Aerodynamics 2

Question 1

Define Boundary Layer

Answer 1

The layer of airflow over the surface of an airfoil, which shows local airflow retardation caused by viscosity. The boundary layer is very thin at the leading edge and grows as it moves over a body. It is composed of laminar flow and turbulent flow.

Question 2

DESCRIBE the different types of flow within the boundary layer

Answer 2

• Laminar flow: the air moves smoothly along streamlines. It produces very little friction, but is easily seperated from the surface.
• Turbulent flow: the streamlines break up and the flow is disorganized and irregular. It produces higher friction drag, but adheres better to the upper surface of the airfoil, delaying boundary layer separation.

Question 3

DESCRIBE boundary layer separation

Answer 3

If the boundary layer does not have sufficient kinetic energy to overcome the adverse pressure gradient, the lower levels of the boundary layer will stagnate and the boundary layer will separate from the surface. Airflow along the surface aft of the separation point will be reversed resulting in a turbulent wake.

Question 4

DEFINE CL MAX AOA

Answer 4

The angle of attack, beyond which C_L begins to decrease is C_LMAX AOA.

Question 5

DEFINE stall

Answer 5

A condition of flight in which an increase in AOA results in a decrease in C_L

Question 6

EXPLAIN how a stall occurs

Answer 6

The adverse pressure gradient is strongest at high lift conditions and high AOA. The boundary layer will not have sufficient kinetic energy to conform to the surface of the airfoil, and will separate. At high AOA, the separation point moves forward toward the leading edge, resulting in a stall.

Question 7

IDENTIFY the aerodynamic parameters causing a stall

Answer 7

The only cause of a stall is excessive AOA. Regardless of flight conditions or airspeed, the airfoil will stall when the AOA exceeds C_LMAX AOA, also known as stalling AOA or critical AOA.

Question 8

COMPARE power-on and power-off stalls

Answer 8

The aircraft will stall at a lower airspeed in power-on stalls because at high pitch attitudes, part of the weight of the airplane is being supported by the vertical component of thrust. Also, in propeller driven aircraft, the portion of the wing immediately behind the propeller continues to produce lift at high angles of attack because the air is being accelerated by the propeller.

Question 9

DESCRIBE the order of losing control effectiveness approaching a stall in the T-6B

Answer 9

Ailerons, elevator, then rudder

Question 10

EXPLAIN the difference between true and indicated stall speed

Answer 10

An airplane will stall at a higher TAS as altitude increases, but will stall at the same indicated airspeed regardless of altitude.

Question 11

EXPLAIN the effects of gross weight, altitude, load factor and maneuvering on stall speed, given the stall speed equation

Answer 11

Increased weight, altitude, and load factor will result in a higher stall speed. You will also experience a higher stall speed in maneuvering flight.

Question 12

STATE the purpose of using high lift devices

Answer 12

The purpose of high lift devices is to reduce takeoff and landing speed by reducing both indicated and true stall speeds.

Question 13

DESCRIBE how different high lift devices affect the values of CL, CL MAX, and CL MAX AOA

Answer 13

Slats and Slots do not change C_L at low AOA, but C_LMAX and C_LMAX AOA are increased

Flaps (both leading edge and trailing edge) increase C_L and C_LMAX, but C_LMAX AOA is actually lower when flaps are deployed.

Question 14

DESCRIBE devices used to control boundary layer separation

Answer 14

• Slots allow high static pressure air beneath the wing to be accelerated through a nozzle and injected into the boundary layer on the upper surface of the airfoil, delaying boundary layer separation at high AOA.
  
  • Fixed slots are gaps at the leading edge of a wing that allow air to flow from below the wing to the upper surface.
  • Slats are moveable leading edge sections used to form automatic slots. These may be deployed aerodynamically, mechanically, hydraulically, or electrically.
• Vortex Generators are small vanes installed on the upper surface of an airfoil that disturb the laminar flow and introduce a turbulent flow to the boundary layer, delaying boundary layer separation.

Question 15

DESCRIBE devices used to change the camber of an airfoil

Answer 15

• Plain Flap: a simple hinged portion of the trailing edge that is forced down into the airstream to increase camber
• Split Flap: a plate deflected from the lower surface of the airfoil. This creates a lot of drag.
• Slotted Flap: Is similar to a plain flap, but opens a narrow slot between the flap and wing.
• Fowler Flap: moves down and aft, increasing camber and significantly increasing wing area as well as opening one or more slots.
• Leading Edge Flaps: change the wing camber at the leading edge and may also open a slot.

