AIRFOIL TERMINOLOGY SERIES

At higher angles of attack, the lift is partly due to pressure reduction on the upper surface and partly due to pressure increase on the lower surface. ⦁ From the foregoing, following conclusions may be drawn:Īt lower angles of attack, the lift arises from the difference between the pressure reduction on the upper and lower surfaces. The pressure reduction on the lower surface simultaneously decreases in both intensity and extent. The stagnation point advances backward on the lower surface and the pressure increase on the lower surface covers a greater part of the surface. This is the principle behind the operation of spoilers and canards.Īs the angle of attack is increased from zero we note that Pressure reduction on the upper surface increases both in intensity and extent until, at large angle of attack, it actually spreads to a small part of the front lower surface. The lift progressively decreases with an increase in angle of attack beyond the angle of attack corresponding to maximum lift.

Reason for the decrease in lift beyond an angle of attack is “separation of flow” on the suction surface. For a given airfoil and at a given airflow velocity, the lift force increases with angle of attack up to a limit and then decreases. The angle of attack (also called angle of incidence) (α) is the angle made between the chord line in the direction of airflow. Component of this resultant force normal to the relative wind direction is called “lift” and the component in the direction of the relative wind is called “drag”. The differential pressure so produced when multiplied by the plan area of the airfoil generates an upward resultant force normal to chord line. The shape of the wing directly impacts the airflow. The maximum velocity and minimum static pressure will occur at a point near-maximum thickness. Air that is passing above and below the airfoil has speeded up to a value higher than the flight path velocity and will produce static pressures that are lower than ambient static pressure. As the velocity changes, the dynamic pressure changes and, according to Bernoulli's principle, the static pressure also changes. It then speeds up again as it passes over or beneath the airfoil. The air approaching the leading edge of an airfoil is first slowed down. Taking an example, the NACA 24013 has a peak thickness of 13%, a design lift coefficient of 0.3, and the maximum camber located 20% behind the leading edge.Īt present, the resources available for computation allow the designers to design and optimize the airfoils specifically tailored to a particular application. The final two digits again indicate the maximum thickness in a percentage of chord. The next two digits, when divided by 2, give the position of the maximum camber in tenths of the chord. The design lift coefficient (cL) is given by the first digit, when multiplied by 3/2, yields it in tenths.

AIRFOIL TERMINOLOGY SERIES

The NACA Five-Digit Series and the Four-Digit Series are quite similar as they use the same thickness forms, but the mean camber line is defined differently and the naming convention is a bit more complex. Using these values, one can compute the coordinates of the entire airfoil using specific equations, For example, the NACA 2415 airfoil has a maximum thickness of 15% with a camber of 2% located at 40% chord from the airfoil leading edge (or 0.4c). Here in, the maximum camber in the percentage of the chord (airfoil length) is given by the first digit, the second indicates the position of the maximum camber and lastly, the maximum thickness of the airfoil in the percentage of the chord is provided by the last two numbers.

The family of airfoils which was curated by utilizing this approach was called the NACA Four-Digit Series.

Also, the families, which included the 6-Series, were more complex shapes which were derived using theoretical methods. The Network of Aquaculture Centres in Asia-Pacific, airfoil series, the 4-digit, 5-digit, and the updated 4-/5- digit, were generated using analytical equations and analogies that described the curvature of the airfoil's mean-line (geometric centerline) as well as the section's thickness distribution along the length.

Airfoil terminology