Aerodynamics and Drag in Aircraft Design

Control Movements

• Each control surface changes the surface's geometry when deflected
• Pitch: Control Column, elevator deflection, nose movement
• Rudder: Rudder pedals, rudder deflection, nose movement
• Ailerons: Control Column, aileron deflection, wing roll
• Trim: Alleviates pressure – typically a wheel or push/pull button

Forces Acting on an Airplane - Flight

• Thrust: Exerted by engine and propellers, pushing air backward, causing forward motion
• Drag: Resistance to forward motion, directly opposes thrust
• Lift: Upward force to sustain flight
• Weight: Downward force due to gravity, opposes lift

Equilibrium

• Steady motion, not a state of rest
• Thrust and drag are equal and opposite
• Lift and weight are equal and opposite

Lift

• Generated mainly through the wings
• Acts perpendicular to relative wind and wingspan
• Exerted through the center of pressure
• Opposes weight; during level cruise, lift equals weight

Airfoil

• Any surface designed to obtain a reaction from the air (lift)
• Curved/Cambered shape produces most lift
• Upper surface generally has greater camber than lower

Lift - Center of Pressure

• The center of pressure of an airfoil cross-section may differ from the entire wing's center of presssure.
• Likewise, the center of pressure of a wing may differ from that of the entire aircraft

Airfoil Terminology

• Leading Edge: Forward edge of the airfoil
• Trailing Edge: Aft edge of the airfoil
• Chord: Line connecting the leading and trailing edges of the airfoil, denoting its length
• Mean Camber Line: Line drawn halfway between the upper and lower surfaces of the airfoil, indicating curvature
• Point of Maximum Thickness: Thickest part of the wing, expressed as a percentage of the chord

Angle of Attack

• The angle between the chord line of an airfoil and the vector representing the relative motion between the body and the air.
• Angle of incidence: Angle between the chord line of the wing and the longitudinal axis of the aircraft
• Angle of 2-4 degrees is typically fixed by the manufacturer.

The Wing

• A wing is many airfoils connected side-by-side
• The geometry of the airfoil may change from one part of the wing to another

Wing Terminology

• Wing root: Part attached to the fuselage
• Wing tip: Part of the wing furthest from the fuselage
• Wing span: Distance from wing tip to wing tip
• Mean Aerodynamic Chord: The average chord length of all the airfoil slices making up the wing
• Span x MAC = Wing area

Wing Terminology

• Aspect ratio: Ratio of a wing's span to its mean aerodynamic chord (MAC) or length/width
• Sweep back: Wing in which the quarter chord line is not parallel to the lateral axis of the aircraft

Wing Terminology

• Dihedral and Anhedral: Degree to which wings are canted upward or downward from the fuselage
• Washin and washout: Change in angle of incidence from wing root to tip
• Washout is more common than washin

How is Lift Created?

• Newton's Laws
• Bernoulli's Principle
• Coanda Effect

Newton's Laws

• First Law: Object in motion tends to stay in motion in a straight line
• Second Law: External force alters uniform motion of a body
• Third Law: For every action, there is an equal and opposite reaction

Newton - Lift

• For every action force, there's an equal and opposite reaction force.
• If no force acts on an object, it will continue at a constant velocity.
• Changing the flow direction requires a reaction force—this is lift.
• The greater the flow is changed, the greater the lift.

Bernoulli's Principle

• The total energy of a system remains constant.
• In fluid flow, if velocity increases, pressure decreases, and vice versa.

Law of Conservation of Energy

• Energy cannot be created or destroyed, only changed.
• In fluid flow, increased velocity means decreased pressure.

Fluid in Motion

• The sum of potential energy (pressure or Ep) and kinetic energy (velocity or Ek) is constant in a system
• Air is compressible and viscous, but for lower flight speeds it is considered incompressible
• For lower flight speeds it is considered an incompressible, perfect fluid

Laminar Flow through a venturi

• There is a curve to the flow.

Volume in = Volume out

• A1V1 = A2V2

Coanda Effect

• Jet flow adheres to nearby surfaces, even when surfaces curve away from the initial flow direction.
• This is useful to direct a jet flow.

