Retractable Landing Gear Explained


Airplanes need a reliable shock absorption method while landing, particularly on rough or uneven terrain. Aircraft landing gear provides needed structural support to the aircraft during landing, takeoff, or taxiing. Conventional landing gears are of two types: fixed and retractable. While fixed landing gear is low maintenance and easy to use, retractable landing gear bolsters efficiency because it reduces aircraft drag while increasing cruising speeds. Retractable gear systems can be operated electrically, hydraulically, manually, or through a hybrid combination of electric and hydraulic systems. However, managing retractable gear systems requires adherence to a standard set of instructions, which will be explained in this blog.

The Origins of Retractable Landing Gear

Landing gear applied to early aircraft was not particularly complex in design. In 1903, the Wright brothers attached a sled to the undercarriage of their vehicle as rudimentary landing gear that could support nearly 220 kg of weight. Then, in 1906, the Santos Dumont 14-bis sported small wheels as a precursor to modern fixed landing gear. Later in the 1920s, reducing in-flight drag experienced by airborne aircraft became a crucial consideration for designers to improve fuel and speed efficiency, as well as overall control and maneuverability. However, very little understanding of aircraft drag prompted the need for advanced research. This is why the Propeller Research Tunnel was set up in 1917 by the National Advisory Committee for Aeronautics at Langley Memorial Laboratory in Virginia. It was a giant wind tunnel used to accommodate aircraft fuselages for closer inspection of their aerodynamic performance. This is where research for improving the design and functionality of retractable landing gear was undertaken, particularly in terms of tire friction, tire mechanics, and cornering forces to develop the modern retractable gear design.

How They Work

Retractable landing gear is a hallmark of high-performance aircraft, and it can be stowed or retracted from the fuselage by a combined movement of associated gears and levers which are powered hydraulically. Furthermore, warning systems within the cockpit indicate when landing gear is fully retracted and locked in place or when it is stowed in the fuselage. Retractable landing gear systems have compartments that open to allow the extension of wheels which consecutively close after their retraction. Moreover, variations in gear door systems are also available according to different aircraft applications.

Types of Retractable Landing Gear

Although retractable landing systems were initially used for amphibious aircraft to aid landing on both water and land, they were later redesigned for employment in civil and military aircraft. Today, three main categories of retractable landing gear are used which are described below:

  • Manual

These include manually driven mechanical systems such as hand pumps or hand cranks operating on independent hydraulic systems. Since manually retractable landing gears are one of the simplest gear retraction systems, they are found only in smaller airplanes such as Mooneys and Culver Cadets. However, reliability and simplicity are the two most significant advantages that make the manual gear retraction system relevant. Where the Mooney uses a Johnson bar for its gear retraction, the Culver Cadets use a jackscrew and rotating hand crank in its manual backup system.

  • Hydraulic

Hydraulic landing gear systems use pressurized hydraulic fluid generated by either an electrical or engine-driven pump to activate specific linkages for raising and lowering landing gear. These parts work by applying hydraulic pressure to struts which function to release locks and move applicable actuators into their retracted position. When landing gear is initiated from the cockpit, corresponding valves open to release pressurized hydraulic fluid into hydraulic cylinders, providing enough force to lower gears. Hydraulic retraction gear is designed to function only within a specific range, where excessive hydraulic pressure is redirected to the reservoir.

  • Electric

An electric, retractable landing system uses an electrically driven motor to activate landing gear from within the cockpit. This motor is attached to a jackscrew or transmission, alongside additional components which make up the gears. However, such landing gear can only be supported by lightweight aircraft since they rely on an electrically-driven jack for raising or lowering gear. When actuated, the landing gear retracts and positions itself below the fuselage through the combined efforts of accompanying components.

Wrapping Up

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