AE101 – Basic Theory
Aerodynamic Theory
Vector (arrow) - a quantity that represents magnitude and direction
Displacement – distance and direction of a body’s movement
Mass(m) – the quantity of molecular material that comprises and object
Volume (v) – the amount of space occupied by an object
Density (£) – mass per unit of volume
Work (W) – done when a force acts upon a body and moves it
Power (P) – rate of doing work, or work done per unit of time, or P=W/t
Horsepower – unit of measurement used to express the amount of power being produced
Weight (W) – the force with which a mass is attracted toward the center of the earth by gravity
Force (F) – mass x acceleration
Moment (M) – what is created when a force is applied at some distance from an axis or fulcrum
M = FDistance
Energy – scalar measure of a body’s capacity to do work
Work cannot occur unless energy is pregnant
Two types of energy:
Potential energy – the ability of a body to do work because of its position or state of being
Function of mass, gravity, and height
Kinetic energy – the ability of a body to do work because of its motion
Function of mass and velocity
Law of Conservation of Energy
Energy cannot be created nor destroyed – but can be transferred
Newton’s Laws
Law of Equilibrium
“a body at rest tends to remain at rest, and a body in motion tends to remain in motion, in a straight
line, at a constant velocity, unless acted upon by an unbalanced force.”
Inertia – the tendency for a body to remain at rest, or in motion
Equilibrium – lack of acceleration in any direction
Law of Acceleration
“an unbalanced force acting upon a body produces an acceleration in the direction of the force that is
directly proportional to the force, and inversely proportional to the mass of the body”
Acceleration = Force/Mass
Law of Interaction
“for every action, there is an equal and opposite reaction”
Atmospheric Properties
Characteristics Important to Understanding Aerodynamics:
Ambient static pressure – a measurement of the weight of an air column over a specific area
Air Density – total mass of air particles for a given volume
Temperature – measurement of the average kinetic energy of the air particles
General Gas Law
Chinese food is expressed as a relationship of the four properties of air
Pressure
Density
Temperature
Universal Gas Constant
If temperature is increased with density constant, pressure must rise
With constant density, pressure and temperature are directly proportional
With constant pressure, density and temperature are inversely proportional
P=DRT, where R is Universal Gas Constant
Properties of Airflow
Our atmosphere is gaseous fluid, therefore, “airflow” is subject to laws of fluid motion
Airflow pressures:
Static pressure (PS) – force that molecules of air exert on each other by their random movement
Dynamic pressure (PD) – measure of impact pressure of large group of air molecules moving together
Total pressure (PT) – sum of static and dynamic pressure
Stream Tube - Closed system where total mass and total energy must always remain constant
Bernoulli’s Equation – the total pressure is constant for an open, continuous flow of fluid
Constant pressure – if dynamic pressure increases at a point, then static pressure must decrease at the same point
Altitude Measurement
ALWAYS EQUATE PRESSURE ALTITUDE WITH 29.92Hg
True altitude – height above Mean Sea Level (MSL)
Pressure altitude – height measured above standard datum plane
Density altitude – pressure altitude corrected for temperature deviations from the standard atmosphere
At higher temperatures, DA increases
Performance decreases at high DA - less power produced when fewer air molecules available
High DA also requires higher True Airspeeds for T/O and LDG
Airspeed Measurement
True Airspeed (TAS) – actual speed at which aircraft moves through airmass
Groundspeed (GS) – speed relative to ground
Indicated Airspeed (IAS) – speed read off airspeed indicator
True airspeed will increase if IAS is held constant while climbing to a higher altitude
Calibrated Airspeed (CAS) – IAS corrected for indicator error or minor sensing errors
Caused by location (installation error) of pitot-static system on airplane
Equivalent Airspeed (EAS) – CAS corrected for errors cause by compressibility effects (F-Factor)
Airfoils and Wing Properties
Airfoil – streamlined shape designed to produce lift as it moves through the air
Mean Camber Line (MCL) – line drawn from leading edge to trailing edge, halfway between upper and
lower surface of airfoil
Chord Line – infinitely long, straight line drawn though leading and trailing edges of airfoil
Chord – segment of Chord Line drawn from leading edge to trailing edge
Root Chord – chord at wing root
Tip Chord – chord at wing tip
Average Chord – average of all chords
Camber – curvature of MCL of an airfoil
Airfoil Types
Symmetric airfoil – zero camber, MCL and chord are the same, no lift at zero angle of attack
Positively cambered airfoil – has MCL above chord, produces lift at zero angle of attack
Negatively cambered airfoil – has MCL below chord, produces downforce at zero angle of attack (car)
Flows
