Reference: Chapter 4, Chapter 5 PHAK

Essential Aerodynamics

Take the Course Don't just 'wing it.' Get the facts on aerodynamic principles that matter-but forget dry textbooks and dense equations. This course covers vital concepts in an easy-to-digest, straightforward manner.

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Learning Objective (Index)

• Learning Objective (Index)
• Homework
• The Four Forces of Flight
• Lift
• Airfoil Design Characteristics
• Airfoil Sections and Terminology
• Varying Angles of Attack
• Bernoulli’s Principle
• Airflow on the Airfoil
• Newton’s Third Law
• Pressure Gradient
• Wing Tip Vortex
• Critical Angle of Attack and Stalls
• Lift Equation
• Lift Creation by Other Factors Which Pilot Have No Control
• High Lift Devices
• Drag
• Parasite Drag
• Form Drag
• Interference Drag
• Skin Friction Drag
• Induced Drag
• Ground Effect
• Lift-Drag Ratio
• Wake Turbulence Avoidance
• Winglets
• Thrust
• Propeller
• Propeller Twist
• Left Turning Tendencies
• Propeller Factor - P-Factor
• Torque
• Gyroscopic Precession
• Spiraling Slipstream
• Weight
• Stability and Controllability
• Controllability
• Forward CG Effects
• Aft CG Effects
• Airplane Axis
• Airplane Stability
• Static Stability
• Dynamic Stability
• Longitudinal Stability (Pitching)
• Lateral Stability (Bank)
• Directional Stability (Yawing)
• Dutch Roll (Free Directional Oscillation)
• Spiral Instability
• Forces in Turn
• Normal, Slipping and Skidding Turn
• Adverse Yaw
• Correcting Adverse Yaw
• Load Factor
• Load Factor and Stalling Speeds
• Vg Diagram (Velocity vs Load Factor)
• Maneuvering Speed (Va)
• Quiz

The Four Forces of Flight

This forces act upon all aircraft in flight. Understanding how these forces work and knowing how to control theme with the power and flight controls are essential to flight

• Thrust
• The forward force produced by the power plant - propeller.
• It opposes the force of drag
• Lift
• The force that acts perpendicular to the flight path
• It opposes the force of weight
• Drag
• A rearward, retarding force caused by airflow disruption limiting the performance of the airplane.
• It opposes the force of thrust
• Weight
• The force that pulls the aircraft downward due to gravity
• It opposes the force of lift

Thrust = Drag

Aircraft will not accelerate or decelerate

Lift = Weight

Aircraft will not climb or descend

Lift

Airfoil Design Characteristics

An airfoil is a structure designed to obtain reaction upon its surface from the air through which it moves or that moves past such a structure

• Air acts in various ways when submitted to different pressures and velocities

Airfoil Sections and Terminology

Flight Path: The path as the airplane travels along

Relative Wind: The airflow that is opposite and parallel of the direction of the flight

Angle of Attack: Is the angle (Angular difference) between the Relative Wind and the Chord Line

Varying Angles of Attack

A pilot can fly an aircraft at varying angles of attack to maintain straight and level flight at various airspeed

• The more airflow an airfoil receives, the more effective it becomes
• If the pilot set an appropriate power setting, pilot should maintain a normal AOA

• The less airflow an airfoil receives, less lift can produce
• Pilot should increase the AOA to maintain a straight and level flight

• The more airflow an airfoil receives, more lift can produce
• Pilot should decrease the AOA to maintain a straight and level flight

Bernoulli’s Principle

When air is subjected to an increase in velocity it is also accompanied by a decrease in its pressure and vice-versa

Airflow on the Airfoil

• Airflow Over the Wing
• Increase travel distance resulting in an increase in velocity an decrease in pressure
• With more Airflow passing through airfoil more amount of Velocity Less amount of Pressure
• Airflow Under the Wing
• Decrease travel distance resulting in a decrease in velocity and increase in pressure
• With more Airflow passing through airfoil more amount of Pressure Less amount of Velocity

0 Airspeed

Medium Airspeed

High Airspeed

Newton’s Third Law

For every action, there is an equal and opposite reaction

Pressure Gradient

Air always moves from areas of High Pressure to areas of Low Pressure

Wing Tip Vortex

• The vortex flows behind the airfoil creating a downwash that extends back to the trailing edge of the airfoil.
• This downwash results in an overall reduction in lift for the affected portion of the airfoil.
• Manufacturers have developed different methods to counteract this action
• Winglet

Critical Angle of Attack and Stalls

Critical Angle of Attack

Is the angle at which an aircraft will stall regardless of its airspeed.