Reducing Induced Drag

• Wing tip shape
• Winglets
• Droopy tips

Parasite Drag

• Form drag: Caused by frontal areas of the aircraft
• Skin friction drag: Caused by air passing over the aircraft surfaces
• Interference drag: Caused by airflow interference between aircraft parts (wings, fuselage, etc.).

Induced Drag

• Byproduct of lift
• Increasing lift increases induced drag
• The more lift, the more induced drag
• Can only be reduced during initial construction
• High aspect ratio wings have less induced drag than low aspect ratio wings

Induced Drag - Formula

• Drag = CD * (1/2) * ρ * v² * S, where
• CD = (CL²) / (π * AR * e)
• v = velocity of airflow
• ρ = air density
• S = wing area (span x MAC)
• AR = aspect ratio
• e = efficiency factor

Induced Drag

• Induced drag is associated with pressure differences above and below a wing's surface.
• As airspeed decreases, the lift coefficient (Cl) must increase to maintain flight.
• This occurs by increasing the angle of attack.
• The higher the angle of attack, the greater the pressure difference between the upper and lower wing surfaces.

Induced Drag - Flow

• Air flow from high pressure to low pressure creates a flow across the wingtips
• Wingspan outward movement. Forward wing motion creates a rotating vortex
• Rotating vortex is an area of low pressure sucking at the trailing edge of the wing (low pressure), leading to induced drag.

Reducing Induced Drag

• Different wing tip designs (e.g., winglets, drooped tips) can help reduce the induced drag created by wingtip vortices.

Form Drag

• Profile of the airframe (landing gear, etc.) causes airflow to separate
• Turbulent wake = cyclones, low pressure
• Narrower profile, smoother edges → less form drag

Skin Friction Drag

• Caused by imperfections in the aircraft surfaces which make airflow resistance
• Reducing skin friction depends on a smooth surface (paint job, clean aircraft)

Interference Drag

• Result of vortexes where airplane parts meet at sharp angles.
• Can be reduced by blending component and using fairings.

Lift and Drag Curve

• Unique relationship between lift and drag
• Factors impacting lift and drag: airfoil shape, wing area, true airspeed, and air density
• Lift to Drag Ratio (L/D): Ratio of lift to drag
• Maximum lift-to-drag ratio (L/D_max): Important design parameter
• Maximum Angle: Point on the curve where the aircraft's L/D is greatest

Thrust Available Chart

• Thrust available decreases as airspeed increases, while drag increases
• Greatest thrust is produced at lower airspeeds

Streamlining

• Shapes reduce turbulent wakes.

Ailerons

• Control roll of aircraft
• Actuated by control column, and connected to the ailerons via cables and pulleys.
• Mass balances are used in the same manner as elevator mass balances.
• Reduces aileron flutter(vibration).

Ailerons

• Achieve balance through design characteristics
• Mass balances work like elevator mass balances
• Helps reduce flutter

Differential Ailerons

• The down-going wing’s aileron is deflected more than the up-going wing's aileron
• Improves control effectiveness
• Balances the forces on the control column

Frise Aileron

• The leading edge of the down-going wing's aileron sticks out into the airflow, creating more drag.
• This counteracts the increased induced drag from the up-going wing's aileron.

Misuse of Rudder

• Rudder (yaw control) should be coordinated with aileron
• To avoid unwanted yawing motions, rudder input must be precise and balanced to match aileron deflections.

The End

• Additional content may exist.

Climbing

• Function of elevators to divide energy from thrust into speed and altitude
• Thrust affects climb, and climbing to a certain absolute altitude isn't possible in terms of thrust alone

Gliding

• Thrust is no longer available.
• Angle vs airspeed.
• 20% further glide with stopped propeller vs windmill
• Windmilling propeller provides negative thrust → Drag
• Best Glide → AoA for maximum L/D

Turns

• Lift vector is inclined away from vertical.
• Creates new horizontal force.
• Centripetal force → counteracts centrifugal force
• Steeper angle → greater rate, less radius → higher speed/greater loading
• Slower rate → larger radius of turn.

Turns

• Lateral stability for climbing/descending turns is affected by the relative airflow for each wing
• Descending turns: Inner wing has higher AoA and more lift; outer wing is traveling faster, with more lift
• Climbing turns: Inner wing has smaller AoA, and outer wing has higher AoA creating more lift

Load Factor

• Loads increase during turns
• Other maneuvers also increase load factors

Stall

• Aerodynamic stall occurs when the airflow over the wing separates due to a high angle of attack
• This separation of airflow creates less lift.

