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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.
When properly implemented, a NACA duct allows air to flow into an internal duct, often for cooling purposes, with a minimal disturbance to the flow. The design was originally called a submerged inlet, since it consists of a shallow ramp with curved walls recessed into the exposed surface of a streamlined body, such as an
It is especially favored in
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
The National Advisory Committee for Aeronautics (NACA) was a United States federal agency founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved and its assets ...
(NACA), the precursor to NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
, in 1945.
Design
Prior submerged inlet experiments showed poor pressure recovery due to the slow-movingboundary 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 cond ...
entering the inlet. The NACA design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotating vortices
In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...
which deflect the boundary layer away from the inlet and draws in the faster moving air, while avoiding the form drag
Parasitic drag, also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and skin friction drag. It affects all objects regardless of ...
and flow separation
In fluid dynamics, flow separation or boundary layer separation is the detachment of a boundary layer from a surface into a wake.
A boundary layer exists whenever there is relative movement between a fluid and a solid surface with viscous f ...
that can occur with protruding scoop designs.
Aircraft applications
When properly implemented, a NACA duct allows air to flow into an internal duct, often for cooling purposes, with a minimal disturbance to the flow. The design was originally called a submerged inlet, since it consists of a shallow ramp with curved walls recessed into the exposed surface of a streamlined body, such as an aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
.
This type of flush inlet generally cannot achieve the larger ram pressures and flow volumes of an external design, and so is rarely used for the jet engine
A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
intake application for which it was originally designed, such as the North American YF-93
The North American YF-93 was an American fighter development of the F-86 Sabre that emerged as a radically different variant that received its own designation. Two were built and flown before the project was eventually canceled.
Design and de ...
and Short SB.4 Sherpa
The Short SB.4 Sherpa was an experimental aircraft designed and produced by the British aircraft manufacturer Short Brothers. Only a single example was ever produced.
The Sherpa was developed during the 1950s for the purpose of testing a nove ...
. It is commonly used for piston engine and ventilation intakes.
Automobile applications
It is especially favored in racing car
Auto racing (also known as car racing, motor racing, or automobile racing) is a motorsport involving the racing of automobiles for competition.
Auto racing has existed since the invention of the automobile. Races of various sorts were organise ...
design. (Practical guidance on designing and building NACA ducts for motor-racing applications) Sports cars featuring prominent NACA ducts include the Ferrari F40
The Ferrari F40 (''tipo'' F120) is a mid-engine, rear-wheel drive sports car engineered by Nicola Materazzi with styling by Pininfarina. It was built from 1987 until 1992, with the LM and GTE race car versions continuing production until 199 ...
, the Lamborghini Countach
The Lamborghini Countach () is a rear mid-engine, rear-wheel-drive sports car produced by the Italian automobile manufacturer Lamborghini from 1974 until 1990. It is one of the many exotic designs developed by Italian design house Bertone, w ...
, the 1996-2002 Dodge Viper
The Dodge Viper is a sports car that was manufactured by Dodge (by SRT for 2013 and 2014), a division of American car manufacturer FCA US LLC from 1992 until 2017, having taken a brief hiatus in 2007 and from 2010 to 2012. Production of the two- ...
, the 1971-1973 Ford Mustang
The Ford Mustang is a series of American automobiles manufactured by Ford. In continuous production since 1964, the Mustang is currently the longest-produced Ford car nameplate. Currently in its sixth generation, it is the fifth-best selli ...
, the 1973 Pontiac GTO
The Pontiac GTO is an automobile that was manufactured by American automaker Pontiac from 1963 to 1974 for the 1964 to 1974 model years, and by GM's subsidiary Holden in Australia for the 2004 to 2006 model years.
The first generation of the G ...
, the Porsche 911 GT2
The Porsche 911 GT2 is a high-performance, track-focused sports car built by the German automobile manufacturer Porsche from 1993 to 2009, and then since 2010 as the GT2 RS. It is based on the 911 Turbo, and uses a similar twin-turbocharged engin ...
, the 1979 Porsche 924
The Porsche 924 is a sports car produced by Porsche in Neckarsulm, Germany,from 1976 until 1988. A two-door, 2+2 coupé, the 924 replaced the 912E and 914 as the company's entry-level model.
Although the 928 was designed first, the 924 was t ...
Turbo, and the Nissan S130
The Nissan S130 is a sports coupé produced by Nissan in Japan from 1978 until 1983. It was sold as the Datsun 280ZX, Nissan Fairlady Z and Nissan Fairlady 280Z, depending on the market. In Japan, it was exclusive to Nissan Bluebird Store loca ...
. It is also prevalent in some motorcycle designs, such as the 1994-1997 Honda VFR750F
The Honda VFR750F is a motorcycle manufactured by Japanese automobile manufacturer Honda from 1986 to 1997.
The model was initially displayed to the press after the 1985 Bol d'Or before it was officially introduced in 1986. The motorcycle is ...
.
See also
*NACA airfoil
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 ...
* NACA cowling
The NACA cowling is a type of aerodynamic fairing used to streamline radial engines installed on airplanes. It was developed by Fred Weick of the National Advisory Committee for Aeronautics (NACA) in 1927. It was a major advance in aerodynamic ...
References
Further reading
* * {{refend Engine technology Aerodynamics Duct