NACA profiles

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Geometry of a profile - 1: zero lift line; 2: leading edge; 3: radius of curvature of the wing nose (nose circle); 4: Curvature maximum profile thickness (max. Thickness); 5: camber; 6: upper profile side (upper surface); 7: trailing edge; 8: camber line (main camber line); 9: lower profile side (lower surface)
Profile line - 1: profile chord (chord), 2: skeleton line (curvature; camber), 3: tendon, 4: skeleton line
A: blue line = profile chord, green line = skeleton line (camber), B: blue circle = radius of curvature (leading edge radius), C: xy coordinate system for the profile geometry (profile chord = x-axis; y-axis is present the front edge of the profile)

The NACA airfoil are two-dimensional cross-sections of airfoils for aircraft wings , by the National Advisory Committee for Aeronautics (NACA, 1915 to 1958 was in 1958 in the NASA on) for the design of wings ( english airfoil design were developed).

The NACA profiles are variations of an original profile. The NACA has created numerous profile tables for the various NACA profiles (NACA catalog) for a standardized description of profiles. These tables contain geometric data and the profile coefficients (lift coefficient c A , drag coefficient c W and moment coefficient c M ) for the different angles of attack .

history

During the 1930s, the NACA investigated various variations of profiles and profile curvatures. The profile thickness, the position of the profile thickness, the position of the profile curvature, the radius of the wing leading edge and other profile parameters were also varied. The NACA first systematically investigated the properties of 78 airfoil profiles in the wind tunnel (a "Variable Density Wind Tunnel") for different thickness families and curvature families at the Langley Research Center in 1933 . This groundbreaking NACA report No. 460 created the basis for the wing construction of many American aircraft from the time of the Second World War ( DC-3 , B-17 , P-38 ).

These first NACA profiles were classified by a four-digit number (4-series; English 4-series ) to which the abbreviation "NACA" was added. After the first four-digit NACA profile series, further NACA profile series were calculated and tested in the following years: 5-, 6- and 7-digit classifications for describing profiles, as well as other modifications.

Even if some NACA profiles are still in use on aircraft that were designed before 1955, the NACA profiles have now been overtaken by advances in computing technology. However, even more modern profiles can be approximated using the NACA profile designation system.

Nowadays, the profiles for the profile design are no longer selected from tables (with the dimensions of the profile and the pressure values), but the profile is constructed individually, according to the specified performance expectations. Because with the “prefabricated” profile method, which also includes the NACA profiles, no locally limited changes to the profile are possible or intended. In addition, wing development (configuration and design) is preceded nowadays by three-dimensional calculations, while only two-dimensional calculations and no three-dimensional geometry definition at all are provided for the NACA profiles (e.g. sweep , skew , fuselage-surface transition ). With three-dimensional wing design, the profiling of the wing is only one aspect of the three-dimensionally optimized flow guidance.

The process of profile development has, as it were, reversed compared to the past. The profile is no longer taken from a profile catalog and the performance data is calculated from it, but a tailor-made profile is calculated according to the specification of the performance data.

prehistory

Separation of the laminar flow on the top of the profile

Although the Wright brothers made the first powered flight in the USA in 1903 , the rapid technical development of aircraft in the following years, including during the war years 1914–1918 , showed that Europe had taken the lead in aircraft development. After all, there has been practical experience and theoretical preparatory work here since the work of George Cayley (1799) and the gliding flights of Otto Lilienthal (1895). As early as 1902, Kutta and 1906 Schukowski had developed a formula for generating profiles (the Kutta-Schukowski transformation ) with which the first lift-generating profiles could be developed.

Among other things, because of the theoretical and technical backwardness of the USA in aviation, the NACA , the "National Advisory Committee for Aviation", was founded in 1915 to promote aviation technology in the USA and to catch up with the European lead. The innovations in aircraft and propulsion construction should be coordinated by the NACA and placed on a scientific basis in order to promote the American aviation industry.

Four-digit NACA series

For the four-digit NACA series, 78 profiles were tested in the wind tunnel. The selection of profiles was quite arbitrary, as there was a lack of theoretical principles. When selecting the profiles and their systematic variation, one could only rely on experience from previous experiments with profile shapes.

The four ordinal numbers represent three geometric values ​​of the profile ( profile curvature , arching reserve and maximum profile thickness ), which are decisive for the properties of the profile. Not all 78 profiles are necessarily used by aircraft, but the test data provided aircraft manufacturers with a wide range of profiles. After the publication of this systematic study, the NACA profiles became widely used. The NACA profile 2412 ( see below ) is still in use today. The numbering of this series allows aerodynamicists to directly select the profile that has the geometric data they want.

