18
$\begingroup$

I often see this particular shape for ram air inlets.

Here on an older 737

It's stretched on the newer 737's but still the same basic shape

A also see it a lot on cars.

1979 Camaro Z28

Lamborghini Countach

Is there some aerodynamic advantage to this shape, and if so why?

$\endgroup$
  • 2
    $\begingroup$ Note that the inlets on many cars are purely cosmetic. $\endgroup$ – Russell Borogove Aug 10 '15 at 21:57
  • 2
    $\begingroup$ @RussellBorogove As is probably the case with the Camaro. I always assumed it was intended to imitate the appearance of an aircraft inlet. But that's probably not the case with the Lamborghini! $\endgroup$ – TomMcW Aug 10 '15 at 23:14
  • 3
    $\begingroup$ @RussellBorogove on the camaro it feeds the engine air intake, the lambo uses it to cool the brakes. $\endgroup$ – ratchet freak Aug 10 '15 at 23:16
  • $\begingroup$ I was just saying that the shape of the Camaro hood scoop is probably that shape for cosmetic reasons whereas the brake cooling duct on the Lambo is probably much more carefully engineered for aerodynamics. $\endgroup$ – TomMcW Aug 10 '15 at 23:19
15
$\begingroup$

Those are called NACA inlets or NACA ducts. As wikipedia mentions:

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.

So yes, there is an aerodynamic advantage. As for the "why", if you're in the mood, you can have a detailed look at the original report (I'm not able to properly summarize it).

$\endgroup$
7
$\begingroup$

This specific inlet type is called a "NACA inlet", "NACA scoop" or "NACA duct", since it had been invented by Francis Melvin Rogallo at NACA in 1941 (PDF) and refined by scientists at NACA (now NASA) Ames. Its main advantage is its simplicity: It just needs a properly shaped cutout in the skin and a rounded rear edge, whereas the airscoops it replaces need carefully shaped contours.

The working principle is quite similar to that of a delta wing, only in this case the actual wing is missing, and is surrounded by sheet metal. But like on the swept leading edge of a delta wing, the swept left and right edges create a vortex which is swallowed by the actual intake at the rear of the cutout. This helps to create a lot of flow for the given area, even though efficiency is below that of a well-shaped airscoop.

The moveable flap in the middle of the cutout is for deflecting some of the air if less than maximum airflow is desired. This item is easy to manufacture, but reduces the efficiency of this type of inlet further.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.