A Definitive Guide to Landing Gear
Supporting enormous weight and landing forces, landing gear is an incredible piece of aircraft engineering. Though they are critical aircraft components, most people do not understand their complexity. Not only do they account for roughly 7% of the maximum takeoff weight, but they also prevent the fuselage from abruptly hitting the ground.
The absorption of the landing force happens in a number of ways. First, the main landing gear strut is equipped with a shock absorption system that functions through the use of compressible fluids. Second, the landing force is distributed over the wheels, allowing the aircraft to move forward and land with ease.
When it comes to landing, the landing gear absorbs large impact loads and prevents them from reaching the airframe. However, it is the struts that absorb the shock and lessen bounce after a sharp touchdown. Finally, wheel brakes are used to shorten landing runs, abort takeoffs, control speed, and most importantly, serve as a parking brake on the ground.
Within small- and medium-sized aircraft, you can find two-wheel landing gear which consists of four wheels on each side of the aircraft with a 2-2 configuration. Meanwhile, a larger aircraft like the Boeing 777 is recognized for adding a third wheel to this configuration. In fact, most heavier aircraft will add an additional landing gear assembly in the center of the fuselage.
If you watch an aircraft take off, you will notice that the landing gear retracts as soon as it leaves the runway. As the landing gear structure is heavy and serves as a significant source of drag, raising it quickly is important so that the aircraft can gain speed. Typically, pilots will do this when a positive rate of climb is achieved. Prior to this, the gear should remain down in case the aircraft needs to carry out an unprecedented landing.
The landing gear is retracted into a compartment in the fuselage. For instance, some aircraft have doors that close over the gear that protects the gear structure and ensures the aerodynamic quality of aircraft. Others, like the 737, will retract into a cavity just below the aircraft belly.
During landing, the gear is lowered when the airspeed reaches a designated level. As lowering it too early can damage the gear, lowering is controlled by the same dual computer system. This procedure is further supported by a backup system in case the hydraulic systems fail. In older aircraft, the gear must be lowered manually.
Ensuring that landing gear is lowered correctly and locked prior to landing is critical. Today, this is indicated by a computer unit using lights in the cockpit. Furthermore, aircraft are typically designed with a secondary, independent system indicating this as well.
Despite technological advancements in the aviation realm, emergency incidents involving landing gear are not impossible. As they have many moving parts and hydraulic systems working in conjunction, a risk still remains. With landing gear extending anywhere between 8 and 15 kilometers before the runway, with the actual distance being determined by the specific aircraft model, what happens when the landing gear does not extend properly?
In the case that the landing gear fails, the gravity drop emergency extension system can be employed. This system consists of a red lever in the cockpit that the pilot needs to extend and turn. As soon as this happens, the landing gear should drop from the bay and lock into place, ensuring that landing can proceed as normal.
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