Question

A conventional fixed-wing aircraft, with a horizontal tail and vertical fin, in steady and level flight is subjected to small perturbations. Which of the following statement(s) is/are true?

• A. Vertical fin has a stabilizing effect on the lateral stability of the aircraft.
• B. Vertical fin has a destabilizing effect on the directional stability of the aircraft.
• C. Presence of wing anhedral increases the lateral stability of the aircraft.
• D. Horizontal tail has a stabilizing effect on the longitudinal static stability of the aircraft.

Answer 1

The Correct Option is A, D

The question is about understanding how different components of a conventional fixed-wing aircraft affect its stability during flight. Let's analyze each of the given options:

1. Vertical fin has a stabilizing effect on the lateral stability of the aircraft:
   The vertical fin, also known as the vertical stabilizer, primarily contributes to the directional stability of the aircraft by preventing yawing motions. However, it also indirectly assists in lateral stability by resisting side slip through yawing resistance. Therefore, this statement is correct.
2. Vertical fin has a destabilizing effect on the directional stability of the aircraft:
   This statement is incorrect. The vertical fin is specifically designed to enhance directional stability by preventing unwanted yaw motions and helping the aircraft maintain its intended flight path.
3. Presence of wing anhedral increases the lateral stability of the aircraft:
   Anhedral wings, which angle downward, actually reduce lateral stability. They are typically used to decrease excessive lateral stability for increased maneuverability in certain aircraft types. Hence, this statement is incorrect.
4. Horizontal tail has a stabilizing effect on the longitudinal static stability of the aircraft:
   The horizontal tail, or horizontal stabilizer, provides stability in pitch (longitudinal stability). It counteracts moments that produce pitching motion, thus maintaining the aircraft in stable flight along the longitudinal axis. Therefore, this statement is correct.

Based on the above explanations, the correct statements are:

• Vertical fin has a stabilizing effect on the lateral stability of the aircraft.
• Horizontal tail has a stabilizing effect on the longitudinal static stability of the aircraft.

Thus, the selected options accurately describe the stabilizing effects of the vertical fin and horizontal tail on the different forms of aircraft stability.