A fixed wing airplane is a type of flying machine that relies on its special shaped wings to generate lift, enabling it to overcome gravity and fly through the air. This category includes airplanes, and their ability to stay in air is achieved through a combination of the aircraft’s forward movement and the specific design of its wings. Fixed wing airplane are distinguished from other types of flying machines, such as rotary-wing aircraft, where wings take the form of a rotating rotor on a central shaft. It’s worth noting that the wings of fixed-wing aircraft can vary in flexibility and design.
Theory of Flight
Flight is a longstanding phenomenon in the natural world, with birds employing not only wing flapping but also gliding with their wings extended to cover long distances.
The hot air balloon achieves its flight based on the buoyancy principal, they float in air with the help of hot air inside it. Hot air being lighter than cold air rises up and stops going further up when the density of the air inside the balloon is equal to the density if air surrounding the balloon.
Heavier than air flight is achieved by the tweaking lift, drag, weight and thrust. In the aircraft, flight is maintained by balancing lift and weight and thrust should be more than the drag.
Forces acting on a fixed wing airplane
Lift
In order for the airplane to fly an upward force must be equal to or greater than the downward force acting on it due to gravity. This upward force is called lift. In heavier than air flight, this force is created by the flow of air over an airfoil. The airfoil is engineered to induce faster airflow over its top surface compared to the airflow beneath it.
The fast flowing air results in the decrease in surrounding air pressure on the top. Since the pressure on the upper surface is lesser than that on the bottom surface of the airfoil it results in the creation of lift force which helps the aircraft to gain lift.
To understand how lift is created we need to understand two equations of physics
The change in pressure due to fast moving air/fluid is represented by Bernoulli’s equation. Daniel Bernoulli, a Swiss mathematician, formulated this equation to explain the changes in pressure exerted by flowing streams of water. The Bernoulli’s equation is written as:
Bernoulli’s equation
To understand the above equation, we need to understand the continuity equation. In a given flow, it asserts that the product of density (ρ), cross-sectional area (A), and velocity (V) remains constant. It is written as below:
Continuity equation
By employing the Bernoulli equation and the continuity equation, one can illustrate the generation of lift when air passes over an airfoil. Envision air moving over an immobile airfoil, like the wing of an aircraft. Upstream from the airfoil, the air moves at a consistent speed. As it encounters the airfoil, it must divide into two streams, with one portion passing over the top and the other beneath it.
Airflow over an airfoil
A typical airfoil possesses an asymmetrical shape, with a larger surface area on top than on the bottom. When air streams over the airfoil, it experiences greater displacement from the top surface compared to the bottom. According to the continuity principle, this displacement, or reduction in flow area, necessitates an increase in velocity. Imagine an airfoil within a water-filled pipe. The water will move swiftly through a narrower section of the pipe. The expansive area of the top surface of the airfoil constricts the pipe more than the bottom surface does. As a result, water will flow faster over the top than the bottom. While the bottom surface of the airfoil does contribute to an increase in flow velocity, it does so to a significantly lesser extent than the top surface.
In accordance with the Bernoulli equation, an increase in velocity leads to a decrease in pressure. This means that as the flow speeds up, the pressure drops. When air passes over an airfoil, it undergoes a decrease in pressure, particularly more so on the top surface compared to the bottom. This difference creates a net positive pressure force directed upwards, resulting in what we identify as lift.
Lift equation
In the equation, where S represents the wing area and the quantity in parentheses denotes the dynamic pressure, when designing an aircraft wing, it is generally advantageous to maximize the lift coefficient as much as possible.
Drag
Any object moving through the air will encounter opposition to the airflow, known as drag. Drag arises from various physical factors. Pressure drag, for instance, is akin to the sensation of resistance experienced while running on a windy day. It occurs because the wind pressure ahead of you is greater than the pressure in the wake behind you.
