Discussion
Statement I: Directional stability deteriorates at high angle of attack.
Statement II: The fin can be blanketed by the wake of the wing and fuselage.
In the light of the above statements, choose the correct answer.
Answer: B
Correct answer: Both Statement I and Statement II are correct
Both are true and the second is the mechanism. At high angle of attack the wing and fuselage shed a broad wake of low-energy air, and a conventional centreline fin sits within it.
Reduced local dynamic pressure means less side force for the same sideslip, so the fin's contribution to \( C_{n\beta} \) falls and directional stability with it. The deterioration matters because it arrives near the stall and in spin entry, exactly where directional control is most needed - hence ventral fins below the wake, twin fins outboard of it, and strakes to re-energise the flow.
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