Aerodynamics 2 Flashcards
(104 cards)
1
Q
Define Boundary Layer
A
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.
2
Q
DESCRIBE the different types of flow within the boundary layer
A
- 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.
3
Q
DESCRIBE boundary layer separation
A
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.
4
Q
DEFINE CL MAX AOA
A
The angle of attack, beyond which CL begins to decrease is CLMAX AOA.
5
Q
DEFINE stall
A
A condition of flight in which an increase in AOA results in a decrease in CL
6
Q
EXPLAIN how a stall occurs
A
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.
7
Q
IDENTIFY the aerodynamic parameters causing a stall
A
The only cause of a stall is excessive AOA. Regardless of flight conditions or airspeed, the airfoil will stall when the AOA exceeds CLMAX AOA, also known as stalling AOA or critical AOA.
8
Q
COMPARE power-on and power-off stalls
A
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.
9
Q
DESCRIBE the order of losing control effectiveness approaching a stall in the T-6B
A
Ailerons, elevator, then rudder
10
Q
EXPLAIN the difference between true and indicated stall speed
A
An airplane will stall at a higher TAS as altitude increases, but will stall at the same indicated airspeed regardless of altitude.
11
Q
EXPLAIN the effects of gross weight, altitude, load factor and maneuvering on stall speed, given the stall speed equation
A
Increased weight, altitude, and load factor will result in a higher stall speed. You will also experience a higher stall speed in maneuvering flight.
12
Q
STATE the purpose of using high lift devices
A
The purpose of high lift devices is to reduce takeoff and landing speed by reducing both indicated and true stall speeds.
13
Q
DESCRIBE how different high lift devices affect the values of CL, CL MAX, and CL MAX AOA
A
Slats and Slots do not change CL at low AOA, but CLMAX and CLMAX AOA are increased
Flaps (both leading edge and trailing edge) increase CL and CLMAX, but CLMAX AOA is actually lower when flaps are deployed.
14
Q
DESCRIBE devices used to control boundary layer separation
A
-
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.
15
Q
DESCRIBE devices used to change the camber of an airfoil
A
- 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.
16
Q
DESCRIBE methods of stall warning used in the T-6B
A
- 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
17
Q
DESCRIBE the stall tendency of the general types of wing planforms
A
- 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.
18
Q
DESCRIBE the various methods of wing tailoring, including geometric twist, aerodynamic twist, stall strips, and stall fences
A
- 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.
19
Q
DEFINE takeoff and landing airspeed in terms of stall speed
A
Takeoff Airspeed: 20% above the power off stall speed.
Landing Airspeed: 30% above stall speed
20
Q
STATE the various forces acting on an airplane during the takeoff and landing transition
A
- Rolling Friction (FR): 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
21
Q
STATE the factors that determine the coefficient of rolling friction
A
- Runway surface
- runway condition
- tire type
- degree of brake application
22
Q
DESCRIBE the effects on takeoff and landing performance, given variations in weight, altitude, temperature, humidity, wind, and braking
A
- 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.
23
Q
DESCRIBE the effects of outside air temperature (OAT) on airplane performance characteristics
A
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.
24
Q
DEFINE maximum angle of climb and maximum rate of climb profiles
A
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.
25
EXPLAIN the performance characteristics profiles that yield maximum angle of climb and maximum rate of climb for turboprops.
**Maximum AOC** **performance depends upon thrust excess**. Occurs at a velocity less than L/DMAX and an AOA greater than L/DMAX AOA for a turboprop
**Maximum ROC performance depends upon power excess.** Occurs at L/DMAX 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.
26
DESCRIBE the effect of changes in weight, altitude, configuration, and wind on maximum angle of climb and maximum rate of climb profiles
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
27
DESCRIBE the performance characteristics and purpose of the best climb profile for the T-6B,
Best climb speed will meet or exceed any obstacle clearance requirements while providing a greater safety margin than slower airspeeds.
28
DEFINE absolute ceiling, service ceiling, cruise ceiling, combat ceiling, and maximum operating ceiling
**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
29
STATE the maximum operating ceiling of the T-6B
31,000 ft
30
STATE the relationship between fuel flow, power available, power required, and velocity for a turboprop airplane in straight and level flight
* 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.
