Which of the following actions is not a way to make an aircraft (more) longitudinally statically stable?

Question

Increasing the horizontal tail surface area

Increasing the wing lift coefficient gradient

Placing the horizontal tail out of the downwash of the wing

Decreasing the wing surface area

Answer 1

To determine which action is not a way to make an aircraft more longitudinally statically stable, let's analyze each option:

1. Increasing the horizontal tail surface area: This action would increase the restoring moment produced by the tail when the aircraft experiences pitch disturbances, thereby improving longitudinal static stability.

2. Increasing the wing lift coefficient gradient: This would generally reduce static stability because a higher lift coefficient gradient means that the wing will produce more lift for a small increase in angle of attack, potentially leading to a more pronounced pitch-up tendency. Thus, this action does not contribute to improved stability.

3. Placing the horizontal tail out of the downwash of the wing: By positioning the horizontal tail outside the downwash zone created by the wings, it can operate more effectively, thus contributing positively to longitudinal stability.

4. Decreasing the wing surface area: This action generally leads to reduced lift and could also increase the aircraft's susceptibility to pitch changes, thereby potentially decreasing stability.

From the analysis above, the action that is not a way to make an aircraft more longitudinally statically stable is:

Increasing the wing lift coefficient gradient.