Factors Affecting Stall

• Aircraft weight
• Center of gravity
• Turbulence
• Turns
• Flaps
• Contamination like snow, ice, dirt, and heavy rain

Preventing Stall

• Using airfoil shape, high-lift devices (flaps), vortex generators, and wash-out

Preventing Stall

• Plain Flap
• Slotted flaps.

Preventing Stall

• Slats and Slats are leading devices helping keep airflow attached, slots permanently mounted, and slats retractable.

Maneuvers

• Spin: Autorotation from aggravated stall, ailerons worsening, and descending wing with higher AoA
• Spiral: Excessive nose-down descending turn that causes loads and structural damage.

Airspeed Limitations

• Rate of aircraft movement relative to air mass
• Various airspeed limitations including maximum permissible dive speed (Vne), normal operating speed (Vno), and maneuvering speed (Va)
• Other speeds associated with aircraft limitations (Vfe, flaps extended).

Axes of Movement

• Aircraft movement along the lateral axis (pitching) is controlled by elevators or stabilizers
• Roll movement along the longitudinal axis is controlled by ailerons.
• Yaw movement along the normal axis is controlled by the rudder.

Roll and Yaw

• Application of rudder to the right
• Left wing (outside of turn) moves faster, and thus has higher lift than the inside wing in a turn.
• This causes more lift on the outside wing (compared to inside).
• Coordination is needed between the ailerons and the rudder to control the roll and yaw during a turn.

Yaw

• Dynamic Yaw: Normal movement around the vertical or normal axis.
• Static Yaw: The aircraft is flying at some angle of sideslip wherein the sideslip axis isn't aligned with the aircraft flight path.
• Sideslip means the aircraft is yawed left or right

Balanced Controls

• Some control surfaces are located in front of the hinge
• Airflow strikes the front portion of the control surface and assists in changing the control surface in the desired direction
• Some control surfaces can be balanced to prevent flutter.

Stability

• Static Stability: Initial tendency to return to the original position when disturbed.
• Dynamic Stability: Overall tendency to return to the original position after the attitude has been changed.

Static Stability

• Positive: Aircraft returns to original orientation after being displaced
• Neutral: Aircraft remains in its new orientation after displacement
• Negative: Aircraft moves farther from original position after displacement

Dynamic Stability

• Decaying oscillations: Moments tend to return the aircraft to equilibrium, but oscillations do not decay.
• Neutral dynamic stability: Moments tend towards equilibrium but oscillations are divergent.
• Unstable dynamic stability: Oscillations increase in magnitude.

Axes of Stability

• An aircraft can has different degrees of stability for different axes
• Designers tailor the characteristics of aircraft to their intended use.
• More maneuverable aircraft often have less stability and are more difficult to fly, while stable aircraft are easier to fly but are more sluggish.

Longitudinal Stability

• Pitch stability: Stability about the lateral axis.
• Factor of influence is size and position of the horizontal stabilizer relative to the center of gravity(CofG); farther from the more stable the plane.

Lateral Stability

• Roll or lateral stability: Stability about the longitudinal axis.
• Incorporated in designs using dihedral, keel effect, and sweepback.
• Dihedral: Wing shape tilting upwards
• Keel Effect: Weight distribution below the wings
• Sweepback: Leading edge of the wing sweeps rearward

Lateral Stability - Dihedral

• Normally found in low-wing aircraft.
• Upward tilt of wings (dihedral angle).
• When one wing drops, the lower wing is at a larger angle of attack, creating greater lift and restoring the aircraft to its original attitude.

Lateral Stability - Keel Effect

• High-wing aircraft have most of their weight located below the wings, so when one wing drops the aircraft's weight creates pendulum-like motion restoring to original attitude.

Lateral Stability

• Anhedral: A downward tilt on wings (opposite of dihedral) can be built into an aircraft.
• Used when a need for superior maneuverability is prioritized over stability in an aircraft.

Sweepback

• Leading edge of the wing sweeps backward
• Found on most large transport aircraft
• During turns, the wing's drop causes the lower wing to have greater AoA and more lift restoring the aircraft to the original attitude

Directional Stability

• Yaw is controlled about the vertical or normal axis.
• Directional stability is ensured when the vertical stabilizer (and other appropriate surfaces) has a larger area behind its center of gravity.