Question 16

DESCRIBE methods of stall warning used in the T-6B

Answer 16

• AOA indicator: calibrated so that the airplane stalls at 18 units AOA regardless of airspeed, attitude, weight or altitude. It autmotaically accounts for the differences in full-flap and no-flap stall angles.
• AOA indexer: Receives input from the AOA prope on the left wing.
• Stick shaker: Also receives input from the AOA probe and is activated at 15.5 units AOA, followed by buffeting

Question 17

DESCRIBE the stall tendency of the general types of wing planforms

Answer 17

• Rectangular wing: Strong root stall tendancy
• Highly Tapered wing: Strong tip stall tendancy
• Swept wings: Strong tip stall tendancy
• Elliptical Wing: even lift distribution, with all sections stalling at the same AOA
• Moderate taper wings: similar to eliptical wing. The pilot loses lateral control during a stall. T-6B uses this design.

Question 18

DESCRIBE the various methods of wing tailoring, including geometric twist, aerodynamic twist, stall strips, and stall fences

Answer 18

• Geometric twist: A decrease in angle of incidence from wing root to wingtip. The root stalls first because of its higher AOA.
• Aerodynamic twist: also called section variation, is a gradual change in airfoil shape that increases CLMAX AOA to a higher value near the tip than at the root, either by decreasing camber or relative thickness of the wing.
• Stall strips: sharply angled piece of metal mounted on the leading edge of the wing root, which causes the boundary layer to separate at a lower AOA in that section.
• Stall Fences: redirect airflow along the chord of the wing thereby delaying tip stall.

The T-6B uses both geometric and aerodynamic twist and has stall strips on the root section of the wing leading edge.

Question 19

DEFINE takeoff and landing airspeed in terms of stall speed

Answer 19

Takeoff Airspeed: 20% above the power off stall speed.

Landing Airspeed: 30% above stall speed

Question 20

STATE the various forces acting on an airplane during the takeoff and landing transition

Answer 20

• Rolling Friction (F_R): friction between the landing gear and the runway.
• Thrust
• Drag
• Net Accelerating Force: Thrust minus Drag and rolling friction.
• Net Decellerating Force: Drag plus Rolling Friction minus Thrust

Question 21

STATE the factors that determine the coefficient of rolling friction

Answer 21

• Runway surface
• runway condition
• tire type
• degree of brake application

Question 22

DESCRIBE the effects on takeoff and landing performance, given variations in weight, altitude, temperature, humidity, wind, and braking

Answer 22

• Weight: Increasing weight increases rolling friction, requires greater lift and a higher takeoff velocity. Doubling weight will increase takeoff distance four times.
• Increasing airfield elevation (altitude), increasing temperature, or increasing humidity will increase Density Altitude (DA). Higher DA requires a higher takeoff velocity and decreases the amount of thrust the engine can provide, thereby increasing takeoff distance.
• Braking: A decrease in braking effectiveness will incresae landing roll.

Mnemonic: “4-H Club”: High, Hot, Heavy and Humid. Whenever three or more of these are present, expect extended takeoff and landing distances.

Question 23

DESCRIBE the effects of outside air temperature (OAT) on airplane performance characteristics

Answer 23

Increasing outside air temperature increases density altitude resulting in less lift. It also decreases thrust available. It will result in a longer takeoff roll, and a lower rate of climb.

Question 24

DEFINE maximum angle of climb and maximum rate of climb profiles

Answer 24

Maximum Angle of Climb (AOC) is a comparison of altitude gained to distance traveled. Maximum vertical velocity for a minimum horizontal velocity.

Maximum Rate of Climb (ROC) is a comparison of altitude gained relative to the time needed to reach that altitude. Results in maximum vertical velocity.

Question 25

EXPLAIN the performance characteristics profiles that yield maximum angle of climb and maximum rate of climb for turboprops.

Answer 25

Maximum AOC performance depends upon thrust excess. Occurs at a velocity less than L/D_MAX and an AOA greater than L/D_MAX AOA for a turboprop

Maximum ROC performance depends upon power excess. Occurs at L/D_MAX AOA and velocity for a turboprop.

Max AOC and max ROC are not used in the T-6B. Best climb speed of 140 KIAS is used instead.

Question 26

DESCRIBE the effect of changes in weight, altitude, configuration, and wind on maximum angle of climb and maximum rate of climb profiles

Answer 26

An increase in weight, increase in altitude, lowering the landing gear, or lowering flaps will decrease max AOC and max ROC performance.

A headwind will increase AOC performance due to the decrease in groundspeed, while a tailwind will decrease AOC. Wind has no effect on ROC

Question 27

DESCRIBE the performance characteristics and purpose of the best climb profile for the T-6B,

Answer 27

Best climb speed will meet or exceed any obstacle clearance requirements while providing a greater safety margin than slower airspeeds.

Question 28

DEFINE absolute ceiling, service ceiling, cruise ceiling, combat ceiling, and maximum operating ceiling

Answer 28

Combat ceiling: Altitude where max power excess allows only 500 fpm ROC.

