Aerodynamic (Lesson 1) (1)

Step on the Left rudder pedal.

The rudder deflects to the Left, causing aerodynamic forces to push the tail to the Right.

The aircraft nose points to the Left.

The longitudinal axis is the axis that passes through the Centre of Gravity (CG) from the nose to tail of an aircraft.

An aircraft rolls around the longitudinal axis, and this motion is controlled by ailerons.

When an aircraft turns to the right:

1. Left ailerons go down:

   • Angle of Attack (AOA) of the left wing increases.
   • Lift increases and the left wing goes up.

2. Right ailerons go up:

   • Angle of Attack (AOA) of the right wing decreases.
   • Lift is reduced and the right wing goes down.

The lateral axis is the axis that passes through the center of gravity (CG) from the left-wing tip to the right-wing tip.

An object at rest will remain at rest when acted on by an outside force.

When a force is applied to a mass, the mass will accelerate.

For a constant mass, force equals mass times acceleration.

The location of the Centre of Gravity (CG) is crucial because:

• It affects the stability and control of the aircraft.
• Misplacement or miscalculation can lead to catastrophic events during flight.
• It is essential for ensuring that the aircraft can perform as intended during various phases of flight.

The Centre of Gravity (CG) is obtained by:

1. Calculating the weight of each component onboard the aircraft.
2. Measuring the distance of each component from a reference point.
3. Recording the results in the weight and balance report to ensure accurate CG placement.

The three axes of an aircraft are:

1. Vertical Axis
2. Longitudinal Axis
3. Lateral Axis

The vertical axis is the axis that passes through the Centre of Gravity (CG) from the sky to the ground.

An aircraft yaws around the vertical axis by using the rudder, which controls the direction of the aircraft's nose during level flight.

An aircraft pitches around the lateral axis by moving the elevator, which controls the angle of the nose up or down.

1. Pull the yoke/control column.

2. The elevator moves up, resulting in a decrease in angle of attack (AOA).

3. The tailplane produces a downward force, pushing the tail down, which causes the aircraft nose to go up.

Yaw around the vertical axis is controlled by the Rudder.

Roll around the longitudinal axis is controlled by the Aileron.

Pitch around the lateral axis is controlled by the Elevator.

C Longitudinal Axis

Stability is the quality of an object, when disturbed, to resist and return to its original position or continue on its original path. It affects the handling characteristics of an aircraft.

The two types of stability in aircraft are Static Stability and Dynamic Stability.

Static stability is the initial tendency of an aircraft to return to its original position when it's disturbed.

Positive static stability is characterized by an aircraft's tendency to return to its original position after being disturbed, as illustrated by a series of airplanes returning to equilibrium after disturbances.

Neutral static stability is characterized by an aircraft remaining in its new position after a disturbance, with no tendency to return to the original position, unlike positive static stability which seeks to return to equilibrium.

Negative static stability is indicated by an aircraft diverging further from its original position after a disturbance, showing an increasing tendency to move away from equilibrium.

Positive static stability refers to the initial tendency of an aircraft to return to its original state of equilibrium after being disturbed.

Neutral static stability is characterized by the initial tendency of an aircraft to remain at a new condition of equilibrium after being disturbed.

Negative static stability indicates an initial tendency for an aircraft to continue moving away from equilibrium after being disturbed.

Dynamic stability refers to the tendency of an aircraft to return to equilibrium (its original position) when disturbed over a period of time. It can be categorized into three types:

1. Positive Dynamic Stability: Oscillations decrease in amplitude over time, returning to stable equilibrium.
2. Neutral Dynamic Stability: Oscillations maintain a constant amplitude around the equilibrium point.
3. Negative Dynamic Stability: Oscillations increase in amplitude over time, leading to instability.

Positive Dynamic Stability is characterized by damped oscillation, where over time, the motion decreases in amplitude, and the object returns to equilibrium.