Directional Stability - Causes of Adverse Yaw

• Slipstream: Rotation of the propeller causes a spin on the slipstream. This puts increased pressure on the left side of the horizontal stabilizer and results in a yaw towards the left.
• Asymmetric Thrust: At high angles of attack (or high power settings), unbalanced thrust occurs (more force on one side than the other), making the aircraft yaw to the left.
• Torque: Propellers turning clockwise (from the pilot's perspective) create a left turning tendency on the aircraft.
• Precession: When forces act on a spinning mass, precession occurs causing a force to be applied 90 degrees to the direction of rotation.
• Turbulence: A disorderly Airflow and makes rudder input more effective for preventing roll, than ailerons.
• Aileron Drag: Aileron drag on the down-going wing reduces adverse yaw
• Misuse of rudder: Lack of rudder coordination can generate yawing motions.

Slipstream

• Propeller rotation creates a spinning motion to the slipstream.
• This creates increased pressures on the aircraft's left side causes a yaw to the left.

Asymmetric Thrust

• At high angles of attack and power settings, the descending propeller blade will have a greater angle of attack than the ascending blade and, thus, generate more thrust on the right side of the aircraft than the left.
• This results in a yaw to the left

Torque

• The clockwise rotation of the propeller causes a left-turning effect on the aircraft.
• The effect can create a yaw motion on the aircraft.

Yaw Correction

• Manufacturers often build slight right-turn tendencies into the aircraft's design during cruise.
• This allows yaw compensation through methods like vertical fin and engine thrust offsets.

Precession

• Spinning objects, such as a propeller, have a property of precession due to their rotational motion (gyroscopic precession).
• The rotational force causes a resultant force in a ninety-degree direction relative to the applied force and in the same rotation direction of the object.

Turbulence

• Very difficult to control (unpredictable).
• Note: Rudder use is usually more effective in stopping roll from turbulence than aileron input.

Aileron Drag

• Rolling the aircraft with ailerons on an upswing increases the upswing wing's lift.
• This also increases the lift produced on the up-going wing which creates more drag than the down-going wing.
• Thus, the aircraft yaw in the opposite direction of rolling motion.
• Differential ailerons (deflection of down-going wing more than up going wing) produce reduction on the increased induced drag on the up-going wing by increasing the form drag on the down going wing reducing the adverse yaw.

Differential Ailerons

• The down-going wing's aileron deflected more than the up-going aileron.
• This increases form drag, countering the increased induced drag on the up side

Frise Aileron

• The leading edge of the down-going wing's aileron sticks out into the airflow, creating more drag.
• This counteracts the increased induced drag from the up-going wing's aileron.

Misuse of Rudder

• Rudder input needs coordination with aileron displacement.
• Uncoordinated rudder input can create yawing motion.

The End

• Additional content may exist.

Climbing

• Function of elevators to divide energy from thrust into speed and altitude
• Effects of varying thrust on climb
• Climbing until reaching absolute altitude is impossible with thrust alone
• Best Rate (Vy) and Best Angle (Vx)

Gliding

• Thrust is no longer available
• Angle vs airspeed relationship
• 20% further glide with stopped prop vs windmilling
• Windmilling propeller provides negative thrust → Drag
• Best Glide (AoA for max L/D).
• Effects of headwinds and tailwinds on glide distance (and pitch adjustment).

Turns

• Lift vector inclined away from vertical
• Creates new horizontal force
• Centripetal force → counteracts centrifugal force
• Steeper angle: increased rate, decreased radius
• Slower rate: increased radius
• Similar principles apply to climbing/descending turns.

Turns

• Lateral stability for climbing/descending turns depends on the relative airflow for each wing.
• Descending turns: Inner wing higher AoA → more lift; outer wing faster → more lift. Compensates each other, keeping the angle of bank constant
• Climbing turns: Inner wing smaller AoA → less lift; outer wing (fast wing) higher AoA → greater speed/more lift. This increases the tendency for the wing to increase its angle of bank

Load Factor

• Load factor increases in turns.
• Other maneuvers can increase load factors rapidly

Stall

• Aerodynamic stall occurs when airflow separates from the wing due to a high angle of attack.