Spanwise Flow – airflow that travels along the span of wing, parallel to leading edge (from root to tip)
Chordwise Flow – flows at right angles to leading edge of airfoil
Pitch attitude – angle between longitudinal axis and horizon
Flight Path – aircraft’s apparent movement through airmass
Relative Wind – apparent motion of air with respect to motion of aircraft
Angle of Attack (AOA) – angle between chordline of airfoil and relative wind
Angle of Incidence – preset AOA on wing, when longitudinal axis parallel to ground
Dihedral Angle – angle of upslope or downslope of wings when viewed from head-on
Wingspan – from wingtip to wingtip
Wing Area (S) – apparent surface area of wing within an outline of wing on the plane of its chord
Wingspan x Average Chord
Wing Loading (WL) – ratio of aircraft’s weight to surface area of wings
Wing Loading = weight/Wing Area
Wing Taper – reduction in chord for given airfoil from root to tip
Measured by dividing Tip Chord by Root Chord (always less than 1)
Sweep Angle – angle between line 25% aft and “kinda” parallel to leading edge, and line parallel to lateral axis
Aspect Ratio (AR) – ratio of winspan to average chord
Glider has larger aspect ratio than Fighter
CG/Weight and Balance
Center of Gravity (CG) – intersection of all three axes, where weight is considered to be concentrated
Point from which movement in all three axes are measured
Aerodynamic Center (AC)
Typically aft of CG
Point where all aerodynamic forces are acting
AE202 – LIFT AND DRAG
LIFT
Four primary forces acting on an aircraft in flight :
Weight (gravity)
Lift (force against weight)
Thrust
Drag (force against thrust)
Equilibrium – absence of acceleration. When the sum of all the forces are equal to zero
An aircraft does not have to be in straight and level flight for equilibrium
Accelerated Flight – opposing forces are not balanced (all other flight than equilibrium)
Aerodynamic Force – the result of pressure and friction distribution over an airfoil
Lift is working perpendicular to the relative wind
Drag is working parallel (and same direction) as the relative wind
There are eight (8) factors that affect LIFT :
Three from the lift equation – an increase in any will produce more lift
1. Air Density
2. Velocity
3. Surface Area
Coefficient of lift accounts for the rest
4. Angle of attack (AOA)
5. Shape of the airfoil (camber)
6. Aspect ratio (how long the wing is)
7. Viscosity
8. Compressibility
**Pilots have no control over the coefficient of lift factors of viscosity, compressibility, or aspect ratio**
The pilot has control over VELOCITY, AOA, and CAMBER (flaps)
CL will increase with an increase in AOA until it reaches CLmax (Critical AOA)
Stall – increase in AOA, decrease in CL (caused by Boundary Separation)
Common Sense : In straight and level flight, as AOA is increased, the pilot will have to decrease velocity to
maintain level flight. In straight and level flight, AOA and velocity are inversely related in the production of lift
Symmetric Airfoil – same airflow over the top and the bottom (zero camber)
Cambered Airfoil – at zero AOA, air must flow further over the top than the bottom
Aerodynamic Twist – decrease in camber from wing root to wing tip. The wing root will stall before the wing tip.
Geometric Twist – a decrease in the angle of incidence from the wing root to wing tip. The wing root is at a greater
angle of attack and will always stall first
DRAG
Because there is always some resistance in motion, drag can never be zero
Two types of drag that combine to create total drage
Parasite Drag – not associated with production of lift - composed of Form, Friction, and Interference Drag
Induced Drag – component always associated with the production of lift
Form Drag – the result of separation of airflow from a surface and the wake that is created by that separation.
Is caused by the differential between the leading edge static pressure and trailing edge static pressure.
Friction Drag – caused by turbulent airflow in the boundary layer. Can be reduced by smoothing the entire plane.
Interference Drag – generated by mixing airstreams between aircraft components, such as the wing and fuselage
An increase in weight will increase induced drag for a particular airspeed, configuration and altitude. Since a
heavier airplane requires more lift, more induced drag is created. The more the AOA, the more induced drag.
A way to reduce induced drag is to install devices to impede spanwise flow.
Total Drag – combination of parasite and induced drag
Ground Effect – a phenomenon that significantly reduced induced drag in increases effective lift when the airplane
is within one wingspan of the ground. This reduction in drag creates more effective lift and allows the
aircraft to float above the runway.
THRUST
Propeller Efficiency – the ability of a propeller to convert engine output into thrust (p.e. = THP / SHP)
Thrust Horsepower (THP) – propeller output
Shaft Horsepower (SHP) – engine output
If you increase airspeed to greater than L/Dmax, you must decrease AOA to maintain level flight
Thrust Available – the amount of thrust that is produced by an engine at a given PCL setting, velocity and density.
