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: 1st Term
Week: 20
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 focuses on the fascinating world of rotary-wing aircraft, which we commonly know as helicopters. Unlike fixed-wing aeroplanes that need runways, helicopters have the unique ability to take off and land vertically, hover in one spot, and fly in any direction. This makes them incredibly valuable. In Ghana, the Ghana Air Force uses them for security and disaster relief, and they are vital for the offshore oil and gas industry in the Western Region for transporting workers to rigs. Understanding how a pilot controls such a complex machine is a fundamental concept in aerospace engineering.
What is a Rotary-Wing Aircraft?
A rotary-wing aircraft generates lift using a set of rotating blades, called a rotor. This is different from a fixed-wing aircraft (like an aeroplane), which generates lift by moving forward through the air, causing air to flow over its wings. The helicopter's main rotor acts as a rotating wing, allowing it to generate lift even when stationary, which enables it to hover. The Four Main Flight Controls
A conventional, single-rotor helicopter has four primary controls that the pilot uses to manipulate the aircraft. The Collective Pitch Control (The "Collective") Location: A lever located on the left side of the pilot's seat. It is moved up and down. Mechanism: When the pilot pulls the collective lever up, a mechanism called a swashplate increases the pitch angle (angle of attack) of *all* the main rotor blades simultaneously and equally. Think of it as making all the blades "bite" into the air more aggressively. Effect on Flight: Pulling Up: Increases the overall lift generated by the rotor system, causing the helicopter to climb or ascend. Pushing Down: Decreases the pitch angle of all blades, reducing lift and causing the helicopter to descend. Analogy: The collective is like the helicopter's "up and down" lever. The Cyclic Stick (The "Cyclic") Location: A stick located in front of the pilot, between their knees (similar to a joystick). It can be moved forward, backward, left, and right. Mechanism: The cyclic changes the pitch of the rotor blades *cyclically*—meaning the pitch of each blade changes as it rotates around the hub. Pushing the cyclic forward: Causes the blade's pitch to be highest as it passes over the tail of the helicopter and lowest as it passes over the nose. This creates more lift at the back, tilting the entire rotor disc forward. Moving the cyclic left/right: Tilts the rotor disc in the corresponding direction. Effect on Flight: The helicopter moves in the direction the rotor disc is tilted. Cyclic Forward: Tilts the rotor disc forward, and the helicopter moves forward. Cyclic Backward: Tilts the rotor disc backward, and the helicopter moves backward. Cyclic Left/Right: Tilts the rotor disc left or right, causing the helicopter to bank and move sideways (strafe) or initiate a turn. Analogy: The cyclic is the helicopter's "directional" stick, controlling forward, backward, and sideways movement. The Anti-Torque Pedals Location: Two pedals at the pilot's feet, similar to the rudder pedals in an aeroplane. Mechanism: This is all about Newton's Third Law of Motion (Action and Reaction). As the engine spins the main rotor in one direction (e.g., counter-clockwise), the body of the helicopter naturally wants to spin in the opposite direction (clockwise). This is called torque effect. The anti-torque pedals control the pitch of the blades on the smaller tail rotor. Pushing a pedal: Changes the tail rotor's blade pitch, which increases or decreases its thrust. This thrust pushes the tail left or right, countering the torque from the main rotor. Effect on Flight: The pedals control the yaw of the aircraft—the direction the nose is pointing. Pushing the left pedal: Makes the helicopter's nose yaw to the left. Pushing the right pedal: Makes the helicopter's nose yaw to the right. In a hover, the pilot constantly makes small adjustments to the pedals to keep the nose straight. Analogy: The pedals are the helicopter's "steering wheel" for pointing the nose left or right. The Throttle Location: Usually a twist-grip on the collective lever itself. Mechanism: The throttle controls the power output of the engine. More power is needed to maintain rotor speed (RPM - Revolutions Per Minute) when the blades are working harder. Effect on Flight: When a pilot pulls up the collective to climb, the blades create more drag. The pilot (or an automatic system called a governor) must increase the throttle to provide more engine power and keep the rotor RPM constant. If the rotor RPM drops too low, the helicopter will lose lift. If it's too high, it can damage the aircraft. The throttle's job is to manage the power to maintain the optimal RPM. Analogy: The throttle is like the accelerator in a car, providing power to the engine.
Guided Practice (With Solutions)