AGARD-B is a standard wind tunnel model (calibration model) that is used to verify, by comparison of test results with previously published data, the measurement chain in a

wind tunnel Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

. Together with its derivative AGARD-C it belongs to a family of

AGARD The Advisory Group for Aerospace Research and Development (AGARD) was an agency of NATO that existed from 1952 to 1996. AGARD was founded as an Agency of the NATO Military Committee. It was set up in May 1952 with headquarters in Neuilly sur Sein ...

standard wind tunnel models. Its origin dates to the year 1952, and the Second Meeting of the AGARD Wind Tunnel and Model Testing Panel in

Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus (legendary) , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...

, when it was decided to define two standard wind tunnel model configurations (AGARD-A and AGARD-B) to be used for exchange of test data and comparison of test results of same models tested in different wind tunnels. The idea was to establish standards of comparison between wind tunnels and improve the validity of wind tunnel tests. Among the standard wind tunnel models, AGARD model configuration B (AGARD-B) has become by far the most popular. Initially intended for the supersonic wind tunnels, the AGARD-B configuration has since been tested in many wind tunnels at a wide range of

Mach number Mach number (M or Ma) (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Moravian physicist and philosopher Ernst Mach. : \mathrm = \frac ...

s, from low subsonic (Mach 0.1), through transonic (Mach 0.7 to 1.4) to hypersonic (up to Mach 8 and above). Therefore, a considerable database of test results is available. AGARD-B ( see figure) is a body-wing configuration. All its dimensions are given in terms of the body diameter "D" so that the model can be produced in any scale, as appropriate for a particular wind tunnel. The body is an 8.5 diameters long

solid of revolution In geometry, a solid of revolution is a solid figure obtained by rotating a plane figure around some straight line (the ''axis of revolution'') that lies on the same plane. The surface created by this revolution and which bounds the solid is the ...

consisting of a 5.5 diameters long cylindrical segment and a nose with a length of 3 diameters and having a local radius defined by the equation . The

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...

is a

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

in the form of an equilateral triangle with a span of four body diameters. Wing section is a symmetric cylindrical arc with a relative thickness t/c of 4%.

Leading In typography, leading ( ) is the space between adjacent lines of type; the exact definition varies. In hand typesetting, leading is the thin strips of lead (or aluminium) that were inserted between lines of type in the composing stick to incre ...

and

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...

s of the wing should be rounded with a radius equal to . However, this specification is unclear. It is obvious that the specified radius can not be applied near the

wingtips A wing tip (or wingtip) is the part of the wing that is most distant from the fuselage of a fixed-wing aircraft. Because the wing tip shape influences the size and drag of the wingtip vortices, tip design has produced a diversity of sha ...

, or large deformations in the plan form of the wing would occur. In the past, this part of the specification was interpreted in different ways by model designers which led to small differences in shapes of the tested models. The recommended solutionHills R.
"A Review of Measurements on AGARD Calibration Models"
, AGARDograph 64, Aircraft Research Association Bedford, England, 1961 is to have the leading- and trailing-edge radii of at the theoretical root chord and to decrease the radii towards the wing tips proportionally to the local chord. A support

sting Sting may refer to: * Stinger or sting, a structure of an animal to inject venom, or the injury produced by a stinger * Irritating hairs or prickles of a stinging plant, or the plant itself Fictional characters and entities * Sting (Middle-eart ...

to be used with the AGARD-B model was defined as well. The initial specificationSpecification for AGARD Wind Tunnel Calibration Models, AGARD memorandum, AGARD, 1955 of the model called for a sting having a diameter of and a length of . In the revised specification the length of the sting was changed to in order to reduce sting interference, but at that moment a number of wind tunnel tests had already been made. Therefore, published test results for the AGARD-B models do not all correspond to theoretical model configuration. The drag characteristics of the AGARD-B model were found to be somewhat sensitive to the

boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condi ...

transition on the model. In order to reduce the scatter of results, in some wind tunnel facilities the model was tested with boundary layer transition trips near the leading edges of the wing and the nose of the body. On the other hand, a number of wind tunnel tests was made without fixed transition. Drag results with and without the fixed boundary layer transition differ, which should not be neglected when comparing test results from different wind tunnel laboratories. In some wind tunnel laboratories, AGARD-B was tested in non-standard configurations, e.g. as a half-model (half-span model).Aoki Y., Kanda H., Sato M., Nagai S., Itabashi Y., Nishijima H., Kimura
"AGARD-B Standard Model Tests in JAXA 0.8 m by 0.45 m High Reynolds Number Transonic Wind Tunnel"
JAXA-SP-09-005, Proceedings of the Wind Technology Association 81st meeting, 2009 Some free-flight tests of the AGARD-B model were performed. For these tests, the standard geometry was modified by adding, at the rear end of the body, two triangular vertical stabilisers, one on the ventral and one on the dorsal side of the body. Size of the vertical stabilizers was 50% of the wing size, i.e. their span was .Piland, R.O., "The Zero-Lift Drag of a 60^o Delta-Wing-Body Combination (AGARD Model 2) Obtained from Free-Flight Tests Between Mach Numbers 0.8 and 1.7", NACA TN-3081, Langley Aeronautical Laboratory, NACA, 1954 AGARD-B standard model is intended primarily for the measurement of aerodynamic forces and moments. Test results are most often presented in the form of nondimensional aerodynamic coefficients in the wind axes system. Reference area for the calculation of the coefficients is the theoretical wing area . Reference length for the

