Aerodynamics 2 Flashcards
DEFINE Mach number
The ratio of an airplanes speed through a given air mass to sound’s speed through the same air mass.
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”.
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.
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.
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.
DEFINE wind shear
A sudden change in wind direction or speed over a short distance in the atmosphere.
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.
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.
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.
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.
STATE the conditions that will lead to a decreasing performance wind shear
A tailwind, or a decrease in headwind.
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.
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.
DEFINE critical Mach
The lowest mach number than an airplane can travel at and create sonic airflow somewhere on the aircraft.
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.
STATE the various forces acting on an airplane during the takeoff and landing transition
- 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
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.
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.
DESCRIBE the effects on takeoff and landing performance, given variations in weight, altitude, temperature, humidity, wind, and braking
- 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.
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.
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.
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
DEFINE autorotation
A combination of roll and yaw that propagates itself due to asymmetrically stalled wings.
DESCRIBE the effect of weight on turn performance
Turn rate and radius are independent of weight.
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)
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.
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.
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.
DEFINE takeoff and landing airspeed in terms of stall speed
Takeoff Airspeed: 20% above the power off stall speed.
Landing Airspeed: 30% above stall speed
STATE the methods for increasing an airplane’s maneuverability
Maneuverabillity may be increased by decreasing stability or by giving the airplane larger control surfaces.
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.
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.
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.
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.
DEFINE adverse yaw
The tendency of an airplane to yaw away from the direction of aileron roll input.