Thrust Excess – occurs if thrust available is greater than thrust required at a particular velocity
Power Available – the amount of power that an engine is producing at a given PCL setting, velocity and density
Power Required – the amount of power required to produce thrust required
Weight Effects
If you increase weight of your airplane, you need to increase lift to overcome it (increase AOA or velocity).
This will always shift the curve on the charts up and to the right.
Altitude Effects
Weight being constant, lift requirements are the same at FL250 and sea level… but velocity must increase.
Maximum engine output decreases with air density so thrust available and power available will decrease
FLIGHT CONTROLS AND EFFECTS
Change In Camber
To change lift on a wing, you control the AOA, velocity (airspeed) and camber of the wing.
Flaps can change the camber of the wing.
*why* With an increase in wing camber, the CL increases but the stall AOA decreases
Lowering the flaps increases lift allowing for aircraft to be flown at slower speeds for T/O, approach and landing.
Since lift is increased, you must decrease angle of attack to maintain level flight. This allows flatter pitch angle
during T/O and landing making it easier to see what’s ahead.
Most aircraft require flaps setting at or below 50% for initial T/O because:
- You gain more lift than increased drag up to the 50% flaps setting
- Flaps are lowered from 50 to 100%, there is substantial increase in drag w/out a beneficial increase in lift.
This extra drag at flaps LDG settings allows for steeper approach angle, improved forward visibility, and
requires higher power setting during approach. However, many aircraft require flaps T/O (50%) during
missed approach, go around, or touch-n-go to reduce extra drag but maintain lift.
Lowering landing gear increases parasite drag; since drag is on lower side, aircraft nose pitches down.
AE104 – PERFORMANCE AND MANEUVERING
Minimum speed for T/O is approx 20% above power-off stall speed
Minimum T/O speed can be reduced by :
Decreasing weight
Increasing wing surface area
Increasing CLmax
Lowering flaps increases camber of the wing
A change in air density will not affect indicated airspeed!
WEIGHT is the greatest factor in T/O distance!
Using T/O flaps will decrease T/O distance
Increasing density altitude results in :
Higher T/O velocity
Lower thrust available
Lower acceleration
Increased T/O distance
High density altitude is caused by three factors :
High airport elevation
Higher temperature
Increased humidity
High, hot, heavy, and humid are bad for T/O performance
Headwind decreases T/O distance since aircraft has positive TAS before beginning sushi roll
Tailwind increases T/O distance since you start at a negative TAS
Direct crosswind have NEGLIGIBLE EFFECT on takeoff distance!
CLIMBS
Max rate of climb is gaining most altitude in a given amount of time. Max rate relies on excess power.
Max angle of climb gains most altitude in distance traveled. Relies on excess thrust.
Climb performance is affected by :
1. Weight
2. Altitude
3. Configuration
Headwind increases max angle of climb
Max rate of climb is not changed by wind
MAX ENDURANCE AND MAX RANGE
Maximum endurance is the maximum time that an airplane can remain airborne on a given amount of fuel.
Max endurance lies on the power required curve at a speed that is less than L/Dmax.
Maximum range is maximum distance that an airplane can travel on a given amount of fuel
Max range is at L/Dmax
CRUISE FACTORS
Weight
Increased weight means more lift is required to maintain level flight at max endurance/range AOA
Velocity must be increased by adding power
This causes max endurance/range to decrease when weight is increased
Altitude
Decreased temperature make turbine engine more efficient
Increases max range and max endurance because of decreased fuel flow
Configuration
Lowering landing gear or flaps will decrease max range/endurance due to power required to overcome drag
MACH NUMBER
Mach number is the ratio of the airplane’s TAS to the local speed of sound (LSOS)
GLIDE PERFORMANCE
Best glide speed – Airspeed flown power-off which provides maximum range
Speed is based on L/Dmax and changes with weight
T-6A best glide speed is 125 KIAS
Glide range is expressed as a ratio of horizontal distance over vertical distance
Glide ratio of 11:1 (T-6A) means T-6 will travel 11,000 feet horizontally for 1,000 feet of altitude loss
Factors that affect glide :
1. Altitude – can glide farther and longer with more altitude
2. Wind – tailwind increases range / headwind decreases range.
Wind has no affect on endurance (does affect range)
3. Configuration – clean equals farther longer glide / dirty equals nearer, shorter glide
Propeller drag significantly decreases glide range and endurance if propeller is not feathered
Weight – best glide speed occurs at L/Dmax and changes with aircraft weight
Best glide speed in heavier aircraft requires faster airspeed which decreases glide endurance
Weight has no impact on maximum glide range
Region of reverse command is area where additional thrust or power is required to fly more slowly
Final approach speed is 30% greater than stall speed!