pitching moment coefficient In aerodynamics, the pitching moment on an airfoil is the moment (or torque) produced by the aerodynamic force on the airfoil if that aerodynamic force is considered to be applied, not at the center of pressure, but at the aerodynamic center ...

is the

mean aerodynamic chord In aeronautics, the chord is an imaginary straight line joining the leading edge and trailing edge of an aerofoil. The chord length is the distance between the trailing edge and the point where the chord intersects the leading edge.L. J. Clan ...

(m.a.c.) equal to while the reference length for the yawing and rolling moment coefficients and is the

wing span The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the other wingtip. For example, the Boeing 777–200 has a wingspan of , and a wandering albatross (''Diomedea exulans'') caught in 1965 had a wingspan of ...

. Moments are reduced to a point in the plane of symmetry of the model, at the longitudinal position of 50% of the m.a.c. (however, in some published results,Anderson C.F., An Investigation of the Aerodynamic Characteristics of the AGARD Model B for Mach Numbers from 0.1 to 1.0, AEDC-TR-70-100, Arnold Engineering Development Center, 1970 moments were reduced to a point at 25% of the m.a.c.).

Drag coefficient In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equ ...

is presented in terms of forebody drag obtained by subtracting, from the total measured drag , the base drag computed from the measured base pressure on the model. Likewise,

Lift coefficient In fluid dynamics, the lift coefficient () is a dimensionless quantity that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. A lifting body is a foil or a com ...

represents forebody lift. Some laboratories have selected to test the AGARD-B standard model for periodic checkouts of the quality of measurements in their wind tunnels.Damljanovic D, Isakovic J. and Rašuo B.
"T-38 Wind-Tunnel Data Quality Assurance Based on Testing of a Standard Model"Journal of Aircraft
Vol. 50, No. 4 (2013), pp. 1141-1149. doi: 10.2514/1.C032081Damljanovic D., Vitic A., Vukovic Ð., Isakovic J.
"Testing of AGARD-B calibration model in the T-38 Trisonic Wind Tunnel"
56 (2), 2006, pp. 52-62

AGARD-C

At the

Wind Tunnel and Model Testing Panel meeting in

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, in 1954, it was agreed to add a third model configuration to the family of AGARD calibration models, by extending the body of the AGARD-B by 1.5 diameters and by adding a horizontal and a vertical tail in the

T-tail A T-tail is an empennage configuration in which the tailplane is mounted to the top of the fin. The arrangement looks like the capital letter T, hence the name. The T-tail differs from the standard configuration in which the tailplane is ...

configuration. The horizontal tail has an area equal to 1/6 of the wing area. Sections of the vertical and horizontal tail are circular arc profiles defined identically to the profile of the wing. Forward of the 1.5 D body extension, the geometry of the AGARD-C model is identical to that of the AGARD-B. Also, the position of the moments reduction point (the aerodynamic centre) is the same as on AGARD-B. The support

for the AGARD-C model is identical to the sting for the AGARD-B model, having a length of aft of model base and a diameter of {{nowrap, 1=0.5 D. The longer body of the AGARD-C model and the existence of the tail make it easier to detect (from anomalies in the wind tunnel test results) if the shock waves reflected from the walls of the wind tunnel test section are passing too close to the rear end of the model. The existence of the tail generally makes this model more sensitive than AGARD-B to flow curvature in the wind tunnel test section.Damljanovic D., Vukovic Ð., Vitic A., Isakovic J., Ocokoljic G
"Observations on Some Transonic Wind Tunnel Tests of a Standard Model with a T-Tail"
66 (4), 2016, pp. 34-39 AGARD-C is primarily used in the transonic wind tunnels and the database of published test results is somewhat smaller than the one for the AGARD-B model. In order to reduce cost and produce more versatile wind tunnel models, actual designs of AGARD-B and AGARD-C are sometimes realized as an AGARD-B configuration to which a body segment with the T-tail can be attached at the rear end to form the AGARD-C configuration ( see figure).

References

Wind tunnels Physical models

AGARD-C

See also

References