NACA airfoil

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The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics (NACA). The shape of the NACA airfoils is described using a series of digits following the word "NACA." The parameters in the numerical code can be entered into equations to precisely generate the cross-section of the airfoil and calculate its properties.

Contents

1 Four-digit series
2 Five-digit series
3 Modifications
4 1-series
5 6-series
6 7-series
7 8-series
8 References
9 Related content

Four-digit series

The simplest airfoils, described using a four-digit number in the following sequence:

One digit describing maximum camber as percentage of the chord.
One digit describing the distance of maximum camber from the airfoil leading edge in tens of percents of the chord.
Two digits describing maximum thickness of the airfoil as percent of the chord.

For example, the NACA 2412 airfoil has a maximum camber of 2% located 40% (0.4 chords) from the leading edge with a maximum thickness of 12% of the chord. Four-digit series airfoils by default have maximum thickness 30% of the chord (0.3 chords) from the leading edge.

The NACA 0015 airfoil is symmetrical, the 00 indicating that it has no camber. The 15 indicates that the airfoil has a 15% thickness to chord length ratio: it is 15% as thick as it is long.

Five-digit series

More complex airfoil shapes, described using a five-digit number in the following sequence:

One digit, when multiplied by 1.5, gives the lift coefficient in tenths.
Two digits, when divided by 2, describe the distance of maximum camber from the leading edge in tenths of chord.
Two digits describe the maximum thickness of the airfoil as percept of the chord.

For example, the NACA 12345 airfoil has a lift coefficient of 0.15, maximum camber 0.115 chords from the leading edge, and a maximum thickness of 45% of the chord. Five-digit series airfoils by default have maximum thickness 30% of the chord (0.3 chords) from the leading edge.

Modifications

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.
One digit describing the distance of maximum thickness from the leading edge in tens of percent of the chord.

For example, the NACA 1234-05 is a NACA 1234 airfoil with a sharp leading edge and maximum thickness 50% of the chord (0.5 chords) from the leading edge.

In addition, for a more precise description of the airfoil all numbers can be presented as decimals.

1-series

A new approach to airfoil design pioneered in the 1930s in which the airfoil shape was mathematically derived from the desired lift characteristics. Prior to this, airfoil shapes were first created and then had their characteristics measured in a wind tunnel. The 1-series airfoils are described by five digits in the following sequence:

The number "1" indicating the series
One digit describing the distance of the minimum pressure area in tens of percent of chord.
A hyphen.
One digit describing the lift coefficient in tenths.
Two digits describing the maximum thickness in tens of percent of chord.

For example, the NACA 16-123 airfoil has minimum pressure 60% of the chord back with a lift coefficient of 0.1 and maximum thickness of 23% of the chord.

6-series

An improvement over 1-series airfoils with emphasis on maximizing laminar flow. The airfoil is described using six digits in the following sequence:

The number "6" indicating the series.
One digit describing the distance of the minimum pressure area in tens of percent of chord.
One subscript digit describing that low drag is maintained that many tenths above and below the specified lift coefficient (fourth digit in the sequence).
A hyphen.
One digit describing the lift coefficient in tenths.
Two digits describing the maximum thickness in tens of percent of chord.
"a=" followed by a decimal number describing the fraction of chord over which laminar flow is maintained. a=1 is the default if no value is given.

For example, the NACA 61₂-345 a=0.5 has the area of minimum pressure 10% of the chord back, maintains low drag 0.2 above and below the lift coefficient of 0.3, has a maximum thickness of 45% of the chord, and maintains laminar flow over 50% of the chord.

7-series

Further advancement in maximizing laminar flow achieved by separately identifying the low pressure zones on upper and lower surfaces of the wing. The airfoil is described by seven digits in the following sequence:

The number "7" indicating the series.
One digit describing the distance of the minimum pressure area on the upper surface in tens of percent of chord.
One digit describing the distance of the minimum pressure area on the lower surface in tens of percent of chord.
One letter referring to a standard profile from the earlier NACA series.
One digit describing the lift coefficient in tenths.
Two digits describing the maximum thickness in tens of percent of chord.

For example, the NACA 712A345 has the area of minimum pressure 10% of the chord back on the upper surface and 20% of the chord back on the lower surface, uses the standard "A" profile, has a lift coefficient of 0.3, and has a maximum thickness of 45% of the chord.

8-series

Supercritical airfoils designed to independently maximize airflow above and below the wing. The numbering is identical to the 7-series airfoils except that the sequence begins with an "8" to identify the series.

References

[Aerospaceweb.org]