31
DEFINE maximum range and maximum endurance profiles
**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/DMAX and an AOA greater than L/DMAX 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/DMAX AOA for turboprops.
* 4.4 units AOA for T-6B
*maximum range velocisty is faster than maximum endurance*.
32
EXPLAIN the performance characteristics profiles that yield maximum endurance and maximum range for turboprops
**Maximum endurance** is found at the bottom of the Power required curve for a turboprop. (a velocity less than L/DMAX and an AOA greater than L/DMAX AOA)
**Maximum range** is found at L/DMAX 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._
33
DESCRIBE the effect of changes in weight, altitude, configuration, and wind on maximum endurance and maximum range performance and airspeed
* **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.
34
DEFINE Mach number
The ratio of an airplanes speed through a given air mass to sound's speed through the same air mass.
35
DEFINE critical Mach
The lowest mach number than an airplane can travel at and create sonic airflow somewhere on the aircraft.
36
STATE the effects of altitude on Mach number and critical Mach number
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.
37
DEFINE maximum glide range and maximum glide endurance profiles
**Maximum glide range** is the greatest distance we can fly without an operating engine and is achieved with a minimum glide angle. L/DMAX AOA gives us the best range velocity (VBEST). VBEST 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 PR curve, which is a lower velocity and higher AOA than L/DMAX.
38
EXPLAIN the performance characteristics profiles that yield maximum glide range and maximum glide endurance
L/DMAX AOA and velocity will result in maximum glade range.
Maximum glide endurance velocity is less than L/DMAX and AOA is greater than L/DMAX AOA.
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
* **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.
40
DESCRIBE the locations of the regions of normal and reverse command on the turboprop power curve
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.
41
EXPLAIN the relationship between power required and airspeed in the regions of normal and reverse command
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.
42
DEFINE nosewheel liftoff/touchdown speed
**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.
43
STATE the pilot speed and attitude inputs necessary to control the airplane during a crosswind landing
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.
44
STATE the crosswind limits for the T-6B
Maximum crosswind component for takeoff or landing in the T-6B is 25 knots.
45
DEFINE hydroplaning
When the airplane's tires skim atop a thin layer of water on a runway.
46
STATE the factors that affect the speed at which an airplane will hydroplane
The speed at which an airplane will hydroplane depends only on the tire pressures.
47
DESCRIBE the effects of propeller slipstream swirl, P-factor, torque, and gyroscopic precession as they apply to the T-6B
* **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.
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
* 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
49
DESCRIBE the effect of lift on turn performance
An increase in lift will result in greater turn performance by allowing an increased angle of bank.
50
DESCRIBE the effect of weight on turn performance
Turn rate and radius are independent of weight.
51
DESCRIBE the effect of thrust on turn performance
An airplanes thrust may limit turn performance since you must have sufficient thrust to overcome the induced drag created at high load factors.
52
DESCRIBE the effect of drag on turn performance
An increase in drag will limit speed, thereby increasing turn rate and decreasing turn radius.
53
DEFINE turn radius and turn rate
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.
54
DESCRIBE the effects of changes in bank angle on turn performance
Increasing bank angle will increase the turn rate and decreas the turn radius (increased turn performance)
55
DESCRIBE the effects of changes in airspeed on turn performance
Increasing airspeed (same bank angle) would decrease the turn rate and increase turn radius (decreased turn performance)
56
DESCRIBE the effects of aileron and rudder forces during turns
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**.
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
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).
58
DESCRIBE the relationship between load factor and angle of bank for level, constant-airspeed-flight
Load factor increases gradually at low angles of bank, but exponentially at angles greater than 60°
59
DEFINE load, load factor, limit load factor, and ultimate load factor
**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.
60
DEFINE static strength, static failure, fatigue strength, fatigue failure, service life, creep, and overstress/over-G
**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.
61
DEFINE maneuvering speed, cornering velocity, redline airspeed, accelerated stall lines, and the safe flight envelope
**Maneuvering speed** (Va) 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** (VNE) 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 CLMAX 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.
