Why are Aircraft wings angled backwards?

Swept Wings

Image from:- en.wikipedia.org

Nowadays almost all Aircraft wings are angled backward. Such wings are known as swept wings. So why we use swept wings in modern aircraft?

Speed of world's first heavier than air aircraft wright flyer was 48kmph. But now speed of modern aircraft is upto 800kmph to 900kmph.

Image from:- en.wikipedia.org

As we know lift to the aircraft is due to pressure difference above & below the aircraft wing. Speed of airflow above the wing is higher than the speed of airflow under the wing. Even if an aircraft is moving with subsonic (less than the speed of sound) speed, the speed of the airflow above aircraft wing can be supersonic (greater than the speed of sound). This supersonic speed causes production of shock waves above aircraft wing. Shockwaves breaks the airflow above aircraft wing. So instead of moving in direction of shape of wing airflow goes straight causing production of drag. This flow causes drag to the horizontal stabilizer behind the aircraft. This creates difficulties to pilot to control aircraft.

So to overcome this problem, engineers placed horizontal stabilizer above its original position (as in bell X-1). So that straight airflow above aircraft wing won't cause any problem to the horizontal stabilizer. But it wasn't so effective.

Image from:- en.Wikipedia.org

So Engineers found another way to overcome this problem. They made aircraft wings swept.

Swept wings reduce the speed of the airflow above it. Speed of airflow gets divided into two components. One component parallel to chord line & other along the leading edge of the wing. This reduces the speed of airflow above the wing. So Shockwave is not produced.

But As we know the pressure difference above & below the wing produce lift. And this pressure difference is due to speed difference above & below the wing. As we are reducing the speed of airflow above the wing, keeping, speed of airflow below wing same this reduces lift to the aircraft. In a case of the high speed its not problem because lift produced is enough for aircraft. But in a case of low speed this is a problem. The Lift produced in a case of low speed is not enough. So some of the aircraft are having movable wings, which gets swept back in a case of high speed & stays normal in a case of normal speed.

Do you know?
Sweep angle of the Airbus A380 is 33.5°

Image from:- en.wikipedia.org


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How winglets work?

How do winglets work?


Image from:- commons.wikimedia.org

If you look at the wing of the aircraft, you will see the bent wing tip. So what is the reason for such bent wing tips? 

Those bent wing tips of the aircraft are known as winglets. Winglets in aircraft are used for the very important purpose. Winglets of aircraft reduce the induced drag produced due to the air above & below the aircraft. If you have read our previous post related to how aircraft fly, then you know that how lift is produced. Air flowing above the wing has more velocity that air flowing below the wing. So, according to Bernoulli's principle higher the velocity lesser the pressure. So Aircraft wing has lesser pressure above the wing & higher pressure below the wing. This pressure difference causes lift.

Image from:en.wikipedia.org

But due to this velocity difference phenomena, air with the higher velocity above the wing pushes air with lesser velocity below the wing causing the production of vortices(Image is shown above). These vortices are like small tornadoes. These vortices produce drag & reduce lift to the aircraft. As these vortices produce disturbance to the flow of air. 

Image from:- en.wikipedia.org

Richard T. Whitcomb(Image is shown above) concluded that Winglets can be used to reduce drag of the aircraft. By reducing drag aircraft can be made more fuel efficient. The idea about the winglets came from birds. Birds bent their wings while flying to reduce drag.


So aircraft wing tips were bent so that vortices produced due to air velocity difference will be small. So less drag will produce. As bent wing will force vortices to form on the side so that vortices won't disturb airflow.

Using winglets made the aircraft more fuel efficient as the drag of the aircraft was reduced.


Thanks for reading!