radiator intakes

[Bill R.]

Hello everyone,

Life can sure get in the way of your dreams sometimes. I was thinking about radiator ducting. Most are in the front, some are on the top of the car and some are ducted from the side of the car.....Was considering a little thought experiment. Has anyone ever ducted air to a radiator from beneath a car? Like as in a NACA duct on a flat bottom. Just curious if anyone has ever tried this.

Bill

 

[Tom]

Bill,

Most high performance guys are focused on keeping air pressure underneath the car low to aid downforce. Dumping hot air from the radiator underneath the car is contrary to that goal.

That said, the F1 guys used to send hot exhaust gases into the diffuser to keep the airstream attached and energized under trailing throttle, but that is a very special thing, with both sophisticated aero hardware/placement, as well as specific engine management.

Tom

 

[Bill R.]

Bill,

Most high performance guys are focused on keeping air pressure underneath the car low to aid downforce. Dumping hot air from the radiator underneath the car is contrary to that goal.

That said, the F1 guys used to send hot exhaust gases into the diffuser to keep the airstream attached and energized under trailing throttle, but that is a very special thing, with both sophisticated aero hardware/placement, as well as specific engine management.

Tom

Actually i was thinking of the opposite. Not dumping hot air underneath the car but taking fresh air from there and running it through a radiator and dumping it out the back of the bodywork thus decreasing pressure underneath the car.

 

[Doug]

Corvette C5, to name just one, grabs the air for the radiator from under the front bumper. This works good, if you have that little plastic spoiler in place to create a low pressure area behind the radiator to draw the air through the radiator.

Using a NACA duct any further back than just under the front bumper, has been tried, but does not work very well. The road to undercarriage gap just does not have the volume of air that you need to cool the car.

 

[Bill R.]

Hi Doug,

Thanks for the reply. I suppose theres a reason why design ideas arent more wide spread.....They dont work! Intuitively it makes sense that there wouldnt be sufficient air beneath a car. Ive looked around a lot and cant find a specific example of that design idea though. Seems like most things have been tried. Do you know of a specific example of that configuration? Anyone know why corvette GTP (the mid engine corvette)style side intakes arent more widespread? Any significant disadvantage to that design?

 

[Doug]

Bill,

The most recent I have read about, and it was an older book @ 2006, was in Allan Staniforth's [ame="http://www.amazon.com/Race-Rally-Car-Sourcebook-Competition/dp/085429984X"]Sourcebook: The Guide to Building or Modifying a Competition Car: Allan Staniforth: 9780854299843: Amazon.com: Books[/ame].

There is a section on a Formula 750 car build by Ray Wilson the Omag 2/Reliant.

It was a pretty radical car, for its class and its time. He made the entire body/chassis out of a singe piece of laid up fiber glass (not many sections bonded together), very small rubber bushings in place of coil springs (I guess it had less than 1/4" of suspension travel, but the rules required that you could not have solid suspension) He was a successful go-kart racer and decided to apply what he had learned in karting to Formula 750 when he built his car.

One of the design features was to cool the car by a NACA duct below/between the two seats. The section goes in to far more detail about the suspension than about cooling/aero, but it does mention that the car did suffer from overheating and he later revised the cooling. The quote from the book is; "The underfloor NACA duct proved reluctant to feed the slightest draught (draft??) to the rear radiator which had to be moved to the front."

As for the Corvette GTP cars side intakes. I think you dont see more of this on street cars because on the GTP car the radiators are behind the passenger compartment. On most street cars they are in the front of the car. I suspect, YMMV, that this is because at high speeds you get great airflow over the front fenders and swirling off the windshield and down the side of the car where the air inlets get the benefit. Here is an example of the airflow with a Lotus Elise in a wind tunnel [ame]http://www.youtube.com/watch?v=_BnHXfvZVFo[/ame]

On street cars you dont get the constant speeds needed to produce this airflow over/around the car. At 20-30MPH the air just is not that organized. To overcome this you would need fans to get the flow. With the fans so near the passenger compartment it gets noisy.

Again, YMMV

 

[Bill R.]

Sounds like an interesting book! Like I said before.... if you can dream it, its probably already been thought of. Not a very innovative attitude but......Theres a lot of great information about what works and what doesnt especially when it comes to race cars. That video is very interesting with the air coming off the fenders going into the side intakes. Shaped by the wind! Beautiful car too. Probably should just buy one of those. Nahh I got to reinvent the wheel. Why?? Not sure... Just sounds like a fun thing to do. Its a good thing to create something beautiful and the process interests me too. Thanks for the info Doug!

