Ever wondered how these big birds come to a stop? Flying at such speeds, braking is not as easy as it seems when you’re seated in the cabin. There is a whole lot of work going on, simplified by levers.
Airplanes are one of the most vital innovations ever. The Wright brothers, in 1905, completed the first successful sustained power flights. Before then, the secret to sustained flights were shared only by the birds of the sky. Over 100 years on and airplanes have revolutionised the world we live in; from the development of the jet aircraft in 1939 – 1943 to the invention of the Boeing 707, Boeing 747 and even the now discontinued-Supersonic airlines (e.g Concorde). Now, the Airbus A380 is the largest passenger airline. It is 50% quieter on takeoff than the Boeing 747-400 and has 40% more cabin size than the Boeing 747-8.
“The lack of engine noise—it’s 50% quieter than a 747-400 on takeoff—was downright eerie. The A380 is so big it’s difficult to sense its speed, and its upper deck is so far away from the engines the noise dissipates” – Time magazine
With speeds up to 900km/hr, braking these large monsters is not an easy task. To reduce the runway required, efficient braking techniques are used in tandem. Seating and relaxing in the plane and touching down safely is one of the greatest reliefs of life, but what really goes down there is pure genius of science.
The operation explained here are mainly with reference to jet aircrafts. Propeller-driven aircrafts have several slight variations. A landing roll consists of touchdown, bringing the aircraft to taxi speed, and eventually to a complete stop. Brakes depend on having weight on the wheels to work efficiently. For this, the top of the wings have control plates called spoilers, which are opened and extended. For small aircrafts, the brakes alone can slow down the craft, but larger aircrafts need the brakes to do less work. To further reduce the stress on the brakes and for even more reliable stopping especially in snowy or rainy conditions, or in cases where the runway is small, reverse thrust is employed. In a nutshell, effective braking of most commercial jet planes involves two or three (in most cases) of these steps:
.Using spoilers on wings to add weight to the brakes
.Reverse thrusting to further reduce the speed
. Applying the brakes to completely halt the aircraft
Spoilers (falsely called air-brakes) are located on the wings of the planes. This is why the wings ‘open’ during landing. Spoilers (also called lift-dumpers) act to “spoil” the lift and provide drag by directing airflow up, using Newton’s First Law. The airflow directed up and the air hitting the spoiler head-on will push the plane down and backwards. In essence, the spoilers act to decrease altitude, decrease lift and reduce speed by improving drag.
Reverse thrust is very helpful in stopping the airplane when the runway is slick or when conditions demand quicker landing. Normally, the brakes and spoilers have plenty of stopping ability. For bigger aircrafts (with weights exceeding over 5600 kg) and/or for more reliable landing, reverse thrusts are employed. The forward thrust of the aircraft is diverted in a direction opposite to that of the travel. The thrust levers are located in the cockpit and are pushed all the way backwards immediately after touchdown to drastically reduce speed. The exhaust of the engine is deflected by doors to create a temporary force in the forward direction and cause deceleration thereby reducing stress on the brakes and reducing landing distance. When the speed has been reduced, the thrust lever is pushed forward to its idle position to prevent debris from being ingested into the engine causing damage.
The brakes are located on the wheels under the wings; the system is conceptually similar to that on cars – disc brakes and hydraulic pressure slowing the vehicle down. These aircraft brakes consist of stators and a multiple rotors. The stators are attached to the hub of the brake and do not rotate. The rotors are disc wheels attached to the inside diameter of the wheels and rotate with it. When the brake pressure is applied, small hydraulic actuators compress the stack of rotors and stators against each other. Over the years, carbon and it’s composites have replaced steel rotors. These handle high temperatures better, as they wear by application, rather than by pressure or heat. Use of carbon brakes also considerably reduce the total aircraft weight as they provide a weight-saving of 5,443 kg to steel brakes. The brake pedals are in the cockpit and the pilot depresses them to operate the brakes.
So next time you are seating down, strapped up tightly, and land successfully after a long journey up in the skies, take a moment to realise this amazing process where one mistake can be so costly.
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