The parameters of the four digits that designate the respective NACA profile of the NACA profile series can be used in equations that are used to calculate the exact cross-section of the wing and its properties.

This scientific work The Characteristics of 78 Related Airfoil Sections from Tests in the Variable-Density Wind Tunnel. to examine the 78 profile shapes was a milestone in the development of aerodynamic profiles. In their report, the authors N. Eastman , Kenneth Jacobs , E. Ward and Robert M. Pinkerton found that there were certain similarities between the various profiles that had shown the best properties in terms of lift coefficient and drag coefficient. The two most important variables for the properties of the profile turned out to be the curvature of the skeleton line and the distribution of the profile thickness above and below this line. The authors developed a series of formulas that made it possible to use these two variables to create a whole family of profile shapes with similar properties. As the methods of profile design (profile design) were refined, more and more variables were included in the calculations. However, these two basic variables remained decisive for the NACA profiles.

The NACA profiles have their origin in a series of wind tunnel measurements for a fully symmetrical profile, with a thickness reserve of 30% (greatest thickness of the wing at 30% of the profile depth ).

The construction principle of the NACA profiles is based on circles that are drawn on a line, the profile center line . A profile shape line is created tangentially around these circles.

Different NACA profiles ( aerodynamic twist ) are often used for the wing root and the wing tip . For example, Paschin I-21 had the NACA profile: NAСА-0012-0009, which means that NAСА-0012 was used on the wing root and NAСА-0009 on the wing tip as the profile shape.

The NACA profile can be varied by arching the profile center line upwards by a certain percentage of the profile depth. Another possible variation is the shifting of the highest point of bulge by a certain percentage of the profile depth to the front or back.

The profiles of the four-digit NACA series are sometimes collectively referred to as the NACA-XXXX series and the profiles with two leading zeros as the NACA-00XX series .

The four-digit NACA series defines the profile by:

  • the 1st digit for which the maximum profile curvature - specified in percent, based on the profile chord (i.e. based on the length of the profile chord).
  • the 2nd digit, for the arching reserve - in tenths of the profile chord (i.e.: in tenths of the length of the profile chord).
  • the 3rd and 4th digits denote the maximum profile thickness - stated in percent, based on the profile chord.

The reserve thickness of the four-digit NACA profiles is always 30%.

The meaning of the digits can also be summarized as: NACA pmxx or NACA pmxx-ab. (The letters pmxx-ab stand for:

  • p - maximum camber (given in% of the profile depth)
  • m - arching reserve (indicated as 1/10 of the profile depth)
  • xx - maximum profile thickness (given in% profile depth)
  • a - index for the nose radius
  • b - thickness reserve.)

If the nose radius and thickness reserve are not specified, then they are a function of the other parameters. In the case of the four-digit NACA series, the maximum profile thickness is by definition, as a standard, 30% of the profile chord (measured from the wing leading edge).

Four-digit NACA profiles
0006 0009 0012 0015 0018 0021
0025          
           
(2206) 2306 2406 2506 (2606) (2706)
(2209) 2309 2409 2509 (2609) (2709)
2212 2312 2412 2512 2612 2712
(2215) 2315 2415 2515 (2615) (2715)
(2218) (2318) 2418 2518 (2618) (2718)
(2221) (2321) 2421 2521 (2621) (2721)
           
(4206) 4306 4406 4506 (4606) (4706)
(4209) 4309 4409 4509 (4609) (4709)
4212 4312 4412 4512 4612 4712
(4215) 4315 4415 4515 (4615) (4715)
(4218) 4318 4418 4518 (4618) (4718)
(4221) 4321 4421 4521 (4621) (4721)
           
(6206) 6306 6406 6506 (6606) (6706)
(6209) 6309 6409 6509 (6609) (6709)
6212 6312 6412 6512 6612 6712
(6215) 6315 6415 6515 (6615) (6715)
(6218) 6318 6418 6518 (6618) (6718)
(6221) 6321 6421 6521 (6621) (6721)
           
0006T 0006B 0012T 0012B 0018T 0018B
2R 1 12 2R 2 12 0012F 0 0012F 1    

The advantages of the wing profiles of the four-digit NACA series are:

  • good coating properties ,
  • only a slight shift of the pressure point over large speed ranges,
  • Roughness on the profile has only a minor influence on the aerodynamic properties of the profile.

