Aerodynamic Principles Lesson 3 PDF

Private Pilot Ground School Lesson 3 of 15: Aerodynamic Principles Chapter 3 Objectives and Completion Standards Objectives Become familiar with aerodynamic principles, including the four forces of flight, stability, maneuvering flight, and load factor. Understand stall and spin char...

Private Pilot Ground School Lesson 3 of 15: Aerodynamic Principles Chapter 3 Objectives and Completion Standards Objectives Become familiar with aerodynamic principles, including the four forces of flight, stability, maneuvering flight, and load factor. Understand stall and spin characteristics as they relate to training airplanes. Learn the importance of prompt recognition of stalls. Completion Standards Demonstrate understanding of stalls, spins, and basic aerodynamic principles during oral quizzing by the instructor. Sequence of Content 3.1 Four Forces of Flight 3.2 Stability Lift Three Axes of Flight Airfoils Longitudinal Stability Pilot Control of Lift Center of Gravity Position Weight Lateral Stability Trust Directional Stability Drag Stalls Ground Effect Spins 3.3 Aerodynamics of Maneuvering Flight Climbing Flight Left-Turning Tendencies Descending Flight Turning Flight Load Factor  3.1 Four Forces of Flight Lift Airfoils Pilot Control of Lift Weight Trust Drag Ground Effect The Four Aerodynamic Forces of Flight Lift: key aerodynamic forces that opposes weight. Weight: downward pull towards the Earth by gravity. Thrust: forward force that propels the aircraft through the air. Drag: force opposing thrust. The four forces acting on an airplane in flight are: lift, weight, thrust, and drag All four forces are in equilibrium in straight-and-level, unaccelerated flight. Sir Isaac Newton's 3 laws of motion 1st Law: An object in motion tends to stay in motion unless acted on by some force. * A running dog won’t slow down unless you pull on his leash. 2nd Law: Force = mass x acceleration (F = ma) * Can a bulldozer & a bullet have the same Force? How? 3rd Law: For every action there is an equal and opposite reaction. * Think about putting your hand out a car window. * Air striking below the hand/wing pushes the hand/wing upward.  Daniel Bernoulli’s “Bernoulli Principle” “As the velocity of a fluid (air) increases, its internal pressure decreases.” Higher Velocity = Lower Pressure Experiment time: Take your slip of paper and create lift! Lift Vocabulary  Wing Vocabulary Imaginary line halfway between the upper surface and lower surface of The rear tip of the wing the airfoil that intersects the chord line at the leading and trailing edges The most forward point of the wing Line from the Leading Edge to the Trailing Edge  The Lift Equation Explained L = CL x ½pv2 x S CL (Coefficient of Lift): wing shape, wing camber, Angle of Attack (AOA). Can change in flight by changing AOA. p (Rho) (Air Density): how many air molecules in a given space - affected by changes in pressure, temperature, altitude, & humidity. Higher air density = more air molecules = more lift. v (Velocity): True Airspeed (TAS): faster airspeed = more lift generated. Can change in flight by changing airspeed. Note velocity is squared indicating it has a large proportional effect to other variables. * When airspeed decreases, you MUST increase the Angle of Attack (AOA) to maintain the same amount of lift. S (wing Surface area): more wing surface area = more lift generated  Quiz Questions Select the true statement regarding the creation of lift. A. The Coefficient of Lift changes due to pressure, temperature, altitude, and humidity. B. When speed decreases, you must increase the angle of attack to maintain the same amount of lift. C. Air Density and Wing Surface area are two components of the Lift Equation that can be changed in flight. B. When speed decreases, you must increase the angle of attack to maintain the same amount of lift.  Summarizing Lift Lift is a result of BOTH Newton’s Third Law and Bernoulli’s Principle: ○ Newton’s 3rd Law: for every action there is an equal and opposite reaction – because there is a downwash at the trailing edge of the wing, there must be an upwash at the leading edge of the wing. Stick your hand out of a high-speed car and move it up and down like a wing changing its Angle of Attack (AOA). ○ Bernoulli’s Principle: As velocity increases, pressure decreases. The curve of the upper portion of the leading edge compresses the air above the wing. That compression, just like in Bernoulli’s Tunnel, increases the air velocity and decreases the air pressure. Think of how a tornado works – fast moving low pressure sucks the slow-moving high pressure from below upward – the same thing is happening on a wing – the low-pressure air above the wing is sucking the high-pressure air under the wing upward. Note: ALL shapes with pressure differentials create lift. Think of how well a Frisbee flies!  