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32-669: After the construction of the Variable Density Tunnel at Langley in 1921, the National Advisory Committee for Aeronautics built a variety of technical research facilities upon which the American aircraft industry was based. These facilities enabled the American aircraft industry to dominate the skies in both commercial and military aviation. By 1945, America's lead in the field of aviation seemed to be evaporating. The technological achievements of

64-519: A 250-hp motor could produce an air speed up to 51 mph (82 km/h). During a fire in 1927, the internal wooden test section of the VDT was destroyed and was rebuilt with an open-throat design before complications required it be rebuilt again with a closed-throat design. The VDT re-entered service in 1930 and continued to aid the Langley staff in measuring the aerodynamic qualities of airfoils until it

96-430: A common centralized power plant. The transonic test section spanned 11 by 11 feet (3.3 x 3.3 m), while the two supersonic sections were smaller: nine by seven feet (2.7 x 2.1 m) and eight by seven feet (2.4 x 2.1 m). Giant valves 20 feet (6 m) in diameter supplied air from one supersonic leg to another. The Unitary Plan Wind Tunnel has three closed-loop wind tunnels, each with its own model test section, but all sharing

128-696: A function of time. In this case, the imaging devices must be synchronized to the excitation. Multi-channel digital delay/pulse generators provide that synchronization. Another area of interest has been the measurement of surface pressure in low-speed wind tunnels. Binary PSP systems are used in low-speed wind tunnel environments where pressure gradients are small and error sources are more significant. Model shift between reference condition and loaded condition, variation in paint thickness, lamp instability, and temperature are significant sources of error in PSP data. Binary PSP mitigates many of these error sources by employing

160-437: A known reference condition which is typically standard atmospheric conditions with the tunnel turned off. A wind-on image at a loaded condition where the wind tunnel is running at condition. And lastly a background image where the ambient light present is captured without the illumination source. The background image is then subtracted from the wind-off reference and the wind-on condition image in data processing. Photographs of

192-435: A low-cost alternative that is less invasive than pressure tap arrays. PSP also offers superior spatial resolution, with each pixel of the imaging camera acting as a pressure tap. PSP can achieve accuracy within 150 Pa of pressure tap measurements with good setup and experience. Time-resolved PSP applications involve pulsed excitation and delay and gating of the imaging devices. One can thus determine pressure differentials as

224-433: A second probe into the paint layer, known as the reference probe. This reference probe is used to ratio out the effects of these errors producing high quality PSP pressure maps at low speeds. The greatest advantage of the new technology is its much reduced preparation time compared to installing an array of pressure taps. The same model can be used for other testing, such as load-bearing tests or radar-reflection tests, since

256-493: A symmetric flexible wall in a nozzle configuration. Typical models in the 11-ft are either a full span (sting mounted), or half span (floor mounted) configuration. A sting-mounted model support is capable of moving the test article to various AOA and AOS setpoints within at 15 degree cone. Typical model measurements acquired may include: Forces and Moments, Steady-State Pressures, Temperatures. Multiple optical test techniques are offered which include: Shadowgraph (which

288-449: A technically competent research organization...[rejuvenating] American aerodynamic research which in time led to the best aircraft in the world." The building in which it was originally located was demolished in 2014; the tank is now on display on the Langley grounds. Pressure-sensitive paint Pressure-sensitive paint (PSP) is a method for measuring air pressure or local oxygen concentration, usually in aerodynamic settings. PSP

320-530: A wind tunnel. If a full-scale airfoil is to be simulated in a wind tunnel by a small-scale model, the Reynolds number can only be matched by increasing the velocity or its density or by decreasing its viscosity. The Variable Density Tunnel was designed and built to be pressurized; solving this issue by increasing the density of the air to raise the Reynolds number. The VDT was subsequently able to provide more accurate measurements of aerodynamic qualities because it

352-419: Is closely related to Schlieren ), Infrared Thermography , Model Deformation and Pressure-sensitive paint . The 9x7ft Supersonic Wind tunnel is capable of speeds from Mach 1.55 to Mach 2.5. Mach number is set by moving an asymmetric, sliding nozzle block. Airflow is produced by an 11-stage, axial-flow compressor that weighs over 450 tons. Variable Density Tunnel The Variable Density Tunnel (VDT)

