QB_AE_FLIGHT_037
Section Question Bank
MSQ · 2 Marks
Flight Mechanics • Flight Dynamics - Adverse Yaw and Frise Ailerons
Which of the following statements regarding lateral-directional control coupling and adverse yaw are **CORRECT**?
(A) Adverse yaw occurs when deflecting ailerons to initiate a roll creates higher induced drag on the upward-moving wing, causing the airplane nose to yaw opposite to the intended turn
(B) Frise ailerons counter adverse yaw by projecting the lower leading edge of the upward-deflected aileron into the bottom airflow, generating compensating profile drag on the down-going wing
(C) Differential aileron gearing applies greater up-deflection to the down-going wing than down-deflection to the up-going wing to balance yawing moments
(D) Adverse yaw naturally rolls the aircraft into a steeper turn without pilot intervention
Answer Key:
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Step-by-Step Verified Solution
### 1. Strategy & Theoretical Principles 1. **Mechanism of Adverse Yaw:** - To roll right, the left aileron deflects downward (increasing lift and induced drag $C_{Di} = C_L^2 / \pi e AR$) and the right aileron deflects upward (reducing lift and induced drag). - The left wing now experiences greater drag than the right wing, producing a yawing moment to the *left* (opposite to the desired right turn). 2. **Remedial Design Features:** - **Frise Ailerons:** The aileron hinge is offset so that when deflected upward, its sharp lower lip protrudes below the wing's lower surface, creating parasitic form drag to counter the induced drag on the opposite wing. - **Differential Ailerons:** The mechanical linkage deflects the upward aileron through a larger angular displacement than the downward aileron, balancing the profile drag against induced drag. 3. **Statement D:** Adverse yaw acts *against* the turn, causing uncoordinated sideslip that requires rudder coordination, not rolling the aircraft into a steeper turn. ### 2. Statement Evaluation - **Statements A, B, C:** **CORRECT.** - **Statement D:** **INCORRECT.** ### 3. Exam Trap & Standard Reference - **Trap Alert:** Downward deflected aileron increases lift and induced drag; upward deflected aileron reduces both. - **Standard Reference:** Nelson, R.C., *Flight Stability and Automatic Control*, Chapter 3.