Just as in T/O, the greatest factor in landing distance is weight
Headwind decreases landing distance due to lower groundspeed… opposite is true
PROPELLER
Slipstream swirl – corkscrewing airflow that travels around fuselage
Strikes vertical stabilizer, pulling tail to right and yaws nose to left
More prevalent at high power settings and low airspeeds
Compensate using right rudder
P-Factor – yawing moment caused by one propeller blade creating more thrust than opposing blade
If free airstream relative wind above thrustline (power-on descent):
Up-going blade (left side) creates more thrust due to higher angle of attack
Causes nose to yaw right
Correct using left rudder
If free airstream relative wind is below thrustline (low airspeed, high AOA flight)
Down going blade (right side) produces more thrust
Causes nose to yaw left
Correct using right rudder
For P-factor to be noticeable:
Engine must be at high power setting
Thrust axis must be displaced from relative wind
Torque Effect – based on Newton’s Third Law of Motion (action = equal and opposite reaction)
Propeller rotates clockwise
Torque effect pushes against fuselage and rotates aircraft counterclockwise
Compensation provided by rudder and Trim Aid Device (TAD)
Gyroscopic Precession –
- Occurs when force is applied to edge of spinning object (propeller), resultant force is created in direction
of applied force, but 90 ahead in the direction of rotation
- pitching nose up causes nose to yaw right
- T-6A compensates for gyroscopic precession effects with the TAD
TURNS
Adverse Yaw
When rolling aircraft to the right, nose initially tracks left
Due to down deflection of aileron on up wing, creating more drag than up-deflected aileron on down wing
Adverse Yaw is minimized through use of rudder
Turns & Lift Vectors
When established in bank, aircraft has tendency to descend
Corrective action is back-stick pressure
During turn, lift vector is divided into two components
Horizontal component
Vertical component –
only component that opposes weight
must increase AOA to compensate for loss in vertical lift
Turn Radius/Rate
Turn performance is measured by two factors:
Turn Radius – radius of circle that flight path defines
Turn Rate – rate of heading change measured in degrees per second
Turn Performance
Turn performance in level, coordinated turn is a factor of velocity and bank angle
Maximum turn rate and minimum turn radius achieved with an aircraft at 90 bank and minimum velocity
Limiting factors to maximum bank angle and minimum velocity in level turn without stalling:
Weight
Altitude
Load factor
Stalling angle of attack
Engine performance
Wing loading
When airspeed or bank angle limited by above factors, max turn rate and min turn radius decreases
Turn performance is ALWAYS measured using only velocity and bank angle existing during turn
Standard Rate Turns
3 per second
Bank angle required is dependent on airspeed
Turn radius increases as airspeed increases
Thrust Requirements
Due to increase in total lift required in a turn, amount of drag is increased
To overcome drag, increase in thrust/power is necessary to maintain level altitude and constant airspeed
Coordinated Turns
Turn and slip indicator ball not centered, not in coordinated flight
Slips
Opposite or insufficient rudder in direction of turn
Turn radius increases, turn rate decreases
Ball is displaced in direction of the turn
Ball and needle on same sides
Skids
Too much rudder in direction of turn
Turn radius decreases, turn rate increases
Ball is displaced in opposite direction of turn
Ball and needle on opposite sides
Dangerous – aircraft could roll inverted and crash if stall (skidded turn stall) occurs at low altitude
“Step on the ball” to correct
LOAD FACTORS
Load Factor vs Bank
Load factor is ratio of Load/Weight
Also called G force or G loading
In a level turn, as bank angle increases, G loading increases
90 Bank
Gs required to maintain level flight are infinite, since no lift vector is perpendicular to ground
All lift parallel to horizon
If turn continued, aircraft will descend
Limit Load Factor – max load factor aircraft can sustain without risk of permanent damage
Ultimate Load Factor – max load factor aircraft can sustain without structural failure (150% of limit load factor)
Symmetric Limits
Symmetric Gs encountered when elevator is only control surface deflected
T-6A symmetric limits are +7 to -3.5 Gs
Asymmetric Limits
Asymmetric Gs encountered when ailerons or rudder are deflected in flight
T-6A asymmetric limits are +4.7 to -1.0 Gs
Limits are lower because lift (G force) on up-going wing is more than what is read on accelerometer
Maneuvering Speed
Speed above which full or abrupt control movements can result in structural damage
Also called cornering velocity – aircraft can make smallest radius turn
STABILITY
Tendency for airplane to return to state of equilibrium (two types):
Static Stability – tendency of object to move toward or away from original equilibrium position
Positive Static Stability – initial tendency of object to return to original equilibrium (ball in bowl)
Negative Static Stability –tendency of object to move away from original equilibrium (upside-down bowl)
Neutral Static Stability – tendency of object to accept new position as a new equilibrium (ball flat surface)
Dynamic Stability – position and measure object after it has been disturbed with respect to time
Positive Dynamic Stability – oscillations get smaller until stopping at equilibrium point
Negative Dynamic Stability – undampened oscillations (ball climbs higher on each pass)
Neutral Dynamic Stability – oscillations never dampened, but remain at constant amplitude
Stability/Maneuverability
Stability and maneuverability are inversely proportional
Stable aircraft (heavies) are hard to turn, but easy to control
Unstable aircraft (fighters) are easy to turn, but hard to control
Longitudinal Static Stability
CG forward of AC is positive contributor to longitudinal static stability
Aircraft pitches down after increase in AOA
Directional Static Stability
Stability of longitudinal axis around vertical axis
Sideslip angle – difference between the flightpath and the longitudinal axis
Sideslip relative wind – component of relative wind parallel to lateral axis
Type Wing Impact
Straight wings – small + contribution to directional static stability due to parasite drag over wing
Swept wings – improved equilibrium and better directional static stability
Fuselage/Tail Impact
When in sideslip, fuselage creates lift, negative contributor to directional static stability
The Vertical Stabilizer is the greatest positive contributor to directional static stability!