Factors Affecting Stall

• Aircraft weight
• CG location
• Turbulence
• Aircraft configurations/manoeuvers
• Flaps
• Contamination (snow, ice, dirt, rain)

Preventing Stall

• Airfoil shape
• High-lift devices (flaps)
• Vortex generators
• Washout

Preventing Stall

• Plain Flaps
• Slotted Flaps

Preventing Stall

• Slots and Slats
• Slats are retractable.

Maneuvers

• Spin: Autorotation after aggravated stall
• Spiral: Excessive nose-down descending turn
• Structural damage possible from high speeds or load factors

Airspeed Limitations

• Rate of aircraft movement relative to air mass
• Various airspeed limitations including maximum permissible dive speed (Vne), normal operating speed (Vno), and maneuvering speed (Va)
• Other speeds associated with aircraft limitations (Vfe, flaps extended).

Axes of Movement

• Lateral axis (pitching): Controlled by elevators or stabilizers
• Longitudinal axis (rolling): Controlled by ailerons
• Normal axis (yawing): Controlled by the rudder

Roll and Yaw

• Application of rudder to the right
• Left wing (outside of turn) moves faster and has greater lift than inside wing
• Coordination needed for roll and yaw control

Yaw

• Dynamic Yaw: Normal movement around the vertical (normal) axis.
• Static Yaw: The aircraft is flying at some angle of sideslip wherein the sideslip axis isn't aligned with the aircraft flight path.
• Sideslip = Aircraft yawed left or right

Balanced Controls

• Some control surfaces are located in front of the hinge
• Airflow strikes the front portion to assist in desired direction.
• Balancing for flutter

Stability

• Static Stability: Initial tendency to return to original position
• Dynamic Stability: Overall tendency to return to original position

Static Stability

• Positive: Aircraft returns to original orientation after a displacement
• Neutral: Aircraft remains in new orientation
• Negative: Aircraft moves away from original position

Dynamic Stability

• Oscillations decay: Moments return aircraft to equilibrium.
• Neutral dynamic stability: Moments towards equilibrium, but oscillations diverge.
• Unstable dynamic stability: Oscillations increase in magnitude.

Axes of Stability

• Aircraft potentially have different stability degrees in their axes.
• Designers need to consider the different stability requirements for a planned purpose and use special designs.
• Maneuverable aircraft are usually less stable. Stable aircraft are usually easier to fly but are more sluggish.

Longitudinal Stability

• Pitch stability: Stability about the lateral axis
• Primarily influenced by the horizontal stabilizer's size and placement relative to aircraft's center of gravity; farther from CoG = more stability

Lateral Stability

• Roll or lateral stability: Stability about the longitudinal axis.
• Achieved through dihedral, keel effect (weight distribution below, below wings), and sweepback.
• Dihedral: Upward tilt on the wings.
• Keel Effect: Weight distribution below the wings
• Sweepback: Leading edge of the wing sweeps rearward

Lateral Stability - Dihedral

• Found on low-wing aircraft
• Upward tilt of wings provides stability as when one wing drops (dihedral angle).
• The lower wing is at a larger angle of attack, creating greater lift which restores the aircraft to its original orientation.

Lateral Stability - Keel Effect

• High-wing aircraft have most of their weight located below the wings
• When one wing drops, aircraft weight acts like a pendulum restoring to original attitude

Lateral Stability

• Anhedral: Downward tilt on the wings (opposite of dihedral) which can be used to provide greater maneuverability in trade off for stability.

Sweepback

• Leading edge of the wing sweeps backward
• Found on most large transport aircraft
• During turns, the wing's drop causes the lower wing to have greater AoA and more lift restoring the aircraft to its original attitude

Directional Stability

• Yaw is controlled about the vertical or normal axis.
• Directional stability is ensured when the vertical stabilizer (and other appropriate surfaces) has a larger area behind its center of gravity.

Directional Stability - Causes of Adverse Yaw

• Slipstream: Propeller rotation generates a spinning motion to the slipstream, creating increased pressure on the left side of the horizontal stabilizer and causing a yaw to the left.
• Asymmetric Thrust: At high angles of attack (or high power settings), unbalanced thrust occurs (more force on one side than the other), making the aircraft yaw to the left.
• Torque: Propellers turning clockwise (from the pilot's perspective) create a left turning tendency on the aircraft.
• Precession: When forces act on a spinning mass (gyroscopic precession) - rotational force causes a resultant force in a direction 90 degrees relative to the applied force and in the same rotation direction as the object.
• Turbulence: Unpredictable airflow. Use rudder over ailerons to control roll in the event of turbulence.
• Aileron Drag: Aileron drag on the down-going wing reduces adverse yaw
• Misuse of rudder: Lack of rudder coordination can generate yawing motions.