62
DESCRIBE the boundaries of the safe flight envelope, including accelerated stall lines, limit load factor, ultimate load factor, maneuver point, and redline airspeed
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.
63
DEFINE asymmetric loading and state the associated limitations for the T-6B
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**.
64
DEFINE static stability and dynamic stability
**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.
65
DESCRIBE the characteristics exhibited by aircraft with positive, neutral, and negative static stabilities, when disturbed from equilibrium
**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
66
DESCRIBE the characteristics exhibited by aircraft with positive, neutral, and negative dynamic stabilities, when disturbed from equilibrium
**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.
67
DESCRIBE the characteristics of damped, undamped, and divergent oscillations, and the combination of static and dynamic stabilities that result in each
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.
68
EXPLAIN the relationship between stability and maneuverability
A stable airplane will tend to be less maneuverable, while an unstable airplane will be very maneuverable.
69
STATE the methods for increasing an airplane's maneuverability
Maneuverabillity may be increased by decreasing stability or by giving the airplane larger control surfaces.
70
STATE the effects of airplane components on an airplane's longitudinal static stability
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
71
EXPLAIN the criticality of weight and balance
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.
72
STATE the effects of airplane components on an airplane's directional static stability
**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
73
STATE the effects of airplane components on an airplane's lateral static stability
**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
74
STATE the static stability requirements for, and the effects of, directional divergence
**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.
## Footnote
*Most airplanes have very strong directional stability.*
75
STATE the static stability requirements for, and the effects of, spiral divergence
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.
## Footnote
*This is easily corrected by control input from the pilot.*
76
STATE the static stability requirements for, and the effects of, dutch roll
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".
## Footnote
*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.*
77
DEFINE proverse roll
The tendency for an airplane to roll in the same direction as it is yawing
78
DEFINE adverse yaw
The tendency of an airplane to yaw away from the direction of aileron roll input.
79
EXPLAIN how an airplane develops phugoid oscillations
**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.
80
EXPLAIN how an airplane develops pilot induced oscillations
**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.
81
DEFINE asymmetric thrust
The directional control problems experienced when one engine of a multi-engine airplane fails and creates a yawing moment toward the dead engine.
82
DEFINE a spin
An assymetric aggrevated stall that results in autorotation.
83
DEFINE autorotation
A combination of roll and yaw that propagates itself due to asymmetrically stalled wings.
84
DESCRIBE the aerodynamic forces affecting a spin
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)
85
STATE the characteristics of erect, inverted, and flat spins
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.
86
DESCRIBE the factors contributing to aircraft spin
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.
87
DISCUSS the effects of weight, pitch attitude, and gyroscopic effects on spin characteristics
**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.
88
STATE how empennage design features change spin characteristics
**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.
89
STATE the cockpit indications of an erect and inverted spin
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)
90
DESCRIBE the pilot actions necessary to recover from a spin
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
91
DESCRIBE a progressive spin
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.
92
DESCRIBE an aggravated spin
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).
93
DESCRIBE wake turbulence
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.
94
DESCRIBE the effects of changes in weight, configuration, and airspeed on wake turbulence intensity
**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.*
95
DESCRIBE the effects of wake turbulence on aircraft performance
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.
96
STATE the takeoff and landing interval requirements for the T-6B
**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
97
DESCRIBE procedure for wake turbulence avoidance during takeoff
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.
98
DESCRIBE procedure for wake turbulence avoidance during landing
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.
99
DEFINE wind shear
A sudden change in wind direction or speed over a short distance in the atmosphere.
100
STATE the conditions that will lead to an increasing performance wind shear
increase in headwind or decrease in tailwind.
101
STATE the conditions that will lead to a decreasing performance wind shear
A tailwind, or a decrease in headwind.
102
DESCRIBE the effects of wind shear on aircraft performance
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.
103
DESCRIBE procedures for flying in and around wind shear
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 (VROT) by the amount of predicted wind shear (up to 10 knots)
3. Rotate to normal climb attitude at increased VROT and maintain attitude.
4. If wind shear is encountered near VROT 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.
104
DESCRIBE wind shear avoidance techniques
* 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.
