You've seen them deploy before landing. But what exactly do flaps do? Flaps are hinged panels on the back of each wing. Wings generate lift by pushing air downward. Faster airflow means more lift. But landing means slowing down dramatically from cruise speed. Slow airflow over the wing produces less lift force. Without help, the aircraft would descend faster than it can safely touch down. Extending flaps makes the wing physically bigger. A bigger wing surface grabs more of the passing airflow. They tilt downward, changing how the wing attacks the air. The changed angle forces more air downward, generating extra lift force. With flap lift helping, the aircraft can land at safe slow speeds. Flaps deploy in stages to control descent rate smoothly and safely. Without flaps, most planes cannot slow down enough to land. That's why every airliner has them. They save lives every single day.
Here's how to think about why flaps matter so much: lift is a balance between wing size and airspeed. The faster air moves over a wing, the more pressure difference it creates, and the stronger the upward force. But when you're landing, you're trading away that speed. You've slowed from maybe 460 miles per hour at cruise to around 150 miles per hour on approach. That's a massive reduction. At those slow speeds, the original wing design just doesn't push hard enough air downward to hold the plane up. Something has to change. Flaps solve this by making the wing bigger and changing its shape at the exact moment you need it most.
The wing surface isn't just flat. It's curved in a specific way called an airfoil. That curve is designed for efficient cruising at high speed. But an airfoil that works beautifully at cruise doesn't work well at landing speeds. When you extend flaps, you're not just adding area. You're rotating sections of the wing downward, increasing the curve and changing the angle at which the wing meets the airflow. This forces the air to bend around the flap more sharply, which means the air has to move faster under the wing. Faster airflow creates more lift, even though the plane itself is going slower. It's like tipping a spoon handle down in water and feeling the resistance increase, even though your hand moved the same speed.
Flaps didn't exist on early aircraft. The first planes had fixed wings, and pilots simply couldn't land slowly enough. They had to descend steeply and land on long, open fields. As planes got heavier and speeds increased, engineers realized they needed a way to increase lift without speed. Flaps were invented in the 1920s and became standard by the 1930s. The first designs were simple hinged panels. Modern flaps are sophisticated, with multiple sections that extend in stages. Some flaps slide forward along a track before tilting down, which keeps the wing working efficiently as they deploy.
The way a pilot uses flaps is gradual and precise. Landing flaps don't extend all at once. A pilot will put out 5 degrees of flap during the initial descent to increase lift slightly. Then 15 degrees as they approach the runway. Finally, full flap, often around 40 degrees, just before touchdown. Each stage lets the pilot control exactly how much extra lift they're creating, so they can manage the descent rate carefully. Extending flaps also creates drag, which is actually helpful during landing because it slows the plane naturally. The bigger the flap angle, the more drag it creates, so the aircraft descends and decelerates at controlled rates.
Different aircraft need different amounts of flap. A small training plane might use only 30 degrees of flap at landing. A large jet transport uses closer to 40 degrees or more. The flap design has to be strong enough to handle the forces of the wind, and the hydraulic systems that move them have to work reliably every time. Flap failures are rare in modern aviation, but they're serious enough that pilots train regularly on how to land without them using special techniques, landing at higher speeds, and using longer runways.
Understanding flaps shows you how planes don't actually defy physics. They work with physics by changing their wing shape to match the task. Cruising requires a different wing shape than landing does. Flaps let a single aircraft serve both needs beautifully. Without them, you'd need either a plane that can only cruise slowly, which wastes time and fuel, or a plane that can't land safely at all. Flaps are the elegant solution that made modern air travel possible.
More videos by Aviation Explained →
Watch on Yesodi → Join Yesodi →