The disadvantages of the four-digit NACA series wing profiles are:

  • only a low lift coefficient,
  • relatively high air resistance,

Profiles of this series were and are used primarily for wings in general aviation aircraft . The four-series symmetrical profiles are used for elevators, rotor blades for helicopters, wings for supersonic aircraft, and stabilizing wings for rockets.

Theoretically, 9999 different NACA profiles can be represented with four digits. In its investigation, however, the NACA graded the variation of the profiles more roughly, so that 114 profiles were considered, of which only 78 were examined more closely in the wind tunnel. The NACA profiles in brackets in the adjacent table were not examined in the wind tunnel.

The profile curvature could have 4 different values ​​(1st digit) - the values ​​0, 2, 4 or 6 (% of the profile depth).
The arching reserve could assume 7 different values ​​(2nd digit) the values ​​0, 2, 3, 4… 7 (i.e. 0%, 20%, 30%, 40% to 70% of the profile depth).
The maximum profile thickness could have 6 different values ​​(3rd and 4th digits) - the values ​​06, 09, 12, 15, 18 or 21 (% of the profile depth).

7 of the symmetrical profiles of the NACA-00xx series were examined. As a special feature, there was also a profile with a maximum profile thickness of 25% (NACA-0025).

If a profile does not have a bulge (1st digit = 0), it also has no bulge reserve (2nd digit = 0). With a leading zero, the 2nd digit must also be a zero (symmetrical profiles of the NACA-00xx series). For example, there cannot be a NACA-0312 profile.

NACA profile 0012

NACA 0012
laminar streamlines around a NACA 0012 profile

The first two digits indicate the camber of the profile . In the specific case, the two leading zeros indicate that there is no profile curvature. The last two digits (12) indicate that the ratio of profile thickness to length of the profile chord is max t / c = 12% (TOC = 0.12). The flow around the profile of the NACA-0012 is a frequent test case in numerical fluid mechanics .

NACA profile 0015

NACA 0015

The NACA profile 0015 is symmetrical. The two leading zeros indicate that there is no curvature of the profile. The 15 indicates that the ratio of profile thickness to length of the chord is 15%. Consequently, with a length of 1 m (length of the profile chord), the profile has a profile thickness of 15 cm.

NACA profile 2412

NACA 2412

The NACA profile 2412 is semi-symmetrical. Airplanes with this wing profile are good-natured to fly, easy for the pilot to handle and easy to build. Since this profile is relatively thick, a stable wing can be built with this profile without much effort. On the other hand, the profile is not particularly fast, but still sufficiently fast. The air flow at the trailing edge of the profile does not have the tendency to peel off. This good-natured behavior is particularly advantageous in the case of disturbances in the profile shape, since minor disturbances (for example construction errors, dents or holes) do not have a particularly negative effect on the aerodynamic behavior of the profile. However, because of the thick wing leading edge (wing nose) , the critical Reynolds number is much higher than it is for more effective wing profiles.

Meaning of the three digits of the NACA-2412 profile:

  • 1st digit: 2 - maximum curvature of 2% (the length of the profile chord),
  • 2nd digit: 4 times 10 = 40%. So the maximum curvature is 40% of the length of the chord (measured from the wing leading edge).
  • 3rd and 4th digits: 12 - the maximum thickness of the profile (profile thickness) is 12% of the length of the profile chord.

Wing leading edge radius: 1.58; Inclination of the radius through the wing leading edge: 0.10

Short version: NACA 2412 has 2% camber, which is 4/10 behind the wing nose and 12% profile thickness (in relation to the profile depth).

The Cessna 150 (23,954 aircraft built) and the Cessna 182 (25,000 aircraft built) had a modified NACA-2412 profile.

NACA profile 6412

NACA 6412

This profile combines a profile the thickness of a NACA 0012 profile with a 64 curve line - the largest profile curvature of 6% (in relation to the profile depth) is 40% of the profile depth.

The NACA 4412 profile is another well-known profile that has found very wide use in light aircraft, e.g. B. Cessna .

Modifications of the four-digit NACA series

Among the 78 profiles examined were also some modifications of the standardized four-digit NACA profiles in order to be able to make a statement about their special aerodynamic properties.

R modifications

NACA 2R 1 12
NACA 2R 2 12

The R-modification (engl. Reversed ; German: vice versa) of the investigation, the NACA profile 2R were 1 12 and 2R 2 12. They have as a modification of the basic profile 0012, a slightly upwardly curved trailing edge. With the symmetrical standard profiles, the rear edge of the profile points directly to the rear. With the arched standard profiles it points slightly downwards, while with the R modifications it points in the opposite direction (R - reversed - reversed) - slightly upwards. The rear edge of the profile, which is slightly upward, reduces the maximum lift coefficient (c A max ). As a result, the drag coefficient (c W ) is reduced. While the maximum lift is significantly reduced, the drag is only reduced to a lesser extent. The basic profile NACA 2R 1 12 was used in almost all Messerschmitt aircraft z. B. Bf 109 , Bf 110 , Me 323 .

