What happened to NACA ducts?

[Shrek]

When and why did they disappear. i was looking at old IMSA GTP cars and there are some of them that would have close to 10 duct on the body and i also thought the ducts reduce drag

[modbaraban]

I saw one on the roof of a Megane Trophy car. But the new model doesn't have it.

[Giblet]

NACA ducts are great for things like turbo inlets for air, when there is a draw in behind, but due to their nature they generate vortices as the air is funnelled in. They also play havoc on the boundary layer of air, effecting negatively any aero surface downstream of the duct.

While the NACA ducts do effect the air less then a protruding scoop, you lose any ram air effect that you would want in the air intake above the drivers head, and in the side pods where you want as much velocity in the air as possible. The faster the cold air gets in, the faster the hot air gets out, keeping temperatures lower than similarly sized NACA ducts.

It is called a NACA duct after the National Advisory Committee for Aeronautics, which was the precursor to NASA.

The Renault would have one for cockpit cooling, as that seems to be one of the last places they are used.

[DaveKillens]

x

[Shrek]

NACA ducts are great for things like turbo inlets for air, when there is a draw in behind, but due to their nature they generate vortices as the air is funnelled in. They also play havoc on the boundary layer of air, effecting negatively any aero surface downstream of the duct.

While the NACA ducts do effect the air less then a protruding scoop, you lose any ram air effect that you would want in the air intake above the drivers head, and in the side pods where you want as much velocity in the air as possible. The faster the cold air gets in, the faster the hot air gets out, keeping temperatures lower than similarly sized NACA ducts.

It is called a NACA duct after the National Advisory Committee for Aeronautics, which was the precursor to NASA.

The Renault would have one for cockpit cooling, as that seems to be one of the last places they are used.

i remember seeing the first designs for NACA ducts either in a book/computer i don't know bu they look way different than the one we use today

[xpensive]

I remember the original Lotus 72 with NACA-ducts for the inboard front-brakes in 1970, but not in later years, any idea why DK?

[DaveKillens]

The Lotus 72 was not only the most successful single design in Formula One, it brought in design changes that even today define a Formula One car. Sidepods and engine airbox never existed until the Lotus 72. When the 72 first made it's debut in 1970, it had the nose-mounted NACA scoops.

Looking closely you can see right through one of the scoops, and this indicates that there was no ducting feeding off the scoop. It just dumped the air into the general region of the front brakes. Interestingly, I believe this is also the first instance of "chimneys", used to exit hot air coming off the brake rotors. But the car required a lot of development work before it started to enjoy success.
In 1970 aero was still evolving, ground effects had not been discovered yet. So the chassis was a simple wedge, that's all, a low drag wedge. But even that was a huge step forward. Compared to a Lotus 49 with identical engines, the 72 was 12 mph faster in a straight line, all because of the decreased drag.
I have tried to investigate as much as possible, and it appears that the NACA ducts disappeared sometime between 1970 and '71. In the original design, both front and rear shocks were mounted inboard and low. The rear shocks were overheating, and were moved outboard. My theory (so far) is that the front shocks also had overheating and the entire front end was redesigned. During this redesign process it was uncovered that the NACA ducts were no longer required. Or maybe some bright chap duct-taped over the NACA ducts and discovered no difference in brake temperatures. Somehow I believe the simpler explanation was what really happened, it usually happens this way.

What a beauty. Take your time, soak it in. Inboard brakes, pullrods, hidden shocks, and rising rate torsion bars.

This car, the Lotus 72 created a lot of history. A front driveshaft is suspected to be the cause of Rindt's fatal crash at Monza, and ever since then, engineers have been very aware about this kind of failure and it's consequences.
In five years of competition, the Lotus 72 participated in as much as 6 seasons and 74 World Championship races but most of all the car owes its fame to its record of success – 20 Grand Prix wins, 2 Drivers Championships and 3 Constructors Championship titles.

And never forget that to many, the John Player Lotus was the most beautiful of all. I am one who agrees.

[Giblet]

Here they are on the fw11, right in front of the rear wheel.

[xpensive]

There is this wonderful story about Ronnie Peterson, arguably the master of the Lotus 72, and his well-known inability to set up a car properly. During a test-session, he came to the pits complaining the car was oversteering.

Colin Chapman and Peter Warr took off to one of the corners to see for themselves, just to discover that the car was actually understeering, but Ronnie was naturally compensating by setting up the car slightly sideways ahead of the corner.

After radically changing the settings, his times remained pretty much the same however.

[xpensive]

Back to topic, as I now can recall, I've read somewhere that Lotus discovered that those chimneys where enough for cooling.

Also that the NACA-ducts sort of "over-cooled" the discs on the straights, leading to hefty temperature-changes at breaking, something which the materials of the time couldn't cope with very well.

Could that be a plausible xplanation, DK?

[xpensive]

Are you aware that terrible monument by Richard Brixel, is within walking distance from my home in Örebro, Sweden, DK?

[Carlos]

"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. It is especially favored in racing car design.
Prior submerged inlet experiments showed poor pressure recovery due to the slow-moving boundary layer entering the intake. This design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotating vortices which deflect the boundary layer away from the intake and draws in the faster moving air, while avoiding the form drag and flow separation that can occur with protruding inlet designs. 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 intake application for which it was originally designed, (the North American YF-93 and Short Sherpa being exceptions.)" Wikipedia

The Scoop on NACA Scoops from FLYING magazine:
http://www.flyingmag.com/technicalities ... page2.html

The NACA (National Advisory Committe for Aeronautics) library of article/1917/1958.
Approximately 3000+ papers:
http://naca.central.cranfield.ac.uk/

NACA Scoop v1.1 Freeware Program
http://www.n1ut.velocity-air.com/progre ... index.html

[xpensive]

Thanks Carlos, great reading! The following was to my mind the best part, priceless;

"Other reasons are more frivolous. NACA scoops look nice. They don't appear to clutter up the surface of the airplane the way protruding inlets would. They at least seem as if they produce no drag. And that double-ogive with its gently sinking floor is an elegant shape that just feels aerodynamic in an undefined sort of way. Looks matter. When reason fails, follow your heart."

[timbo]

How about this car

[riff_raff]

The laws of physics have not changed recently, so NACA ducts work the same now as they did 20 years ago.

NACA inlet ducts can be very effective when designed and located properly. In order to function well, they must be located on a surface with relatively smooth airflow, with the streamlines in a favorable direction (ie. no yawing), and with a non-diverging surface. A modern F1 car does not have much body work that meets these requirements, so that's why you don't see F1 cars using too many NACA ducts now days.

Regards,
Terry