In the animation, the forces acting on the airfoil profile of an aircraft are displayed. An aircraft with a Clark Y airfoil is shown. The angle of attack of the wing can be varied. The forces represented as vectors adjust accordingly.
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Description of the Animation
The lift force (blue) and the drag force (red) result from the lift coefficient CL and the drag coefficient CD, respectively. These coefficients are represented by curves in the animation. Alternatively, these coefficients can also be displayed as a polar diagram.
The angle of attack α is the angle between the chord line (imaginary connecting line between the leading and trailing edge of the profile) and the direction of the oncoming flow. When the angle of attack is increased, the lift initially increases until a stall occurs at the critical angle of attack (usually between 15° and 20°) and the lift suddenly collapses.
The magnitude of the lift force can be calculated using the following formula:
[ F_L = C_L cdot frac{rho}{2} cdot v^2 cdot A ]
- CL: Lift coefficient. The lift coefficient depends on the shape of the wing. The value is determined through measurements in a wind tunnel or through simulations.
- ρ (Rho): Density of the air through which the wing moves. It is given in kilograms per cubic meter (kg/m³) and can vary depending on altitude, temperature, and humidity.
- v: Velocity of the object through the air in meters per second (m/s)
- A: Reference area in square meters (m²). This is the projected wing area viewed from above (planform area).
The formula for calculating the drag force is (CD: drag coefficient):
[ F_D = C_D cdot frac{rho}{2} cdot v^2 cdot A ]
The ratio of lift to drag is called the glide ratio E:
[ E = frac{C_L}{C_D} = frac{F_L}{F_D} ]
The higher the glide ratio, the more efficient the profile. The Clark Y airfoil typically achieves its best glide ratio at an angle of attack of about 4° to 6°.
The term ρ/2 · v² is also referred to as dynamic pressure or ram pressure q and has the unit Pascal (Pa) or N/m².
Typical values for the Clark Y airfoil:
- Maximum lift coefficient CL,max: approximately 1.3 to 1.5
- Minimum drag coefficient CD,min: approximately 0.008 to 0.01
- Best glide ratio: approximately 60 to 80
- Critical angle of attack: approximately 15° to 17°