A small profile radius is very critical for maximum lift. The NACA profile 2R 2 12 (also written 2R (2) 12) is a modification of the 0012 profile. The profile thickness is 12%. The NACA profile 2R 2 12 has a negative curvature at the rear edge of the profile, through which the skeleton line is directed upwards by 2 ° at the rear edge to avoid the negative pitching moment (c M ) around the aerodynamic center, which results in unstable pitching behavior when the Angle of attack would cause it to decrease.

Other derivatives of the 0012 profile are the NACA profiles 2R 2 15 and 2R 2 18.

Profiles 0012 and 2R 1 12 each have c A max = 1.53 and profile 2R 2 12 has c A max = 1.47.

B and T modifications

NACA 0018T
NACA 0018B

There are B and T modifications of the symmetrical profiles. The attached "T" (English tall ; German: slim) stands for a smaller nose radius and the attached "B" (English broad ; German: wide) stands for a larger nose radius than the standard profile.

Examples:

  • 0006; 0006T; 0006B;
  • 0012; 0012T; 0012B;
  • 0018; 0018T; 0018B.

The profile changes of the B and T modifications were achieved by systematically changing the equation that defines the normal profile. The resulting change mainly affects the nose radius, but to a lesser extent the rest of the profile. Only the profile thickness and the profile rear edge remain unchanged.

Nose radius (on the leading edge of the profile)
  T series Standard series B series
0006 0.10 0.39 1.19
0012 0.40 1.58 3.80
0018 0.89 3.55 7.15

F modifications

NACA 0012F 0
NACA 0012F 1

The F-modifications ( flexed ; German: curved) 0012F 0 and 0012F 1 are based on a 0012 profile whose rear edge is curved downwards (0012F 1 ) or not curved downwards, i.e. straight backwards ( 0012F 0 )

These profiles have been left unchanged compared to the standard profile in the front third (profile depth: 0.0 to 0.3) and have only been modified at the rear edge. From a profile depth of 0.7, the profile has a very thin profile throughout up to the rear edge. The middle third of the profile (profile depth: 0.3 to 0.7) connects the front and the rear third with an evenly curved curve. The profiles of the F modification (0012F 0 and 0012F 1 ) have a very strong change in profile thickness along the profile depth.

With these modifications, the NACA wanted to simulate profiles that have flexible trailing edges. The 0012F 0 profile has a straight trailing edge that was intended for high speed conditions. The rear edge of the 0012F 1 profile is angled downwards in a circular arc.

Both profiles achieve a very large maximum lift (c A max ), with the drag (c W ) still remaining in a reasonably small size. The drag-lift ratio is only slightly less favorable than with the NACA profile 2412.

Two NACA profiles on one wing

Many more modern aircraft of the old generation that still have NACA profiles at all often have a combination of two or more wing profiles ( aerodynamic twist ) on the same wing , with the profiles usually being indicated at the wing root and at the wing tip:

Five-digit NACA series

In the late 1930s, the NACA carried out further research on wing profiles to increase their maximum lift. That led to the five-digit NACA series.

The first digit (maximum curvature) and the last two digits (maximum profile thickness) provide the same information as with the four-digit NACA series. However, the second digit shows the twentieth of the tread depth and not, as in the four-digit series, the tenth of the tread depth.

Example: The profile NACA 23012 is used by the Beechcraft Bonanza . Here the second digit stands for 3/20. The third digit can only have the values ​​"0" or "1". “0” stands for a profile without profile curvature and “1” for a profile with profile curvature - curved skeleton line ( mean camber line or meanline ).

The five-digit NACA series describes more complex profile shapes than the four-digit series. The digits define the profile as follows:

  • the 1st digit is multiplied by 0.15 and then gives the lift coefficient (see polar diagram );
  • the 2nd and 3rd digits are divided by 2 and give p - the distance from the front edge of the profile to the maximum profile curvature (as a percentage in relation to the profile depth);
  • the 4th and 5th digits indicate the maximum profile thickness (as a percentage in relation to the profile depth);

The skeleton line is defined in two sections:

The x and y coordinates are normalized by the line of the profile depth (??). The constant m was chosen so that the greatest profile curvature occurs at x = p.

