Aerodynamics Dane Johannessen
Overview Aerodynamics What are the forces?
How do these forces affect flight? What factors affect these forces?
What is Aerodynamics? The study of forces acting on an object in motion as it passes through air.
Laws of Motion Objects in motion stay in motion
Force is the change in momentum with respect to time For constant mass For every action there is an equal and opposite reaction
What are the forces? Lift Drag Weight Thrust
Lift The vertical forces pushing up on a body during flight.
General Equation: L = Lift Force ρ = density v = velociy A = area Cl = Lift coefficient that is usually determined experimentally
Lift in Air Foils Based on pressure differences (Bernoulli’s Principle) Top Higher velocity and decreased pressure Bottom Lower velocity increased pressure
Factors Affecting Lift
Shape of object Higher curve = greater lift Size of the object L = constant x A Velocity of the object L = constant x v² Properties of the air L = constant x ρ Angle of attack Increased angle = increased lift
Demonstration For more information on paper airplanes
Drag Drag is the force that acts in the same direction as airflow
General Equation: Fd = Drag Force ρ = density v = velocity A = area Cd = Drag Coefficient that is usually determined experimentally
How Shape Affects Drag Different shapes of the same frontal area lead to different drag coefficients:
Lift to Drag Ratio General Equation:
Weight Weight is the force on an object due to gravity
Based on mass and gravitational acceleration General Equation: W = Weight Force m = mass g = gravity
Thrust Thrust is the force that propels an object through air
General Equation: F = thrust force t = time m = mass v = velocity ṁ = mass flow rate ṁ = ρvA
Thrust Producers of thrust Main thing to take away Propellers
Fans in jet engines Hot gases from rocket engines Main thing to take away Thrust must be greater than weight
Thrust to Weight Ratio General Equation: If F/W is high
High acceleration High Climb rate If F/W > 1.0 Acceleration can be vertical
Summary Aerodynamics 4 Forces on a plane Lift > Drag
Dependent on shape, size, velocity, air, angle Drag Dependent on shape Weight Thrust Lift > Drag Thrust > Weight
Sources Helpful Websites
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