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The NACA cowling is a type of
The NACA 
The test aircraft, a Curtiss AT-5A Hawk biplane, featuring a Wright Whirlwind J-5 radial engine, reached an airspeed of equipped with the NACA cowling compared to without it.
The idea that the NACA cowling produced thrust through the
''The high-speed frontier: Case histories of four NACA programs, 1920- SP-445, NASA (1980), Chapter 5: High-speed Cowlings, Air Inlets and Outlets, and Internal-Flow Systems: The ramjet investigation
/ref>
Abstract of NACA TN 301 report and .pdf file
Archive of NACA reports 1917-1958
{{Aircraft components Aircraft aerodynamics Aircraft components
The NACA cowling is a type of aerodynamic
Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...
fairing used to streamline
Streamline may refer to:
Business
* Streamline Air, American regional airline
* Adobe Streamline, a discontinued line tracing program made by Adobe Systems
* Streamline Cars, the company responsible for making the Burney car
Engineering
...
radial engine
The radial engine is a reciprocating engine, reciprocating type internal combustion engine, internal combustion engine configuration in which the cylinder (engine), cylinders "radiate" outward from a central crankcase like the spokes of a wheel. ...
s installed on airplane
An airplane (American English), or aeroplane (Commonwealth English), informally plane, is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, Propeller (aircraft), propeller, or rocket engine. Airplanes come in a vari ...
s. It was developed by Fred Weick of the National Advisory Committee for Aeronautics
The National Advisory Committee for Aeronautics (NACA) was a United States federal agency that was founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved and its ...
(NACA) in 1927. It was a major advancement in aerodynamic drag
In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or b ...
reduction, and paid for its development and installation costs many times over due to the gains in fuel efficiency
Fuel efficiency (or fuel economy) is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical energy, chemical potential energy contained in a carrier (fuel) into kinetic energy or Mechanical work, w ...
that it enabled. NACA won the 1929 Collier Trophy
The Robert J. Collier Trophy is awarded annually "for the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance, efficiency, and safety of air or space vehicles, the value of which has been t ...
for its development.
History and design
The NACA cowling
A cowling (or cowl) is the removable covering of a vehicle's engine, most often found on automobiles, motorcycles, airplanes, and on outboard boat motors. On airplanes, cowlings are used to reduce drag and to cool the engine. On boats, cowlings ...
enhanced speed through drag reduction while improving engine cooling.
The cowling consists of a symmetric, circular airfoil that is wrapped around the engine. In a normal planar airfoil, like a wing, the difference in airspeeds, and their associated changes in pressure, on the top and bottom surfaces, enhances lift. In the case of the NACA cowl, the ring-shaped airfoil is positioned so this lift effect is forward. This thrust does not fully counter the drag of the cowl but greatly mitigates it.
The difference in airspeed on the two sides is due not only to the shape of the airfoil, but also the presence of the cylinders on the inside surface, which serves to further slow the airflow. Nevertheless, the total airflow through the cowl is generally greater than it would be with no cowl as the air is sucked through the cowl by the air flowing around it. This has the side-effect of keeping the fast moving air primarily on the cylinder heads where it is most needed, as opposed to flowing between the cylinders and crankcase where it does little for cooling. Furthermore, turbulence after the air passes the free-standing cylinders is greatly reduced. The sum of all these effects reduces drag by as much as 60%. The test conclusions resulted in almost every radial-engined aircraft being equipped with this cowling, starting in 1932.
The test aircraft, a Curtiss AT-5A Hawk biplane, featuring a Wright Whirlwind J-5 radial engine, reached an airspeed of equipped with the NACA cowling compared to without it.
The idea that the NACA cowling produced thrust through the Meredith effect
The Meredith effect is a phenomenon whereby the aerodynamic drag produced by a cooling radiator may be offset by careful design of the cooling duct such that useful thrust is produced by the expansion of the hot air in the duct. The effect was di ...
Meredith, F. W: "Cooling of Aircraft Engines. With Special Reference To Ethylene Glycol Radiators Enclosed In Ducts", Aeronautical Research Council R&M 1683, 1936. is fallacious—although in theory the expansion of the air as it was heated by the engine could create some thrust by exiting at high speed, in practice this required a cowling designed and shaped to achieve the high-speed exit of air required (which the NACA cowling was not), and in any case, at 1930s airspeeds, the effect was negligible.Becker, J.''The high-speed frontier: Case histories of four NACA programs, 1920- SP-445, NASA (1980), Chapter 5: High-speed Cowlings, Air Inlets and Outlets, and Internal-Flow Systems: The ramjet investigation
/ref>
See also
*NACA airfoil
The NACA airfoil series is a set of standardized airfoil shapes developed by this agency, which became widely used in the design of aircraft wings.
Origins
NACA initially developed the numbered airfoil system which was further refined by the Un ...
*NACA duct
A NACA duct, also sometimes called a NACA scoop or NACA inlet, is a common form of low- drag air inlet design, originally developed by the U.S. National Advisory Committee for Aeronautics (NACA), the precursor to NASA, in 1945.
Design
Prior su ...
*Townend ring
A Townend ring is a narrow-chord (aircraft), chord cowling ring fitted around the cylinders of an aircraft radial engine to reduce drag and improve cooling. It was patented in 1929, and found use on various aircraft of the 1930s and into the 1940s ...
References
Other source
*Aeronautic exhibit inSmithsonian Institution
The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums, Education center, education and Research institute, research centers, created by the Federal government of the United States, U.S. government "for the increase a ...
, Washington, D.C.
External links
Abstract of NACA TN 301 report and .pdf file
Archive of NACA reports 1917-1958
{{Aircraft components Aircraft aerodynamics Aircraft components
Cowling
A cowling (or cowl) is the removable covering of a vehicle's engine, most often found on automobiles, motorcycles, airplanes, and on outboard boat motors. On airplanes, cowlings are used to reduce drag and to cool the engine. On boats, cowlings ...