Cruise ceiling: altitude at which an airplane can maintain only a 300 fpm ROC.

Service ceiling: altitude at which an airplane can maintain only a 100 fpm ROC.

Absolute ceiling: The altitude at which an airplane can no longer perform a steady climb since maximum thrust excess is zero.

Operational ceiling: 31,000 ft for the T-6B

Question 29

STATE the maximum operating ceiling of the T-6B

Answer 29

31,000 ft

Question 30

STATE the relationship between fuel flow, power available, power required, and velocity for a turboprop airplane in straight and level flight

Answer 30

• Fuel flow varies directly with the power output of the engine (PA).
• Minimum fuel flow for equilibrium flight will be found on the power required (PR) curve.
• The power required curve will tell us the velocity we must fly to acheive equilibrium flight. The pilot must adjust the throttle to eliminate thrust excess.

Question 31

DEFINE maximum range and maximum endurance profiles

Answer 31

Maximum endurance is the maximum amount of time that an airplane can remain airborne on a given amount of fuel.

• Found at a velocity less than L/D_MAX and an AOA greater than L/D_MAX AOA for a turboprop.
• 8.8 units AOA for T-6B

Maximum range is the maximum distance traveled over the ground for a given amount of fuel.

• ]Found at L/D_MAX AOA for turboprops.
• 4.4 units AOA for T-6B

maximum range velocisty is faster than maximum endurance.

Question 32

EXPLAIN the performance characteristics profiles that yield maximum endurance and maximum range for turboprops

Answer 32

Maximum endurance is found at the bottom of the Power required curve for a turboprop. (a velocity less than L/D_MAX and an AOA greater than L/D_MAX AOA)

Maximum range is found at L/D_MAX AOA for turboprops in a no wind condition.

Max range airspeed would be higher than L/D max with a headwind and lower with a tailwind.

Question 33

DESCRIBE the effect of changes in weight, altitude, configuration, and wind on maximum endurance and maximum range performance and airspeed

Answer 33

• Weight: An increase in weight will decrease maximum endurance and maximum range, and increase max endurance and max range airspeeds.
• Altitude: max endurance and max range increases. These will also be at a higher TAS.
• Configuration: max endurance and max range will decrease when flaps or landing gear are extended.
• Wind: Headwinds will decrease maximum range while tailwinds will increase max range. Wind has no effect on maximum endurance.

Question 34

DEFINE Mach number

Answer 34

The ratio of an airplanes speed through a given air mass to sound’s speed through the same air mass.

Question 35

DEFINE critical Mach

Answer 35

The lowest mach number than an airplane can travel at and create sonic airflow somewhere on the aircraft.

Question 36

STATE the effects of altitude on Mach number and critical Mach number

Answer 36

As altitude increases, temperature decreases, resulting in a higher mach number for the same TAS. Critical Mach number will remain the same regardless of altitude.

Question 37

DEFINE maximum glide range and maximum glide endurance profiles

Answer 37

Maximum glide range is the greatest distance we can fly without an operating engine and is achieved with a minimum glide angle. L/D_MAX AOA gives us the best range velocity (V_BEST). V_BEST is 125 KIAS for the T-6B.

Maximum glide endurance is a matter of minimizing rate of descent. It is acheived at the bottom of the P_R curve, which is a lower velocity and higher AOA than L/D_MAX.

Question 38

EXPLAIN the performance characteristics profiles that yield maximum glide range and maximum glide endurance

Answer 38

L/D_{MAX<strong> </strong>}AOA and velocity will result in maximum glade range.

Maximum glide endurance velocity is less than L/D_MAX and AOA is greater than L/D_MAX AOA.

Question 39

DESCRIBE the effect of changes in weight, altitude, configuration, wind, and propeller feathering on maximum glide range and maximum glide endurance performance and airspeed

Answer 39

• Weight: An increase in weight will result in increased velocities for max glide range and max glide endurance, but the AOA will remain the same. Weight will not change the glide range, but will decrease glide endurance.
• Altitude: An increase in altitude will increase max glide range and max glide endurance of an airplane.
• Wind: A headwind will decrease max range while a tailwind will increase max range. Wind has no effect on glide endurance.
• Configuration: By extending the landing gear or flaps, the sink rate will increase and the glide range will decrease
• Propeller Feathering: Feathering the propeller result in significantly increased glide range and glide endurance over a windmilling propeller.

Question 40

DESCRIBE the locations of the regions of normal and reverse command on the turboprop power curve

Answer 40

The region of normal command for a turboprop occur at velocities greater than maximum endurance airspeed (the lowest point on the power required curve).

The region of reverse command for a turboprop occurs at velocities less than maximum endurance airspeed.

