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Principles of Aircraft Flight

Jul 21, 2024

Principles of Aircraft Flight

Introduction

  • Critical question: How do airplanes fly?
  • Analysis beyond FAA requirements
  • Importance of understanding flight mechanics

Airplane Components

Main Parts

  • Propeller: Located at the front, driven by engine
  • Fuselage: Main body where passengers sit
  • Tail Components:
    • Vertical Part: Includes rudder, tilts side to side
    • Horizontal Part: Includes elevator, moves up and down
  • Wings: Extend from fuselage, may have struts for support
  • Landing Gear: Wheels at the bottom (sea planes have different setup)

Four Main Forces on an Airplane

  • Lift: Upward force
  • Weight: Downward force, counteracts lift
  • Thrust: Forward force
  • Drag: Opposes thrust
  • Balance: Lift > Weight to climb, Thrust > Drag to move forward

Theories of Lift

Correct Theory

  • Airfoil Cross-Section: Shape of the wing
  • Conservation of Momentum: Air pushed down, wing pushed up

Incorrect Theory: Equal Transit Theory

  • False Claim: Air molecules traveling over top and bottom must meet at the same time
  • Reasons It's Wrong:
    • No physical principle enforcing equal transit
    • Experimentally disproved
    • Paper airplanes demonstrate flaws

Bernoulli's Principle

  • Explanation: Decrease in pressure correlates with increase in velocity
  • FAA Exam: Know that increased velocity = decreased pressure

Factors Affecting Lift

  • Shape and Size of Airfoil: Different shapes/areas affect lift
  • Angle of Attack: The angle between the wing and relative wind impacts lift
  • Fluid Characteristics: Density, viscosity, and compressibility of air

Challenges in Calculating Lift

  • Complexity: Difficult due to turbulent flow and three-dimensional factors
  • Navier-Stokes Equations: Complex equations for predicting lift
  • Limitations: Difficult to solve, practical approximations used

Measuring Lift

  • Wind Tunnels: Common method for experimental measurements
  • Coefficient of Lift (C<sub>L</sub>): Calculated experimentally

Flaps and Spoilers

  • Usage:
    • Increase lift but also increase drag
    • Mostly used during take-off and landing

Stability and Control

Three Axes of Flight

  • Longitudinal Axis: Nose to tail (pitch)
  • Lateral Axis: Wingtip to wingtip (roll)
  • Vertical Axis: Perpendicular through aircraft (yaw)

Aircraft Movements

  • Pitch: Controlled by elevator
  • Roll: Controlled by ailerons
  • Yaw: Controlled by rudder

Stability Types

  • Stable: Returns to original position after disturbance
  • Unstable: Deviates further after disturbance

Stalls and Spins

  • Stall: Caused by excessive angle of attack, loss of lift
  • Spin: Uncoordinated stall, very dangerous

Forces in Maneuvering Flight

  • Climbing: Lift exceeds weight
  • Turning: Forces not in equilibrium, requires coordinated control

Left-Turning Tendencies

  1. Torque: Reaction to propeller rotating clockwise
  2. P-Factor: Asymmetrical thrust due to angle of attack
  3. Corkscrew Effect: Spiraling airflow from propeller impacting vertical stabilizer
  4. Gyroscopic Precession: Force applied 90 degrees ahead of rotation

Modern Aircraft Design

  • Blended Wing Body: Efficient but impractical due to existing infrastructure

Summary

  • Lift generation and factors
  • Forces on an airplane and stability
  • Left-turning tendencies and their causes
  • Different aircraft configurations

Are there any questions?

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