Lateral Static Stability
Stability around the longitudinal (roll) axis
Laterally stable aircraft return to wings level
Dihedral wings – causes increased AOA and lift on down-going wing during sideslip
Wing dihedral is the greatest positive contributor to lateral static stability!
Wing location
High wing – positive contributor to lateral stability, rolls aircraft to wings level
Low wing – negative contributor to lateral stability
Wing Sweep - positive contributor to lateral stability
Vertical stabilizer - positive contributor to lateral stability
Dynamic Effects
Lateral and directional stability are interrelated, called cross-coupling
Yaw will cause roll and a roll will cause yaw
Effects of cross-coupling
Directional Divergence
Aircraft will continue to yaw and increase sideslip angle in response to initial sideslip
Result of negative directional static stability
Spiral Divergence
Yaw and roll continue in reaction to initial sideslip, producing tight descending spiral
Caused by weak lateral stability sensing new relative wind
Aircraft aligns with new relative wind (strong directional stability) by yawing into it
Advancing wing creates more lift and causes plane to roll once again
Dutch Roll
Caused by combination of strong lateral and weak directional stability
Roll produces a sideslip, strong lateral stability reacts by correcting to wings level
Also causing nose to yaw in direction of sideslip
Weak directional stability reorients nose to relative wind
Advancing wing causes roll opposite original sideslip
Cycle repeats
Nose of aircraft experiencing Dutch Roll scribes a figure eight in air
Proverse Roll
Tendency of aircraft to roll in same direction of yaw
Caused by increased airflow on advancing wing, creating more lift, which increases roll
More prevalent in swept-wing aircraft
Adverse Yaw
Tendency of aircraft to yaw away from direction of roll
Caused by increased lift on up-going wing
More induced drag retards the forward movement of that wing
Resulting in nose yawing in opposite direction of roll
Not effects of cross-coupling
Phugoid Oscillations
Long period oscillations (20 to 100 sec per cycle) or altitude and airspeed with constant AOA
Upward gust causes aircraft to gain altitude but lose airspeed
When airspeed is lost, aircraft noses over, and reverse occurs
Pilot usually corrects situation without realizing
Pilot Induced Oscillations
Short period oscillations (1 to 3 sec per cycle)
Can occur over any axes
Greatest hazard occurs over pitch axis during landing
Pitch PIO results from pilot and longitudinal stability both attempting to correct at same time
Pilot inputs come too late resulting in overcontrol
To correct, neutralize stick and let aircraft correct itself
AE106 – STALLS
Stall Aerodynamics
Airfoil Boundary Layer – layer of air on surface of airfoil where streamlines show local retardation due to viscosity
Laminar Flow – produces lift
Turbulent Flow – does not produce lift
Boundary Layer Characteristics
Forward edge to max point of thickness
Displays laminar flow moving from high to low pressure
Airflow accelerates, kinetic energy builds
High boundary layer surface adherence
Max point of thickness to trailing edge
Changes from laminar flow to turbulent flow
Moves from low to high pressure, airflow decelerates
Encounters adverse pressure gradient
Decreasing boundary layer adherence
Adverse Pressure Gradient
Air does not want to go from low to high pressure
Caused by low pressure behind max point of thickness
Creates turbulent flow
Controlled by kinetic energy of the relative wind
Impact of High AOA on Boundary Layer
Kinetic energy decreases
Adverse pressure gradient increases
Boundary layer separation point (turbulent flow) moves forward on airfoil
Boundary Layer Separation
Point in streamline where airflow no longer adheres to the airfoil
Caused by decreasing ratio of kinetic energy vs adverse pressure gradient
Creates loss of lift
Point of boundary layer separation is constant
Stall
Condition in flight where increase in AOA results in decrease in Coefficient of Lift (CL)
Stall AOA remains constant for any given airfoil
Stall airspeed variable based on conditions
STALL CHARACTERISTICS
Power-Off Stalls
Power setting: idle
Stall airspeed: higher
Stall warning: closer to stall
Roll Tendency: right
Power-On Stalls
Power setting: above idle
Stall airspeed: lower
Stall warning: further from stall
Roll Tendency: left
Loss of Control Effectiveness
Occurs in alphabetical order
Ailerons
Elevator
Rudder