Airflow Over a Wing Video Bernoulli’s Principle: as airflow is compressed over wing (upwash), air velocity speeds up and pressure decreases Lower pressure above the wing and high pressure below the wing Lower pressure above the wing pulls the wing upward  Lift Vectors and Pressure Distribution L L Vertical Component L of Lift (VCL) Total Lift L L L L L L H L L L L The direction of H H the wind in relation to the direction of the Point on wing chord line where lift is flight path. concentrated – aka, the Center of Lift  Angle of Attack The Critical AOA is(AOA) Angle of attack (AOA) is the angular difference between the chord line and the relative wind. the angle of attack above which air cannot flow smoothly over the surface of the wing resulting in a stall 🡪 the wing is still producing some lift, but it is not enough lift to overcome the effect of weight Aircraft always stall sat the same angle of attack, regardless of airspeed, flight attitude, or weight. Most Cessna 172s don’t have an AOA indicator, so we use the indicated airspeed to help determine the approximate stall point. As altitude increases, the indicated airspeed at which a given airplane stalls in a particular configuration will remain the same regardless of altitude. Well Below Critical AOA Nearing Critical AOA Beyond Critical AOA Airflow begins to separate from Airflow completely separates Airflow adheres to top of wing. top of wing at rear moving from top of wing. forward. Chord Chord Chord Line Line Line Relative Relative Relative Wind Wind Wind  Quiz Questions Select the true statement regarding stalls. A. For a given airplane, stalls always occur at the same angle of attack (AOA), regardless of airspeed, flight attitude, or weight. B. For a given airplane, stalls occur at different airspeeds, regardless of angle of attack, weight, or flight attitude C. When an aircraft wing stalls, no lift is produced on that wing. A. For a given airplane, stalls always occur at the same angle of attack (AOA), regardless of airspeed, flight attitude, or weight. Angle of Attack (AOA) vs. Coefficient of Lift (CL) - Increasing the AOA will increase lift until the maximum Coefficent of Lift (CLMAX) – this is the Critical AOA. - All aircraft stall at the Critical AOA. - The aircraft is still producing lift in a stall, but not enough to overcome the force of weight.  Wing Shapes and Where on Wing Stalls Progress Taper: wing narrows towards tip. Regular – used by Cessna 172 Moderate Taper High Taper Elliptical - curved Pointed Tip Sweepback Why do you think the Cessna 172 uses the “Regular” shaped wing? Flaps Flaps: increases the Angle of Attack (AOA) and surface area of the wing. Extending wing flaps (“lowering flaps”) increases both lift & drag Lowering flaps reduces stall speed. Up Down  Quiz Questions How does lowering the flaps affect drag and lift? A. Decreases both drag and lift B. Decreases drag and increases lift C. Increases both drag and lift C. Increases both drag and lift  Forms of Drag Induced Drag: formed from the production Min Drag of lift. L/Dmax - Increases as AOA/lift increases. - Decreases as airspeed increases. Parasite Drag Drag that is not produced by the production of lift. Increases as airspeed increases. There are 3 forms of Parasite Drag: ○ Form Drag Drag due to the shape of the aircraft ○ Interference Drag Parasite From the interference of airflows from different parts of the aircraft ○ Skin Friction Drag  Quiz Questions What are the three forms of Parasite Drag? A. Skin Friction drag, Interference drag, and Form drag B. Form drag, Induced drag, and Interference drag C. Interference drag, Friction drag, and Induced drag A. Skin Friction drag, Interference drag, and Form drag  Ground Effect Ground Effect is an increase in lift caused primarily by a reduction in Induced Drag. Occurs within 1 wingspan of the ground & increases the closer you are to the surface. The amount of thrust required to produce lift is reduced so the airplane can lift off at a lower-than-normal speed. Pro: Helps with Soft Field Takeoffs Con: causes the aircraft to “float” above the runway during landings, typically from having too much airspeed.  