Stalls

An aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical AOA.

• A stall can occur at any pitch attitude or airspeed.

Stall Recovery

Lift Equation

$Lift = (Coefficient of lift * Air Dendity * Velocity Square * Surface Area Of The Wing)/2$

L = Lift

CL = Coefficient of Lift

Is just a number that is associated with:

A particular shape of an airfoil

The airfoils angle of attack

p = Air Density

V2 = Velocity

S = Surface Area of the Wing

Lift Creation by Other Factors Which Pilot Have No Control

This factors are regarding wing design

• Planforms
• Elliptical
• Ideal Subsonic planform
• minimum induced drag for a given aspect ratio

• Tapered
• Good at weight and stiffness
• Is not as efficient aerodynamically as elliptical

• Regular
• Tendency to stall first at the wing root so provides adequate stall warning
• Adequate aileron effectiveness
• Quite stable
• Low cost, Low speed airplanes

• Sweepback
• For airplanes developed to operate at very high speeds
• For grater aerodynamics cleanness and greater strength
• Require very precise and professional flying technique

• Camber
• Is the curvature of the wing


• Camber are focus design to increase the maximum coefficient of lift
• Minimize the stall speed of the aircraft
• Aspect Ratio
• Is the relation between the Length and Width
• The grater aspect ratio, the grater creation of lift

• Wing Area
• Is the total surface area of the wing
• The larger wing area, more lift the wing can produce

High Lift Devices

Flaps

• Flaps are the most common high-lift devices used on aircraft.
• Are attached to the trailing edge of the wing.
• These surfaces increase both lift and induced drag for any given AOA.
• They may be extended when needed and retracted into the wing’s structure when not needed.
• Do not extend flaps with a airspeed higher than Vfe (Max airspeed with flaps extended)
• In the Cessna 152 Vfe = 85knots kias
• Fowler flap and Slotted fowler flap change the camber and increase surface area, creating a lot of lift without producing tons of induce drag

• Initially small set of flaps (10º) increase a lot the lift without increasing the drag

• With more flaps, lift increase slightly and drag increase a lot, allowing making steep descend on approaches

Cessna 152 Flaps

• Single-Slot type
• Electrical Power
• Max deflection of 30°
• The circuit is protected by a 15 ampere circuit breaker

Leading Edge Devices

Are applied to the leading edge of the airfoil, the most common types are the fixed slots, movable slats, leading edge flaps and cuffs

Drag

Is the force that resists movement of the aircraft through the air

Parasite Drag

Form Drag

Is generated due to its shape and airflow around it.

Interference Drag

Comes from the intersection of airstreams that creates eddy currents, turbulence or restrict smooth airflow

Skin Friction Drag

Is the aerodynamic resistance due to the contact of moving air with the surface af an aircraft

❔

every surface, no matter how smooth is, has a rough surface when viewed under a microscope

Induced Drag

Is the drag creating when an airfoil creates lift. Byproduct of lift

• When an airfoil creates lift, the air that is below the wing with a high pressure tends to go upward on the tip of the wing, creating the wingtip vortices

• Induced drag decreases as the airspeed increases

• Alexander Lippisch
• Min 9:47
• Min 11:02
• Min 13:50

Ground Effect

Is found when the airplane is operating very close to the ground.