Question 41

EXPLAIN the relationship between power required and airspeed in the regions of normal and reverse command

Answer 41

In the region of normal command, more power is required for the airplane to go faster while maintaining altitude.

In the region of reverse command, more power is required for the airplane to fly at slower airspeeds and maintain altitude.

Question 42

DEFINE nosewheel liftoff/touchdown speed

Answer 42

The lowest speed that a heading and course along the runway can be maintained with full rudder and ailerons deflected when the nosewheel is off the runway; The minimum safe airspeed that the noswheel may leave the runway during takeoff, or the minimum airspeed at which the nosewheel must return to the runway during landing.

Question 43

STATE the pilot speed and attitude inputs necessary to control the airplane during a crosswind landing

Answer 43

The pilot must approach at a speed above NWLO/TD. He will maintian directional control with the rudder and apply ailerons to overcome the lateral stability that is trying to roll the airplane away from the crosswind.

Question 44

STATE the crosswind limits for the T-6B

Answer 44

Maximum crosswind component for takeoff or landing in the T-6B is 25 knots.

Question 45

DEFINE hydroplaning

Answer 45

When the airplane’s tires skim atop a thin layer of water on a runway.

Question 46

STATE the factors that affect the speed at which an airplane will hydroplane

Answer 46

The speed at which an airplane will hydroplane depends only on the tire pressures.

Question 47

DESCRIBE the effects of propeller slipstream swirl, P-factor, torque, and gyroscopic precession as they apply to the T-6B

Answer 47

• Torque will tend to roll the airplane’s fuselage counter-clockwise. Rudder and the automatic Trim Aid Device (TAD) are the primary means of compensating for engine torque.
• Propeller Factor (P-factor) is the yawing moment caused by one prop blade creating more thrust than another. It will cause the airplane to yaw right at high speeds and yaw left at low airspeeds.
• Slipstream Swirl is the corkscrew motion that the propeller imparts to the air. It causes the airplane to yaw left when at high power settings and low speeds.
• Gyroscopic Precession is a consequence of the properties of spinning objects. When a force is applied to the rim of a spinning object, a resultan force is created 90° ahead in the direction of rotation. Pitching the nose of the T-6B down causes the airplane to yaw left.

Question 48

DESCRIBE what the pilot must do to compensate for propeller slipstream swirl, P-factor, torque, and gyroscopic precession as they apply to the T-6B

Answer 48

• To compensate for torque, the pilot must apply right rudder at high power settings
• To compensate for P-factor, the pilot must apply right rudder when at high power and low airspeeds and left rudder when at high power and high airspeeds.
• To compensate for slipstream swirl, the pilot must apply right rudder when at high power and low airspeeds.
• To compensate for gyroscopic precession, the pilot must apply right rudder while pitching down, and left rudder when pitching upt

Question 49

DESCRIBE the effect of lift on turn performance

Answer 49

An increase in lift will result in greater turn performance by allowing an increased angle of bank.

Question 50

DESCRIBE the effect of weight on turn performance

Answer 50

Turn rate and radius are independent of weight.

Question 51

DESCRIBE the effect of thrust on turn performance

Answer 51

An airplanes thrust may limit turn performance since you must have sufficient thrust to overcome the induced drag created at high load factors.

Question 52

DESCRIBE the effect of drag on turn performance

Answer 52

An increase in drag will limit speed, thereby increasing turn rate and decreasing turn radius.

Question 53

DEFINE turn radius and turn rate

Answer 53

Turn radius (r) is a measure of the radius of the circle the flight bath scribes.

Turn rate (ω) is the rate of heading change measured in degrees per second.

Question 54

DESCRIBE the effects of changes in bank angle on turn performance

Answer 54

Increasing bank angle will increase the turn rate and decreas the turn radius (increased turn performance)

Question 55

DESCRIBE the effects of changes in airspeed on turn performance

Answer 55

Increasing airspeed (same bank angle) would decrease the turn rate and increase turn radius (decreased turn performance)

Question 56

DESCRIBE the effects of aileron and rudder forces during turns

Answer 56

Aileron is used to set the angle of bank while rudder is used to coordinate the turn. Too much rudder in the direction of the turn will result in a skid. Opposite, or insufficient rudder the direction of the turn will result in a slip.

Question 57

EXPLAIN the aerodynamic principle that requires two G’s of backstick pressure to maintain level, constant airspeed flight, at 60 degrees angle of bank

Answer 57

In a turn, the lift vector is divided into two components, the horizontal component of lift which turns the airplane and the vertical component of lift which opposes gravity. In a level turn, the vertical component of lift must be equal to weight, therefore as bank increases, total lift must increase. at 60 degrees of bank, lift must be double weight. Load factor is equal to lift over weight (2 G).

