α The velocity field V about the airfoil is represented as a superposition of a freestream and a vortex sheet. I feel the following about this concept. 1. Very uncertain 2. Somewhat uncertain 3. Somewhat comfortable 4. Very comfortable V � (s) V V Vα The circulation of V1(x, y) about the circuit of perimeter stot is �1. A constant � αV is now added to make α αV. V2 = V1 + � α What is αV2’s circulation �2 about the same circuit? 1. �2 = �1 − |� α V| stot 2.* �2 = �1 3. �2 = �1 + |� αV| stot VdsAn airfoil in steady motion at speed V1 has circulation �1. The speed is suddenly increased to V2 = 2V1. What is the circulation �v of the shed vortex? 1. �v = −�1/2 2.* �v = −�1 3. �v = −2�1 V = 2VV � 1 1 12 v� = ? Initial steady motion After velocity increaseA vortex sheet is � placed on the x axis in a freestream V�. The average Vu + αx-velocity ( αV�) · ˆı / 2 on the sheet itself, will 1. Increase 2. Decrease 3.* Not changeWhich type of control surface deflec-tion will cause the largest change in the magnitude of the zero-lift angle? 1. A 2.* B 3. It will be the same for A and B 10A 0.3c B 0.3c 10� A wing has nearly-uniform circulation �(y) over the span. What is the associ-ated vortex sheet strength �(y)? 4.* � 1. 2. y y � � y 3. 4. yA wing has nearly-uniform circulation �(y) over the span. What is the associ-ated downwash w(y)? 4.* � � � � y y yy 1. 2. 3. 4.Two wings are operating at the same velocity and lift. Wing B has doubled chords compared to wing A. How do their Di’s compare? 1. (Di)A > (Di)B 2.* (Di)A = (Di)B 3. (Di)A < (Di)B A BTwo wings with the same area are op-erating at the same velocity and lift. Wing A has a 5% larger span. How do their CDi’s compare? 1.* (CDi)A � 0.90 (CDi)B 2. (CDi)A � 0.95 (CDi)B 3. (CDi)A � (CDi)B A BTo design a wing with an elliptic load distribution at a given V� and b, which variable is NOT in our power to manip-ulate? 1. �geom(y) geometric twist 2. �L=0(y) zero-lift angle 3.* �i(y) induced angle 4. c(y) chord 5. c�(y) lift coefficient 6. They can all be manipulated 7. Not sureIn our elliptic-loaded wing design ex-ample, we increase the constant chord by 10%. What will NOT change in our wing? 1. �geom(y) geometric twist 2.* �i(y) induced angle 3. c�(y) lift coefficient 4. Not sureA wing with a non-elliptic loading has e = 0.900 (� � 0.10). The deviation from elliptic loading is halved. new e ? 1. 0.900 2. 0.925 3. 0.950 4.* 0.975 5. Not sure � �1 sin � 2bV A e = 0.900 What is the � �1 sin � 2bV A e = ?For a particular aircraft, changing the aspect ratio by +10% changes C3/2/CD L by +8%, but also changes total weight by +6%. To reduce flight power, the aspect ratio should be 1. Increased 2.* Decreased 3. Not
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