• When the airplane is in ground effect, there is a reduction in downwash and wingtip vortices
• Reduce the induced drag
• Is a greater concern during takeoff and landings

Lift-Drag Ratio

Is the amount of lift generated by a wing compared to its drag. A ratio of LD indicates airfoil efficiency

• Aircraft with more L-D Ratio are more efficient
• When an aircraft misses the engine power, the best Lift-Drag Ratio is the Vg (Best Glide Speed) Best generated lift with less amount of parasite and induce drag

Wake Turbulence Avoidance

When an airplane is creating wingtip vortices, those are moving out, down and away from the aircraft producing them, creating a hazard for the aircrafts that are moving below and behind

AC 90-23G - Aircraft Wake Turbulence

Official websites use .govA .gov website belongs to an official government organization in the United States.

www.faa.gov

Avoiding During Cruise Flight

1. Pilot should avoid flying though another aircraft flight path
2. Pilot should avoid following another aircraft on a similar flight path at an altitude within 1.000 ft of the preceding aircraft

Winglets

Thrust

Is the force which pulls the aircraft forward. Thrust must be greater than drag to start moving the aircraft

Propeller

The propeller is also considered an airfoil because it is a structure that interacts with the airflow to produce a desire effect (horizontal lift)

Propeller Twist

In order for a propeller to produce uniform thrust along the entire length of its blades, it is twisted to change the AOA Angle of Attack

Left Turning Tendencies

Because the propeller rotates clockwise as seen from the cockpit, there are 4 inherent tendencies that will cause the airplane to want to turn to the left

Propeller Factor - P-Factor

• When an airplane is flying at a positive (or increased) angle of attack, the “bite” of the downward moving blade is greater than the “bite” of the upward moving blade. Since the downward moving blade is on the right side (as seen from the cockpit) this moves the center of thrust to the right of the propeller hub. Thus, creating a left turning tendency. This is corrected by proper use of the right rudder by the pilot.

❔

Use of the wood propeller for better explanation

Torque

• Newton’s Third Law of Physics states: “For every action there is an equal and opposite reaction.” Because the propeller blades are rotating clockwise (as seen from the cockpit) the airplane will have a natural tendency to want to rotate in the opposite direction (counter-clockwise) creating a left turning tendency. This will be most pronounced during the takeoff roll with high power settings.

• Airborne: Force acting in longitudinal axis, creating a left roll tendency

• Ground: Because the aircraft have the force of rolling to the left, as the left side is moving down, the left main landing gear result with more ground friction (drag), causing a turning moment to the left

Gyroscopic Precession

• Gyroscopic Precession means that a spinning object will have a resultant force that is experience 90 degrees after (in the direction of rotation) of an effective or applied force.
• This turning tendency is most common on tailwheel aircraft during the takeoff roll and can be better understood with the visual aid.

Spiraling Slipstream

• The high-speed rotation of an aircraft propeller gives a spiraling rotation to its slipstream. At high propeller speeds and low forward (aircraft) speed, this spiraling rotation is very compact and exerts a strong sideward force on the aircraft’s vertical stabilizer. This force pushes the nose of the aircraft to the left and results in a left turning and left yawing tendency

Weight

Gravity is the force that pull all the bodies to the center of the earth

• The CG may be considered as a point at which all the weight of the aircraft is concentrated
• Lift is required to counteract the aircraft weight
• When Lift = Weight, there is a Straight-and-Level flight
• When Lift > Weight, there is a Climb
• When Lift < Weight, there is a Decent

Stability and Controllability

Controllability

The ability of an aircraft to respond to the pilot’s control

CG Effects On Aircraft Performance - Free CFI Tool

This free, interactive diagram helps you show your students how forward and aft centers of gravity affect performance.

www.boldmethod.com

Airplane Axis

An imaginary line about which a body rotates.

All aircraft has 3 axes of rotation

Airplane Stability

-Is the quality of an aircraft to correct for conditions that may disturb its equilibrium and to return to the original flight path.

Static Stability

Is the initial tendency to return to equilibrium

Dynamic Stability

How the aircraft will respond to a disturbance over time

Longitudinal Stability (Pitching)

Is the quality that makes an aircraft stable about its Lateral axis

• Location of the wings with respect to CG
• Location of the horizontal tail surface with respect to the CG
• Area or size of the tail surface
• With CG forward of the Center of Lift and with an aerodynamic tail-down force, the aircraft usually tries to return to a safe flying attitude.