STALL AIRSPEED FACTORS
Factors Affecting Stall Airspeed
Gross Weight
Heavier = higher stall airspeed
Lighter = lower stall airspeed
Altitude
True stall airspeed increases with altitude
Indicated stall airspeed remains the same
Load Factor
Lift must equal weight to maintain level flight/equilibrium
Increased G loading is equivalent to increased weight
Bank Angle
Higher bank angles require higher G loading to maintain level flight
Increased weight, altitude, load factor, or bank angle all increase stall speed
Boundary Layer Control
Used to suppress boundary layer separation (stall) –most common – leading edge slats
Provides increased maneuvering capabilities and decreased landing speed/distance
T-6A STALLS
TAD Operation During Stall
Slows Adverse Yaw
Provides directional stability
T-6A Aerodynamic Stall Warning
Caused by turbulent airflow striking empennage
Point of occurrence
Power-off stall – approx 3 knots before stall
Power-on stall – slightly more than 3 knots before stall
T-6A Artificial Stall Warning
AOA gauge
AOA indexer
Stick Shaker - 5-10 KIAS prior to stall
AE107 – SPINS
SPIN DEVELOPMENT
Stall + Yaw = Spin
Spin Axis – Aerodynamic point around which stall and yaw forces act to sustain spin rotation
Post Stall Gyration – Aerodynamic forces during stall that result in movement around pitch, roll, and yaw axes
Higher airspeed at stall entry = greater poststall gyration tendency
Lower airspeed at stall entry = lower poststall gyration tendency
Poststall gyration can result in introduction of yaw and spin entry
Key factor for poststall gyration is AIRSPEED
Autorotation –
Combination of roll and yaw that propagates and gets worse due to asymmetrically stalled wings
Caused by unequal lift and drag forces acting on each wing
Wing Lift and Drag Characteristics
When aircraft stalled, intro of yaw creates an AOA difference between wings
Lift and drag unbalanced
Creates rolling and yaw tendency, causing spin entry and autorotation
Outside wing
Has lower AOA than inside wing
In a stall, lower AOA = more lift, less drag
Inside Wing
Has higher AOA
In a stall, higher AOA = less lift, more drag
Lift differential between inside and outside wings sustains rolling motion around spin axis
Drag differential between wings sustains yawing motion around spin axis
Spin Classifications
Erect Spin
Entered from positive G stall
Characterized by nose-down, upright attitude, and positive Gs
Inverted Spin
Entered from negative G stall
Characterized by nose-down, inverted attitude, and negative Gs
Deciding factor is G Load at induction of spin, ENTRY ATTITUDE NO FACTOR
SPIN AERODYNAMICS
Factors Affecting Spins
Conservation of angular momentum (CG location/spin axis)
Acceleration factor (pitch)
Pitch and Rotation Rate
Steeper pitch and increased rotation rate occurs due to:
Control inputs
Aircraft weight
Spin direction
Aileron Effect on Spin
Ailerons set to neutral for spin recovery
Any deflection will make spin more oscillatory
Rudder Effect on Spin
Dramatic effect on spin/spin recovery
Spin acceleration/rotation rate sensitive to amount of rudder surface acting in resistance to relative wind
Vertical drag component creates nose-down force
Horizontal drag component decreases rotation rate
Both maximized with anti spin rudder (opposite of spin direction)
Pro-Spin Rudder
Minimizes resistance to relative wind
Nose pitches up and spin accelerates
Anti-Spin Rudder
Maximizes resistance to relative wind
Spin slows and nose pitches down
Elevator Effect on Spin
Elevator/horizontal stabilizer create little lift, lots of drag in spin
Vertical drag component creates nose-down force
Nose down force increases with rotation rate, minimized with full-up elevator
Nose down elevator (accelerated)
Maximizes vertical drag
Nose pitches down
Spin accelerates
Nose up elevator (unaccelerated)
Minimizes vertical drag
Nose pitches up
Spin decelerates
Progressive Spin
Caused by maintaining full up elevator while holding anti-spin rudder
Characterized by lowering of nose and spin direction reversal
Aggravated Spin
Caused by maintaining pro-spin rudder and moving stick forward of neutral
Characterized by immediate increase in nose down pitch and increased roll rate
Effect of Gross Weight on Spin
Lighter Aircraft
Faster spin entry
Increased oscillations
Faster recovery
Heavier Aircraft
Slower spin entry
Less oscillations
Takes longer to enter spin, thus uses up more energy prior to spin entry
Slower recovery
Aircraft Pitch Attitude Factors
