Consider an infinite wing with a NACA 1412 airfoil section and a chord length of 3 ft. The wing is at an angle of attack of 5° in an airflow velocity of 100 ft/s at standard sea-level conditions. Calculate the lift, drag, and moment about the quarter-chord per unit span.

i)  23.9 Ib  ( lift )

ii) 0.25 Ib  ( drag )

iii) -2.68 ft. Ib ( moment about )

Explanation:

Given data:

Angle of attack of wing = 5°

airflow velocity = 100 ft/s

NACA 1412 airfoil section

i) calculate The lift

L =

= dynamic pressure = 11.9 Ib/ft^2 ( as calculated using    )

s = area = ( 1ft ) ( c ) = ( 1 ) ( 3 ) = 3ft^2

= lift coefficient  = 0.67 ( refer to appendix D at an angle of 5° )

Hence the lift ( L) = 11.9 * 3 * 0.67 =  23.9 Ib

ii) calculate The drag

D =

= 11.9 Ib/ft^2

s = 3ft^2

Cd ( drag coefficient ) = 0.007

hence drag  ( D ) = 11.9 * 3 * 0.007 = 0.25 Ib

iii) calculate Moment about

=

qo = 11.9

s = 3 ft^2

c = 3 ft

= - 0.025

hence moment about = ( 11.9  *  3  * 3 * - 0.025 ) =  -2.68 ft. Ib

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