NACA duct installation advise

[L66TEY]

I'm looking to install the present CC NACA duct to my 2010 R300D - aim being to reduce engine bay temperature. 
Anyone done this, or could offer some installation advise with do's and don'ts?
With thanks
Chris

[ScottR400D]

I stand to be corrected but I’m not sure that will achieve your aim. 

Firstly, I think the purpose, as far as CC are concerned, is to increase airflow to the intake on plenum cars. It’s too far back to feed air to the engine compartment. 

It’s also in an area of turbulence so won’t bring much air in anyway for any purpose. It’s probably little more effective than the mesh. NACA ducts need smooth airflow with a good boundary layer to work well. 

It might work a bit placed on the top of the hood near the front but unlikely to be any better then the current louvres. 

But if you like the look.......... 

[R400svn]

I love the look of these also and had wondered about fitting one to my sv to assist air getting to my air filter intake on the RBTBs as it all tucked under the bonnet unlike in the s3 

[David_Long]

From my wind tunnel exploits with Simon Mcbeath, and a discussion over this very issue, it may not work quite as you might expect. Your aim would be to remove air from under the bonnet, rather than force air in. The Caterham has low pressure above the bonnet so it is simply a case of adding some more apertures in the bonnet.  But you could also add a diffuser, or even a wing to help draw air out from under the rear of the car.

The NACA duct is often misunderstood and it works in two ways:  to slowing the air (and therefore increasing pressure) causing air to flow into the aperture, secondly it forms a vortex along its edge that 'rolls' more are in.   A pet hate of Simon was NACA ducts that stand proud of the surface - like the picture above - as it completely destroys the vortex. They need to be flush mounted.

[David_Long]

Some pictures  https://drive.google.com/file/d/1f-13BdE2xKW8Br8frZ5QKzlLYmJA3ZHc/view?usp=sharing  and https://drive.google.com/file/d/1h8onK9OLgJXL4PO0F2HJirVuLFBmesql/view?usp=sharing

[simon_h]

That particular naca duct was purely done for the intake to the airbox for the 485. It’s no worse than the teardrop vent but we needed a bigger hole that was in a different place to fit it all in. It’s surface mounted because they didn’t want a raw metal edge showing 

[ScottR400D]

You’re right David, the raised surface makes the duct useless. The edges of the aperture of the duct also need to have sharp edges to create the vortices from the boundary layer, where there is one.

I didn’t realise there was low pressure over the whole of the hood. As you say all that should then be needed is more holes. 

So it seems that this particular product, mounted as and where shown isn’t going to do much at all other than give a bigger hole as Simon says? Having now seen an under hood image of the 485 I see what he means. 

[David_Long]

The wind tunnel suggested that the rear of the bonnet has lowest pressure. I think the leading edge may be high as bonnets don't fly off when you forget to clip them up. The sides are high pressure too and that probably bleeds some way over the curved section.

[ScottR400D]

I would have thought the sides would be quite turbulent with the front suspension and wheel etc. 

[aerobod - near CYYC]

With the air brake, I mean windscreen on, the air pressure at the base of the windscreen and very rear of the bonnet will be high pressure compared with the aeroscreen, with lots of turbulent flow off the edges of the windscreen and significant low pressure behind (if the roof is off). I'm not sure if there is any area behind the headlights and suspension that could guarantee laminar flow across a NACA duct intake, more likely just a bit of a ram air effect due to the sloping sides forcing the air outwards and increasing it's pressure, without accelerating it appreciably (that would decrease it's pressure) due to the flat side profile from the edge of the nosecone to the scuttle.

[L66TEY]

Thank you all for your comments. 

Admittedly, like R400SVN, I do simply like the look - and now understand that CC haven't quite got this right from a true NACA duct effect perspective.

Hence, now not surprised to find CC is not listed here;
https://www.windingroad.com/articles/news/ten-of-the-greatest-uses-of-naca-ducts-in-automotive-history/

Having said that - surely the NACA duct on the 485 does a good enough job, as it complies with EU5 and has stonking performance.

