## Definition of lift and drag

total force by fluid acting on the body

lift perpendicular to the free stream

Source of total forca (or lift and drag)

shear stress on the surface of the body (parallel to the body)

pressure on the surface of the body (normal to the surface + inward)

Definition of wind

A wing is any body which produces much more lift more than drag, when set a suitable angel to a given free stream

Characterictic:

1. Streamlining

2. Rounded leading edge (L.E) (Head)

3. Sharp Trailing edge (T.E) (Tail)

Cross Section of wing -> airfoil / hydrofoil (Section)

Aspek Rasio \(AR=\frac {a}{b}\) for rectangular wing

more general definition \(AR = \frac {(span)^{2}}{platform-area}=\frac{b^{2}}{s}\)

for rectangular wing S=b.c

\(AR=\frac{b^{2}}{S}=\frac{b^{2}}{b.c}\)

Foil Section

There are two points L and T on an aerofoil such that straight line LT is Longer than any other stright line joining two point on the airfoil

The leading edge is the one that faces the oncoming flow

Anggel of attack (or angle of incidence), \(\alpha\) the angle between the direction of the free stream and the direction of chord line

Define a local coordinat system

O: at the leading edge

X: on the chord line toward edge (T.E)

Y: Perpendicular Chord, toward upper surface\(**\color**{Orange}2x\)

Upper surface : \(y=\eta_{u}(x)\) for \(Y \geq 0\)

Lower surface : \(y=\eta_{l}(x)\) for \(Y \leq 0\)

camber line: \(\eta_{c}(x)=\frac{\eta_{u}(x)+\eta_{l}(x)}{Z}\)

thickness: \(\eta_{t}(x)=\eta_{u}(x)-\eta_{e}(x)\)

\(\Rightarrow\)max thickness, \(t=max (\eta_{t}(x))\)

\(\Rightarrow\)camber height, \(m=max (\eta_{c}(x))\)

\(\)thickness-chord ratio: \(\frac{t}{c}\)

for low speed air plane : \(\frac{t}{c}~12% – 14%\)