Slipstream

• Propeller rotation creates a spinning motion to the slipstream, and thus increased pressure on the left side of the horizontal stabilizer.

Asymmetric Thrust

• At high angles of attack and power settings, the descending propeller blade will have a greater angle of attack than the ascending blade. This consequently, produces more thrust on the right side of the aircraft than the left. This results in a yaw to the left.

Torque

• Propeller rotation (clockwise from a pilot's perspective) creates a torque, thus a left turning tendency.

Yaw Correction

• Manufacturers can compensate for yaw by building slight turn tendencies into the aircraft (right turns are usually compensated)
• This can be done by offsetting the vertical fin or the engine thrust line.

Precession

• Spinning objects, such as a propeller, exhibit gyroscopic precession.
• Appling force 90 degrees in the direction of rotation.

Turbulence

• Difficult to control as it's unpredictable.
• Rudder control is typically more effective in controlling roll from turbulence than ailerons.

Aileron Drag

• Up-going wing creates more lift during roll, causing increased drag.
• The aircraft yaw opposite to the roll's intended direction.
• Differential/Frise ailerons help reduce this negative yaw effect due to aileron drag. They create additional drag on the down-going wing which reduces the adverse yaw.

Differential Ailerons

• Down-going wing’s aileron deflected more than up-going wing.
• Increasing form drag counters the increased induced drag on the up side.

Frise Aileron

• Down-going wing's leading edge portion protrudes into the airflow, adding drag that offsets the increases in induced drag on the up side.

Misuse of Rudder

• Uncoordinated rudder input with aileron (roll input) displacement can result in undesirable/unwanted yawing motions.

The End

• Additional content may exist.

Climbing

• Function of elevators to divide energy from thrust into speed and altitude. Effects of varying thrust on climb. Climbing to certain absolute altitude isn't possible with thrust alone. Best Rate (Vy) and Best Angle (Vx) and their formulas .

Gliding

• Thrust is no longer available.
• Angle vs airspeed relationship
• Different glide types and variations.
• Best Glide (AoA for max L/D).
• Effects of headwinds and tailwinds on glide distance (and pitch adjustment).

Turns

• Lift vector is inclined away from vertical
• Creates new horizontal force
• Centripetal force → counteracts centrifugal force
• Steeper angle: increased rate, decreased radius → higher speed/greater loading
• Slower rate: increased radius and the lateral forces affect stability.
• Similar principles apply to climbing/descending turns.

Turns

• Lateral stability for climbing/descending turns influenced by relative airflow and by each wing
• Descending turns: Inner wing higher AoA → more lift; outer wing faster → more lift; compensation for the opposing wings
• Climbing turns: Inner wing smaller AoA → less; lift; outer wing higher AoA → greater speed/more lift; tendency to increase the angle of bank (causing more lateral forces which thus affect stability)

Load Factor

• Load factor increases in turns.
• Other maneuvers can increase load factors rapidly.

Stall

• Aerodynamic stall occurs when airflow separates from the wing.

Factors Affecting Stall

• Aircraft weight
• Center of gravity
• Turbulence
• Turns and configurations
• Flaps
• Contamination (snow, ice, dirt, rain)

Preventing Stall

• Airfoil shape selection
• High-lift devices
• Vortex Generators
• Washout

Preventing Stall

• Plain Flaps
• Slotted Flaps.

Preventing Stall

• Slats, use of slots, slat devices

Maneuvers

• Spin: Autorotation after aggravated stall
• Spiral: Excessive nose-down descending turn that causes large loads and structural damage

Airspeed Limitations

• Rate of aircraft movement relative to air mass
• Various airspeed limitations, including maximum permissible dive speed (Vne), normal operating speed (Vno), maneuvering speed (Va), and other speeds connected to flaps (Vfe, Vx).