Question 58

DESCRIBE the relationship between load factor and angle of bank for level, constant-airspeed-flight

Answer 58

Load factor increases gradually at low angles of bank, but exponentially at angles greater than 60°

Question 59

DEFINE load, load factor, limit load factor, and ultimate load factor

Answer 59

Load is a stress-producing force that is imposed upon an airplane or component.

Load factor (n) is the ratio of total lift to the airplane’s weight.

Limit Load Factor is the greatest load factor an airplane can sustain without any risk of permanent deformation.

Ultimate Load Factor is the maximum load factor that the airplane can withstand without structural failure.

Question 60

DEFINE static strength, static failure, fatigue strength, fatigue failure, service life, creep, and overstress/over-G

Answer 60

Static strength is a measure of a material’s resistance to a single application of a steadily increasing load or force.

Static failure is the breaking or serious permanent deformation of a material due to a single application of a steadily increasing load or force.

Fatigue strength is a measure of a material’s ability to withstand a cyclic application of load or force.

Fatigue failure is the breaking of a material due to a cyclic application of load or force.

Service life is the number of applications of load or force that a component can withstand before it has the probability of failing.

Creep is when a metal is subjected to high stress and temperature and it tends to stretch or elongate.

Overstress/Over-G is the condition of possible permanent deformation or damage that results from exceeding the limit load factor.

Question 61

DEFINE maneuvering speed, cornering velocity, redline airspeed, accelerated stall lines, and the safe flight envelope

Answer 61

Maneuvering speed (V_a) or cornering velocity is the indicated airspeed that an airplane can achieve its maximum turn rate and minimum turn radius. The slowest velocity that an airplane can generate its limit load. It is usually the recommended turbulent air penetration airspeed.

Redline airspeed (V_NE) is the maximum permissible airspeed for an airplane. Beyond the redline airspeed, a pilot may experience control problems and structural damage to the aircraft due to aeroelastic effects.

Accelerated stall line: a curved line describing the number of g’s that can be generated at a given indicated airspeed as a function of C_LMAX angle of attack for a particular airfoil. Also called maximum lift.

Safe flight envelope: The portion of the V-n diagram that is bounded on the left by the accelerated stall lines, on the top and bottom by the positive and negative limit loads, and on the right by redline airspeed. An aircraft may operate in its safe flight envelope without exceeding its structural or aerodynamic limits.

Question 62

DESCRIBE the boundaries of the safe flight envelope, including accelerated stall lines, limit load factor, ultimate load factor, maneuver point, and redline airspeed

Answer 62

The safe flight envelope is bounded on the left by the accelerated stall lines, on the top and bottom by the positive and negative limit loads, and on the right by redline airspeed. An aircraft may operate in its safe flight envelope without exceeding its structural or aerodynamic limits. load factor is the vertical scale, while airspeed is the horizontal scale. maneuver point is the point where the accelerated stall line and the limit load factor line intersect.

Question 63

DEFINE asymmetric loading and state the associated limitations for the T-6B

Answer 63

Assymetric loading refers to uneven production of lift on the wings of an airplane. It may be caused by a rolling pullout, trapped fuel, or hung ordnance.

In the T-6B, the maximum load factor during asymmetric loading is +4.7 to -1.0 G’s.

Question 64

DEFINE static stability and dynamic stability

Answer 64

Static stability is the initial tendency of an object to move toward or away from its equilibrium position.

Dynamic stability is the position with respect to time or motion of an object after a disturbance.

Question 65

DESCRIBE the characteristics exhibited by aircraft with positive, neutral, and negative static stabilities, when disturbed from equilibrium

Answer 65

Positive: initial tendency toward its original equilibrium position after disturbance

Neutral: initial tendency to accept the displacement position

Negative: initial tendency to continue moving away from equilibrium following a disturbance

Question 66

DESCRIBE the characteristics exhibited by aircraft with positive, neutral, and negative dynamic stabilities, when disturbed from equilibrium

Answer 66

Positive: the aircraft will tend to oscillate less over time as it returns to its original equilibrium position.

Neutral: the aircraft will continue to oscillate over time, never settling back at its original position.

Negative: the aircraft will experience greater oscilations over time.

Question 67

DESCRIBE the characteristics of damped, undamped, and divergent oscillations, and the combination of static and dynamic stabilities that result in each

Answer 67

Damped oscillation is when oscillations are reduced over time. This would result from positive static and dynamic stability.

Undamped oscillation is when the oscillations continue at the same rate and magnitude. This would result from positive static stability, but neutral dynamic stability.

Divergent Oscillation is when the oscillations grow in magnitude over time. This would result from positive static stability and negative dynamic stability.

Question 68

EXPLAIN the relationship between stability and maneuverability

Answer 68

A stable airplane will tend to be less maneuverable, while an unstable airplane will be very maneuverable.

