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Why we love NACA ducts

Why we love NACA ducts Classic and Performance Car

Not just great looking but extremely functional, NACA ducts have appeared on some great cars. Here's why we love them

How could we not be enamoured to something that not only serves a practical engineering purpose but also looks so damned sexy? Admittedly home-made bonnets festooned with NACA ducts can look ridiculous, but think of their perfect symmetry on a Ferrari F40 or Lamborghini Espada bonnet, or adding such a muscular flash to a Countach’s flanks, heightening the impression of speed standing still. Better still, some say, a single bonnet inlet, not centrally located but nicely offset to one side.
That said NACA ducts have a very real job to do in cooling and airflow and they do it very well, not least because they do not create the drag that you get with a sticky-out airscoop.
The submerged inlet as it was initially called was devised by (and derives its name from) the US’s National Advisory Committee for Aeronautics and is believed to create vortices that drag in the faster moving air while barely disrupting its flow over the bodywork. We say “believed to” because precisely why its tapering ramped channel works better than other inlets is debated even today.
On which note, it was the subject of a confidential technical paper in October 1945 by a quartet of Americans who concluded that “an entrance of this type possess desirable critical speed and pressure recovery characteristics when used on a fuselage or nacelle in a region of low incremental velocity and thin boundary layer”.
Thanks to the general marvelousness of NASA (which succeeded NACA), you can download the full report here.
Words: John Simister

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