• What is landing gear and what is it for?

    A whole lot more than just wheels

Aeroplanes spend most of the time in air but when they are on ground, they need a system to absorb both the force of landing and their own weight and that’s what a landing gear is for.

By definition, the landing gear is the part of the aeroplane designed to absorb kinetic energy originated during contact with the runway, be it on landing or take off.

As you can imagine, a landing gear is an essential part of an aeroplane; but even so, it is much more complex than you probably think. This is why, in today’s post, we tell you all about this topic: what landing gear is, the parts which make it up, different types and much more! Read on!


Undercarriage or landing gear – Are they the same?

Basically, in aircraft, undercarriage is the British English term while landing gear is the lexical item used in American English.

We can also say that landing gear is the undercarriage of an aircraft, as it also refers to the section of a vehicle that is underneath the main part.

For vehicles, it contains the chassis, for aircraft, the landing gear and lowest parts of the fuselage.

Origins of landing gear

In the first years of aviation, aeronautical pioneers faced a problem: designing a structure that would support the weight of an aeroplane on ground.

As incredible as it may seem, the first designs relied on human strength for this task, that is, it was the actual pilot who would, by means of his legs, be in charge of starting the take-off run as well as braking when landing.

In 1903, the Wright brothers equipped their aeroplane, the Flyer I, with skis so that the plane would slide on the ground. These were the precursors of landing gear in aeroplanes.

Only shortly afterwards, in 1906, the Santos Dumont brothers equipped their 14-bis with small wheels; however, these lacked any shock absorbers and landings were rather abrupt.

With the Dayton Wright RB-1, in 1920, the first retractable landing gear emerged, and it was activated manually by pilots, by means of a crank. From this moment on, technological progress and development have transformed the first systems into the landing gear we now know.

Types of landing gear

Fundamentally, there are two types of landing gear: fixed and retractable, however, within the first classification, there are various other types. Let’s first look at all the different types that exist.

Fixed landing gear

Those which are always visible are fixed landing gear. They are typically used in smaller and lighter aeroplanes with the objective of avoiding being overweight with heavier and more complex systems which would only have a low performance in terms of speed and fuel consumption.

In addition, there is another classification for fixed type landing gears: with or without fairing. The fairing is a covering that is placed around the wheels, improving their aerodynamics and allowing them to reach higher speeds with lower fuel consumption.

Retractable landing gear

Those which are not visible, or are hidden structurally inside the fuselage of the aeroplane and are activated by the pilot when needed. Commercial aeroplanes or those used in the last part of pilots’ training, have retractable landing gear.

Where is landing gear located?

Depending on the layout of landing gear, we can distinguish between conventional and tricycle landing gear.

Conventional landing gear

This was the first system used because of wing and engine layout; it was the configuration that was best suited to the centre of gravity of the first aircraft. The conventional landing gear is made up of two posts beneath the wings or roughly at the same height of wings, and a wheel at the tail.

Although they have the advantage of being aerodynamically good, in the case of fixed and sturdy retractable landing gear, conventional landing gear has various disadvantages, such as having low visibility on ground, sustentation power on take-off due to the leaning position of the aircraft, or difficulty landing when there’s turbulence or crosswind.

Tricycle landing gear

This type of landing gear consists of two posts which are situated beneath the wings of the aeroplane or fuselage and another post under the nose which also has a directional device.

The tricycle landing gear makes landing much simpler, even if there’s crosswind or tailwind. It also eliminates the danger of flipping over, allowing touch down in a horizontal position.

Parts of the landing gear

A landing gear is composed of numerous parts that allow the whole to function correctly and fulfil all the different functions it’s designed for. Its main parts are:

  • Aeroplane tail skid: this is the back wheel in conventional landing gear.
  • Nose wheel: it’s the main wheel in tricycle undercarriage and includes a shock absorbing system that is adequate to the weight and power of the aeroplane.
  • Brake system: it is included and fundamental in all types of landing gear.
  • Retractable systems: these are the gates that guard retractable landing gear and are activated from the cockpit, by a hydraulic mechanism.

The wheel of the nose, furthermore, is one of the most important parts. Various components make it up and each of them fulfils a very specific function:

  • The hydraulic cylinder works as a shock absorber.
  • The tork link is similar to a pair of scissors and keeps the nose and wheels aligned while the hydraulic cylinder expands and contracts.
  • Anti-shimmy is a mechanism which reduces lateral movement of the wheel during take-off and landing.

Aircraft tyres are the hardiest part of a landing gear

The wheel is the most basic part of the landing gear. Although they aren’t the be all end all, they make contact with the ground first and are therefore very important.

Tyres, such as the ones used for cars, are made of rubber. Despite looking quite similar they are really very, very different. Let’s look at them in detail.

  • In cars we use air to keep the pressure whilst in aviation nitrogen is used. It is a very stable inert gas that minimises the risk of explosion and also works as a temperature compensator.
  • In cars, tyres use a pressure of 2.5 bars, aircraft, on the other hand use 15 bars, or six times as much!
  • The useful life of the covers or tyres of an aeroplane is very limited: 400 landings in winter and 300 in summer. This is due to the high temperatures reached: they heat up to over 100 degrees in less than 3 seconds.
  • The price of each tyre is €1,000 and they usually do not belong to airlines but are hired for a set number of landings.

Did you know that the landing gears of some of the largest commercial aircraft, such as the Airbus A380 or the Boeing B777-X, have up to 10 pairs of wheels? Impressive!

Why is there smoke on landings?

If you’ve ever been to an airport to see planes land you’ll have seen that sometimes white smoke comes out of the wheels.

During landing, the rubber on the tyres melts due to the high temperatures reached when coming into contact with the runway, leaving a thin layer adhered to the tarmac. The white smoke we see is the result of the fusion of the rubber and asphalt.

To get rid of it, airports have trucks especially for this that periodically eliminate the remaining rubber left on the runways.

This task is fundamental for operational safety as, if rubber is left and it expands, it can reduce the breaking capacity of aeroplanes.

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