Neutral Dynamic Stability is defined by undamped oscillation, where once disturbed, the motion does not change in amplitude.

Negative Dynamic Stability is characterized by divergent oscillation, where over time, the motion increases in amplitude and becomes more divergent.

Static Stability refers to the initial tendency of an aircraft to return to its original position after a disturbance, while Dynamic Stability involves the aircraft's behavior over time after the disturbance.

• Static Stability:

  • Immediate response to disturbances.
  • Can be positive, neutral, or negative.

• Dynamic Stability:

  • Long-term response to disturbances.
  • Involves oscillations and damping over time.

Understanding both types of stability is crucial for ensuring safe flight operations.

1. Manoeuvrability: The quality of an aircraft that permits it to be manoeuvred easily.

2. Controllability: The quality of the aircraft's response to the pilot's control application when manoeuvring.

Longitudinal Stability is the quality of an aircraft that makes it stable about the Lateral Axis. It ensures that when the aircraft is disturbed, it will return to a level attitude. For instance, if the aircraft pitches up due to a disturbance, the restoring moment will cause it to pitch down, stabilizing the flight.

The key factors affecting longitudinal stability include:

1. Location of Wing relative to the Center of Gravity (CG)
2. Location of Horizontal Tail Surface relative to the CG
3. Size of Tail Surface

Most aircraft are designed with a Nose Heavy Tendency, where the wing's Coefficient of Lift (CL) is located to the rear of the Center of Gravity (CG).

The horizontal stabilizer produces a nose-up moment to compensate for the nose-down tendency of the aircraft, which is achieved by setting it at a negative Angle of Attack (AOA).

In level flight, the upward force created by the wing is balanced with the downward forces, maintaining stable flight.

Balance in level flight is crucial for longitudinal stability as it ensures that the aircraft maintains a steady flight path without unwanted pitch changes. When an aircraft is balanced, the center of gravity (CG) is aligned with the aerodynamic center (AC), allowing for stable flight. Any disturbance can lead to a pitch-up or pitch-down moment, affecting the aircraft's ability to return to its original flight attitude.

When there is a reduction in power, the thrust decreases, leading to decreased airspeed. This results in less downwash on the horizontal stabilizer, causing less downward force and making the aircraft pitch down due to the stronger downward force at the nose.

The aircraft gains airspeed when it pitches down, which increases downwash. This stronger downwash results in a stronger downward force on the horizontal stabilizer, causing the aircraft to pitch upward.

The cycle of pitching down and regaining airspeed repeats, but with less amplitude, indicating that the aircraft is dynamically stable.

At cruise speed, the tail load is balanced. At low speed, the tail load is lesser, while at high speed, the tail load is greater, indicating the relationship between speed and tail load.

• If the thrust line is higher than the CG, the aircraft will tend to pitch down when power is increased.

• If the thrust line is lower than the CG, the aircraft will tend to pitch up when power is increased.

Lateral stability is the quality of an aircraft that makes it stable about the lateral axis. It helps to counteract the rolling effect when one wing is lower than the other.

The four main factors that contribute to an aircraft's lateral stability are:

1. Dihedral
2. Sweepback
3. Keel Effect
4. Weight Distribution

Positive lateral stability helps to stabilize the rolling effect when one wing goes lower than the wing on the opposite side of the aircraft, ensuring smoother flight and control.

The dihedral angle is the upward angle of an aircraft's wings. It helps to stabilize the aircraft about the longitudinal axis and increases lateral stability.

When an aircraft is disturbed, the lift vector is tilted. This tilting causes the horizontal component of the lift vector to create a sideslip, leading to an increase in angle of attack (AOA) on the wing that is slipping into the wind, resulting in increased lift. This creates a restoring moment that helps return the aircraft to level flight.

Sweepback refers to the angle formed by an aircraft wing or airfoil where the leading or trailing edge slopes backwards from the fuselage. This design feature helps to stabilize the aircraft about the longitudinal axis and increases lateral stability.