Example: For the profile curvature line 230, p = 0.3 / 2 = 0.15 and m = 0.2025.

The advantages of the wing profiles of the five-digit NACA series are:

  • greater maximum lift coefficient than the four-digit series,
  • low pitching moment (engl: pitching moment ),
  • Roughness on the profile has only a minor influence on the aerodynamic properties of the profile.

The disadvantages of the wing profiles of the five-digit NACA series are:

Profiles of this series were and are mainly used for wings in general aviation aircraft , for piston-powered bombers and transporters, commuter aircraft (feeder) and business aircraft .

Examples: NACA 23009, NACA 23012, NACA 23015, NACA 23018

NACA 12045

For example, the NACA 12045 profile has a maximum profile thickness of 45% of the profile depth (4th and 5th digits). This maximum profile thickness is 10% of the profile depth (from the wing leading edge; 2nd and 3rd digits). The maximum bulge is 1% (first digit).

NACA 23012

The NACA 23012 profile combines a 230 profile line with a 0012 profile thickness (the four-series). The 230 profile line has a lift coefficient C A = 0.3 and a profile curvature of 15%. TOC = 0.12. (see also S-impact profiles )

Modifications of the four-digit and five-digit NACA series

The four- or five-digit NACA series can be modified with an additional two-digit code. This code is appended to the NACA series, separated by a hyphen.

  • The 1st code digit describes the rounding (the radius of curvature) of the wing leading edge (0 stands for a particularly sharp wing leading edge; 6 stands for the original rounding of the wing leading edge; 9 stands for a particularly round edge; the numbers in between are also used):
  • the 2nd code number describes the distance between the greatest profile thickness in tenths of a percent in relation to the profile depth.

Examples: NACA 0008-34, NACA 0010-34, NACA 0010-35, NACA 0010-64, NACA 0010-65, NACA 0010-66, NACA 0012-34, NACA 0012-64

NACA 1234-05

The NACA 1234–05 profile is a NACA 1234 profile with a sharp leading edge of the wing (1st code digit). The greatest profile thickness (maximum profile thickness) is 50% of the profile depth (2nd code digit; 5: 10 = 0.5; this corresponds to 50%).

For even greater precision, the two code digits can also be written with additional decimal places. Example: NACA 1234-0.2 5.8 .

One series

Name factor (engl. For the 1-series 1-series ) is the leading one in the profile name. The 1 series is also referred to as the 16 series or the NACA 16-xxx series. The development of the 1 series is based more on theoretical considerations than on variations in geometric relationships.

In the 1930s a new approach to profile design was adopted. Until then, the profile shapes were built first and then their properties were measured in the wind tunnel . In the 1930s, people began to formulate the desired lift properties and then calculate the profile from this before it was built.

The 1 series was used to investigate profile modifications that were particularly intended for the high-speed range, in particular for propeller profiles. The position of the profile thickness is then optimized in order to generate a low induced air resistance and thus to achieve a high critical Mach number .

The profiles of the 1 series are described with five digits, except in cases where the “designed” lift coefficient is equal to or greater than 1.0.

The profiles of the NACA single series are characterized by five digits:

  • the 1st digit represents the classification of the series. The "1" indicates that it is a profile of the ones series;
  • the second digit describes the distance between the minimum pressure area and the leading edge of the wing (expressed as a percentage in relation to the length of the chord). The number must be multiplied by 10.
  • the 3rd position is a hyphen;
  • the 3rd digit describes the lift coefficient (as a measure of the profile curvature). The number must be multiplied by 10.
  • the 4th and 5th digits describe the maximum profile thickness (expressed as a percentage in relation to the length of the profile chord).

Examples: NACA 16-006, NACA 16-009, NACA 16-012, NACA 16-015, NACA 16-018, NACA 16-021

NACA 16-123

The NACA 16-123 profile has a "minimum pressure" which is 60% of the profile depth (from the wing leading edge; 2nd digit). The lift coefficient is 0.1 (3rd digit). The maximum profile thickness is 23% of the profile depth (from the wing leading edge; 4th and 5th digits).

NACA 16-015

NACA 16-015

The NACA 16-015 profile is identical to the NACA 0015-45 profile. The modified NACA profile of the 4-series has a leading edge index of 4 and a maximum profile thickness at 50% of the profile depth. The curvature of the camber line is zero.

Six-digit NACA series

In the late 1930s, aerodynamicists turned their attention to laminar flow . The laminar profiles of the six series had their maximum profile thickness far behind the wing leading edge. The first aircraft with laminar profiles was the North American P-51 Mustang . The laminar profiles of the 6 series are still widely used in high-speed aircraft today.

