Have you ever seen an airplane going backwards on the runway? You may have seen cars going backward, but airplanes only moving forward in the sky and on the ground. You may think, if cars can do it, why not for airplanes? But still, it is not easy to imagine a large and heavy airplane to reverse. The Incheon Airport will satisfy your curiosity about whether an airplane can go backwards!
Impossible in the Sky! How About on the Ground?
We will give you the answer right away! First, airplanes can’t go backwards in the sky. It’s easy when you understand the principle of the airplane. Airplanes can fly due to a lift, a force generated when its wings move through the air. The lift originates from the momentum of an airplane that goes forward, in other words, airplanes can’t go backwards in the air.
But some airplanes can move backwards on the ground! It is different though from how cars drive backwards, the way we are well aware of.
Cars go backwards by delivering the power of the engine to the wheels. When the driver shifts into reverse, one serrated wheel is added in the course of delivering the power, which changes the direction of rotation contrary to that of the movement forward.
However, the wheels of an airplane don’t receive any power, unlike those of a car. An airplane can go backwards by generating the momentum in the opposite direction. Almost all airplanes have the device to reverse the direction of momentum of their engine—going backwards by shifting the direction of exhaust fumes. This method, however, is rarely used. Why?
No Reverse Thrust on the Runway!
It is because going backwards that way is extremely dangerous on the runway! It differs by model, but generally airplanes weigh hundreds of tons, and if such heavy airplanes generate reverse momentum, its engine and the airframe can be extremely burdened. It can even blow up an object nearby on the runway. In other words, regardless of its feasibility, reverse thrust is not used because it can lead to a secondary damage.
Thus, reverse thrust on the apron or aircraft stand is banned by the Aviation Act. Then, why are airplanes equipped with the thrust reverser if the reverse thrust is banned by the law? In fact, the thrust reverser is used like a brake of a car. It is used to reduce the speed of the airplane when it is landing. When it is used this way, using the reverse thrust is legally allowed.
Towing Car, a Small Giant in the Airport
For those who take an airplane often might not get it because from time to time, airplanes do go backwards after boarding. In fact, this is done by a towing car carrying the airplane. A towing car is a car that tows the airplane on the runway. In order to prevent the damage that can be caused by the reverse thrust of an airplane, towing cars are used to carry airplanes backwards on the runway.
For reference, an airplane is 15 times heavier than a towing car. The secret of the Herculean strength of a towing car lies in its engine. A towing car has an engine displacement of 10,000 cc, 5 times greater than that of an ordinary vehicle. Its gear can be shifted up to four forward and three backward (a total of seven), which enables it to carry the airplane around with enormous power.
Now, is your curiosity of an airplane going backwards satisfied? To summarize, airplanes can’t go backwards in the sky and can on the ground. For the sake of safety, airplanes don’t use its own device to go backwards on the runway but instead, it is carried by a towing car. If you see an airplane going backwards one day in the Incheon Airport, try to look for a towing car below it!