Static Stability

• Most aircraft are designed so that the wings Center of Lift is to the rear of the CG creating a “Nose Heavy”. This required that there be a slight downward force on the horizontal stabilizer in order to balance the aircraft
• Horizontal stabilizer have a slight negative AOA, holding the tail down, counterbalancing the “heavy” nose

Dynamic Stability

• If the aircraft’s speed decreases, the speed of the airflow over the wing is decreased. As a result of this decreased flow of air over the wing, the downwash is reduced, causing a lesser downward force on the horizontal stabilizer, letting the aircraft start pitching down, increasing the airspeed
• As the aircraft continues in the nose-low attitude and its speed increases, the downward force on the horizontal stabilizer is once again increased. Consequently, the tail is again pushed downward and the nose rises into a climbing attitude.
• Because the aircraft is dynamically stable, the nose does not lower as far this time as it did before, and does not climb as much as did before

How to know which type of static and dynamic stability have your aircraft?

1. Trim the aircraft for “hands off” control in level flight.
2. Then, momentarily give the controls a slight push to nose the aircraft down.
3. If, within a brief period, the nose rises towards the original position, the aircraft is statically stable.
4. Ordinarily, the nose passes the original position (that of level flight) and a series of slow pitching oscillations follows.
1. If the oscillations gradually cease, the aircraft has positive stability;
2. if they continue unevenly, the aircraft has neutral stability;
3. if they increase, the aircraft is unstable.

Auto-Recovery

RPReplay_Final1649542321.mp4

Last modified by juan jose munoz 3 years ago

drive.google.com

Lateral Stability (Bank)

Is the ability that makes an aircraft stable about its Longitudinal Axis

• Positive lateral stability helps to stabilize the lateral or rolling effect when one wing gets lower than the other

Dihedral

Some aircraft are designed so that the outer tips of the wings are higher than the wing roots. The upward angle thus formed by the wings is called dihedral.

1. When a gust causes a roll, a sideslip will result.
2. This sideslip causes the relative wind affecting the entire airplane to be from the direction of the slip.
3. When the relative wind comes from the side, the wing slipping into the wind is subject to an increase in AOA and develops an increase in lift.
4. The wing away from the wind is subject to a decrease in angle of attack, and develops a decrease in lift.

Sweepback and wing location

When a disturbance causes an aircraft with sweepback to slip or drop a wing, the low wing presents its leading edge at an angle that is more perpendicular to the relative airflow. As a result, the low wing acquires more lift, rises, and the aircraft is restored to its original flight attitude.

• 10º of sweepback on a wing provides about 1º of effective dihedral
• High wing configuration can provide about 5º of effective dihedral over a low wing configuration

Keel Effect

Keel effect acts as a pendulum. When the plane is disturbed and one wing drops, the weight acts as a pendulum and returns the wings to level, creating a lateral stability

• More effective in high wings configuration aircrafts

Directional Stability (Yawing)

When the aircraft have a slight rotation to the right about its vertical axis, the relative wind hits the left side of the vertical stabilizer, causing left pressure, resisting the aircraft to yaw to the right and returning to its original position with a positive dynamic stability

• The area of the vertical fin and the side of the fuselage aft of the cg are the prime contributors the make the aircraft act like a weather vane, pointing it nose into the relative wind
• To provide additional positive stability to that provided by the fuselage, a vertical fin is added. (Vertical Stabilizer)
• The fin acts similar to the feather on an arrow in maintaining straight flight. Like the weather vane and the arrow, the farther aft this fin is placed and the larger its size, the greater the aircraft’s directional stability.