The six-digit NACA series profiles are an improvement on the single series profiles. The focus is on improving the laminar flow.

The six-digit NACA series includes more complicated profile shapes, for the design of which less geometric methods were used, but rather mathematical-theoretical approaches were used. The theoretical basis for this could be created on the basis of measurements from the previous NACA series. The NACA-6 profiles are no longer classified according to geometric aspects, but - in contrast to the four and five-digit NACA series - according to the speed distribution on the top and bottom of the profile.

The profiles of the six-digit NACA series are characterized by 6 digits:

  • the 1st digit represents the classification of the series. The "6" indicates that this is a profile from the six-digit NACA series;
  • the 2nd digit describes the position of the minimum pressure area or area of ​​minimum pressure in the case of a shock-free flow in tenth of the profile depth (i.e. the length of the profile chord);
  • The 3rd digit is subscripted (foot digit) and describes the range of the deviation of the lift coefficient in tens of percent from the design lift coefficient - the width of the range of the lift number (in tenths) at which the flow around the smooth symmetrical Profile has a laminar character. The lift coefficient can be within a certain range below or above the design lift coefficient. With the design lift coefficient, there are favorable pressure gradients on both the underside and the top of the profile.
  • the 4th character is a hyphen;
  • the 4th digit designates the design lift coefficient in tens of percent, which is a measure of the lift in the case of a shock-free flow, and thus a measure of the size of the profile curvature; The design lift coefficient is the lift coefficient Ca at α = 0 °.
  • the 5th and 6th digits designate the maximum profile thickness in tens of percent (the number must be multiplied by 10.) (specified as a percentage in relation to the length of the profile chord) - i.e. the thickness ratio.

NACA 65 2 -015

The NACA 65 2 -015 profile belongs to profile series 6, has a laminar area of ​​0.2, the pressure minimum is 50% of the profile depth. This profile has no buoyancy when the flow is impactless, because it is symmetrical and not curved. The thickness ratio (max. Profile thickness / profile depth) is 15%.

NACA 61 2 -345

With the NACA 61 2 -345 profile, a = 0.5 has the “minimum pressure area” at 10% of the profile depth. The profile has a low drag 0.2 above and below the buoyancy coefficient of 0.3, as it works inside the laminar cell . The profile has the greatest profile thickness at 45% of the profile depth. 50% of the profile depth is flowed around in a laminar manner.

NACA 64 1 -412

The NACA 64 1 -412 profile has a pronounced laminar flow characteristic, a maximum profile curvature of 2.2% and a profile thickness of 12%. The profile achieved in inverted flight a good boost.

6A series

The 6A series is a modification of the six-digit NACA series in which the skeleton line has been modified.

Example: 63A409: the first digit describes the affiliation to the six-digit NACA family, the second digit the value on the profile chord with the minimum pressure gradient. The A is a specific constant of the six-digit NACA family and is defined as A = 0.8. The fourth digit indicates the “designed” lift coefficient (in tenths; c A = 0.4). The last two digits indicate the relative thickness as a percentage (9% d / l).

Examples: 63A112, 63A210, 63A412, 63A415, 63A418, 63A421, 63A615, 63A010; Grumman F-14 NACA 64A209.65 mod (note: mod stands for modified) and 64A208.91 (wing root and wing tip)

Seven-digit NACA series

Further advances in maximizing laminar flow were made by considering the pressure distribution on the top of the wing separately from the pressure on the underside of the wing.

The profiles of the seven-digit NACA series are described by seven digits:

  • the 1st digit represents the classification of the series. The "7" indicates that this is a profile of the seven-digit NACA series;
  • the 2nd digit describes the distance between the suction tip on the upper side of the wing in ten percent in relation to the profile depth;
  • the 3rd digit describes the distance between the suction tip on the underside of the wing in ten percent in relation to the profile depth;
  • the 4th digit is a letter that refers to the standard profile that is already available from the earlier NACA series;
  • the 4th digit indicates the lift coefficient. The number must be multiplied by 10;
  • the 5th and 6th digits indicate the maximum profile thickness in tens of percent (the number must be multiplied by 10.) (given as a percentage in relation to the length of the profile chord);
  • the 7th specification is an "a =", followed by a decimal number that indicates the proportion of the profile depth up to which the laminar flow is maintained. The standard value a = 1 (laminar flow is present over the entire profile depth; 100%) is not recorded.

