Written By Singapore Air Charter Admin

Aircraft/Airplane Flaps: Purpose, Functions And Types

In aviation, aircraft flaps are crucial to managing the dynamics of flight. These movable panels on the wings serve various critical roles, including adjusting lift, controlling speed, and enhancing overall stability.

Whether during takeoff, cruising, or landing, understanding the function of flaps in aircraft and what they do on a plane is key to appreciating their impact on flight safety and efficiency.

This article explores the mechanisms of airplane flaps, their functions, and the types of flaps used in aircraft. By examining how these devices influence the aerodynamics of flight, we gain insight into their indispensable role in modern aviation.

What Are Airplane Flaps?

Airplane flaps are movable panels located on the wings of an aircraft. These essential components are strategically designed to alter the shape of the wings during various phases of flight, such as takeoff, cruising, and landing.

The mechanics of how flaps operate can be fascinating yet straightforward. Typically, flaps are hinged on the back portion of each wing and can be extended or retracted by the pilot depending on the requirements of the flight segment.

When extended, they increase the surface area and curvature of the wing. This alteration enhances the wing’s ability to generate lift at lower speeds, which is crucial during takeoff and landing when the aircraft must operate efficiently at lower velocities.

Moreover, flaps are instrumental in controlling the aircraft’s angle of descent and speed during the approach to landing. By extending the flaps, pilots can achieve a steeper descent without increasing speed, offering greater control and safety during this critical phase of flight.

What Is The Purpose Of Flaps On An Airplane?

Aircraft flaps serve multiple critical functions that enhance both the safety and efficiency of flight operations, particularly during the takeoff and landing phases.

Here’s how flaps on an airplane work to fulfil their roles:

  • Increase Lift: When the flaps are extended, they increase the camber or curvature of the wing. This modification raises the wing’s maximum lift coefficient, allowing the aircraft to generate more lift even at lower speeds
    This capability is crucial for maintaining slower approach and landing speeds, ensuring safer handling and reducing the runway length required for takeoff and landing.
  • Increase Drag: Deploying flaps also significantly increases the drag on the wing. This additional drag is beneficial as it enables the aircraft to adopt steeper descent angles during the approach without gaining excessive speed.
    Such control is particularly valuable for navigating through obstacle-rich environments during landing.
  • Maintain Control at Lower Speeds: By increasing the lift produced by the wing, extended flaps allow the aircraft to fly at slower speeds without risking a stall.
    This reduction in stall speed is vital during the critical phases of flight, such as takeoff and landing, improving overall aircraft performance and safety.
  • Control Airflow Around the Wing: Flaps help divert the air around the wing as needed. Depending on whether the aircraft is taking off or landing, flaps can be adjusted to either increase lift or increase drag.
    When retracted, flaps align with the wing, minimising drag and allowing for more efficient lift during cruise flight.

8 Types Of Flaps In Aircraft

In modern aircraft, flaps are vital components designed to enhance the aerodynamic performance during different phases of flight. Each type of flap serves a specific purpose and is tailored to meet the aerodynamic needs of various aircraft types.

#1. Plain Flaps

Plain flaps are the most fundamental type of aircraft flaps. Located at the trailing edge of the wing, these flaps are hinged so that they can pivot downward when extended.

By doing so, plain flaps increase the curvature and surface area of the wing, which in turn enhances lift. However, this type of flap is somewhat limited in its capability, primarily due to the way air interacts with it.

When plain flaps are extended, they increase the wing’s angle of attack. This modification allows the wing to generate more lift at lower speeds, which is particularly useful during takeoff and landing.

However, as the flaps move down, the airflow over the wing can separate more sharply from the surface, leading to increased airflow separation. This phenomenon results in a larger wake behind the wing, significantly increasing induced drag.

Despite their simplicity, plain flaps are quite effective in their primary role of increasing lift, but their simplicity also means they generate more drag than more sophisticated flap designs.

They are similar in appearance and function to ailerons, but unlike ailerons, which are designed to help control the aircraft’s roll, plain flaps extend down together, affecting both wings simultaneously.

In essence, while plain flaps do boost lift, they primarily add a considerable amount of drag. This makes them less efficient than other types of flaps for certain manoeuvres or in aircraft that require more precise control over drag and lift dynamics.

#2. Split Flaps

Split flaps are a distinctive type of airplane flap that enhance functionality during aircraft operations, especially during landings.

Unlike other flap designs where the entire section of the wing’s trailing edge moves, split flaps involve only the lower surface of the wing. This design causes the flap to extend downward from the lower surface, markedly increasing drag while also adding some lift.

Primarily, split flaps are used to generate significantly more drag compared to plain flaps. This feature is particularly useful for deceleration during landings, allowing for a steeper and more controlled descent without increasing the airspeed.

While their main function is to increase drag, split flaps also aid in lift by altering the air dynamics around the lower wing surface, which effectively pushes the air downwards and increases the overall lift produced by the wing.