 

[Bill R.]

Dont like cutting holes in it, ala Ferdinand Piëch.....But I think the radiator up front is asthetically and functionally the best way to go.

 

[Tom]

Bill,

Sorry about misunderstanding. Anyway, you want to draw intake air from a high pressure area, which puts you back to the same problem - if it is high pressure at the intake, it's probably high pressure just ahead of it, and very close to front axle line.

I think that is the very reason the intake on the Vette changed from underneath to in front - it made it harder for the racing cars to draw high pressure air for the radiator, while maintaining downforce.

The riddle I'd love to solve is how to vent high pressure in the front wheel wells without cutting holes in the top of the fender.

 

[Doug]

Bill,
The riddle I'd love to solve is how to vent high pressure in the front wheel wells without cutting holes in the top of the fender.

Your thinking to high. Do the DTM thing and put the vents at the bottom:thumbsup:

Sure, you may need to fab a shorter door.

 

[Bill R.]

Bill,

Sorry about misunderstanding. Anyway, you want to draw intake air from a high pressure area, which puts you back to the same problem - if it is high pressure at the intake, it's probably high pressure just ahead of it, and very close to front axle line.

I think that is the very reason the intake on the Vette changed from underneath to in front - it made it harder for the racing cars to draw high pressure air for the radiator, while maintaining downforce.

The riddle I'd love to solve is how to vent high pressure in the front wheel wells without cutting holes in the top of the fender.

Thats OK Tom! A pictures worth a thousand words! I've found 914 V8 conversions that vent the hot air from the radiator into the wheel well. Talked to a conversion guy about it too. He said even though the air is hot its still much cooler than the brakes. So brake cooling is not an issue.
For an all out race car im sure that wouldnt be great though. Seems theres always vents on top of the wheel wells. So adding pressure to that area probably wouldnt be advantageous either. Maybe vent it just behind the front wheels like the picture Doug posted. Was considering Has anyone ever shaped the wheel spokes into a high efficiency fan for drawing air from underneath the car? I think i've seen porsche wheels that function that way or was for brake cooling.... not sure. Anyways....def want a high pressure source of air for cooling. Thanks for the input!

 

[Bill R.]

Your thinking to high. Do the DTM thing and put the vents at the bottom:thumbsup:

Sure, you may need to fab a shorter door.

I like it! Looks like the driver would be in a super reclined position. I once saw an article about the GT40 and how the air was originally routed through the car was costing them "x" number of horsepower. It was a good amount! Someone came in and made it much more efficient.

I'm actually planning on making my car a one piece body. No doors. The whole body will come off to get at the bits and pieces underneath though.

 

[Doug]

Has anyone ever shaped the wheel spokes into a high efficiency fan for drawing air from underneath the car? I think i've seen porsche wheels that function that way or was for brake cooling.... not sure. Anyways....def want a high pressure source of air for cooling. Thanks for the input!

The Corvette C4 for one had them. I loved the idea and I am not sure why it fell out of favor.

If you are using a front mount radiator, I did like the thing the Porshe 911 was doing for a time. They had the radiator vents directly in front of the front wheels. The worked great as a aero front air dam that only worked at speed. I think it fell out of favor because you tried to get the air to turn a sharp corner to get to the exits, and air does not like to turn sharp corners.

Like a read once (paraphrased): without a fan you cant make air go anywhere, you can only suggest where you want it to go.

 

[Tom]

my old M5 has directional wheel covers to help extract air out of the rim, and pull air across the disc I think.

I know the Gardner Douglas guys had a wheel with a fan shaped center section, don't know if they are still producing them.

With regards to the DTM method of extracting air, I suspect that you need quite a bit of open real estate behind the wheel to allow the appropriate shaping to get the air out. I don't have the space in my car!
Something I had thought about was running a large silicon tube from the top of the wheel well to the back of the car where it would empty in a low pressure area. But it would have to be a big tube, which would be a pain to package. Even if the theory is vaguely correct, it might not work anyway.
Another possibility would be to run a smaller tube hooked to some vacuum generator. But now things are getting complicated!

 

[Bill R.]

Spud I know what you mean about mounting complexities. Im trying to stick with the KISS principle. Keep it simple stupid. It seems the simplest design is usually the most elegant and efficient way of doing things. Found a picture of 956 wheels that look like they're designed to extract air from a wheel well. Doug....thanks for the pictures and the input. I think your right about the nature of air and fans. Many Jet engines designs make the air go around some very sharp corners! Garrett TFE731 is a good example.