Question 69

STATE the methods for increasing an airplane’s maneuverability

Answer 69

Maneuverabillity may be increased by decreasing stability or by giving the airplane larger control surfaces.

Question 70

STATE the effects of airplane components on an airplane’s longitudinal static stability

Answer 70

The wings having an aerodynamic center that is forward of the center of gravity decreasing longitudinal static stability.

Swept wings move the aerodynamic center aft, thus increasing its longitudinal stability

The fuselage also creates lift, and it’s aerodynamic center is generally ahead of the airplane’s CG, decreasing longitudinal static stability.

The horizontal stabilizer has an aerodynamic center far aft of the center of gravity, thus having the greatest positive effect on longitudinal stability

Question 71

EXPLAIN the criticality of weight and balance

Answer 71

The location of the center of gravity is critical to longitudinal stability. By moving cargo, ordnance, and fuel we can change the location of the center of gravity. The neutral point defines the farthest aft CG position without negative stability. With the CG ahead of the neutral point the airplane will be positively stable, but if it moves aft of the neutral point, it will become negatively stable and the pilot will have difficulty controlling it in flight.

Question 72

STATE the effects of airplane components on an airplane’s directional static stability

Answer 72

Straight wings have a small positive effect on directional static stability

Swept wings further increase directional stability

Fuselage has a negative effect on directional stability

Vertical Stabilizer is the greatest positive contributor to directional static stability

Question 73

STATE the effects of airplane components on an airplane’s lateral static stability

Answer 73

Dihedral effect of the wings is the greatest positive contributor to lateral static stability.

High-mounted wing will increase lateral stability, while a low-mounted wing decreases lateral stability.

Wing sweep also increases lateral stability

Vertical Stabilizer tends to improve lateral stability

Question 74

STATE the static stability requirements for, and the effects of, directional divergence

Answer 74

Negative directional static stability will result in directional divergence. This is a condition of flight in which the reaction to a small initial sideslip results in an increase in sideslip angle, which could cause out of control flight.

Most airplanes have very strong directional stability.

Question 75

STATE the static stability requirements for, and the effects of, spiral divergence

Answer 75

Spiral divergence occurs when an airplane has strong directional stability and weak lateral stability. If an airplane’s wing dips, directional stability will cause the airplane to yaw in that direction, developing into a tight descending spiral.

This is easily corrected by control input from the pilot.

Question 76

STATE the static stability requirements for, and the effects of, dutch roll

Answer 76

Dutch roll is the result of strong lateral stability and weak directional stability. The airplane responds to a disturbance with both roll and yaw motions that affect eachother. Appears to be “tail wagging”.

It can be tolerated and may eventually dampen out, but it is not acceptable in a figher or attack airplane when the pilot is trying to aim at a target.

Question 77

DEFINE proverse roll

Answer 77

The tendency for an airplane to roll in the same direction as it is yawing

Question 78

DEFINE adverse yaw

Answer 78

The tendency of an airplane to yaw away from the direction of aileron roll input.

Question 79

EXPLAIN how an airplane develops phugoid oscillations

Answer 79

Phugoid oscillations are long period oscillations of altitude and airspeed while maintaining a nearly constant angle of attack. For instance, an airplane struck by an upward gust of wind would gain altitude and lose airspeed, eventually when enought airspeed was lost, the airplane would nose over gaining airspeed and losing altitude. When enough airspeed was regained, the nose will pitch back up, restarting the process.

Question 80

EXPLAIN how an airplane develops pilot induced oscillations

Answer 80

Pilot induced oscillations (PIO) are short period oscillations of pitch attitude and angle of attack that occurs when a pilot is tryping to control airplane oscillations that happen over approximately the same time span as it takes to react.

When the pilots inputs coincide with the airplanes natural stability corrections the result is an over correction to each oscilltion. If the pilot releases the controls, the airplane will correct itself.

Question 81

DEFINE asymmetric thrust

Answer 81

The directional control problems experienced when one engine of a multi-engine airplane fails and creates a yawing moment toward the dead engine.

Question 82

DEFINE a spin

Answer 82

An assymetric aggrevated stall that results in autorotation.

Question 83

DEFINE autorotation

Answer 83

A combination of roll and yaw that propagates itself due to asymmetrically stalled wings.

Question 84

DESCRIBE the aerodynamic forces affecting a spin

Answer 84

Every aircraft exhibits different spin characteristics, but they all have stall and yaw about the spin axis.

If yaw is induced during a stall, it will create an AOA difference between the left and right wings, which causes the airplane to roll. This creates an even higher AOA on the downgoing wing, but reduces the AOA of the up-going wing. While both wings are stalled, they do not lose all of their lift, nor are they equally stalled. The higher the AOA on the down-going wing, the more drag it creates, creating a yawing motion about the spin axis. The combined effects of roll and yaw cause the airplane to continue its autorotation.

