Landing Gear

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How the Landing Gear Works

Main landing gear of an Airbus A340

For aircraft, the landing gear supports the aircraft when it is not flying, allowing it to take off, land and usually to taxi without damage. Wheels are typically used but skids, skis, floats or a combination of these and other elements can be deployed depending both on the surface and on whether the aircraft only operates vertically (VTOL) or is able to taxi along the surface. Faster aircraft usually have retractable undercarriage, which folds away during flight to reduce air resistance or drag.

Main landing gear of an Airbus A380, it has 20 wheels plus 2 in front

Main landing gear of an Airbus A380

Wheeled undercarriages normally come in two types: conventional or “taildragger” undercarriage, where there are two main wheels towards the front of the aircraft and a single, much smaller, wheel or skid at the rear; or tricycle undercarriage where there are two main wheels (or wheel assemblies) under the wings and a third smaller wheel in the nose.

Conventional Landing Gear, Taildragger

The taildragger arrangement was common during the early propeller era, as it allows more room for propeller clearance. Most modern aircraft have tricycle undercarriages. Taildraggers are considered harder to land and take off (because the arrangement is usually unstable, that is, a small deviation from straight-line travel will tend to increase rather than correct itself), and usually require special pilot training. Sometimes a small tail wheel or skid is added to aircraft with tricycle undercarriage, in case of tail strikes during take-off. The Concorde, for instance, had a retractable tail “bumper” wheel, as delta winged aircraft need a high angle when taking off. The Boeing 727 also has a retractable tail bumper. Some aircraft with retractable conventional landing gear have a fixed tailwheel, which generates minimal drag (since most of the airflow past the tailwheel has been blanketed by the fuselage) and even improves yaw stability in some cases.
Another arrangement sometimes used is central main and nose gear with outriggers on the wings. This may be done where there is no convenient location on either side to attach the main undercarriage or to store it when retracted.

Earlier Bleriot XI didn´t have a wheel in the rear

The DC-3 is a good example of conventional landing gear

Tricycle landing gear

Tricycle gear is essentially the reverse of conventional landing gear or taildragger. On the ground, tricycle aircraft have a visibility advantage for the pilot as the nose of the aircraft is level, whereas the high nose of the taildragger can block the view ahead. Tricycle gear aircraft are much less liable to ‘nose over’ as can happen if a taildragger hits a bump or has the brakes heavily applied. In a nose-over, the aircraft’s tail rises and the propeller strikes the ground, causing damage. The tricycle layout reduces the possibility of a ground loop, because the main gear lies behind the center of mass. However, tricycle aircraft can be susceptible to wheel-barrowing. The nosewheel equipped aircraft also is easier to handle on the ground in high winds due to its wing negative angle of attack. Student pilots are able to safely master nosewheel equipped aircraft more quickly

Tricycle landing gear type in a Boeing 777

To decrease drag in flight some undercarriages retract into the wings and/or fuselage with wheels flush against the surface or concealed behind doors; this is called retractable gear. If the wheels rest protruding and partially exposed to the air stream after being retracted, the system is called semi-retractable.
Most retraction systems are hydraulically operated, though some are electrically operated or even manually operated. This adds weight and complexity to the design. In retractable gear systems, the compartment where the wheels are stowed are called wheel wells, which may also diminish valuable cargo or fuel space.

Pilots confirming that their landing gear is down and locked refer to “three green” or “three in the green.”, a reference to the electrical indicator lights from the nosewheel and the two main gears. Red lights indicate the gear is in the up-locked position; amber lights indicate that the landing gear is in transit (neither down and locked nor fully retracted).
Multiple redundancies are usually provided to prevent a single failure from failing the entire landing gear extension process. Whether electrically or hydraulically operated, the landing gear can usually be powered from multiple sources. In case the power system fails, an emergency extension system is always available. This may take the form of a manually operated crank or pump, or a mechanical free-fall mechanism which disengages the uplocks and allows the landing gear to fall due to gravity. Some high-performance aircraft may even feature a pressurized-nitrogen back-up system.

Nose wheel of an Airbus A320

Main landing gear of an Airbus A320

Schematic diagram of hydraulic landing gear

Main landing gear of an Embraer Legacy 600

Brake lines in an Embraer Legacy 600

View from the interior of the wheel compartment in a Boeing 737, you can see the hydraulic systems.

Landing gear of a Boeing 777

Main landing gear of a Boeing 787 Dreamliner

Ikarus C42b with skis instaled.

Tandem landing gear

Yhe ones with multiple tires behind each other and are used in very large airplanes like the Antonov An-225 Mryia, it has 7 pairs of wheels in each side of the aircraft and 2 front landing gears with 2 wheels each.

Main landing gear of an Antonov AN-225 Mryia

Main landing gear of a C5A Galaxy

C-17 Landing gear in action

Main landing gear of an Ilyushin I1

Nose landing gear of the Concorde

Beautiful close up of the nose landing gear of the Concorde.

Picture: Anne H

The Concorde was equipped with an extra tail wheel to prevent tail strikes in landings an take offs.

The main landing gear must be designed to load extremely heavy weights.

This MD-11 took out the runway and broke the conventional tarmac.

Multiple brake system used in the MD-80, the main landing gear weights 858 kg, plus two brake systems 219 kg each, plus two wheels 152 kg each, and the total weight of the landing gear is 1600 kg each main landing gear in a MD-80.

Brake system used in the main landing gear of a Boeing 777

Beautiful landing in slow motion

Landing Gear Retraction Sequence

Procedure for remove and install the wheels and brakes in an Airbus A320.

The brake system has sensors to monitor the temperature during landing and they are cooled with a fan mounted under the cover.

Electric taxiing – Safran & Honeywell EGTS

EGTS is an electric taxiing system incorporated in the main landing gear. There is an electric motor in each main landing gear and is driven by the power generated by the APU, allowing the airplane to taxi with the main engines off, saving fuel and protecting for damage by little rocks entering the turbofan.

The installation procedure of the EGTS system in an Airbus A320

Slow motion video of a Boeing 777-200ER landing.

Lockheed C-5 Galaxy landing

Main landing gear in a  Boeing 787 Dreamliner

Embraer 175 nose landing gear

Rare system in C5 Galaxy

Testing the main landing gear in an Airbus A380.

Autor: Daremen

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