Question

In a conventional configuration airplane, the rudder can be used:

• A. to overcome adverse yaw during a turning maneuver
• B. to overcome yawing moment due to failure of one engine in a multi engine airplane
• C. for landing the airplane in crosswind conditions
• D. for enhancing longitudinal stability

Hint:

Map each axis to its primary surface: roll \(\Rightarrow\) ailerons, pitch \(\Rightarrow\) elevator (longitudinal), yaw \(\Rightarrow\) rudder (directional). When in doubt about a control surface's effect on stability, match axis-to-axis and you'll avoid confusions like (D).

Answer 1

The Correct Option is A

Step 1: Recall the primary aerodynamic roles.
The rudder is the primary control surface for yaw about the vertical axis; it provides directional control and contributes to directional (weathercock) stability. The surfaces linked to longitudinal (pitch) stability are the horizontal tail and elevator, not the rudder.
Step 2: Evaluate each option.
(A) Adverse yaw in turns. During aileron-induced roll, the downgoing aileron increases drag on the rising wing, yawing the nose opposite to the turn (adverse yaw). Coordinated rudder input counters this yaw to keep the turn coordinated (ball centered). \(\Rightarrow\) True.
(B) Asymmetric thrust / engine failure. In multi-engine aircraft, failure of one engine creates a yawing moment toward the dead engine. Applying rudder toward the live engine (and sometimes banking a few degrees) provides the required yawing moment to maintain directional control. \(\Rightarrow\) True.
(C) Crosswind landing. Two common techniques are crab-and-decrab and sideslip. In both, rudder is used to align the longitudinal axis with the runway centerline just before or during touchdown, countering the crosswind-induced drift. \(\Rightarrow\) True.
(D) Longitudinal stability. Longitudinal stability concerns restoring moments in pitch, governed by the horizontal tail/elevator and static margin. The rudder affects directional (yaw) stability; it does not "enhance longitudinal stability." \(\Rightarrow\) False.
\[ \boxed{\text{Correct uses of the rudder: (A), (B), (C).}} \]