The spin axis is the aerodynamic axis around which stall and yaw forces act to sustain spin rotation.

The poststall gyration phase begins the instant the airplane stalls, and is where the pilot introduces yaw necessary for a spin.

The incipient stage begins after the poststall gyrations have introduced yaw and ends when the spin is fully developed. (up to two rotations)

Question 85

STATE the characteristics of erect, inverted, and flat spins

Answer 85

An Erect Spins is characterized by a nose down, upright attitude and positive Gs.

An inverted spin is characterized by an inverted attitude and negative Gs on the airplane. The position of the vertical stabilizer causes the airplane to recover easily. They are very disorienting to the aircrew and difficult to enter

A flat spin is characterized by a flat attitude and transverse “eyeball out” Gs. The control surfaces are inneffective. Cockpit indications are similar to an erect spin, except airspeed may vary.

Question 86

DESCRIBE the factors contributing to aircraft spin

Answer 86

The location of the spin axis relative to the center of gravity. Due to conservation of angular momentum, the CG closer to the spin axis results in an increased rotation rate.

Ailerons applied in the direction of spin will cause increased roll and yaw oscillations, while ailerons applied opposite of spin rotation will tend to dampen roll and yaw oscillations. Ailerons are not used to recover from a spin in a T-6B

Rudder in a spin is used to create drag, not lift, to create a yawing moment. Rudder deflected in the same direction as the spin, will result in less drag, while rudder deflected opposite the direction of the spin will create more drag, slowing the rate of rotation.

Elevator Full aft stick results in the flatest pitch attitude and the lowest spin rate, referred to as an unaccelerated spin. Any stick position other than full aft will result in a steeper pitch attitude and an increase in rotation rate, referred to as an accelerated spin.

Question 87

DISCUSS the effects of weight, pitch attitude, and gyroscopic effects on spin characteristics

Answer 87

Weight: A heavier airplane will have a slower spin entry with lesser oscillations due to its large moment of inertia. A lighter airplane will enter a spin more quickly, with greater oscillations possible, but will also recover from a spin faster.

Pitch attitude: A high pitch attitude will result in a slower spin entry with lesser oscillations due. At lower pitch attitudes, the aircraft stalls at a higher airspeed and entries are faster and more oscillatory.

Gyroscopic effects: Due to the effects of gyroscopic precession on the propeller, a T-6B in a right spin will tend to pitch down, resulting in higher rotation rate and a more oscillatory entry. In a left spin, a T-6B will tend to pitch up, having a flatter attitude, slower rotation rate and smoother entries.

Question 88

STATE how empennage design features change spin characteristics

Answer 88

The design of the vertical stabilizer and rudder and the placement of the horizontal control surfaces will significantly effect spin recovery. If airflow to the vertical fin is blocked by the horizontal surfaces, it will not be effective at stopping the autorotation. With the T-6B, the horizontal stabilizer is farther aft, exposing more of the rudder during a spin.

The T-6B also uses a dorsal fin, strakes, and ventral fins to decrease the severity of spin characteristics.

Dorsal Fin: attached to the front of the vertical stabilizer to increase its surface area. Decreases the spin rate and aids in stopping autorotation.

Ventral Fin: located beneath the empenage. Decreases the spin rate and aids in maintaining a nose-down attitude.

Strakes: located in front of the horizontal stabilizer. Increase the surface area of the horizontal stabilizer, keeping the nose pitched down and preventing a flat spin.

Question 89

STATE the cockpit indications of an erect and inverted spin

Answer 89

Erect Spin:

• Altimeter: Rapidly decreasing
• AOA: 18+ units (pegged)
• Airspeed: 120-135 KIAS
• Turn needle: pegged in direction of spin
• VSI: 6000 fpm (pegged)
• Attitude gyro: may be tumbling (60° nose down)

Inverted Spin:

• Altimeter: Rapidly decreasing
• AOA: 0 units (pegged)
• Airspeed: 40 KIAS
• Turn needle: pegged in direction of spin
• VSI: 6000 fpm (pegged)
• Attitude gyro: may be tumbling (30° nose down)

Question 90

DESCRIBE the pilot actions necessary to recover from a spin

Answer 90

1. Gear, flaps, and speed brake - Retracted
2. PCL - idle
3. Rudder - full opposite to turn needle deflection
4. Control stick - forward of neutral with ailerons neutral
5. Smoothly recover to level flight after spin rotation stops

Question 91

DESCRIBE a progressive spin

Answer 91

A progressive spin will result if, during the recovery phase, the pilot puts in full opposite rudder, but inadvertently maintains full aft stick. After one or two more spins in the initial spin direction, the nose will pitch steeply down and the airplane will snap into a reversed direction of rotation more violently than a normal spin entry.