When a disturbance causes a wing to drop, the following occurs:

1. Aircraft sideslips due to the drop of the wing.
2. Airflow comes at a sideways angle.
3. The lower wing meets the wind at a more perpendicular angle than the upper wing.
4. Consequently, the lower wing produces more lift, creating a restoring force that rolls the aircraft back to level flight.

The Pendulum Effect, also known as the Keel Effect, stabilizes the aircraft in the longitudinal axis. In high-wing aircraft, the fuselage, located below the wings, acts as a weight that swings about the longitudinal axis. When disturbed, the fuselage behaves like a pendulum, helping to return the aircraft to a wings-level position.

Directional stability is the quality of an aircraft that makes it stable about the Vertical Axis. It ensures that when disturbed, the aircraft's nose returns to its original heading.

The two main factors that contribute to an aircraft's lateral stability are:

1. Vertical Stabilizer or Fin
2. Sweepback

Positive directional stability helps to stabilize the aircraft by ensuring that when it is disturbed, the design factor causes the nose of the aircraft to point back to its original heading.

When an aircraft rotates about its vertical axis, more relative wind strikes the area after the center of gravity (CG) than the area forward of the CG. This results in a larger side force acting on the area after the CG, creating a restoring moment that turns the nose of the aircraft back to its original heading.

The 'Weathercock Effect' refers to the phenomenon where an aircraft, when disturbed and rotating about its vertical axis, experiences a restoring moment due to the differential relative wind striking the areas before and after the center of gravity (CG), helping to return the aircraft to its original heading.

When an aircraft is disturbed, such as yawing to the left, the right wing has a longer leading-edge perpendicular to the relative airflow. This results in:

1. Increased airspeed on the forward wing (right wing).
2. More drag on the right wing due to the increased airspeed.
3. The additional drag pulls the right wing back, helping to turn the aircraft back to its original flight heading.

Thus, sweepback tends to correct yaw by creating differential drag between the wings.

Dutch Roll is a coupled Lateral/Directional oscillation caused by the difference in strength between Lateral and Directional stability of an aircraft. It is characterized as a dynamically stable motion that typically occurs in aircraft with relatively strong Lateral Stability and relatively weak Directional Stability.

Most airliners are equipped with a Yaw Damper to counteract the effects of Dutch Roll, helping to stabilize the aircraft during this oscillation.

A yaw damper pulls aircraft movement information from a series of accelerometers or rate sensors in the rudder and translates it into the proper amount of calming rudder inputs.

Spiral instability occurs when directional stability is significantly stronger than lateral stability. This imbalance leads to the following effects:

• The strong directional stability causes the aircraft's nose to yaw into the resultant wind when disturbed.
• The relatively weak lateral stability fails to restore balance quickly.
• The outside wing travels faster than the inside wing, generating more lift on the outside wing.
• This results in an overbanking tendency, which can lead to a steeper spiral if not corrected by the pilot.

Lift is created due to the difference in air pressure above and below the airfoil. The airfoil shape causes the air to travel faster over the top surface than the bottom surface, resulting in lower pressure above the wing and higher pressure below it. This pressure difference generates an upward force known as lift.

An object at rest will remain at rest unless acted on by an outside force.

An object in motion continues in motion with the same speed and in the same direction unless acted upon by an outside force.

Newton's Second Law states that when a force is applied to a mass, the mass will accelerate. The relationship is defined by the equation F=ma, where F is the force, m is the mass, and a is the acceleration.

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that forces always occur in pairs; when one object exerts a force on another, the second object exerts a force of equal magnitude but in the opposite direction on the first object.

For every action, there is an equal and opposite reaction.

For horizontal flow, an increase in velocity must be accompanied by a decrease in pressure.

As air enters the narrow portion of the tube, the velocity increases and the pressure decreases. After passing through the constriction, both the velocity and pressure return to their original values in the wider portion of the tube.