Dutch Roll (Free Directional Oscillation)

When Lateral Stability is stronger than Directional Stability

How this happened

1. When the aircraft is disturb doing a roll to the right, the strong lateral stability creates more lift in the lower wing, lifting up and returning to a wings level
2. Because the lower wing creates more lift also creates more drag, creating a yaw to the right
3. The weak directional stability correct for the right yawing overshooting pushing the aircraft in a left roll
4. Repeat 1,2 and 3 to the opposite side until the oscillations stop (Positive dynamic stability)

Spiral Instability

When Directional Stability is stronger than Lateral Stability

How this happened

1. When the lateral equilibrium of the aircraft is disturbed by a gust of air and a sideslip is introduced
2. The strong directional stability tends to yaw the nose into the resultant relative wind while the comparatively weak dihedral lags in restoring the lateral balance.
3. Due to this yaw, the wing on the outside of the turning moment travels forward faster than the inside wing and, as a consequence, its lift becomes greater.
4. This produces an overbanking tendency which, if not corrected by the pilot, results in the bank angle becoming steeper and steeper.
5. At the same time, the strong directional stability that yaws the aircraft into the relative wind is actually forcing the nose to a lower pitch attitude.
6. A slow downward spiral begins which, if not counteracted by the pilot, gradually increases into a steep spiral dive.
1. Usually the rate of divergence in the spiral motion is so gradual the pilot can control the tendency without any difficulty.

Forces in Turn

When an aircraft turn, lift and weight forces are divided into

Normal, Slipping and Skidding Turn

• Remember always step on the ball to maintain a coordinated flight and turn

• Importance to know the difference of a skid and a slip and the risk of a skidding turn or attitude

Adverse Yaw

• Adverse yaw occur in a right or left roll
• As depicted, in a left turn, the upper wing increase lift and also increase drag, creating an opposite yaw from the direction of the roll
• Pilot must apply rudder pressure to counter for the adverse yaw
• Adverse yaw increase at lower airspeed because of the decrease of effectiveness of the vertical stabilizer and rudder

Correcting Adverse Yaw

Differential Ailerons

• Aileron that moves downward does not move as much as the aileron that moves upward
• This helps increase drag on the descending wing, compensating the drag and eliminating almost the adverse yaw

Coupled Ailerons and Rudder

• When rudder and ailerons moves together to the same side

Frise Type Ailerons

• The aileron that is being raised, pivot on an offset hinge. This projects the leading edge of the aileron into the airflow and creates drag.

Load Factor

is measured in Gs (acceleration of gravity) a unit of force equal to the force exerted by gravity on a body at rest and indicates the force to which a body is subjected when it is accelerated.

Basically: An object subjected to 2Gs will weight double what it weights at 1G

• In a constant altitude, during a coordinated turn in any aircraft, the Load Factor is the result of two forces
1. Centrifugal force
2. Weight
• The load factor increas at a terrific rate after a bank has reached 45º to 50º
• The load factor for any aircraft in a coordinated level turn at 60º bank is 2Gs
• The load factor in an 80º bank is 5.76Gs, the wings must produce lift equal to these load factors if altitude is to be maintained
• A 90º bank with a constant altitude turn is not mathematically possible

Load Factor and Stalling Speeds

• Any aircraft, within the limits of its structure, may be stalled at any airspeed. When a sufficiently high AOA is imposed, the smooth flow of air over an airfoil breaks up and separates, producing an abrupt change of flight characteristics and a sudden loss of lift, which results in a stall.
• An aircraft stalling speed increases in proportion to the square root of the load factor
• If the Vs of an aircraft is 50 knots, can be stalled at 100 knots by inducing a load factor of 4Gs
• A pilot should be aware of:
• The danger of inadvertently stalling the aircraft by increasing the load factor, as in a steep turn or spiral
• When intentionally stalling an aircraft above the Va, tremendous load is imposed

Vg Diagram (Velocity vs Load Factor)

Flight operating strength of an aircraft is presented in a Vg diagram. Diagram varies for each different type of aircraft

• Increasing load factor below Va will cause the airplane to stall
• Increasing load factor above Va will cause structural damage or faliure

Maneuvering Speed (Va)

Is the boundary between when an airplane will stall vs when it can experience structural damage when subjected to increased load factor

Why Does Va Change With Weight?

• It all has to do with the airplane’s Critical Angle of Attack
• Heavier airplanes must fly at higher AOA to maintain altitude in straight-and-level flight
• Lighter airplanes can fly at lower AOA to maintain altitude in straight-and-level flight

How To Calculate Va

Quiz