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384-406: Is paint-like coating which fluoresces under a specific illumination wavelength in differing intensities depending on the external air pressure being applied locally to its surface. A model surface is painted with the PSP coating with an airbrush or automotive type paint gun. The PSP consists of an oxygen sensitive probe suspended in an oxygen permeable binder. The model is then placed in an oven so

416-475: Is rated to produce up to 65,000 Horsepower and 7200 volts . Combined, the main drive system can produce up to 260,000 horsepower. Drive speed is currently controlled by a liquid rheostat system. The Transonic wind tunnel is a closed-return, variable density tunnel with a fixed test section geometry. The 11-ft is capable of speeds from Mach 0.25 to Mach 1.4. Airflow is produced by a three-stage, axial-flow compressor. Supersonic conditions are achieved by moving

448-895: The Douglas DC-8 , DC-9 , and DC-10 were all tested here; as well as military aircraft such as the F-111 fighter, the C-5A Galaxy transport and the B-1 Lancer bomber. In addition to aircraft, in the 1960s and 1970s all NASA crewed space vehicles including the Space Shuttle and SLS have been tested in the Ames Unitary Plan Wind tunnel complex. The major element of the tunnel complex is its main drive system. The main drive consists of four wound-rotor-type induction electric motors connected in tandem. Each motor

480-707: The Lockheed P-38 Lightning . Additionally, the VDT served in testing thin airfoil designs and low-drag airfoils that were used to design the P-51 Mustang and reduced drag by close to two thirds. On October 3, 1985, the United States National Park Service recognized the Variable Density Tunnel as a National Historic Landmark. The nomination cited the VDT as responsible for establishing "NACA as

512-437: The aerodynamics of scale models, the density of the air used in a wind tunnel must also be scaled to replicate realistic conditions that would affect the full-scale aircraft . The Reynolds number is a quantification of the complex behaviors of dynamic fluids and is calculated as the ratio of inertia forces to the viscous forces in the flow. The Reynolds number is defined as where: The wind tunnels that were used before

544-418: The 1940s. Langley Research Center historian, James R. Hansen , wrote that the VDT provided results superior to the atmospheric wind tunnels used at the time and was responsible for making NACA , the precursor to NASA , "a world leader in aerodynamic research". It is now on display on the Langley grounds, near the old Reid Conference Center and is a National Historic Landmark . In order to accurately measure

576-545: The American aircraft industry, including the Ames Unitary Plan Wind Tunnel Complex. Construction of this facility began in 1950-1951 and continued until 1955. Because no one wind tunnel could meet all the demands for additional research facilities simulating the entire range of aircraft and missile flight, NACA chose to build the Ames tunnel with three separate test sections drawing power from

608-645: The German missiles and jet aircraft indicated a lag in American aeronautical research. In 1949, Congress passed the Unitary Plan Act , under which the Federal government coordinated a national plan of facility construction encompassing NACA, as well as the Air Force , private industry, and universities. The Unitary Plan resulted in the construction of a new series of wind tunnel complexes to support

640-428: The PSP layer can cure. Once cured, the model is placed in a wind tunnel or appropriate test environment. LED lamps of a specific wavelength are used to excite the pressure-sensitive probe within the paint. Once excited, the pressure-sensitive probe is transitioned to a higher energy state where it may either emit a photon or be quenched by local oxygen present. This competing process of emission and quenching determines

672-553: The aerodynamic forces on the whole model, beam balances are connected to the model. However, it is also imperative to understand how those forces are distributed across the aerodynamic surfaces of the aircraft, and this understanding is more difficult to obtain. The classic approach has been to use an array of pressure taps to measure surface pressure distributions on a model. Pressure taps provide limited spatial resolution and are often limited by model geometry and can be very expensive to integrate into complex geometries. PSP provides

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704-435: The creation of the VDT could only operate at normal atmospheric pressures. As a result, scale models in early wind tunnels encountered air with Reynolds numbers that were off by a factor equal to the inverse of the model's scale (i.e. a 1:10 model would be off by a factor of 10). Without properly scaling the Reynolds number, the air flowing over a scale model would react very differently with a full-scale aircraft than it would in