Historically, split flaps were conceptualised by Orville Wright and were commonly used up until the 1930s, after which aircraft technology rapidly evolved.

One of the most renowned aircraft equipped with split flaps is the Douglas DC-1. Today, these flaps are mostly seen on vintage or historic aircraft, as more advanced and efficient designs have taken precedence in modern aviation.

#3. Slotted Flaps

Slotted flaps are among the most common types of flaps used in both small and large aircraft today. Their design is characterised by a slot between the flap and the wing’s trailing edge, which allows high-pressure air from beneath the wing to flow through to the upper surface of the flap.

This slot plays a crucial role in their functionality by energising the wing’s boundary layer, which delays airflow separation. This mechanism allows the wing to handle higher angles of attack during critical operations such as takeoffs and landings, thereby enhancing lift while controlling drag.

The key advantage of slotted flaps is their ability to significantly increase lift without a proportional increase in drag. This efficiency is achieved through the slot that allows high-pressure air from the lower wing to mix with the slower-moving air above the flap, thereby reducing the energy loss typically associated with other flap types.

Consequently, slotted flaps are highly versatile and can be found on many aircraft, from light aircraft like the Cessna 172, known for its distinctive slotted flaps, to larger commercial and cargo jets.

In contrast to plain flaps that simply hinge downward, slotted flaps are designed to extend outward first, then downward. This action increases the wing’s surface area and optimises the airfoil shape to maximise aerodynamic efficiency.

The increased wing camber produced by slotted flaps further enhances their lift-generating capability, making them ideal for various operational scenarios, particularly in aircraft that require short-field performance.

#4. Fowler Flaps

Fowler flaps are a sophisticated type of aircraft flap known for their ability to significantly enhance lift without proportionally increasing drag. These flaps operate by sliding backwards along tracks or rails before hanging downward.

This dual-action movement increases the wing area and alters the wing’s curvature, which is crucial for maximising lift during critical phases such as takeoff and landing.

The first stage of extending Fowler flaps involves them moving outwards, away from the wing root, which increases the surface area of the wing without greatly altering the airflow, thus providing significant lift with minimal drag.

As the flaps extend further, they also hinge downward, increasing the wing’s camber and creating even more lift, albeit with a corresponding increase in drag. This staged extension makes Fowler flaps particularly effective for large aircraft where the balance between lift and drag is crucial for safe operation.

Fowler flaps are commonly seen on commercial airliners. The design allows these large jets to manage the enormous speed differences experienced between cruise speeds and slower landing or takeoff speeds.

At high cruise speeds, minimal wing area is desirable to reduce drag. However, during landing, the increased wing area provided by the extended Fowler flaps allows the aircraft to fly safely at much lower speeds.

Notable examples of aircraft equipped with Fowler flaps include the Boeing 747 and Airbus A380, which contribute significantly to the aircraft’s performance during takeoff and landing.

#5. Zap Flaps

Zap flaps are a less common but intriguing type of flap that combines elements of split and slotted flaps to optimise aircraft performance by enhancing lift and drag.

These flaps function through a split flap design where the movable bottom portion of the wing not only hinges downwards but also slides aft on tracks, thus increasing the wing’s effective surface area and camber.

This unique configuration allows Zap flaps to substantially increase maximum lift and drag, making them especially useful during takeoff and landing when additional lift is required.

Although more commonly associated with military aircraft, their design principles serve specific aerodynamic purposes that can benefit specialised aviation applications.

Zap flaps were developed in the early 1930s by aeronautical engineer Edward Zaparka and were named after him. They saw limited use in commercial aviation, partly due to their complexity and the rapid evolution of aircraft flap technology.

However, they were notably employed on the Northrop P-61 Black Widow during World War II. This aircraft benefited from the enhanced aerodynamic control provided by Zap flaps, particularly in the demanding scenarios typical of wartime operations.

#6. Krueger Flaps

Krueger flaps are specialised high-lift devices on the leading edge of aircraft wings. They are primarily employed to augment lift during critical low-speed operations such as takeoff and initial climb.

Unlike other flap types, Krueger flaps are mounted directly on the leading edge and are designed to extend downwards and forward from the underside of the wing.

When deployed, Krueger flaps effectively increase the wing camber and surface area. This modification results in a higher maximum lift coefficient, enabling the aircraft to maintain lift at lower speeds without risking a stall. A key feature of Krueger flaps is the creation of a slot between the flap and the wing.

This slot allows high-pressure air from below the wing to flow over the upper surface, energising the boundary layer and delaying airflow separation. This innovative design significantly reduces the stall speed and enhances the aircraft’s safety during slow flight phases.

Krueger flaps are typically found on various aircraft, from early jets like the Boeing 707, which used them as their primary leading-edge device, to modern large aircraft such as the Boeing 747.

The 747, for example, uses a variant known as Variable Camber Krueger (VCK) flaps. These flaps are made from fibreglass and designed to deform into an aerodynamically optimal shape when extended.

