Aero Ii Ch.9

Front 1

Define static stability and dynamic stability.

Back 1

Static Stability
o The initial tendency of an object to move toward or away from its original
equilibrium position.
Dynamic Stability
o Is the position with respect to time, or motion of an object after a
disturbance.

Front 2

Identify the stability conditions of various systems based on their tendencies and
motion.

Back 2

Static Stability
o Positive Static Stability

Front 3

Explain the relationship between stability and maneuverability.

Back 3

Maneuverability and stability are opposites.
• A stable airplane tends to stay in equilibrium and is difficult for the pilot to move
out of equilibrium.
• A maneuverable plane departs from equilibrium easily and is less likely to return
to equilibrium.

Front 4

State what may be done to increase an airplane’s maneuverability.

Back 4

Give an airplane weak stability allows airplane to move quickly from its trimmed
equilibrium attitude.
• Give an airplane larger control surfaces which would generate large moments by
producing greater aerodynamic forces.

Front 5

Define longitudinal stability and neutral point.

Back 5

Longitudinal Stability
o Stability of the longitudinal axis around the lateral axis (pitch)
• Neutral Point
o Is the location of the center of gravity, along the longitudinal axis that
would provide neutral longitudinal static stability. Can be thought of as
the aerodynamic center for the entire airplane.

Front 6

Explain the contribution of straight wings, wing sweep, fuselage, horizontal
stabilizer, and neutral point location to longitudinal static stability.

Back 6

Straight Wings – The wings of most conventional airplanes are negative
contributors to longitudinal static stability.
• Wing Sweep – Sweeping the wings back is a positive contributor to longitudinal
static stability.
• Fuselage – is a negative contributor to longitudinal stability.
• Horizontal Stabilizer – will have the greatest positive effect on longitudinal
static stability.
• If the neutral point location is behind the airplane’s center of gravity the
component will be a positive contributor to longitudinal static stability.
If the neutral point location is in front of the airplane’s center of gravity the
component will be a negative contributor to longitudinal static stability.

Front 7

Define directional stability, sideslip angle, and sideslip relative wind.

Back 7

Directional Stability
o Stability of the longitudinal axis around the vertical axis (yaw).
• Sideslip angle (

Front 8

Explain the contribution of straight wings, swept wings, fuselage, and vertical
stabilizer to directional static stability.

Back 8

Straight wings have a small positive effect on directional static stability.
• The swept design of a wing will further increase directional stability.
• The Fuselage is a negative contributor to the airplane’s directional static stability.
• The vertical stabilizer is the greatest positive contributor to the directional static
stability of a conventional designed airplane.

Front 9

Define lateral stability.

Back 9

Stability of the lateral axis around the longitudinal axis (roll).

Front 10

Explain the contribution of dihedral and anhedral wings, wing placement on the vertical axis, swept wings, and the vertical stabilizer to lateral static stability.

Back 10

Dihedral wings are the greatest positive contributors to lateral static stability.
• Anhedral wings are the greatest negative contributors to lateral static stability.
• High mounted wing is a positive contributor and a low mounted wing is a
negative contributor to lateral static stability.
• Swept wings are laterally stabilizing.
• Vertical Stabilizer – When in a lateral sideslip, the vertical stabilizer senses an
AOA, so it produces lift. Since the tail is above the airplane’s center of gravity ,
this lift produces a moment that tends to right the airplane.

Front 11

Describe directional divergence, spiral divergence, Dutch roll, and phugoid
motion.

Back 11

Directional Divergence
o Condition of flight in which the reaction to a small initial sideslip results
in an increase in sideslip angle.
o Directional Divergence is caused by negative directional static stability.
• Spiral Divergence
o Occurs when an airplane has strong directional stability and weak lateral
stability.
• Dutch Roll
o Is the result of strong lateral stability and weak directional stability.
• Phugoid Motion
o Are long period oscillations (20 to 100 seconds) of altitude and airspeed
while maintaining a nearly constant AOA.

Front 12

State the stability conditions that produce directional divergence, spiral
divergence, Dutch roll, and phugoid motion.

Back 12

Directional Divergence
o Directional Divergence is caused by negative directional static stability.
• Spiral Divergence
o Occurs when an airplane has strong directional stability and weak lateral
stability
• Dutch Roll
o Is the result of strong lateral stability and weak directional stability.
• Phugoid Motion
o Being struck by an upward gust, an airplane would gain altitude and lose
airspeed. Oscillations of pitch attitude do occur, but are often minor.

Front 13

Describe proverse roll, adverse yaw, and pilot induced oscillations.

Back 13

Proverse Roll
o Tendency of an airplane to roll in the same direction as it is yawing.
• Adverse Yaw
o Tendency of an airplane to yaw away from the direction of aileron input.
• Pilot Induced Oscillations (PIO)
o Are short period oscillations of pitch attitude and AOA.

Front 14

Explain how pilot induced oscillations relate to the T-34C.

Back 14

The T-34C and T-37B are not subject to pilot induced oscillations since it does
not have strong longitudinal static stability

Front 15

Describe the effects of asymmetric thrust, propeller slipstream swirl, P-factor,
torque, and gyroscopic precession as they apply to the T-34C.

Back 15

Asymmetric Thrust (T-37)
o none
• Propeller Slipstream Swirl (T-34)
o The propeller imparts a corkscrewing motion to the air that flows around
the fuselage until it reaches the vertical stabilizer where it increases the
AOA on the vertical stabilizer.
• P-Factor (T-34)
o Yawing moment caused by one prop blade creating more thrust than the
other.
o If the relative wind is above the thrust line, the up going propeller blade on
the left side creates more thrust since it has a larger AOA with the relative
wind. This yaws the nose to the right.
o If the relative wind is below the thrust line, such as in flight near the stall
speed, the down going blade on the right side will create more thrust and
will yaw the nose to the left.
• Torque (T-34)
o is a reactive force based on Newton’s 3rd law of motion A force must be applied to the propeller to cause it to rotate clockwise. A
force of equal magnitude, but opposite direction is produced which tends
to roll the airplane’s fuselage counter clockwise.
• Gyroscopic Precession (T-34 & T-37)
o When a force is applied to the rim of a spinning object (such as a
propeller), parallel to the axis of rotation, a resultant force is created in the
direction of the applied force, but occurs 90° ahead in the direction of
rotation.

Front 16

Describe what must be done to compensate for asymmetric thrust, propeller
slipstream swirl, P-factor, torque, and gyroscopic precession as they apply to the T-34C

Back 16

Asymmetric Thrust (T-37)
none
• Propeller Slipstream Swirl (T-34)
o Right rudder and lateral control stick inputs are required to compensate for
the slipstream swirl.
• P-Factor (T-34)
o Depending on the relative wind, rudder control inputs will compensate for
P-Factor.
• Torque (T-34)
o T-34 uses elevator trim tabs t compensate for torque.
• Gyroscopic Precession (T-34 & T-37)
o Proper rudder control inputs will compensate for Gyroscopic Precession.