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Four- and five-digit series airfoils can be modified with a two-digit code preceded by a hyphen in the following sequence: One digit describing the roundness of the leading edge, with 0 being sharp, 6 being the same as the original airfoil, and larger values indicating a more rounded leading edge.
For example, an airfoil of the NACA 4-digit series such as the NACA 2415 (to be read as 2 – 4 – 15) describes an airfoil with a camber of 0.02 chord located at 0.40 chord, with 0.15 chord of maximum thickness. Finally, important concepts used to describe the airfoil's behaviour when moving through a fluid are:
English: Potential-flow streamlines around a NACA 0012 airfoil at 11° angle of attack, with upper and lower streamtubes identified. Computed using the Wolfram Demonstrations Project Code Potential Flow over a NACA Four-Digit Airfoil by Richard L. Fearn and beautified in Adobe Illustrator CS3.
TT: the usual two-digit maximum camber in percent of chord; Accordingly, the given example “77887” is nonsensical. You simply cannot have a an “8” in the middle position: it _must_ be either “0” or “1”. An 87%-of-chord thickness is also highly dubious: _none_ of the canonical NACA profiles (10 5-digit and 87 4-digit) go beyond 25%.
Further development resulted in two patents and a family of airfoils known as the KF airfoil and KFm airfoils (for Kline–Fogleman modified). The two patents, US Patent # 3,706,430 and US Patent # 4,046,338, refer to the introduction of a step on either the bottom (KFm1) or the top (KFm2) of an airfoil , or on both the top and bottom (KFm4).
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Supercritical airfoils feature four main benefits: they have a higher drag-divergence Mach number, [21] they develop shock waves farther aft than traditional airfoils, [22] they greatly reduce shock-induced boundary layer separation, and their geometry allows more efficient wing design (e.g., a thicker wing and/or reduced wing sweep, each of which may allow a lighter wing).
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