For an airplane to get off the ground, it needs to create more lift force vertically than its own weight. One of the main ways airplanes generate this force is by converting the forward thrust of the engines into a vertical force. Most airplanes achieve this lift by having a wing that pushes air down. The airplane is pushed up if enough air is pushed down, as every force generates an equal and opposite force. Another way that helps many airplanes achieve this lift is, a wing whose cross-section has a shape called an ‘airfoil’. An airfoil has a curved top and usually has a flatter bottom. As the plane moves faster, the airfoil shape helps the air move faster over the top surface of the wing compared to the bottom surface. This makes the air move downward without creating a lot of air resistance. Many people like to explain airfoils by pointing out that an airfoil placed at a angle creates a pressure difference, with lower pressure above the wing and higher pressure below, resulting in lift - this is true, but the main lift comes, as already explained, from the change in direction of the air by the wing.
To initially take off, this lift force needs to overcome gravity, this happens once the airplane reaches a takeoff speed, for the Boeing 737, this speed is around 150mph, or 250 km/hour. Some airplanes can take off at 30mph. Others, like fighter jets might need to go over 200mph.
Additionally, during takeoff, pilots use the airplane’s flaps and (on some airplanes) slats. These are adjustable surfaces on the wings that can be extended to increase the wing’s surface area and curvature. When deployed, these lift enhancing devices help keep the air moving smoothly on the wing even when the wing is put at a high angle with respect to the air. So, flaps provide extra lift, helping the airplane to take off at lower speeds and climb more steeply. They also help the airplane to land more slowly. This is especially useful on short runways.
Another thing pilots can do to ensure a smooth takeoff is carefully calculate when to start gently pulling back on the control stick or yoke to raise the nose of the aircraft while going down the runway. After the takeoff, the airplane enters the climb phase.
When the climb is established, the pilot will bring up the flaps and landing gear, and adjust power.
For a long time, it continues to climb until it reaches its cruising altitude. At this point, the pilots reduce the engine thrust to maintain a steady speed and reduce air resistance. This phase allows the plane to cover long distances efficiently before preparing for descent and landing at its destination.
Image Sourcing: https://www.sciencemill.org/upcoming-events-2/2018/12/26/up-up-and-away-physics-of-flightSeptember 14, 2024