Quiz Questions What is a result of Ground Effect? A. Induced drag increases the closer the aircraft is to the ground B. More lift is produced within 2 wingspans of the runway C. Thrust required to produce lift is reduced so the aircraft can lift off at a lower-than-normal speed C. Thrust required to produce lift is reduced so the aircraft can lift off at a lower-than-normal speed  Three Ways a Pilot Can Control Lift Changing airspeed Changing angle of attack Employing high-lift devices such as trailing edge flaps  3.2 Stability Three Axes of Flight Longitudinal Stability Center of Gravity Position Lateral Stability Directional Stability Stalls Spins  Three Axes of Moving the elevator controls Flight Moving the aileron controls Moving the rudder controls Controlled by forward/aft Controlled by turning Controlled by pushing rudder pressure on yoke yoke left/right left/right Longitudinal Stability : - Longitudinal Stability: pitching motion, or tendency of aircraft to move about its lateral axis (running along the Lateral Axis through the Center of Lift (CL) line in the wings) - Longitudinally stable aircraft tend to return to CP trimmed AOA after displacement. - Think of the Center of Lift (CL) (aka, Center of Pressure (CP)) as the point the aircraft would balance on a string. - The Center of Gravity (CG) is the pivot point (fulcrum) of the aircraft where all the weight is centered. The aircraft rotates around the CG in the air. - The Tail Down Force (TDF) is the opposing force to the CG required to keep the aircraft balanced – it Aircraft are has negative AOA (negative lift) which pulls the tail designed to downward – downwash from the prop & wing TDF increases the TDF keep the CG - More thrust (power) = more TDF = higher AOA forward of the CL CL/CP CG TDF  CG Position Affects Longitudinal Stability - The position of the CG is determined by the distribution of weight. - The CG is typically in front of the CL (CP) - this improves longitudinal stability. - The CG has a forward limit and an aft limit providing CG “envelope.” - The area within the envelope is considered the CG “range.” - When the CG is within the CG range, it is considered controllable & longitudinal stable – the elevator should be effective during all approved maneuvers. - CG TOO FORWARD: if the CG is forward of its Forward CG limit, the aircraft becomes “nose heavy” – the elevator may be unable to hold the nose up & could cause a nose strike during landing. - CG TOO AFT: (more dangerous) if the CG is aft of its Aft CG limit, the aircraft becomes “tail heavy” – the elevator may Center of Gravity (CG) limits are listed in every POH be unable to recover from a a stall or spin condition.  Quiz Questions What is an undesirable flight characteristic of an airplane with a CG located aft of the aircraft’s aft CG limit? A. Nose strike during landing B. Difficulty recovering from a stalled condition C. Stalling at a lower-than-normal airspeed B. Difficulty recovering from a stalled condition Lateral Stability : along the Longitudinal Axis - Helps return wings to a level attitude. - Primarily aircraft design, but pilot can adjust by weight distribution (fuel selection in fuel tanks) - Dihedral: stabilizes the aircraft along the longitudinal axis - upward angle of airplanes wings with respect to horizontal (shallow V) – if one wing lifts & other drops, AOA & lift increase on dropped wing rolling the aircraft level - For prop aircraft: prop wash during high power & low airspeeds decreases lateral stability (and longitudinal stability) – less airflow over the outer portion of the wings (ailerons)  Quiz Questions Dihedral is used to stabilize the aircraft around which axis? A. Lateral Axis B. Vertical Axis C. Longitudinal Axis C. Longitudinal Axis Directional Stability: along the Vertical Axis Primarily from Vertical Stabilizer on the tail Aircraft acts like a weather vane pivoting along the CG If nose pivots left, tail must pivot right Propwash circles the aircraft cabin and fuselage primarily striking the tail of its left side – this pushes the tail right & swings the nose left – contributes to Adverse Yaw (tendency of propeller aircraft to yaw to the left at high thrust/power)  Stability Concepts Static Stability Dynamic Stability (waves) Positive — the tendency for an Positive — oscillating back to the aircraft to return to the position from position from which the aircraft was which it was displaced (Cessna 172s displaced (damped oscillations) are designed for Positive Static Neutral — constant amplitude Stability) oscillations Neutral — neither returning or Negative — oscillations increasing deviating. Constant attitude away from the position from which Negative — the tendency for an the aircraft was displaced aircraft to deviate from the position Maneuverability from which it was displaced Controllability Maneuverability is the characteristic of Controllability is the ability of and an aircraft that permits us to maneuver airplane to respond to your control it easily and allows it to withstand the inputs. stress from the maneuvers. An airplane said to be inherently stable will require less effort to control.  