How Do Planes Stop on Landing?

Aviation Informative clam shell, Flaps, manual braking, retard, spoilers, taxi speed, thrust reversal, turbulence 3 years ago

” 50..40..30….10…RETAAAAAARD” !!!

Sounds familiar? Not unless you’re a pilot/ have been in the cockpit right before the tires hit the runway and BOOM!. A few seconds later, the aircraft comes to a screeching halt, and off comes the seatbelts!

Ever wondered how or what it takes to bring a gigantic machine to 0 KMPH from cruising speed? Well, here we have the beauty of science at play and it is generally either one or mostly a combination of the four mentioned below.

FLAP SEQUENCING

The first one is the sequence of flaps. This helps the aircraft to decelerate, thus reducing the speed before touchdown. Pilots can extend the flaps to any configuration to meet the demand for deceleration. The lower percentage of the flaps helps to give the plane a lift but as a certain percentage is crossed (normally 30%), the drag starts to prevail over lift, causing the airplane to slow.

SPOILERS

Spoilers are small, hinged plates on the top portion of wings. They can be used to slow an aircraft or to make the aircraft descend if they are deployed on both wings. Spoilers can also be used to generate a rolling motion for an aircraft if they are deployed on only one wing.

Most common spoiler functions include disrupting some type of airflow passing over and around a moving vehicle (in this case, an aircraft wing). A common spoiler diffuses air by increasing amounts of turbulence flowing over the shape, “spoiling” the laminar flow and providing a cushion for the laminar boundary layer.

In-flight, they effectively increase the aircraft’s rate-of-descent without causing an accompanying increase in airspeed. Once the main landing gear is firmly on the runway, the pilot deploys the spoilers to their fully extended position, creating the maximum amount of drag to slow the aircraft from its touchdown speed of approximately 120-to-140 MPH to a more proper braking speed of 60-80 MPH. Once the aircraft has decelerated to taxi speed, spoilers are stowed.

THRUST REVERSAL

Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine’s thrust for it to act against the forward travel of the aircraft, providing deceleration.

Many high by-pass ratio engines reverse thrust by changing the direction of the fan airflow. Since a majority of the thrust is derived from the fan, it is unnecessary to reverse the exhaust gas flow. Propeller-powered aircraft reverse action by changing the pitch of the propeller blades.

There are three common types of thrust reversing systems used on jet engines: the target, clam-shell, and cold stream systems.

MANUAL BRAKING

Aircraft brakes stop a moving aircraft by converting its kinetic energy to heat energy using friction between rotating and stationary discs located in brake assemblies in the wheels. Brakes provide this critical stopping function during landings to enable airplanes to stop within the length of the runway.