With given power setting, stall speed varies inversely with pitch attitude
Lower pitch attitude = higher stall speed = faster entry with more oscillations
Higher pitch attitude = slower stall speed = slower entry with fewer oscillations
Aircraft Power Setting Factors
With given pitch attitude, stall speed varies directly with power setting
Lower power setting = higher stall speed = faster entry with more oscillations
Higher power setting = slower stall speed = slower entry with fewer oscillations
Spin Direction Factors
Gyroscopic precession
T-6A propeller is a clockwise rotating gyroscope
Right Spin
Stabilizes at lower pitch
Stabilizes slower with more oscillation
Rotation rate increased
Left Spin
Stabilizes at higher pitch
Stabilizes faster with less oscillations
Rotation rate decreased
AE108 – WAKE TURBULENCE AND WIND SHEAR
Wake Turbulence occurs ANY TIME AIRCRAFT PRODUCES LIFT
Spanwise Flow
Moves around wingtip and creates wingtip vortices
Left = clockwise
Right = counterclockwise
Disturbance caused by wingtip vortices called Wake Turbulence
Vortices Factors
Weight
Heavies have more intense wake turbulence, but:
ALL AIRCRAFT CREATE WAKE TURBULENCE
Speed
Slower aircraft = more induced drag = stronger vortices
Slow flying aircraft produce stronger vortices
Configuration
With flaps/gear extended, aircraft can maintain level flight with a lower AOA
Thus, clean configuration = stronger vortices
Greatest vortex strength will occur when aircraft is heavy, clean, and slow
Size and Speed Characteristics
Vortex core diameters equal about ¼ of the generating aircraft’s wingspan (heavies ~25-50’)
Also stay close together (within ¾ of the generating aircraft’s wingspan)
Vortices interact and merge causing even larger field of influence
Short wingspan aircraft flying into these vortices are most susceptible to wake turbulence
Vortex Movement Characteristics
Vortices from heavy aircraft start to sink immediately about 400-500’/minute
Then level off about 800-900’ below flight path
Vortices lose strength with time and distance – dissipate to light chop
HAZARDS
Induced Roll
Primary hazard is loss of control because of induced roll
Capability to counteract induced roll depends on control responsiveness
Induced Flow Field
Created by interactions of both vortices
Could encounter downward flow or air equal to 1500’/minute
Disastrous at traffic pattern or approach altitudes
Vortices in Ground Effect
No-wind
Vortices move apart laterally at 5 knots
Usually break up within 2500 feet of point they entered ground effect
Crosswind
5 knot crosswind doubles one side, makes other stationary
Can move over parallel or intersecting runway
Helicopter Vortices
Small airplanes should avoid operating within 3 rotor diameters of any hovering helicopter
Give same spacing consideration as conventional airplane
AVOIDANCE
Takeoff Spacing Requirements
Minimum 2 minutes behind heavy aircraft (41,000 - 255,000 punts +)
Adjust liftoff point
Takeoff at least 300’ prior to heavy aircraft’s rotation point
Maintain flight path above his
Takeoff after nose wheel touchdown point
Landing Spacing Requirements
Minimum 3 minutes behind aircraft (41,000 - 255,000 pounds +)
Adjust landing point
Land beyond nose gear touchdown point
Land prior to aircraft’s rotation point
Parallel and Intersecting Runways (within 2500’)
Assure interval of at least 2 minutes before attempting to take off or land
WIND SHEAR
Wind Shear
Sudden change in wind direction and/or speed over short distance in atmosphere
Wind change can be very abrupt
Caused by low level jet streams, wind funneling, land-sea breezes, fronts, and thunderstorms
Effects and Hazards
Increasing Performance Wind Shear
Decreasing Performance Wind Shear
Microburst
Most common type of vertical wind shear
Generally small diameter downdraft (few hundred feet – 2.5mi)
Short lived ~ 20min
Average wind speed change is 50 knots
Caused when heavy rain showers generate intense, violent outflow of air near the ground
Severe downdrafts (up to 7000’/minute)
Vertical and horizontal wind changes and strong rotational vortices produced
Most likely to occur mid-afternoon in the summer
Microburst effects
Strong increase in headwind, indicated airspeed, and lift
Causes pitch up and climb
Do not reduce power, apply nose down force, or attempt to correct
Followed by sever downdraft then transition from severe headwind to strong tailwind
Loss of indicated airspeed, lift, and pitch down
Then apply power and back pressure to correct – hope for altitude
AVOID AT ALL COSTS