This ability to adapt shape maximises aerodynamic efficiency and contributes to the aircraft’s performance during takeoff and landing.

#7. Gouge Flaps

Gouge flaps, named after their inventor Arthur Gouge of Short Brothers, are a unique type of split flap introduced in the mid-1930s.

Unlike more conventional flap designs that simply hinge downwards, Gouge flaps are engineered to slide backwards along curved tracks before the trailing edge is forced downward.

This dual-action mechanism increases both the chord and the camber of the wing, significantly altering the wing’s aerodynamic characteristics.

The primary advantage of Gouge flaps lies in their ability to increase the wing’s surface area and camber, thereby enhancing lift at lower speeds. This increase in lift is crucial for operations requiring short takeoff distances and lower takeoff speeds.

While their application was somewhat limited, primarily installed on Short Brothers aircraft like the Sunderland and Stirling during World War II, Gouge flaps improved aircraft performance in short runway scenarios.

Gouge flaps share some operational similarities with Fowler flaps, as both types extend backwards to increase wing area and camber. However, unlike Fowler flaps, Gouge flaps do not incorporate boundary layer energising slots, which limits their ability to manage airflow separation as effectively.

#8. Slotted Fowler Flaps

Slotted Fowler flaps combine the mechanics of both Fowler and slotted flap designs to achieve superior aerodynamic efficiency. These flaps are predominantly used on large commercial aircraft to maximise lift and control airflow during critical phases of flight, such as takeoff and landing.

The design of Slotted Fowler flaps allows them to slide backwards along tracks on the wing, increasing both the wing’s chord and surface area without initially adding significant drag. This movement extends the wing’s surface, providing crucial additional lift needed during takeoff.

As the flaps deploy further and hinge downward, they also increase the wing’s camber. This adjustment significantly enhances the wing’s capacity to generate lift at lower speeds, which is especially useful during the slow speeds of landing.

The “slotted” aspect of these flaps involves a strategic gap that forms between the wing and the extended flap. This slot channels high-pressure air from beneath the wing to flow over the top surface of the flap, energising the boundary layer.

This is critical for maintaining lift at higher angles of attack and delaying airflow separation. This design feature helps to stick the airflow to the flap’s surface, markedly reducing the risk of aerodynamic stalling at lower speeds.

Slotted Fowler flaps are celebrated for their efficiency and versatility. They are particularly notable on aircraft like the Boeing 747, which employs double or even triple-slotted Fowler flaps.

These multiple slots optimise the airflow over the flap, further delaying separation and enhancing lift capabilities. The phased deployment of these flaps provides optimal lift with minimal drag during takeoff and increases both lift and drag during landing, allowing for safe operation at slower speeds.

Conclusion On What Do Flaps Do On A Plane

Aircraft flaps play a role in enhancing the performance, safety, and efficiency of aircraft during all critical phases of flight. Understanding what flaps do on a plane and the purpose of flaps on an airplane is crucial for appreciating how they influence the complex dynamics of flight.

Each flap type has been meticulously designed to adjust the wing’s lift and drag characteristics, which are fundamental to achieving the desired performance across different flying conditions.

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Frequently Asked Questions Flaps In Aircraft

What Is The Difference Between The Upper And Lower Surfaces Of Wing Flaps?

The upper and lower surfaces of wing flaps play different roles in airflow management during flight. The upper surface is crucial for managing airflow separation and maintaining lift, especially at higher angles of attack.

In contrast, the lower surface of the flap interacts with the high-pressure air below the wing, helping to increase the overall lift and control drag, which is critical during slower flight operations like landing.

Why Are One Or More Slots Important In The Design Of Certain Flaps?

Slots in flaps are essential for enhancing aerodynamic efficiency by allowing high-pressure air from beneath the wing to pass through to the upper surface.

This airflow helps energise the boundary layer, which delays airflow separation and reduces the likelihood of aerodynamic stalling. Consequently, slots enable the wing to sustain lift at higher angles of attack and slower speeds, which is crucial during the takeoff and landing phases.

How Do Wing Flap Settings Vary During Different Flight Operations?

Wing flap settings are adjusted by pilots based on the specific needs of different flight phases. For takeoff, flaps are typically set to a lower degree to increase lift without creating excessive drag.

During landing, flaps are extended further to maximise lift in the face of reduced speeds, which also increases drag and helps slow the aircraft. In cruising, flaps are usually retracted to streamline the wing and minimise drag, optimising fuel efficiency.

Can The Extension Of Flaps Affect The Overall Lifespan Of An Aircraft Wing?

Frequent extension and retraction of flaps can indeed influence the structural integrity and lifespan of an aircraft wing. The mechanical stress imposed on the flaps and the wing during these operations can lead to wear and fatigue over time.

Regular maintenance and inspections are crucial to manage this wear and ensure that the flaps and the wing continue to function safely within their operational lifespan.