Skin friction, also known as viscous drag, is the type of drag encountered by swimmers. It arises from the movement of water along a swimmer’s body, generating a frictional force that hinders forward motion. A rough surface will produce more frictional drag compared to a smooth one. To minimize viscous drag, swimmers aim to achieve the smoothest contact surfaces possible. Similarly, aircraft wings are engineered with smooth surfaces to diminish drag.
Similar to lift, drag is directly proportional to dynamic pressure and the surface area it affects. The drag coefficient, akin to the lift coefficient, quantifies how much dynamic pressure transforms into drag. However, in contrast to the lift coefficient, engineers typically aim to minimize the drag coefficient. This is because lower drag coefficients are preferred, as they enhance an aircraft’s efficiency by reducing drag.
Drag equation
Weight
The weight of an aircraft is a critical constraint in aircraft design. Heavier planes, especially those intended for carrying substantial payloads, necessitate greater lift. They may also require more thrust for ground acceleration. In small aircraft, the distribution of weight is crucial. Achieving the correct balance is essential for flight, as an excess of weight in the front or back can lead to instability. Weight can be determined using a variation of Newton’s second law:
Weight equation
Where, W is the weight, m is the mass and g is acceleration due to gravity on Earth.
Thrust
Propulsion encompasses various principles of physical science, including thermodynamics, aerodynamics, fluid dynamics, and physics. The concept of thrust is best described by Newton’s second law. The fundamental expression of this law is:
Newton’s second law of motion
This law states that force (F) is equal to mass (m) times acceleration (a), where acceleration represents the rate of change of velocity over time. Consequently, thrust (T) is generated by accelerating a mass of air.
Summary
Fixed wing airplane fly through the principles of aerodynamics, which involve the interaction of various forces acting on the aircraft. Here’s a summary of how it works:
Lift
Lift is the force that opposes the weight of the aircraft and allows it to become airborne. It is generated by the shape of the wings (airfoil) and the relative motion of the air over and under the wing. The wing’s curved shape creates a pressure difference, with lower pressure on top and higher pressure below, resulting in an upward force.
Drag
Drag is the resistance encountered by the airplane as it moves through the air. It’s caused by the friction between the air and the aircraft’s surfaces. Pilots and engineers work to minimize drag to improve fuel efficiency and overall performance.
Weight
Weight is the force due to gravity acting on the aircraft. It acts downward through the center of gravity. Lift must be greater than weight for the aircraft to become airborne.
Thrust
Thrust is the forward force provided by engines. It propels the aircraft through the air. In jet engines, this is achieved by expelling high-speed exhaust gases rearward, creating a reaction in the opposite direction (Newton’s third law of motion).
Control Surfaces
Fixed wing airplane have control surfaces that allow pilots to adjust their orientation and direction in flight. These include ailerons (for roll control), elevators (for pitch control), and a rudder (for yaw control).
Pitch, Roll, and Yaw
Pitch is the up and down motion (controlled by the elevator), roll is the tilting motion (controlled by ailerons), and yaw is the side-to-side motion (controlled by the rudder).
Stability
Stability in flight is crucial for safe operation. Aircraft are designed to be longitudinally stable, meaning they tend to return to their original pitch angle after disturbances.
Controlled Flight
In steady, level flight, lift equals weight, and thrust equals drag. Any changes in these forces result in changes in the aircraft’s speed, altitude, or direction.
Takeoff and Landing
During takeoff, the pilot increases thrust to overcome drag, allowing the aircraft to accelerate until there’s enough lift to become airborne. During landing, the pilot reduces thrust and uses control surfaces to descend and touch down safely.
Navigation
Once in flight, pilots use a combination of instruments and visual references to navigate. Modern aircraft often rely on advanced avionics systems for navigation, communication, and monitoring of various parameters.
Remember that this is a simplified summary. The actual dynamics of flight are quite complex, involving detailed aerodynamic principles, engine mechanics, and sophisticated control systems. Pilots and engineers undergo extensive training to understand and manage these intricacies.
Thank you for reading this post, don't forget to subscribe our Youtube Channel.