an airfield for landing at about 240km /hour, great heat is generated when the wheels come in contact with the runaway surface; hence all the wheels have a thermal protection system incorporated in the landing gear tires. This consists of high temperature resistant thermal tiles that absorb the heat generated when the wheels come in contact with the runaway. It should be noted that the pilot will only open the landing gear system when nearing an airfield at speeds of 300km/hr or less and an altitude of 100 meters.

One of the essentials of modern aircraft is the need to have the landing gear mechanism integrated with the aircraft design. This is a part of Avionics, which allows an aircraft system to transfer analog or digital data with the help of a wireless, data line or any other medium. Aircraft systems components and connectors will also form part of this module. This is often referred to as Flight Management System (FMS). The FMS is very versatile and outputs for automatic control of the aircraft right from take off to the final approach and landing are provided. This data is displayed through electronic flight instruments as well as aircraft monitoring and navigation systems. The undercarriage and the landing gear mechanism form part of this FMS. Avionics refers to all electronic and electromechanical systems and subsystems installed in an aircraft. It is essential for the safety of the aircraft and flight crew.

The key part of any FMS element is a Flight Management computer and a display unit. The entire information is displayed through a system of data buses. Data buses facilitate interchange of data with digital and other computerized systems and instruments. Information about the landing gear is provided through the Flight Management System which incorporates The LGCIU( Landing Gear Control Info unit) which controls the operation of the landing gear including retraction.

The Landing gear mechanism which incorporates advanced electronics and computer science is thus one of the more important parts of an aircraft system and requires detailed study and knowledge

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Comments (1)

why do we have tricycle configuration of wheels why not some other mechanism or configuration???