Any benefit from air straighteners?

[Joenavy85]

Originally Posted by Frank Lee

I've read (IIRC Hucho) that a properly designed radiator inlet/outlet duct system can theoretically add thrust due to the addition of the heat energy. Since they said "theoretically" I take it nobody has done it, or measured it?

It has been done on Air Racers (P-51 Mustangs primarily) at Reno using the same concept (and using heat from the oil cooler as well), but I don't recall hearing about how much it helped the speed, if at all. It makes sense to me in theory, I would imagine the ducting would have to be precisely shaped to minimize any drag on the way out, I would also imagine that it would take up a fair amount of space which would make it impractical for smaller cars.

[winkosmosis]

Originally Posted by Frank Lee

I've read (IIRC Hucho) that a properly designed radiator inlet/outlet duct system can theoretically add thrust due to the addition of the heat energy. Since they said "theoretically" I take it nobody has done it, or measured it?

That said, I don't know all the ramifications (pun!) of having such a system.

I do recall that my '64 Spitfire had nicely ducted flow to the radiator, probably to help a marginal cooling system with marginal inlet area get the job done. Careful attention to ducting may allow a smaller radiator to work, or allow the energy-consuming fan to come on less. But if the vehicle doesn't have a cooling system deficiency I don't know what gain there could be.

How is that possible? The expansion of the air isn't directional, so it's just as much pushing forward as backward

[ncs]

Meredith Effect - Wikipedia, the free encyclopedia

The P51 Mustang is suppose to benefit from it as well.

[aerohead]

Originally Posted by Peter7307

Daox,
The idea is the put the air straightener ahead of the radiator to introduce "clean air" (in the aerodynamic sense) to the matrix as opposed to having the radiator sit in a disturbed air flow.

Bill,
I don't have a picture or a link.
What I had in mind was a box structure to sit ahead of the radiator and let the air enter the radiator in a more controlled fashion.
The logic being this would then allow a smaller radiator for the same job.

Most formula car designers go to great length to make sure their radiators sit in clean air within the limitations of the rules so this is an extension of that idea.

The best I can think of just now is a lightweight box the same dimensions as the radiator matrix. Into this box is a series of tubes or vanes to direct airflow similar to an egg crate arrangement used to separate glasses or bottle inside cardboard boxes.

Peter.

Peter,remember,F-1 cars/Indycars ,are horrifically dirty aerodynamically.When on 'traffic' it's hard to get any ram air due to all the turbulence.Not a problem for passenger cars separated by a safe distance.

[Pendragon]

Originally Posted by Joenavy85

It has been done on Air Racers (P-51 Mustangs primarily) at Reno using the same concept (and using heat from the oil cooler as well), but I don't recall hearing about how much it helped the speed, if at all. It makes sense to me in theory, I would imagine the ducting would have to be precisely shaped to minimize any drag on the way out, I would also imagine that it would take up a fair amount of space which would make it impractical for smaller cars.

The many time National Champion Formula One Air Racer, Nemesis, was designed by a group of guys who worked at the famed Lockheed "Skunk Works". The ducting (for an air cooled engine) on Nemesis was sufficiently complex that they told people that they could show it to them and they still would not understand it.

Many automobiles wind up with high pressure areas in the engine compartment that complicates both cooling and aerodynamics. Several production automobiles are now incorporating automatic temperature controlled louvered grill systems to deal with aerodynamics without the risk of a too small grill opening.

[lunarhighway]

found an image of the standard p51 radiator. as far as thrust goes, i believe this setup did indeed generate enough thrust to cancel out the radiator drag. on early fighters radiators where often placed in locations where the propeller caused undesirable airflow that limited cooling, giving the need for even bigger radiators and thus more drag.(think of planes like the german stuka the hawaker typhoon or the p40... the later famous for the shark teeth painted on the radiator housing) on the p51 the radiator was moved back to clear this area and carefully designed so that the small intake supplied the needed airflow and the heated air provided enough thrust to cancel out the drag so the sum of all there things meant the radiator didn't add to the overall drag, wich made this a very fast, but also economical plane, because good fuel economy meant these planes could escort the bombers deeper over ememy territory

keep in mind that these where masive engines running for hours,generating a lot of heat, and while this heat energy was usually wasted, it energy still came from the fuel. the more efficient an engine will be the less heat there will be generated and the less potential for thrust. but also the less cooling drag will be needed so

i don't think normal car engines and driving conditions will lend itself well to harvesting this effect, but a propperly ducted radiator should improve cooling and reduce drag when done right

[mort]

I hope somebody can make something automotive out of this, but...
The p-51, for example, cruises at over 300 mph and uses about 1000 hp to do that. The heat coming out of the radiator is about 70 hp, and assuming the outlet nozzle for this Meredith Effect is not a de Laval (supersonic through the throat) I think the highest theoretical efficiency is about 10% So it seems that the radiator drag was under 7 hp to begin with.

Applied to a car, the lower speed, lower heat and styling constraints make it look very difficult. I'm guessing that at cruise a normal car sees about the same amount of drag due to the radiator as the amount of heat dumped through the radiator.

-mort

[Peter7307]

Thanks to all who posted.

Peter.