Axes of Movement

• Lateral axis (pitching): Controlled by elevators or stabilizers.
• Longitudinal axis (rolling): Controlled by ailerons.
• Normal axis (yawing): Controlled by the rudder

Roll and Yaw

• Application of rudder to the right
• Left wing (outside of turn) moves faster, thus resulting in higher lift compared to the inside wing. This causes more lift on the outside wing
• Coordination of both ailerons and rudder for effective roll and yaw control

Yaw

• Dynamic Yaw: Normal movement around the vertical/normal axis.
• Static Yaw: Aircraft flying at sideslip with its sideslip axis not aligned with the aircraft flight-path.
• Sideslip: Aircraft yawed left or right.

Balanced Controls

• Some control surfaces are located forward of the control surfaces hinge.
• Airflow strikes the front portion of the control surface and helps achieve the desired direction of control
• Mass balancing can be used to compensate for flutter.

Stability

• Static Stability: Initial tendency towards returning to the original position.
• Dynamic stability: Overall tendency towards returning to the original position.
• Positive, neutral, and negative static stability types.

Static Stability

• Positive static stability: Aircraft returns to original orientation after a disturbance.
• Neutral static stability: Aircraft stays in new orientation (often found in training aircraft).
• Negative static stability: Aircraft moves further away from original position, away from intended direction.

Dynamic Stability

• Stable, neutral, or unstable dynamic stability can occur.
• Stable: Oscillations decay.
• Neutral: Oscillations don't decay.
• Unstable: Oscillations diverge (increase in magnitude)

Axes of Stability

• Aircraft can have differing degrees of stability around each of its axes.
• Aircraft designers can tailor characteristics to their intended purposes.
• Maneuverable aircraft are less stable than stable ones.

Longitudinal Stability

• Pitch stability (stability about the lateral axis)
• Largely determined by the relative size and position of the horizontal stabilizer (relative to center of gravity [CofG]). The farther from CoG, the more stable the aircraft.

Lateral Stability

• Roll or lateral stability (stability about the longitudinal axis).
• Achieved through dihedral, keel effect, sweepback designs
• Dihedral: Upward tilt of the wings
• Keel effect: Weight distribution placement below wings
• Sweepback: Leading edges positioned at the rear

Lateral Stability - Dihedral

• Common on low-wing aircraft.
• Upward tilting of wings (dihedral angle); when one wing drops, the lower wing's angle of attack increases, creating greater lift to restore the aircraft to its original attitude.

Lateral Stability - Keel Effect

• Common on high-wing aircraft.
• Most of the weight is located below wings.
• When one wing drops, the aircraft weight creates pendulum-like motion.

Lateral Stability

• Anhedral: Downward tilting of the wings (opposite of dihedral).
• Can improve the maneuverability even if it makes the aircraft a little less stable (trade-off)

Sweepback

• The leading edge of the wing angles backward (sweepback).
• Common on large transport-category aircraft.
• Reduces the effect of airflow on the wing, as the lower wing will be at a greater angle of attack and create more lift during turns.

Directional Stability

• Yaw is controlled around the vertical/normal axis.
• Important that the vertical stabilizer has a greater side area behind the center of gravity to ensure directional stability.

Directional Stability - Causes of Adverse Yaw

• Slipstream: Propeller rotation creates the slipstream that spins from back of propeller, and the pressure increased on the left side of the horizontal stabilizer and causes a yawing motion to the left.
• Asymmetric Thrust: At high angles of attack more thrust on one side (descending blade) than the other (ascending blade). Creates a yawing motion to the left
• Torque: Propeller's clockwise rotation from the pilot's perspective. Leads to left-turning moment.
• Precession: Spinning mass has a property called gyroscopic precession. Forces on one side of the mass causes reaction 90 degrees away from the applied.
• Turbulence: Airflow disorder, rudder input is effective in controlling roll.
• Aileron drag: The aileron drag will be increased on the down-going wing. This drag will counteract the increased induced drag on the up side reducing adverse yaw.
• Misuse of rudder: Lack of coordination between ailerons and rudder input may lead to unwanted yawing motions.

Slipstream

• Propeller rotation leads to a spinning effect on the approaching airflow.
• Increased pressure on the aircraft's left side, and the resultant yaw to the left.

Asymmetric Thrust

• At high angles of attack or high power setting, descending blade has more angle of attack, and thus produces more thrust on the right side of the aircraft creating adverse yaw to the left.