My vision was to fit one each side, one for engine bay cooling (worth pointing out my 2010 model doesn't have the side mesh "breather") and the other to improve air flow to the inlet manifold - ala the 485. Albeit, I've realised the part only fits the bonnet contour on the inlet side.

However, I have to say Im now v intrigued by David's suggestion about adding a "Diffuser", on the basis of this reducing engine bay temperature (leading to an assumed increase in engine performance) plus they look IMO great - this sounds like another "want" modification. 

But without having the funds for a Reverie Carbon one, is there a cheaper aluminium one on the market  for the S3 chassis?
 

[timb2117]

Gosh I defer to my extremely knowledgeable colleagues above - however aesthetic is a personal thing and a diffuser on a road car, sort of goes against the less is more ethos.

I had a naca duct carefully mounted on nosecone brilliant to get air into air intake, also I note the lifted rear bonnets on many many rally cars - a mate measured big engine bay rally finishing changes v.s cooked engine -simply by leaving rear of his rx7 bonnet chocked open. Its about moving hot air out not ramming more in is my limited understanding. 

Maybe consider big fat extraction louvres along sides low down? particularly to help clear heat from the exhaust section, I have also had good results using silvered glass fibre heat protection wrap

on vulnerable areas around the exhaust (battery, sensors, rubber hoses, and passenger footwell all heat shielded to good effect.) Doesn't look as pretty but retains my precious external aesthetic. 

[Tazio]

As a first step, why not reduce the temperature at source, and ceramic coat the exhaust primaries?, and then consider making some sort of enclosed ducting behind the rad, to exhaust that source of heat out of the top of the nosecone, as per 620?

[Mrp]

Fit a 620 Nose cone ?

[admaraujo]

Didn't the CSR "extracted" radiator's hot air through the cut on top of the nosecone, blanking/conducting it through there?

[Toughie]

It does, indeed, as there's a big plastic deflector set at about 45 degree incline behind the radiator.  I don't know if that was Caterham's attempt to vent the hot air, or part of their attempt to reduce the amount of front end lift.  Presumably it's inducting air from under the front of the car. 

I do wonder if I could get cooler air in, somehow.

[Ed White]

I can offer a lovely carbon NACA duct if anyone is tempted.....

[L66TEY]

Hi Ed,
Always interested in carbon LOL.
What NACA duct are you offering, do you have a photo you could post on here?
Chris

[Curly]

In the need to increase airflow out of the engine bay I was wondering if reversing the ducts so the vent faced back along the side panels would allow air to flow through the radiator and then exit.

Just a thought  - but interested in the POBC knowledge

[L66TEY]

I like your thinking Curly. 

Especially as the CC NACA duct will only fit the "wrong" way round on the exhaust side (Duratec). 

With your suggested approach surely the NACA duct would do the same job (or perhaps even better) than the small side mesh that present Caterham's feature. 
 

[ScottR400D]

There’d be no aerodynamic effect from a ND fitted the wrong way round. 

I doubt it would be as good as a small hole with a mesh let alone better.  

As has been said, if there’s a real concern about under hood temperature it might be better to address the problem rather than try to alleviate the symptom. 

[Toughie]

That's a good point, Scott.  I wonder, if it were fitted the right way round, but upside down (so it sticks up from the bonnet) might there be a negative pressure in the slipstream, sucking the air out of the engine bay?

Though it would probably look fairly ugly.

[ScottR400D]

They just don’t work that way. NDs are not particularly effective if they’re properly made and optimally positioned let alone a poorly designed one, backwards, in the wrong place!! 

It was once said that “the NACA duct is only useful in applications where you really don't want much air, at least not as much as you hoped, and certainly less than you expect”.

That’s a proper one. 

 

[Toughie]

No, no.  Not backwards, I said upside down, to suck air out. 

But I do take your point, and that's a great quote, worth keeping in mind, thank you.

[pete_h]

The other approach I have seen is to extend the side skins by the engine bay outwards where they meet the cockpit, to leave a gap to allow hot air to escape.