Static Stability Concept Cessna 172s are designed for Positive Static Stability Stall: wing exceeds Critical AOA – lift can no longer overcome weight  Secondary Stalls Secondary stalls occur after the initial stall when the aircraft does not have enough airspeed for the Angle of Attack (AOA) and stalls again. Secondary stalls are prevented by initiating first stall recovery and levelling the aircraft near the horizon to build airspeed (> Best Angle of Climb (VX) airspeed) before raising the nose again.  Spin Concepts Two requirements for a spin: stall and yaw BOTH wings are stalled in a spin Lower wing stalls more than the raised wing (creating yaw) ○ Stall happens unevenly across the wings ○ Lower wing has less lift & more drag - pulls the airplane downward in direction of lower wing Aircraft rotates vertically downward in a corkscrew pattern * Which direction would an aircraft spin if the right wing was raised during a stall? Spin Visualized  Spin Recovery: Acronym (PARED) 1. Power (throttle) - idle 2. Ailerons - neutral 3. Rudder - full 4. Elevator – briskly opposite direction of full forward. rotation Neutralize rudder after spin stops 5. Dive – Recover Back yoke pressure Let’s watch of video of a Cessna 172 Spin Recovery to return to level flight  Quiz Questions Select the true statement regarding spins. A. Both wings are stalled in a spin B. The lower wing has more lift and less drag C. The first step in spin recovery is full opposite rudder A. Both wings are stalled in a spin  3.3 Aerodynamics of Maneuvering Flight Climbing Flight Left-Turning Tendencies Descending Flight Turning Flight Load Factor  Climbing Flight - Aerodynamic forces still in equilibrium – flight path is just inclined upward - Total force of weight no longer perpendicular to the flight path – instead, has 2 components: 1st: acting perpendicular (90˚) to flight path 2nd: rearward component of weight - same direction as drag - Climb: increase pitch with increase power for sustained climb Left-Hand Turning Tendencies: Torque - Newton’s 3rd Law of Motion: for every action there is an equal and opposite reaction. - For the prop turning clockwise action, there is an equal and opposite aircraft turning counterclockwise reaction – this reaction rolls the aircraft to the left around the longitudinal axis. Front View Rear View Left-Hand Turning Tendencies: Gyroscopic Precession - Occurs only when aircraft attitude changes. - A spinning propeller is a gyroscope. - When the aircraft changes pitch, force is applied to the top of the spinning propeller. - Gyroscopic Precession: a force applied to a gyro (top of spinning prop) acts in the direction of rotation and approximately 90˚ ahead of the point where force is applied (prop center yaws left). Let’s spin up the bicycle wheel to demonstrate Gyroscopic Precession Left-Hand Turning Tendencies: Asymmetric Thrust (aka, P-Factor) - Occurs during climbs: high AOA and high power settings. - Most U.S. propellers spin clockwise - the descending blade on the right side (seen from the cockpit) has a higher AOA compared to the ascending blade on the left. - The higher blade AOA on the right side produces more thrust than the left. - Higher right side thrust yaws the aircraft left around its Vertical Axis. - P-Factor: (P = Prop): assymetrical thrust caused by a higher Angle of Attack on the right side descending propellor blade which causes the aircraft to yaw to the LEFT. - Counteract this tendency by stepping on the right rudder pedal. - Your mantra: “Step on the Ball!”  Quiz Questions What is P-Factor? A. For the prop turning clockwise action, there is an equal and opposite aircraft turning counterclockwise reaction B. A force applied to a gyro (top of spinning prop) acts in the direction of rotation and approximately 90˚ ahead of the point where force is applied (prop center yaws left). C. Asymmetrical thrust caused by a higher angle of attack on the right descending propeller blade, which causes an aircraft to yaw to the left. C. Asymmetrical thrust caused by a higher angle of attack on the right descending propeller blade, which causes an aircraft to yaw to the left. Left-Hand Turning Tendencies: Spiraling Slipstream - Spiraling Slipstream: spinning propwash spiraling around the aircraft