-
DESCRIBE the characteristics of damped, undamped, and divergent oscillations, and the combination of static and dynamic stabilities that result in each
-
EXPLAIN the relationship between stability and maneuverability
- More stable = less maneuverable
- A stable airplane tends to stay in equilibrium and is difficult for the pilot to move out of equilibrium.
- The more maneuverable an airplane is, the easier it departs from equilibrium, and the less likely it is to return to equilibrium.
-
STATE the methods for increasing an airplane's maneuverability
- Give it weak stability
- Give it larger control surfaces.
-
STATE the effects of airplane components on an airplane's longitudinal static stability
- Longitudinal stability is the stability of the longitudinal axis around the lateral axis (pitch stability)
- Wings
- If the Aerodynamic Center (AC) is behind the COG, it will have a positive impact on longitudinal static stability because of its initial tendency to return to equilibrium.
- If the AC is ahead of the COG, it will have a negative impact on longitudinal static stability.
- Fuselage
- AC is usually located ahead of the CG.
- It is a negative contributor to longitudinal static stability.
- The Horizontal Stabilizer
- Designed for lateral axis, its contribution to longitudinal static stability is determined by the moment it produces around the CG.
- Since it's AC is well behind the plane's CG, the horizontal stabilizer has the greatest positive effect on longitudinal static stability.
- The pitching moment can be increased by increasing the distance between the airplane's CG and the stabilizer's AC, or by enlarging the horizontal stabilizer.
- Shorter planes need a larger stabilizer and vice versa.
- The Neutral Point
- the location of the center of gravity along the longitudinal axis that would provide neutral longitudinal static stability.
- It can be thought of as the aerodynamic center for the entire plane.
- The NP is fixed on conventional planes, but CG can change.
- As the CG is moved aft, the airplane's static stability decreases.
- The NP defines the farthest aft CG position without negative stability.
- Once the NP is aft of the NP the airplane becomes unstable.
-
EXPLAIN the criticality of weight and balance
If the CG is aft of the NP, the plane becomes unstable and difficult to control in flight.
-
STATE the effects of airplane components on an airplane's directional static stability
- Directional Static Stability
- the stability of the longitudinal axis around the vertical axis. (yawing)
- When an airplane yaws, its momentum keeps it moving along its original flight path for a short time. (sideslip)
- Wings
- -Straight Wings
- the advancing wing on a straight winged plane has a momentary increase in airflow velocity as it moves forward.
- Parasite drag increases and pulls it back to its equilibrium position.
- The retreating wing has less velocity and less parasite drag, which helps bring the nose to the relative wind.
- Straight wings have a small positive effect on directional static stability.
- -Swept Wings
- Swept wings will further increase directional stability.
- The advancing wing not only experiences an increase in parasite drag, but also an increase in induced drag due to the increase chordwise flow.
- The retreating wing experiences more spanwise flow.
- The result is an airplane that comes back into the relative wind.
- Fuselage
- AE is forward of the airplane's CG.
- When the airplane enters a sideslip, an angle of attack is created on the fuselage.
- The lift created at eh fuselage AC pulls the nose away from the relative wind, increasing sideslip angle.
- Fuselage is a negative contributor to directional stability.
- Vertical Stabilizer
- Greatest Positive contributor to directional stability.
- Sideslip creates an increase in AOA, creating horizontal lifting force on the stabilizer that is multiplied by the moment arm distance to the CG.
- The moment will swing the nose of the plane back into the relative wind (equilibrium).
- Inverse relationship between tail size and moment arm length. The smaller the distance, the larger the stabilizer must be.
- 2 small can accomplish the same effect as one large.
-
STATE the effects of airplane components on an airplane's lateral static stability
- Lateral Static Stability
- The stability of the lateral axis around the longitudinal axis. (roll)
- Wings
- -Dihedral effect
- dihedral wings cause an increase in AOA and lift on the down-going wing.
- The up-going wing has a reduced AOA and a decrease in lift.
- The difference creates a rolling moment that rights the plane and stops the sideslip.
- Diehedral wings are the greatest positive contributors.
- Straight are neutral, anhedral are the greatest negative contributors.
- -Wing Placement
- A high mounted wing is a positive contributor
- A low mounted wing is a negative contributor to lateral static stability.
- -Wing Sweep
- Swept wings are laterally stabilizing.
- Vertical stabilizer
- Tends to right the plane since the tail is above the plane's CG when it senses an AOA and produces lift
-
STATE the static stability requirements for, and the effects of, directional divergence
- Directional divergence is a condition of flight in which the reaction to a small initial sideslip results in an increase in sideslip angle.
- Caused by negative directional static stability.
- If the vertical stabilizer becomes ineffective for some reason, directional divergence could cause out of control flight.
- Most planes have strong directional stability to prevent this from occurring.
-
STATE the static stability requirements for, and the effects of, spiral divergence
- Occurs when a plane has strong directional stability and weak lateral stability.
- For example, a plane is disturbed so that its wing dips and starts to roll to the left.
- Since it has weak lateral stability it cannot correct itself and the flight path arcs to the left.
- The plane senses a new relative wind from the left and aligns itself with the new wind by yawing into it (strong directional stability).
- The right wing is now advancing and the increased airflow causes the plane to roll even more to the left.
- The plane will continue to chase the relative wind and will develop a tight descending spiral.
- It is corrected by control input from the pilot
-
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 plane responds to a disturbance with both roll and yaw motions that affect each other.
- For example, a gust causes the plane to roll left, producing a left sideslip.
- The strong lateral stability increases lift on the left wing and corrects it back to wings level.
- At the same time, the nose of the airplane yaws left into the sideslip relative wind. This leaves the airplane wings level, with the nose cocked to the left.
- Weak directional stability now swings the nose to the right to correct it back to the relative wind.
- The left wing advances faster, causing the plane to roll right, and the scenario repeats itself.
-
EXPLAIN how an airplane develops pilot induced oscillations
- It occurs when a pilot is trying to control airplane oscillations that happen over approximately the same time span as it takes to react.
- A pilot tries to push the nose-down to correct the plane. The input may coincide with the stability correction, causing the nose to over correct and end up low.
-
DEFINE asymmetric thrust
- Thurst unequal on different part of the plane.
- For example, an engine fails and the thrust is unequal.
- it will create a yawing moment toward the dead engine.
-
EXPLAIN how an airplane develops phugoid oscillations
- Phugoid oscillations are long period oscillations (20 to 100 seconds) of altitude and airspeed while maintaining a nearly constant AOA.
- Upon being struck by an upward gust, the airplane would gain altitude and lose airspeed.
- When enough airspeed is lost, the airplane will nose-over slight, commencing a gradual descent, gaining airspeed and losing altitude.
- When enough airspeed is regained, the plane will nose-up slightly and restart the process.
-
DEFINE proverse roll
- the tendency of an airplane to roll in the same direction as it is yawing.
- yawing left will cause the right wing to accelerate faster, causing it to increase lift and roll left.
-
DEFINE adverse yaw
- The tendency of an airplane to yaw away from the direction of aileron roll input.
- When the airplane rolls, it has more lift on the up-going wing than the down-going wing.
- This causes an increase in induced drag on the up-going wing that will retard that wing's forward motion and cause the nose to yaw in the opposite direction of the roll.
|
|