If you look at commercial jets — as well as many privately owned airplanes — you’ll probably notice that most have sweptback wings. In other words, their wings don’t extend straight out from the sides. Instead, they angle backwards to form a V shape.
In swept wing technology the airplane wings are swept back at an approximate angle of 35 degrees. This angle varies as a result of an increase in wing length.
Generally speaking, the faster an airplane is intended to fly, the greater the angle of its wing sweep. So, what’s the purpose of swept wings, and is it really necessary for commercial airplanes?
The main reason airplanes have swept wings is to reduce turbulence. During the flight, airplanes encounter turbulence from the friction created as air runs across the plane’s wings. The speed at which an airplane flies will affect the amount of turbulence it encounters.
At faster speeds, airplanes encounter more turbulence due to the increased friction of the air running across their wings. In some cases, the air can travel faster than the speed of sound, resulting in heavy turbulence that’s not only a nuisance for passengers but also a danger to the aircraft’s structural integrity.
Swept wings, however, are designed to reduce turbulence by slowing down the air as it moves across the surface of the wings. As previously mentioned, swept wings are longer than straight wings. Therefore, air moves more slowly across them, which reduces the amount of turbulence the airplane encounters.
On a straight-wing airplane, all of the airflow over the wing travels parallel to the aircraft’s chord line. But, on a swept wing, only some of the air flows parallel to the chord line. The other part flows perpendicular to the chord – this is called spanwise flow.
Airliners, like all airplanes, fly because of the greater air pressure on the bottom side of the wings than on the top side. Air moves more smoothly on the top side of the wings than on the bottom. But when airliners move faster and faster, the airspeed that moves over the top side of the can wing exceeds the speed of sound. This results in the vibration in the plane body because of the resulting shock waves.
When an aircraft approaches the speed of sound, the airflow over the wing reaches supersonic speed before the airplane itself does, and a shock wave forms on the wing. The airflow behind the shock wave breaks up into a turbulent wake, increasing drag. The idea of swept-back wings was tested on high-speed supersonic planes.
Supersonic and subsonic refer to speeds faster or slower than the speed of sound. Anything going faster than the speed of sound, which is 343.2 m/s (1,126 ft/s), is travelling at supersonic speeds. Anything going slower than the speed of sound is travelling at subsonic speeds.
When speed increases, so do turbulence and drag, as a result of air friction on the wings. Swept back wings technology was introduced to solve this instability and vibration in supersonic jets at high speed. Wings are angled towards the back end, which creates an imaginary increase in wing length.
Airliners can achieve high speed, almost twice the speed of sound in the case of the Concord. Air travels further on the top side, thus safeguarding the airliner from shock waves.