cowling, wings, & fuselage before striking the left side of the Vertical Stabilizer. - Rotates the tail of the aircraft right around the Vertical Axis and rotates the nose left. Vertical Axis Tail yaws right Nose yaws left  Descending Flight - Aerodynamic forces still in equilibrium – flight path is just inclined downward - Total force of weight no longer perpendicular to the flight path – instead, has 2 components: 1st: acting perpendicular (90˚) to flight path 2nd: forward component of weight - same direction as thrust - Descent: decrease pitch with decreased power for sustained descent Turning Flight: increase AOB = increase back pressure to keep level Vertical Component to Lift (VCL): lift component parallel & opposing weight Horizontal Component to Lift (HCL): primary force causing an aircraft to turn - lift component perpendicular to VCL & weight Total Lift: vector representing combination of Horizontal & Vertical Lift Components – opposes Resultant Load Resultant Load: created in a turn – force parallel and opposing Total Lift – measure of weight supported by the wings – the Load Factor is 1G (measure of Earth gravity) in straight-and-level flight and increases with increasing AOA Centrifugal Force: apparent force opposing HCL – pulls aircraft away from turn direction lift of lift of Increase AOA = Increase Lift = Increase Induced Drag Aileron deflected down Aileron of lift deflected up of lift Decrease AOA = Decrease Lift = Decrease Induced Drag  Quiz Questions What is the primary force causing an aircraft to turn? A. Centrifugal force B. Horizontal Component of Lift C. Vertical Component of Lift B. Horizontal Component of Lift  Turning Flight: to keep Coordinated – STEP ON THE BALL Coordinated: rate of Slip: rate of turn is too Skid: rate of turn is too turn equals AOB – nose slow for AOB – nose great for AOB – nose on turn radius outside turn radius inside turn radius  Load Factor - Load Factor: ratio of load supported by the wings to the actual weight of the airplane - Maintaining level flight: as AOB increases, the Load Factor (Gs) & Stall Speed Increase - Stall speeds (VS1 & VSO) are found in the aircraft POH - The maximum AOB is most Normal category training aircraft is 60 ˚ Maintaining coordinated, level flight at 60˚ AOB – what is the Load Factor (Gs)? What is the % increase in stall speed? ?  Quiz Questions Select the true statement regarding load factor. A. Load Factor is the ratio of the load supported by the airplane’s wings to the actual weight of the airplane. B. Stall speed decreases as load factor increases. C. The maximum angle of bank in most normal category training aircraft is 90˚. A. Load Factor is the ratio of the load supported by the airplane’s wings to the actual weight of the airplane. Understanding the Load Factor Chart Load Factor (G Unit) increases with an increase in Angle of Bank (AOB˚) This chart represents the load the aircraft experiences only while attempting to maintain the current altitude *** You CAN roll to 90˚ AOB without placing any Applies ONLY additional load on the aircraft if you don’t try to when trying to maintain altitude by pulling back on the yoke maintain altitude The Load Factor at 0˚ AOA = 1.0 (1 G) To find the weight of an aircraft at different AOA˚: multiply the aircraft weight (lbs) x the load factor (n) Example: Aircraft weight: 2,300 pounds Angle of Bank (AOB˚): 60˚ Load factor at 60˚ AOB: 2.000 (2 Gs) Aircraft Weight (2,300 pounds) x 60˚ AOB Load factor (2.000) = 4,600 pounds The airplane structure would be required to support 4,600 pounds during a 60˚ banked turn while maintaining altitude.  Limit Load Factor - Limit Load Factor: ratio of the load supported by the airplane’amount of stress (Load Factor in Gs) an aircraft can withstand before structural damage or failure. - Maneuvering Speed (VA): the max airspeed of full, abrupt control movement without overstressing the airframe. Any airspeed > VA can overstress the aircraft during maneuvers and turbulence. At airspeeds < VA, aircraft will stall before overstress. VA varies with weight – VA decreases with decreasing weight (subject to more rapid acceleration from gusts and turbulence). V-g Diagram Let’s discuss some real word scenarios. Homework for Next Time Read: Jeppesen’s Guided Flight Discovery Private Pilot Handbook ○ Chapter 4: The Flight Environment Read: FAA’s Pilot’s Handbook of Aeronautical Knowledge ○ Chapter 14: Airport Operations ○ Chapter 15: Airspace Read: FAR/AIM ○ AIM Section 2-3 ○ AIM Section 4-3-25  Any Questions? Email: [email protected] Zac’s Cell: (318) 205-2748 Avian Front Desk: (360) 674-2111