Question 92

DESCRIBE an aggravated spin

Answer 92

An aggravated spin is caused by maintaining pro-spin rudder while moving the control stick forward of the neutral position. It is characterized by a steep nose-down pitch attitude (~70°) and an increase in spin rate (~280° per second).

Question 93

DESCRIBE wake turbulence

Answer 93

Wake turbulence is a result of the wingtip vortices formed when an airplane produces lift. Flying through wake turbulence can result in structural damage, wing stall, or compressor stall.

Question 94

DESCRIBE the effects of changes in weight, configuration, and airspeed on wake turbulence intensity

Answer 94

Weight: A heavier airplane must produce more lift to maintain level flight, and will therefore create stronger wingtip vortices.

Airspeed: Vortex strength has a direct correlation to induced drag. Since induced drag is dominant at lower airspeeds, a slower aircraft will have stronger vortices.

Configuration: If flaps are lowered, more lift is created at the wing root, which decreases the pressure differential at the wingtip.

The greatest vortex strength occurs when the airplane is heavy, slow, and clearn.

Question 95

DESCRIBE the effects of wake turbulence on aircraft performance

Answer 95

The primary hazard to aircraft is loss of control caused by induced roll. It is difficult for airplanes with short wingspans (compared to the generating airplane) to counter the induced roll.

A second hazard, called Induced flow field, is created by the interactions of both vorticed resulting in a downwash between them of up to 1500 fpm. This can be disasterous to an aircraft that is already descending at a low power setting.

Question 96

STATE the takeoff and landing interval requirements for the T-6B

Answer 96

Minimum takeoff spacing: 2 minutes behind a heavy aircraft (over 255,000 lbs) same is recommended for large aircraft

Minimum landing spacing: 3 minutes behind a heavy aircraft

Question 97

DESCRIBE procedure for wake turbulence avoidance during takeoff

Answer 97

When taking off behind a large airplane that is departing ahead of you, ensure you liftoff at least 300 feet prior to the larger airplane’s point of rotation and conduct your climb-out to remain above his flight path.

If departing after a larger aircraft has landed, plan to rotate at a point forward of where the larger aircraft’s nosewheel touched down.

Question 98

DESCRIBE procedure for wake turbulence avoidance during landing

Answer 98

When landing behind a larger airplane, stay at or above the larger airplane’s final approach path and land beyond its nosewheel touchdown point.

When landing behind a larger aircraft that has just departed, ensure that your touchdown point is prior to the large aircraft’s rotation point.

Question 99

DEFINE wind shear

Answer 99

A sudden change in wind direction or speed over a short distance in the atmosphere.

Question 100

STATE the conditions that will lead to an increasing performance wind shear

Answer 100

increase in headwind or decrease in tailwind.

Question 101

STATE the conditions that will lead to a decreasing performance wind shear

Answer 101

A tailwind, or a decrease in headwind.

Question 102

DESCRIBE the effects of wind shear on aircraft performance

Answer 102

An increasing performance wind shear will increase IAS, increase lift, and result in a steeper angle of climb when taking off.

A decreasing performance wind shear will decrease IAS, reducing lift, and resulting in a shllower angle of climb on takeoff. A rapid drop of airspeed could result in stall.

Question 103

DESCRIBE procedures for flying in and around wind shear

Answer 103

If windshear cannot be avoided in the T-6B, use these procedures in areas of suspected wind shear.

For takeoff:

1. Use the longest suitable runway. Considering crosswind, obstacles, runway surface conditions, etc.
2. Use takeoff flaps, but delay rotation (V_ROT) by the amount of predicted wind shear (up to 10 knots)
3. Rotate to normal climb attitude at increased V_ROT and maintain attitude.
4. If wind shear is encountered near V_ROT abort if possible

For Landing:

1. Set flaps to takeoff and increase approach speed by the amount of wind shear potential (up to 10 knots).
2. Establish the proper approach pitch, trim, and power setting by 1000 ft AGL. Resist the temptation to make large power reductions.
3. Remember that increasing landing speed means longer landing distances.

Question 104

DESCRIBE wind shear avoidance techniques

Answer 104

• Delay takeoff or landing until wind shear condition no longer exists.
• Consider going around if windshear is experienced during landing
• Consider diverting to another airport
• Be alert for any convective activity that might be forecast
• Visual cues include virga, localized blowing dust, rain shafts with rain diverging from the core, and any indication of lightning or tornado-like activity may indicate a microburst.
• LLWAS, NEXRAD Dopplar radar, and onboard aircraft systems may help the pilot aviod wind shear.
• PIREPS and Weather Alerts are one of the best sources of wind shear information.