NACA 712A345

The NACA 712A345 profile has a suction tip that is 10% of the profile depth on the top of the wing and 20% on the underside of the wing. The standard profile "A" is used. The lift coefficient is 0.3. The maximum profile thickness is 45% of the profile depth.

Eighth NACA series

The eight series of NACA profiles was developed with the aim of achieving advantageous properties close to the speed of sound. The naming of the profiles is identical to the seven-digit NACA series. Only the first digit is an “8” to indicate that it is a profile from the eighth NACA series.

Profile measurement

Image 1

The profile shape for the construction of the profile is taken from tables with the xy coordinates for the profile allowance. These tables were calculated from the profile formula.

The profile coordinates are calculated in the area of ​​the front edge and the front third of the profile depth with short distances on the x-axis, since the y-values ​​change significantly even with small changes in the x-values ​​and the front edge is particularly critical for aerodynamics (Image 1). For the further course of the profile shape, it is sufficient for normal aerodynamic applications if the support points for the construction of the profile are no longer quite as close. In the area of ​​the trailing edge of the profile, the distances on the x-axis are sometimes selected to be narrower in order to calculate the xy coordinates. Of course, the formulas for the construction of the profile allow the calculation of any number of xy values ​​of the profile surface. To determine the exact position of the thickness reserve and the bulge reserve, smaller steps are also required on the x-axis (if the corresponding formulas are not used).

NACA profile 2412 (xy coordinates)
Upper surface Lower face
x value y value x value y value
0 0 0 0
1.25 2.15 1.25 1.65
2.5 2.99 2.5 −2.27
5.0 4.13 5.0 −3.01
7.5 4.96 7.5 −3.46
10 5.63 10 −3.75
15th 6.61 15th −4.10
20th 7.26 20th −4.23
25th 7.67 25th −4.22
30th 7.88 30th −4.12
40 7.80 40 −3.80
50 7.24 50 −3.34
60 6.36 60 −2.76
70 5.18 70 −2.14
80 3.75 80 −1.50
90 2.08 90 −0.82
95 1.14 95 −0.48
100 0 100 0
  • x-values: Distance from the leading edge, along the profile chord
  • y-values ​​for the profile top (y o ) and the profile bottom (y u )
  • y-values ​​of the top and bottom of the profile: y o + y u
  • y-values ​​of the relative curvature: f '(is identical to the y-coordinates of the skeleton line: y o - (y o + y u ) / y)
NACA profile 23018 (xy coordinates) (example: Dornier Do 28D Skyservant )
x y o y u y o + y u f '
0 0 0 0 0
1.25 4.09 −1.83 5.92 1.13
2.5 5.29 −2.71 8.00 1.29
5.0 6.92 −3.80 10.72 1.56
7.5 8.01 −4.60 12.61 1.71
10 8.83 −5.22 14.05 1.81
20th 10.36 −6.86 17.22 1.57
30th 10.55 −7.47 18.02 1.54
40 10.04 −7.37 17.41 1.34
50 9.05 −6.81 15.86 1.12
60 7.75 −5.94 13.69 0.91
70 6.18 −4.82 11.00 0.68
80 4.40 −3.48 7.88 0.46
90 2.39 −1.94 4.33 0.23
100 0.19 −0.19 0.38 0

In spite of certain successes in the design of wing profiles, these profile shapes were hardly created through theoretical considerations until 1940, but rather through trial and error . The profile shapes were drawn by eye, thoroughly tested and optimized with small changes. At that time, massive amounts of test data were obtained in wind tunnels, but due to the lack of a uniform classification and different symbols and units, they were difficult or impossible to compare. For example, the representation of curved profiles in the xy table was not uniform. In the Göttingen profiles, the x-axis lay tangentially (from below) on the profile, while in the NACA profiles the x-axis is identical to the profile chord.

With the investigation of entire profile families, the profile design became more systematic. Based on a symmetrical standard cross-section, the profile curvature was modified. The first series of tests of this kind were carried out at the Royal Aircraft Factory (RAF) (later renamed the Royal Aircraft Establishment ) in Farnborough . Systematic variations of the profile curvature from the symmetrical profile RAF 30 ( RAF profile ) were used to develop profiles RAF 31, RAF 32, RAF 33, etc. The same thing happened with the standard profile RAF 40 and RAF 15. The numbers 15, 30 and 40 only mean that it was the 15th, 30th and 40th test profile of the RAF.

