How does a positive dihedral angle affect lateral stability and roll coupling?

How does a positive dihedral angle affect lateral stability and roll coupling?

• A. Positive dihedral increases lateral stability in sideslip by generating restoring roll moments due to the vertical lift component; reduces adverse roll coupling.
• B. Positive dihedral decreases lateral stability and increases adverse roll coupling.
• C. Positive dihedral only affects directional stability, not lateral.
• D. Positive dihedral has no effect on stability.

Answer: (A)

Positive dihedral produces a restoring rolling moment in a sideslip, which boosts lateral stability. When the aircraft slips to one side, the wing farther from the direction of the slip (the downwind wing) sees a higher effective angle of attack and generates more lift. Because the wings are at different heights, this differential lift creates a rolling moment about the center of gravity that tends to raise the downwind wing and lower the upwind wing, pushing the aircraft back toward wings-level. This restoring moment is the dihedral effect at work, making the sideslip decay rather than grow. At the same time, that same mechanism counteracts adverse roll coupling, which is the tendency for yaw to induce an undesired roll. By producing a roll toward level when sideslipping, positive dihedral reduces this coupling, helping the airplane stabilize more quickly in directional disturbances. So, positive dihedral increases lateral stability in sideslip and reduces adverse roll coupling.

Positive dihedral produces a restoring rolling moment in a sideslip, which boosts lateral stability. When the aircraft slips to one side, the wing farther from the direction of the slip (the downwind wing) sees a higher effective angle of attack and generates more lift. Because the wings are at different heights, this differential lift creates a rolling moment about the center of gravity that tends to raise the downwind wing and lower the upwind wing, pushing the aircraft back toward wings-level. This restoring moment is the dihedral effect at work, making the sideslip decay rather than grow.

At the same time, that same mechanism counteracts adverse roll coupling, which is the tendency for yaw to induce an undesired roll. By producing a roll toward level when sideslipping, positive dihedral reduces this coupling, helping the airplane stabilize more quickly in directional disturbances.

So, positive dihedral increases lateral stability in sideslip and reduces adverse roll coupling.