Aerodynamics 2 spins and wv shear

Question 1

DEFINE a spin

Answer 1

An assymetric aggrevated stall that results in autorotation.

Question 2

DEFINE autorotation

Answer 2

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

Question 3

DESCRIBE the aerodynamic forces affecting a spin

Answer 3

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 4

STATE the characteristics of erect, inverted, and flat spins

Answer 4

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 5

DESCRIBE the factors contributing to aircraft spin

Answer 5

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 6

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

Answer 6

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 7

STATE how empennage design features change spin characteristics

Answer 7

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 8

STATE the cockpit indications of an erect and inverted spin

Answer 8

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 9

DESCRIBE the pilot actions necessary to recover from a spin

Answer 9

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 10

DESCRIBE a progressive spin

Answer 10

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 11

DESCRIBE an aggravated spin

Answer 11

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 12

DESCRIBE wake turbulence

Answer 12

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 13

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

Answer 13

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 14

DESCRIBE the effects of wake turbulence on aircraft performance

Answer 14

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 15

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

Answer 15

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 16

DESCRIBE procedure for wake turbulence avoidance during takeoff

Answer 16

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 17

DESCRIBE procedure for wake turbulence avoidance during landing

Answer 17

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 18

DEFINE wind shear

Answer 18

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

Question 19

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

Answer 19

increase in headwind or decrease in tailwind.

Question 20

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

Answer 20

A tailwind, or a decrease in headwind.

Question 21

DESCRIBE the effects of wind shear on aircraft performance

Answer 21

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 22

DESCRIBE procedures for flying in and around wind shear

Answer 22

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 23

DESCRIBE wind shear avoidance techniques

Answer 23

• 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.