Lesson Notes By Weeks and Term v4 - SHS 2
Aircraft Structures and Control
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Aircraft Structures and Control
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Subject: Aviation And Aerospace Engineering
Class: SHS 2
Term: 2nd Term
Week: 3
Grade code: 3.1.3.LI.2
Strand code: 1
Sub-strand code: 3
Content standard code: 3.1.3.CS.2
Indicator code: 3.1.3.LI.2
Theme: Core Concepts in Aerospace Engineering
Subtheme: Aircraft Structures and Control
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This lesson introduces the primary flight controls of rotary-wing aircraft, focusing on the helicopter as the main example. While we often see aeroplanes with their familiar wings, helicopters possess a unique and fascinating ability to hover, take off and land vertically, and fly in any direction. Understanding how a pilot controls these complex machines is a fundamental concept in aerospace engineering. In Ghana, helicopters are used by the Ghana Armed Forces for security, in the oil and gas industry for transport to offshore rigs, and for emergency medical services.
This section breaks down the complex systems of a helicopter into understandable parts. The main idea is that a helicopter flies not by changing the speed of its main rotor for every manoeuvre, but by changing the *angle* (or pitch) of the individual rotor blades. What is a Rotary-Wing Aircraft? A rotary-wing aircraft is an aircraft that generates lift using a set of rotating blades, called a rotor. The most common example is the helicopter. Unlike a fixed-wing aircraft (like an aeroplane), a helicopter's "wings" are in constant motion. The Four Primary Flight Controls
A pilot uses four main controls to fly a helicopter. Let's examine each one in detail. The Collective Pitch Control (The "Collective") This control is responsible for making the helicopter climb or descend vertically. Location: A lever located to the left of the pilot's seat, which the pilot raises or lowers. Pilot Action: To Climb: The pilot *pulls up* on the collective. To Descend: The pilot *pushes down* on the collective. Mechanism: When the collective is pulled up, it increases the pitch angle of all the main rotor blades simultaneously and equally. "Pitch" refers to the angle of the blade as it cuts through the air. A higher pitch angle means the blade "bites" into the air more aggressively, generating more lift. Aircraft Response: Pulling Up: More lift is generated across the entire rotor disc, causing the helicopter to climb straight up. Pushing Down: The pitch angle of all blades decreases, reducing lift and causing the helicopter to descend. If lowered enough, the helicopter can enter a controlled descent called autorotation in case of engine failure.
Analogy: Imagine holding a small paper fan. If you hold the blades flat (low pitch), they move a little air. If you angle them more (high pitch), they move a lot more air. The collective changes the angle of *all* the helicopter blades at the same time. The Cyclic Pitch Control (The "Cyclic") This control is responsible for horizontal movement—flying forward, backward, left, or right. Location: A stick located between the pilot's knees, similar to a joystick. Pilot Action: The pilot pushes the stick in the direction they want the helicopter to go. To Fly Forward: Push the cyclic stick *forward*. To Fly Backward: Pull the cyclic stick *back*. To Fly Left/Right: Push the cyclic stick to the *left/right*. Mechanism: This is the most complex control. The cyclic doesn't just tilt the whole rotor system. Instead, it *cyclically* changes the pitch of each blade as it moves around its 360-degree rotation. For example, to fly forward, the cyclic mechanism (via a device called a swashplate) decreases the pitch of a blade as it rotates towards the front of the helicopter and increases its pitch as it rotates towards the back. This creates a difference in lift across the rotor disc. More lift is generated at the back, and less at the front, causing the entire rotor disc to tilt forward. As the rotor disc tilts, the lift force also tilts, pulling the helicopter in that direction. Aircraft Response: The helicopter moves in the direction the cyclic stick is pushed. This allows for precise, directional flight and hovering in place by making fine adjustments. The Anti-Torque Pedals (The "Pedals") These controls are responsible for controlling the yaw of the aircraft—the direction the nose is pointing. Location: A set of two pedals at the pilot's feet, similar to the rudder pedals in an aeroplane. Pilot Action: The pilot pushes the left or right pedal. To Yaw Left: Push the *left* pedal. To Yaw Right: Push the *right* pedal. The "Why" - Newton's Third Law: For every action, there is an equal and opposite reaction. The helicopter's engine spins the main rotor in one direction (e.g., counter-clockwise). This action causes an opposite reaction, making the helicopter's body (the fuselage) want to spin in the opposite direction (clockwise). This is called torque. Without something to counter it, the helicopter would spin out of control. Mechanism: The anti-torque pedals control the tail rotor. The tail rotor is a smaller, vertically mounted propeller at the back of the helicopter. Pushing the pedals changes the pitch of the tail rotor blades. This changes how much horizontal thrust the tail rotor produces. By increasing or decreasing this sideways thrust, the pilot can precisely control the torque effect and make the helicopter's nose point in the desired direction. Aircraft Response: Push Left Pedal: Increases tail rotor thrust (if the main rotor spins counter-clockwise), pushing the tail to the right and causing the nose to yaw to the left. Push Right Pedal: Decreases tail rotor thrust, allowing the main rotor's torque to push the tail to the left, causing the nose to yaw to the right. The Throttle This control manages the power of the engine, ensuring the rotor spins at the correct speed (RPM - Revolutions Per Minute). Location: Usually a twist-grip on the collective lever, like a motorcycle throttle. Pilot Action: The pilot twists the grip to increase or decrease engine power. Mechanism: In modern helicopters, a device called a "governor" or FADEC (Full Authority Digital Engine Control) automatically adjusts the throttle to keep the rotor RPM constant, even when the pilot changes the collective pitch. However, the pilot can override this. Aircraft Response: Ensures the rotor has enough energy to provide lift. For example, when the pilot pulls up on the collective, the increased blade pitch creates more drag. The governor automatically increases the throttle to maintain the correct rotor RPM.
Guided Practice (With Solutions)