Question

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.

Answer 1

i) 23.9 Ib ( lift )

ii) 0.25 Ib ( drag )

iii) -2.68 ft. Ib ( moment about )

Step-by-step explanation:

Given data:

Angle of attack of wing = 5°

airflow velocity = 100 ft/s

NACA 1412 airfoil section

i) calculate The lift

L =
`q_(0)`
`sc_(1)`

`q_(0)` = dynamic pressure = 11.9 Ib/ft^2 ( as calculated using
`1/2 * p_(0) * v^(2) _(0)` )

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

`c_(1)` = 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 =
`q_(0) sc_(d)`

`q_(0)` = 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

`M_{(c)/(4) }` =
`q_(0) scc_{m_{(c)/(4) } }`

qo = 11.9

s = 3 ft^2

c = 3 ft

`c_{m_{(c)/(4) } }` = - 0.025

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