It was only with the NACA profiles that the system of profile numbers became scientific, as the information on the profiles was now encoded in the various digits of the profile number. With the advances in theoretical aerodynamics, the naming system of the NACA profiles was unfortunately more and more modified and expanded in the course of the various NACA series, longer and longer alphanumeric names were used and the system of profile numbers became inconsistent.

More profile series

historical development of the profiles (1909–1944)

Even before the NACA series, there were systematic profile investigations in Göttingen , but these are not as well known and were of a smaller scope. The Göttingen profiles were developed from this. Since the 1910s, systematic series of tests with profile shapes have been carried out at the Aerodynamic Research Institute in Göttingen , from which the Göttinger Profile Catalog was created. These profiles have the abbreviation "Gö" and three distinguishing digits. Gö profiles are not subject to any recognizable system, but are named according to the order in which they were included in the profile catalog. The catalog contains e.g. E.g. also profiles of double deckers from the First World War. Were known z. B. the profiles Gö 532 / Gö 549 / Gö 676 often used on gliders of the 1930s.

Series of experiments by Virginius E. Clark in the USA led to the Clark profiles , the most famous of which is the Clark-Y from 1922. There is a variant of this profile with a slightly raised trailing edge called the Clark-YH and used in the Hawker Hurricane , the Ilyushin Il-2 and the Jakowlew Jak-3 . The original Clark-Y is still very common in model making today.

With the introduction of computer-aided calculation methods from the 1960s onwards, it was possible to directly specify the aerodynamically decisive pressure distribution and derive the profile contour from it. At the beginning of the 1980s, Prof. Dr. Richard Eppler developed the numerical Eppler program.

  • Eppler-Profiles Richard Eppler and Franz Xaver Wortmann carried out investigations on laminar profiles after 1955. Each profile was tailored to a specific task. Unlike the NACA profiles, they were not theoretical variations on an original profile. The Eppler profile catalog contains well over 1000 computer-calculated profiles, the best known of which is the E-603, which was used in the Grob Astir series .
  • Wortmann profiles (designation "FX"). The rear group of numbers describes the profile thickness in per mille, i.e. 126 ‰ = 12.6% for the FX60-126. The letters H and K between them stand for low-torque rotor blade profiles (H = helicopter) z. B. FX 66-H-159 or for special flap profiles (K = flap) z. B.FX 67-K-150. The Wortmann FX60-126 profile was used for years on the outer wings of the plastic gliders made by Alexander Schleicher ( ASW 12 - ASW 22 ).
  • NT profiles (NT stands for "New Technology"; also referred to as TNT - "Hydrofoil New Technology") from Dornier .
  • HQ-Profiles (HQ stands for Horstmann / Quast but also for Helmut Quabeck): The profiles of Horstmann and Quast were created at the Institute for Design Aerodynamics at DLR Braunschweig and are used by a number of person-carrying aircraft, etc. a. used in many gliders, such as B. on the inner wing of the Schleicher ASH 25 (HQ17 / 14.38). Helmut Quabeck's profiles are more likely to be used in model flying. For example the HQ / ACRO profile series (special profiles for aerobatics ), but also the HQ / S ( S- flap profiles ) and the HQ / W profile series (profiles for flap applications ).

An outdated classification of profile shapes is based on the geometric properties of the profiles:

literature

  • Edgar Gorrell, S. Martin: Aerofoils and Aerofoil Structural Combinations . In: NACA Technical Report . No. 18 , 1917.
  • Ira H. Abbott, Albert E. von Doenhoff: Theory of Wing Sections: Including a Summary of Airfoil Data . Dover Publications, New York 1959, ISBN 978-0-486-60586-9 .
  • Richard Eppler: Airfoil Design and Data . Springer, Berlin / New York 1990, ISBN 978-3-540-52505-9 .

Web links

Individual evidence

  1. ^ A b N. Eastman, Kenneth Jacobs, E. Ward, Robert M. Pinkerton: The Characteristics of 78 Related Airfoil Sections from Tests in the Variable-Density Wind Tunnel . (PDF; 4.5 MB) NACA: Technical Report No. 460, 1933 (English)
  2. ^ WF Linsey, DB Stevenson and Bernard N. Daley: Aerodynamic characteristics of 24 NACA 16-series airfoils at mach numbers between 0.3 and 0.8. NACA, Technical note No. 1546, 1948 (PDF; 2.4 MB)
  3. ↑ The Development of Cambered Airfoil Sections Having Favorable Lift Characteristics at Supercritical Mach Numbers , NACA report
  4. ↑ Donald J. Graham: Technical Note No. 1771 . 1948, hdl: 2060/19930082444 (English); Final report of the NACA on the development of the eight series