Torque

• Propeller's clockwise rotation from pilot's perspective gives rise to a left-turning moment.

Yaw Correction

• Manufacturers often compensate for this with slightly right-turning tendency in flight
• Vertical fin and/or engine thrust line offset can be used.

Precession

• Spinning objects experience gyroscopic precession.
• Application of force 90 degrees from applied/rotation direction

Turbulence

• Difficult to control.
• Rudder control is typically more effective than ailerons.

Aileron Drag

• Increased lift on wing on upswing. Increase on drag on upgoing wing.
• Aircraft yaws opposite to the intended roll direction
• Differential/frise ailerons reduce adverse yaw effect.

Differential Ailerons

• Down-going wing aileron deflected more than up-going.
• Increased form drag countering the increased induced drag on up-side

Frise Aileron

• Down-going wings leading edge protrudes into airflow to decrease adverse yawing movement.
• This extra drag offsets the increased induced drag of the up-going wing.

Misuse of Rudder

• Rudder input must coordinate with aileron displacements to avoid yawing motions.

The End

Climbing

• Elevators adjust to divide energy from thrust into speed and altitude. Effects of varying thrust on climb, reaching a fixed absolute altitude that is not possible via thrust alone. Best Rate (Vy) and Best Angle (Vx)

Gliding

• No thrust available. Angle vs airspeed relationship is needed.
• 20% further glide with stopped propeller vs windmilling.
• Windmilling propeller provides negative thrust → Drag.
• The Best Glide → AoA that results in maximum L/D. Effects of headwinds/tailwinds and pitch adjustment on glide distance.

Turns

• Lift vector from vertical; creates horizontal force
• Centripetal force counteracts centrifugal force
• Steeper angles have greater rate and smaller radii, producing higher than usual speeds/loading
• Lower angles of attack have higher radii and slower rates, creating moderate loading

Turns

• Lateral stability in climbing/descending turns is affected by relative airflow and each wing's specific behaviour.
• Descending turns: Inner wing higher AoA → more lift; outer wing faster → more lift. Compensation of each other → constant angle of bank
• Climbing turns: Inner wing smaller AoA → less lift; outer wing faster → higher AoA → increased lift; greater tendency to raise angle of bank

Load Factor

• Load factor increases in turns
• Any sudden maneuver or rapid change in plane configuration will also increase this factor

Stall

• Aerodynamic stall occurs when airflow separates from the wing due to high angles of attack.

Factors Affecting Stall

• Aircraft weight
• Centre of gravity location
• Turbulence
• Airplane configurations
• Flaps
• Contamination (snow, ice, dirt, rain)

Preventing Stall

• Airfoil shape
• High lift devices (flaps)
• Vortex generators
• Washout design

Preventing Stall

• Plain Flaps
• Slotted Flaps.

Preventing Stall

• Slots/Slats devices

Maneuvers

• Spin: Autorotation from aggravated stall
• Spiral: Excessive nose down descending turn, high loads, and possible damage.

Airspeed Limitations

• Rate of aircraft movement relative to air mass
• Various airspeed limitations, including maximum permissible dive speed (Vne), normal operating speed (Vno), maneuvering speed (Va), and other speeds connected to flaps (Vfe, Vx).

Axes of Movement

• Lateral axis (pitching): Controlled by elevators or stabilizers.
• Longitudinal axis (rolling): Controlled by ailerons.
• Normal axis (yawing): Controlled by the rudder

Roll and Yaw

• Application of rudder to the right
• Left wing (outside of turn) moves faster, thus increasing lift compared to inside wing. This causes more lift on outside wing
• Coordination needed for effective roll and yaw control

Yaw

• Dynamic Yaw: Normal movement around the vertical (normal) axis.
• Static Yaw: Aircraft flying at sideslip with its sideslip axis not aligned with aircraft flight-path.
• Sideslip = aircraft yawed left or right

Balanced Controls

• Some control surfaces are positioned in front of the hinge of the control surfaces
• Airflow assists in controlling the

This quiz explores the various types of drag that affect aircraft performance, including parasite, form, skin friction, and interference drag. It also examines factors that can enhance the lift-to-drag ratio and the role of flight controls and design features like fairings. Test your knowledge on these fundamental concepts of aerodynamics.