Question that you may be asked?
Airplane rolls in direction of rudder input what is it.. Proverse roll, adverse yaw, spiral divergence, dutch roll. Or a variation of this type of question.
PROVERSE ROLL
Proverse roll is the tendency of an airplane to roll in the same direction as it is yawing. When an airplane yaws, the yawing motion causes one wing to advance and the other wing to retreat. This increases the airflow on the advancing wing and decreases airflow over the retreating wing. A difference in lift is created direction as it yawed. Proverse roll is even more pronounced on swept wing airplanes since the advancing wing will have more chordwise flow and will produce more lift.
ADVERSE YAW
Adverse yaw is the tendency of an airplane to yaw away from the direction of aileron roll input. When an airplane rolls, it has more lift on the up-going wing than on 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. The aircraft produces adverse yaw each time the ailerons are deflected (rolling into and out of a turn).
We can do three things to overcome this problem. The first method is to use spoilers instead of ailerons. The spoiler is deflected into the airstream from the upper surface of the wing. This spoils the airflow and reduces lift, causing the airplane to roll. The spoiler increases the para- site drag on the down-going wing, offsetting the induced drag on the up-going wing and helps reduce or eliminate adverse yaw. The second method is to use a rudder input to offset ad- verse yaw. The third is actually a design method of building the aircraft with differential ailerons.
PHUGOID OSCILLATIONS
Phugoid oscillations are long period oscillations (20 to 100 seconds) of altitude and airspeed while maintaining a nearly constant angle of attack. Oscillations of pitch attitude do occur, but are often minor. Upon being struck by an upward gust, an airplane would gain altitude and lose airspeed. A large but gradual change in altitude and airspeed occurs. When enough airspeed is lost, the airplane will nose-over slightly, commencing a gradual descent, gaining airspeed and losing altitude. When enough airspeed is regained, the nose will pitch up, start- ing the process over. The period of this oscillation is long enough that the pilot can easily correct it. Often, due to the almost negligible changes in pitch, the pilot may make the necessary corrections while being completely unaware of the oscillation.
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 each other. For example, a gust causes the airplane 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 out to the left.
The weak directional stability now swings the nose to the right to correct the nose back into the relative wind. This causes the left wing to advance faster than the right wing, a situation which produces more lift on the left wing and rolls the airplane to the right, creating a right sideslip. The strong lateral stability corrects the wings back to level, while the nose yaws right into the sideslip relative wind. This leaves the airplane wings level, with the nose cocked out to the right. As the nose yaws left into the relative wind, the wings will roll left which starts the entire process again.
The airplane appears to be “tail wagging” . This condition can be tolerated and may eventually dampen out. However, it is not acceptable in a fighter or attack airplane when the pilot is trying to aim at a target.
SPIRAL DIVERGENCE
Spiral divergence occurs when an airplane has strong directional stability and weak lateral stability . For example, an airplane is disturbed so that its wing dips and starts to roll to the left. Because the airplane has weak lateral stability it cannot correct itself and the flight path arcs to the left. The airplane 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 airplane to roll even more to the left. The airplane will continue to chase the relative wind and will develop a tight descending spiral. This is easily corrected by control input from the pilot.