736-436: The intensity response of the paint layer. The result is a dimmer fluorescence where there is higher pressure and brighter response at lower pressures. The intensity emitted from the surface is then recorded through a long-pass filter by a CCD or scientific grade camera and stored for conversion to pressure using a previously determined calibration. Images of the paint layer are recorded at three conditions. A wind-off image at

768-478: The model are measured, and are used to predict the response of an airplane when subjected to equivalent airflows. Automobiles are also subjected to aerodynamic testing in wind tunnels . Automobile companies use data collected in these tests to measure areas of high and low pressure. This data helps engineers improve designs to increase performance for the vehicles. By changing these designs, engineers can help improve gas mileage and reduce noise. In order to measure

800-493: The same drive motors. The drive motors power compressors to propel the air within the wind tunnel circuit. Because of this shared layout, only one UPWT test section can be used at a time. The three wind tunnels that are part of this system are: The Unitary Plan Wind Tunnel was declared a National Historic Landmark in 1985. The American West Coast aircraft industry quickly capitalized on the Ames Unitary Plan Wind Tunnel Complex. The famed Boeing fleet of commercial transports and

832-623: The surface can be obtained from outside the wind tunnel's test section, which means that the model need never be disturbed or touched in order to obtain the pressure distribution. Computer-aided photography can be used to produce false-color images , where the color range corresponds to the pressure variations. Due to the high cost of constructing airplanes , the first designs of proposed aircraft are usually subjected to aerodynamic testing in wind tunnels . In these tunnels, models (usually subscale) are subjected to airflows to simulate an actual airplane in free flight. The aerodynamic forces acting on

864-415: Was 2 + 1 ⁄ 8  in (54 mm) thick. The tank required 85 tons (77.3 tonnes) of steel. The test section was 5 ft (1.5 m) in diameter to match an existing NACA Wind Tunnel No. 1, which was an open-circuit tunnel operating at atmospheric pressure. The variable-density wind tunnel had a closed-circuit design with an annular return flow to minimize the volume of the tank. A fan powered by

896-566: Was able to accurately replicate how air would respond at full-scale. In 1920, the National Advisory Committee for Aeronautics brought Max Munk , a German aerospace engineer and student of Ludwig Prandtl at University of Göttingen , to work for them in America. After the end of the First World War , Munk required two presidential orders to work at NACA, and reportedly had difficulty adjusting to NACA's organizational structure, which

928-402: Was deemed obsolete in the 1940s and converted into a pressure tank for other wind tunnels. The VDT was decommissioned in 1978 and was declared a National Historic Landmark in 1985 because of its historical influence setting the foundation for the beginning of space flight. The tunnel was used for research for over 20 years, up to the 1940s. The VDT was mainly used to test airfoils as wing design

960-562: Was not as strictly defined as those in Germany. Regardless, he proposed his revolutionary Variable Density Tunnel design in the same year. The large, steel pressure tank of the VDT was designed with a working pressure up to 20 atmospheres and was constructed by Newport News Shipbuilding and Dry Dock Company in Newport News, Virginia . The tank was 34.5 ft (10.5 m) long and 15 ft (4.6 m) in diameter. The tank's wall

992-635: Was the most pressing problem in early aeronautics. Notably, the VDT produced the data for 78 classical airfoil shapes that were published in 1933 in "The Characteristics of 78 Related Airfoil Sections from Tests in the Variable-Density Wind Tunnel," NACA Technical Report 460. This data was used in designing American World War II aircraft such as the Douglas DC-3 , the Boeing B-17 Flying Fortress , and

Unitary Plan Wind Tunnel (Mountain View, California) - Misplaced Pages Continue

1024-527: Was the second wind tunnel at the National Advisory Committee for Aeronautics ( NACA ) Langley Research Center . Proposed by German aerospace engineer, Max Munk , student of Ludwig Prandtl , it was the world's first variable density wind tunnel and allowed for more accurate testing of small-scale models than could be obtained with atmospheric wind tunnels. The VDT was actively used as a wind tunnel from 1923 until its retirement in

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