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54 Cards in this Set
- Front
- Back
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Define stability
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Tendency of an object to return to its state of equilibrium once disturbed from it
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What are the two kinds of stability?
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Static and Dynamic
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What is static stability?
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Initial tendency of an object to move toward or away from its original equilibrium position
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What is dynamic stability?
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Motion of an object after a disturbance / position w/ respect to time
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What is positive static stability?
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Initial tendency toward original equilibrium
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What is negative static stability?
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Initial tendency to continue moving away from original equilibrium
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What is neutral static stability?
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Initial tendency to accept displacement position as a new equilibrium
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What is positive dynamic stability?
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Damped oscillation
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What is neutral dynamic stability?
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Undamped oscillation
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What is negative dynamic stability?
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Divergent oscillation
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What is the relationship between positive static stability and positive dynamic stability?
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If positive static, any dynamic; if not positive static, not positive dynamic
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Define longitudinal stability
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Stability of the longitudinal axis around the lateral axis (pitch)
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Define Lateral stability
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Stability of the lateral axis around the longitudinal axis (roll)
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Define Directional stability
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Stability of the longitudinal axis around the vertical axis (yaw)
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What type of stability exists with CG forward of the AC?
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positive longitudinal static stability
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What type of stability exists with the AC forward of the CG?
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negative longitudinal static stability
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What type of contributor to stability are wings of most conventional airplanes and why?
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Negative contributor to longitudinal static stability b/c airplane's CG is behind AC of wing
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What effect does sweeping an airplane's wings back have on stability?
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Increase longitudinal and directional static stability
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What type of contributor to stability is the fuselage?
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Negative contributor to longitudinal and directional static stability
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What type of contributor to stability is the horizontal stabilizer?
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greatest positive effect on longitudinal static stability
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What is the neutral pont?
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AC for entire airplane
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What effect does moving the CG have on stability?
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Moving aft = less stability, behind NP = negative stability
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What effect do wings have on directional static stability?
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Straight wings: small positive effect; Swept wings: greater positive effect
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What effect does the vertical stabilizer have on static stability?
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Greatest positive contributor to directional, some positive effect on lateral
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What is beta (B)
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sideslip angle
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What effect does a dihedral wing have on lateral stability?
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Greatest positive contributor
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What effect does a anhedral wing have on lateral stability?
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Greatest negative contributor
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What effect does a high wing placement have on lateral stability?
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positive contributor
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What effect does a low wing placement have on lateral stability?
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negative contributor
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What effect do swept wings have on lateral stability?
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positive contributor
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What is directional divergence?
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Condition of flight in which the reaction to a small initial sideslip results in an increase in sideslip angle.
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What causes directional divergence?
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negative directional stability - i.e. loss of vertical stabilizer
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What causes spiral divergence?
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Strong directional stability and weak lateral stability
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What causes dutch roll?
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Strong lateral stability and weak directional stability
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What is a dutch roll?
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Tail wagging - sideslip --> yaw --> roll --> repeat
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What are phugoid oscillations?
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Long period oscillations (20-100 seconds) of altitude and airspeed while maintaining nearly constant AOA
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What is proverse roll?
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Tendency of an airplane to roll in the same direction as it is yawing
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Which type of wing has more pronounced proverse roll?
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Swept wing
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What is adverse yaw?
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Tendency to yaw away from the direction of aileron roll input
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What 3 things can overcome adverse yaw?
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Use spoilers instead of ailerons, use rudder input to offset, use differential ailerons
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What are pilot induced oscillations (PIO)?
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Short period oscillations of pitch attitude and angle of attack (porpoising)
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What causes pilot induced oscillations (PIO)?
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Attempting to control oscillations that happen the same time span it takes to react
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What is the solution to pilot induced oscillations (PIO)?
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Freeze stick slightly aft of neutral (not a concern in the T-34C)
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What causes asymmetric thrust and what may result?
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One engine failure; causes yawing force, may cause proverse roll
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What are the 4 conditions that produce a left yaw / turning tendancy?
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Slipstream swirl, P-factor, Torque, Gyroscopic precession
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What is slipstream swirl?
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Air from the propeller increasing the AOA on the vertical stabilizer
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When is the slipstream swirl most pronounced?
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High power setting, low airspeed, high angle of attack
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What is P-factor?
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Propeller factor: yawing moment cause by one prop blade creating more thrust than the other (difference btwn up-going and down-going blades)
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When and how does the p-factor effect flight?
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Low airspeeds: high AOA, will yaw left; High airspeeds (>150 for T-34C): low AOA, will yaw right
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Two conditions required for p-factor?
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Engine at high power condition, Thrust axis displaced from relative wind
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Which direction will Torque rotate an aircraft?
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Counter-clockwise (opposite of propellor rotation)
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What compensates for torque in the T-34C?
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Elevator trim (+/- 4.5 degrees on each side)
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What is gyroscopic precession?
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A force applied to the rim of a spinning object will create a resultant force in the direction of the applied force, 90 degrees ahead in the direction of rotation
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When and what effect does gyroscopic precession have on an airplane?
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Pitching nose down will yaw aircraft to left (plays roll in spin entry); pulling nose up will yaw right
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