3 Ways Airplanes Brake After Landing
A typical airliner, say the 777, lands at a speed of around 260km/h. With some simple calculations, we see that the kinetic energy of the plane is extremely large:
K = ½mv² = ½(190000kg)(72m/s)² = 492.5MJ of energy
Using solely wheel braking is far from enough to dissipate all the kinetic energy an airliner holds during landing. Let’s take a look at the other two braking systems in detail!
Disc Brakes
Disc brakes are in the gears of the aircraft. Disc braking is the most traditional braking system, similar to the braking system found in most cars. Disc brakes consists of a pair of static calipers that squeeze pads against a rotating disc, which is attached to the landing gear. Note that braking too hard with disc brakes may cause smoke or fire, and due to wearing, disc brakes have to be replaced every 1,000 flight cycles.
During wet and icy conditions, disc brakes become no longer functional due to the high probability of aquaplaning. Thus, the aircraft has to rely on spoilers and reverse thrust until the plane slows down to a relatively low speed when disc brakes can finally be used.
Spoilers
“Oh no! The wing just opened up!”
Nope, these are flaps designed to open up upon landing, and they’re called spoilers. Essentially, spoilers open upwards to increase drag, which is effective for bringing the plane quickly to a relatively low speed. However, as drag only has a large effect on the plane when it’s traveling fast, using only spoilers is not enough to bring the plane to a full stop.
Note that spoilers do not function the same as ailerons or flaps: flaps extend downward, and even though it does somewhat slow the aircraft, its main function is to generate extra lift; and ailerons are located at the end of the wings, primarily used to roll the aircraft to one side.
Spoilers are similar to flaps in the way that if the left spoilers are armed, the right spoilers are armed as well, unlike ailerons. (Some planes may use ailerons instead of flaps by opening both ailerons in the same direction).
Reverse Thrust
There are quite a few different types of reverse thrusters, but the concept is the same: to redirect airflow forward.
The A330s and A340s use the clamshell door design; more modern engines use the cold stream design, such as the 777, 787, and the A350. Although they’re a rare sight nowadays, the 737–100/200 and many jets with rear-mounted engines use the bucket reverser design. No matter the design, they all get the job done with the same concept.
