Lateral Stability

Question 1

Lateral stability

Answer 1

Lateral stability is stability about the airplane’s longitudinal axis, which extends from nose to tail.
This helps to stabilize the lateral or rolling effect when one wing gets lower than the wing on the opposite side of the airplane.

Question 2

Side slip

Answer 2

Results From Airplane Banking But Not Turning.

Question 3

Dihedral

Answer 3

Spanwise Inclination of a Wing.
The most common procedure for producing lateral stability is to build the wings with a dihedral angle varying from one to three degrees.
Dihedral is the measured angle made by each wing above a line parallel to the lateral axis.
Excessive dihedral has an adverse effect on lateral maneuvering qualities.

Question 4

Sweep back

Answer 4

The swept wing is responsive only to the wind component (perpendicular to the wing’s leading edge).
If the wing is operating at a positive lift coefficient, the wing into the wind has an increase in lift, and the wing out of the wind has a decrease in lift.
Lowered Wing
●More Perpendicular to Relative Wind resulting in more effective wing area

Question 5

Keel effect

Answer 5

During flight, the side area of the airplane’s fuselage and vertical fin react to the airflow in much the same manner as the keel of a ship.
That is, it exerts a steadying influence on the airplane laterally about the longitudinal axis.
Such laterally stable airplanes are constructed so that the greater portion of the keel area is above and behind the center of gravity.
When the airplane slips to one side, the combination of the airplane’s weight and the pressure of the airflow against the upper portion of the keel area (both acting about the CG) tends to roll the airplane back to wings-level flight.

Question 6

Vertical wing placement

Answer 6

Mid Wing
●Neutral Stability
Low Wing
●Negative Stability
High Wing
●Positive Stability

Question 7

Vertical stability

Answer 7

•Stability about the airplane’s vertical axis (the sideways moment) is called yawing or directional stability

•Yawing or directional stability is the more easily achieved stability in airplane design

•The area of the vertical fin and the sides of the fuselage aft of the center of gravity are the prime contributors which make the airplane act like a weathervane, pointing its nose into the relative wind

Question 8

Dutch roll

Answer 8

Dutch Roll is a coupled lateral/ directional oscillation that is usually dynamically stable but is objectionable in an airplane because of the oscillatory nature.
The response of the airplane to a disturbance from equilibrium (due to wind, turbulence, etc) is a combined rolling/yawing oscillation in which the rolling motion is phased to precede the yawing motion.
Positive Dynamic Stability
●Lateral
Strong Dihedral Effect
●Directional
Weaker Weathervane Tendency
Pilot Fatigue.
Passenger Discomfort.

Question 9

Adverse yaw

Answer 9

●Yaw That Results From Deflection of Ailerons
●Opposite Direction of Turn

Question 10

Spiral instability

Answer 10

Spiral instability exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.
Due to this yaw, the wing on the outside of the turning moment travels forward faster than the inside wing and as a consequence, its lift becomes greater.
This produces an overbanking tendency which, if not corrected by the pilot, will result in the bank angle becoming steeper and steeper.