Why can't radiators be moved under the body?
 

I'm thinking of larger vehicles like pickups and SUVs here... (for improved fuel economy AND reduced emissions.)

To improve the front end aerodynamics on the bigger boxier vehicles why don't they cut the rad requirements into two - place a small wide radiator up front and then put a secondary backup radiator under the body of the vehicle? (It could easily be protected / armored to prevent rocks etc. from doing any damage. Maybe even laid inside the box frames on the heavier duty vehicles. Maybe the whole rad could go under some vehicles!!!)

Alternatively, they could go to LED headlights that span across the whole the front end and then stretch the radiator from fender to fender thus substantially cutting down on the required height.

1. Cost
2. Vulnerability
3. Value added to consumer greater than 1 and 2?

Plus underneath a vehicle like a truck, you have exhaust to contend with. It's proximity to said exhaust could heat the engine more.

In addition, you would have to engineer a way to get the air to pass through it to cool as a traditional radiator does which could make the airflow under the vehicle more turbulent that it already is perhaps hurting FE.

This is all speculation of course ...

seriuos off road trucks usually run fans in the pickup bed, but I fail to see the benefits on a road going vehicle. Since the radiator needs airflow, might as well bleed a little off the high pressure area on the front of the vehicle. It's the extra air that hurts the aerodynamics. Standard radiator placement usually also minimizes the radiator hose run.

Old Saab 92b's run radiators behind their 2 cycle 2 cylinder engine. This is vented to the cab as the heater core.

How about instead of a radiator that air flows through, they use a radiator that air flows OVER, with thin fins sticking up into the airflow?

Moving a standard rad to another location is not usually recommended, because it needs air flowing through it. A surface radiator, with air just flowing over it, has to duplicate the surface area of the regular one, which is considerable. If you are able to have true laminar flow over it, you need far more area. However, the usual case is a turbulent, but attached boundary layer. So, how to produce a large, contoured heat exchanger, able to contain pressurized fluid? The tube and panel solar collectors are a good model. It should be possible to make a composite panel using aluminized fiberglass (40% by weight) to improve heat conduction, and mold in coolant ducts that double as panel stiffeners. Vulnerability to damage is certainly an issue, as is weight, however, the potential savings are about 20% of the total drag. Perhaps a combined radiator/belly pan would make a good add-on, for more combined savings.

Bob, what about a radiator with fins sticking into the airflow like a heatsink?

http://www.epiacenter.com/pictures/r...atsink_800.jpg

Fins add surface area to the car overall, but they can keep the cooler more compact. That would be a compromise between the two designs. The 1911 Napier had external tubes, resembling fins on a surface.

It's probably not something that "can't" be done (or, said more correctly, it's probably something that "can" be done)... But I agree with Frank Lee... there is additional cost, there is additional vulnerability... and the consumer is the one that will pay for that... what is the benefit for the consumer? If the consumer is looking to buy a truck or SUV, then the consumer will have specific reasons for making that choice and it's unlikely that fuel efficiency and lower emissions are going to rank very high on that list. I would not want to pay extra for something that I don't even want.

i'd rather recommend a more ducted radiator, like in the p51 mustang fighter plane for example. i've noticed if you compare a modern engine bay is full to the brim, modern computer design to place all the components probably has to do with it... this means the average engine bay is almost 50% smaller than lets say that on a 60's or 70's car.

now modern cars make good use of this extra space to produce more interior space, but in theory one could have a reasonably dimentioned car with quite some space for ducting up front

a well designed ducts could lead to a smaller radiator and that could be placed lower underneath the car, the bottom of the duct being integrated in the undertray