4 Forces of Flight

Forces Acting on an Aircraft Thrust Drag Lift Weight (or Load) *All forces are in equilibrium during unaccelerated flight* Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Thrust Moves the airplane through the air The forward force produced by a powerplant In equilibrium Thrust = Drag Controlled by pilot via Throttle Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Drag Opposes the force of Thrust Parallel and in the opposite direction of the relative wind Controlled by pilot by “dirtying the airplane” Comes in two types: Parasitic Drag Induced Drag Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Lift Result of the dynamic effect of air acting across the airfoil Keeps the airplane flying Can be controlled by the pilot (to an extent) Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Weight (Load) Force of gravity acting upon the mass of the entire system Doesn’t always oppose lift Load is the opposition of lift We’ll come back to this Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Newton’s Laws 1st Law: Object at rest, remains at rest, unless outside forces act upon 2nd Law: Force = Mass x Acceleration 3rd Law: Every action has an equal and opposite reaction Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

Bernoulli’s Principle As the velocity of a fluid increases, its overall pressure decreases Think of the following illustration of a tube: Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

Bernoulli’s Principle and the Airfoil The airfoil is a cut off portion of Bernoulli's tube An airfoil is any surface that provides aerodynamic force when interacting with a stream of air Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Newton’s Third Law As air hits wing, wing must go upward while air goes downward Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Labeling the Airfoil The Airfoil interacts with the fluid by pushing some upward and some downward Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Angle of Incidence The wing is mounted on the airplane in such a way that the chord line at the wing tip is more aligned with the longitudinal axis than the root Some people refer to this as twist Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Angle of Attack An increase of the angle of attack will lead to more lift being generated That is, until the airfoil reaches its “Critical Angle of Attack” Any increase further than the Critical AoA, the airfoil will “stall” Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Stall A stall is caused by the separation of airflow from the wing’s upper surface The result is the loss in production of lift with a exponentially proportional increase in drag An airfoil will ALWAYS stall when reaching its Critical AoA Stalls will always occur regardless of airspeed Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

YOU CAN STALL AT ANY AIRSPEED! I REPEAT YOU CAN STALL AT ANY AIRSPEED! Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Stall vs. Airspeed Airspeed is just a reference to the stall Consider a pilot going downward to the earth: If the pilot decided to pull back on the yoke to regain level flight too quickly He will increase the AoA beyond its critical value The pilot will stall until he reduces the AoA and generates airflow over the wings Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. F-16 Stalls at 400 Knots https://www.youtube.com/watch?v=Rv9YC-gaNYo Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Stall Strips Two metal strips attached to leading edge Disrupt airflow at high AoA This causes the wing area behind them to stall before the wingtips Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Pilot Control of Lift Change Angle of Attack Increase Speed High-Lift Devices Flaps Flaps are used to increase the efficiency of the wing and to decrease stall speed Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Drag and Lift The two are directly proportional Any change in lift results in a proportional change in drag Likewise any change in drag results in a change of lift The Aeronautical Engineer must determine the best use of this tradeoff Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Flaps and Stalls Increase lift (and drag) Increases the wing’s camber Changes the average chord line Both of these together change the angle of attack Also remember Newton’s 3rd Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Center of Gravity The place where all of the weight is concentrated on the system Imagine a string holding up the airplane Does it stay straight and level? Does it flip forward or backward? Does it roll? Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Drag in Context We said earlier that drag opposes thrust (or power) Comes in the form of Parasitic or Induced Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Parasite Drag Caused by the aircraft surface which deflects or interferes with the smooth airflow around the aircraft Divided into three types: Form Interference Skin-friction Drag Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Form Drag Results from the turbulent wake from the separation of the surface of a structure Determined by the size and shape of the structure protruding into the wind Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Interference Drag When airflow around one part of the airflow interacts with the airflow around adjacent parts Example: Wings join the fuselage Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Skin Friction Drag Caused by the roughness of the surfaces of the airplane Even though they appear clean, they may be rough under a microscope Cirrus wing vs. Archer wing Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Induced Drag Generated by the airflow circulation around the wing as it creates lift “Drag due to lift” High pressure underneath joins low pressure above Causes a spiraling vortex which trails behind each wing Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Drag Proportionality Induced drag is inversely proportional to the square of the speed Parasite drag is directly proportional to the square of speed Combine Induced and Parasite – Total Drag The place where the lowest amount of total drag occurs is known as L/D Max L/D Max is the lowest drag, but the greatest lift – resulting in the speed of best glide Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Total Drag Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. Ground Effect The result of the earth’s surface altering the airflow patterns about the airplane Airplane may become airborne before reaching its recommended takeoff speed Induced drag decreases and excess speed in the flare may cause floating Happens within one wingspan of the surface Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.

© 2015 Coast Flight Training. All Rights Reserved. References Pilot’s Handbook of Aeronautical Knowledge Since the beginning of time, humans have always been fascinated with birds. We have always wanted to fly, but could never understand the relationship between lift and weight. As early as the 1500s, Leonardo Da Vinci began making sketches of wings. However, these sketches were flawed due to their birdlike nature. © 2015 Coast Flight Training. All Rights Reserved.