Understanding How Airplane Flaps Work for Safer Flights
If you’ve ever flown on an airliner and looked out the window, you’ve likely noticed the flaps extending from the wing during landing. These flaps change the shape of the wing and are a clear indicator that the aircraft is slowing down to approach the runway.
But what exactly do flaps do on a plane?
Not all aircraft have flaps, but the majority do, including smaller planes like Piper and Cessna, as well as large commercial airliners like Airbus. While the flaps on smaller planes might not be as large or complex as those on bigger jets, they serve the same essential purpose.
Let’s break down the function and mechanics of airplane flaps, continuing our series on flying basics.
What Are Airplane Flaps?
Flaps are considered secondary flight controls. Unlike primary flight controls (such as the elevator, rudder, and ailerons), which directly control the plane’s movement, secondary flight controls like flaps help modify certain flight characteristics.
The primary purpose of flaps is to adjust the wing’s shape, enabling it to generate more lift at slower speeds. This allows the aircraft to safely approach runways at steeper angles while avoiding obstacles.
Flaps are categorized as high-lift devices, and they’re usually located on the trailing edge of the wing, close to the fuselage. Most airplanes use an electric motor to extend the flaps, and pilots control the flaps through a cockpit switch.
To see where flaps fit into the bigger picture of an aircraft’s systems, check out The Anatomy of an Airplane: Essential Components Every Pilot Must Know.
How Do Airplane Flaps Work?
The process starts when the pilot uses a control in the cockpit to activate the flaps. This control is typically mounted on the panel, with a handle resembling a flap lever. Many planes use a system with built-in detents or notches that let the pilot set specific flap positions (e.g., “Flaps 1” or “Flaps Approach”).
Some aircraft, like the Piper Archer, have a manual flap system. Instead of relying on a motor, Piper Archers use a handle between the front seats that resembles a parking brake. As the handle is lifted, the flaps are extended in three positions: 10, 25, and 40 degrees. This system is simple, reliable, and doesn’t rely on an electric motor, reducing the chance of failure.
What Are the Dangers of Differential Flap Extension?
It’s crucial for pilots to understand the flap system on their specific aircraft. For example, many low-wing planes use a single strut to connect both flaps, ensuring they extend together evenly. However, some planes, like the Cessna 172, utilize pulleys, cables, and bellcranks to independently control the flaps. If one component fails, it’s possible for one flap to extend while the other does not, leading to asymmetric flap extension.
In this scenario, the aircraft may start to roll toward the side with the extended flap. If left uncorrected, this can cause issues that ailerons may not be able to counteract. To avoid this, pilots should be familiar with their aircraft’s systems and remain vigilant while extending flaps. If asymmetric extension occurs, the pilot should retract the flaps and level the aircraft.
Types of Flaps
Flaps come in four main types, each serving different needs in aircraft design:
- Plain Flaps: The simplest type of flap. These extend downward and increase the wing’s angle of attack, generating more lift but also increasing drag.
- Split Flaps: These are less common but can be found on some small twin-engine planes. The lower portion of the wing moves, while the upper portion remains fixed. Like plain flaps, split flaps increase lift and drag.
- Slotted Flaps: These flaps extend downward, revealing a slot that allows air to flow over the upper surface. This design is more effective at higher angles of attack and significantly boosts lift. Slotted flaps are often used in small aircraft like the Cessna 172 for improved short-field performance.
- Fowler Flaps: Common on larger aircraft, Fowler flaps extend both downward and outward, increasing the wing’s surface area. This helps generate more lift at slower speeds, making them ideal for landing and takeoff. Airliners rely on Fowler flaps for efficient flight at varying speeds.
The Aerodynamics Behind Flaps
Flaps work by altering the wing’s chord line, which is an imaginary line drawn from the leading edge to the trailing edge of the wing. By extending the flaps, the pilot changes the chord line, which increases the angle of attack (the angle between the chord line and the relative wind). This increase in angle generates more lift, but it also adds induced drag.
While flaps enable aircraft to fly at slower speeds while maintaining lift, the trade-off is increased drag. Some flap designs create more drag than others, which is why pilots must understand how different aircraft handle during slow flight.
Read more about the importance of aerodynamics in pilot training here.
Ailerons vs Flaps
Ailerons and flaps are both crucial flight controls, but they serve different purposes. Ailerons are located near the wingtips and control the aircraft’s roll, allowing the pilot to turn. Flaps, on the other hand, are typically closer to the wing root and increase lift and drag to facilitate slower flight during takeoff and landing.
While ailerons help with maneuverability and turns, flaps are vital for maintaining lift at lower speeds, making them especially important during takeoff and landing.
In summary, flaps are a key component in managing the lift and drag of an aircraft, allowing for safer, more controlled takeoffs and landings. Whether you’re flying a small Piper or a large commercial jet, understanding how flaps work is essential for smooth, safe flying.
Once you understand how flaps affect aircraft performance, the next step is learning how they come into play during real-world operations, like Understanding Holding Patterns: A Guide for Pilots.
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