A NACA 22104 airfoil is operating at AOA = 3°. The lift-coefficient at this AOA is 0.15. Determine the value of angle of attack at designed lift co-efficient.(a) 4.36°(b) 4.36rad(c) 0.05 rad(d) 0.05°I have been asked this question in an interview for job.Enquiry is from Airfoil Selection-3 in chapter Airfoil and Geometry Selection of Aircraft Design

A NACA 22104 airfoil is operating at AOA = 3°. The lift-coefficient a

1.	A NACA 22104 airfoil is operating at AOA = 3°. The lift-coefficient at this AOA is 0.15. Determine the value of angle of attack at designed lift co-efficient.(a) 4.36°(b) 4.36rad(c) 0.05 rad(d) 0.05°I have been asked this question in an interview for job.Enquiry is from Airfoil Selection-3 in chapter Airfoil and Geometry Selection of Aircraft Design
Answer» The correct choice is (a) 4.36° For explanation: Given NACA 22104 airfoil. AOA = 3°, Cl = 0.15 at 3° Based on NACA -5 digit SERIES DESIGN Cl = FIRST digit0.15 = 20.15 = 0.3 Now, for thin airfoil LIFT curve slope = 0.11 per degree 0.11 = (design Cl – Cl at 3°) / (AOA –3°) 0.11 = (0.3-0.15) / (AOA -3°) 0.11*(AOA -3°) = 0.15 Hence, at designed Cl, AOA = (0.15/0.11) + 3° = 4.36°.

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