PROCEDURES
Detection Methods
Departure/Arrival Weather Reports
High potential for microburst or wind shear activity with:
Gusty winds, heavy rain, and/or thunderstorms
Be alert for convective activity
Visual Cues
Virga, localized blowing dust, rain shafts with rain diverging from center, lightning/tornado activity
Wind Shear Alert Systems
NEXRAD Doppler radars and Low Level Wind Shear Alert Systems (LLWAS)
PIREPS
Best source of info, only way to disseminate in timely manner
Make one, include location of wind shear encounter and estimate of magnitude
AVOID/DIVERT
Wind Shear Takeoff Procedures
Use longest suitable runway
Use TO flaps, delay rotation by amount of predicted shear (up to 10 knots)
Rotate to normal climb attitude
If wind shear encountered near rotation speed, abort if possible
Wind Shear Approach Procedures
Use TO flaps and increase approach speed by amount of predicted shear (up to 10 knots)
Resist temptation to make large power reductions
Expect longer landing distance because of increased approach speed
If go-around necessary, establish nose-up attitude and apply max power
Unexpected Wind Shear Recovery
Strong wind shear and microbursts must be avoided!
Take following steps to attempt recovery:
Ensure PCL at MAX
Increase pitch attitude to no less than 15 for best rate of climb
DO NOT allow airspeed to decrease below 110 KIAS or AOA to increase above 10.5 units
If ground impact certain, consider immediate ejection
Once climb established, raise flaps and gear
Do not rely solely on VSI to determine positive rate of climb
Begin reducing pitch and angle of attack in anticipation of exiting the downdraft
INSTRUCTOR’S “GOOD TO KNOW” INFOMARTIAN
With an increase in weight, in order to achieve an increase in altitude, you must increase
Either velocity and/or AOA
Slipstream swirl is corrected by using
Right rudder
In order to climb, power available must be greater than
Power required
L/DMAX is the point where ______ is a minimum.
Drag
Power Available is produced at a given
PCL setting
An infinitely long, straight line drawn though leading and trailing edges of airfoil is the
Chord Line
A segment of Chord Line drawn from leading edge to trailing edge of wing is
Chord
When you see 29.92, you immediately think of
Pressure Altitude
Total Pressure – Static Pressure =
Dynamic Pressure (IAS)
Poststall Gyration is affected by
Airspeed (not power setting)
A CG location forward of AC benefits
Directional Stability
The point where all aerodynamic forces act is called the
Aerodynamic Center
In straight and level flight, Thrust Required =
Total Drag
Know T-6A G Limits
As velocity increases, induced drag decreases, and parasite drag
Increases
As flaps are lowered, lift is increased, and drag is
Increased
When gear are lowered, power available
Stays the same
What factor effects lift the most?
Velocity (squared in lift equation)
The sum of all forces = 0, and all forces are balanced in
Equilibrium flight
Know Types of Drag
The airspeed at which first evidence of local supersonic flight is realized is called
Critical mach
Thee result of separation of airflow from a surface and the wake that is created by that separation is called
Form Drag
In order to maintain a level turn, you must add power in order to overcome
Induced Drag
Turbulence in the Boundary Layer is caused by
Skin friction drag
Load Factor is defined as
Load (Gs)/aircraft weight
When you increase weight, you increase
Induced drag
With an increase in altitude, you generally have a
Decrease in temperature
With an increase in altitude, Thrust Required __________ and Power Required _________
Remains the same, increases
What aircraft part reduces Boundary Layer Separation?
Slats (not on T-6A)
What develops Thrust Available?
Engine/Propeller
The purpose of Aerodynamic Twist is to ensure that the
Root of wing stalls first, maintaining aileron response
Thrust Horsepower comes from the _______ while Shaft Horsepower comes from the _______
Propeller, Engine
Thrust Horsepower is ALWAYS _________ and less than __________
Less than 1, Shaft Horsepower
At 60 bank, you must pull ______ to maintain level turn
2 Gs
Turn Rate/Radius is affected by
Bank Angle/Airspeed
How does weight affect Turn Rate/Radius?
It doesn’t
Pilot Induced Oscillations (PIO) and pitch are affected by
Pilot inputs and Longitudinal (pitch) Stability
The maximum G induced without permanent damage is called
Limit Load Factor
The maximum G induced without structural failure is called
Ultimate Load Factor