Compressed air for drag reduction ( Coanda slots )

[Joenavy85]

Originally Posted by Vwbeamer

How about steam? The rigs make a lot heat that is wasted already, looks like steam would act pretty much like compressed air....just thinking

might as well mod it to be like the Crower 6 stroke

[Nerys]

WOH now thats a good idea!! I was thinking crap no easy way to duct air to the back of the car without increase FA. but think piping is easy to use to transport STEAM. I wonder how much you would need to be viable. IE how much steam would I need to vent to have a measurable effect at 45mph for 80 minutes. how many gallons of water would that be? would simply wrapping the tubing around the exhaust give me enough heat? how would I control the water flow rate and keep it from simply pouring out before conversion to steam? is just wrap the pipe long enough to insure its steam?

would my little 3cyl even make enough heat for that to work?

VERY intriguing idea!

[DonR]

Would it be possible to use a double layer undertray as a duct from the front & then have it angle up sharply to the rear of the car? You could still run a shallow angle as a diffuser to manage under car air & have a "ramp" riveted onto the top to angle the air upwards into the low pressure area.

[gone-ot]

...look up NASA's "boundary-layer" wing tests.

[menaus2]

I like the steam Idea... Wikipedia says that from water to steam is about a 1600x volume increase. I think with a proper boat tail you might be able to get the air volume displaced at speed to the point where it could make sense. Hopefully you could do a major radiator size decrease or even delete and see weight savings. Air compression/steam is limited so to have any use is predicated on focusing on the aero first.

[Nerys]

Hmm thats not much 1600x means a cup would probably fill the suck zone but then you need at least a cup a second quickie math 3600 cups an hour or about 225 gallons.

damn won't work. 225 gallons masses 1710 pounds more than the mass of the car. DRAT. I was really hoping for something their.

[vacationtime247]

Found this interesting. Might be cool if you could stand the sound.
VT247

" Back in 1970 an innovative concept in automotive racing briefly saw the light of day before being deemed “unfair” and “illegal.” While the Chaparral 2J never dominated and often had mechanical issues, it opened a world of possibilities and a new way to think about aerodynamics.

The biggest problem with wings, spoilers, and other air directing instruments often used in motor sports is that the slower a car moves the less effective they become. With little air moving over the vehicle’s surface around a sharp road course how could someone overcome this simple but serious problem and achieve superior traction at any speed? Jim Hall came up with an answer- suction the car to the track. Using a skirt to trap air under the vehicle and suck it out the back, the 2J qualified seconds ahead of the next closest competitors in CamAm.

In honor of the historical 2J, a group of 13 engineers from P&G have created their own truly “sucky” car. This time it’s a Corvette. Adding a bit of irony is that this particular vette is twin turbocharged. So technically- it also blows.

Using an M1 tank blower powered by a 45-horsepower snowmobile engine, the 2J2 sucks air through a skirt under the car and out through the passenger seat. The team built the car as an entry into the Grassroots $2007 Challenge, which limited spending on the car at just $2,007. Yes, twin-turbocharged AND suctioned to the ground for just over two-grand. "

Cheaparral 2J2 – The twin turbo Corvette that sucks | autoinsane

[Piwoslaw]

That's a nice find, VT247. It's like taking an air dam to a whole new level.

But I'm afraid that the energy required to suck the air from under the car is much greater than any savings from reduced underbody drag. I remember reading (early-to-mid 90's??) that Mercedes (?) had wheels with fan blade shaped spokes to suck air out from under the car, but the losses from pumping air outweighed any gains.

[max_frontal_area]

Originally Posted by jamesqf

Perhaps this is already answered somewhere, and I missed it, but why go to the trouble of compressing air when you already have a large volume of hot gas under pressure, flowing out the exhaust? Just duct it to the appropriate places, making sure that it doesn't get into the cabin...

the amount of of tailpipe "jet propulsion" on a gasser is negligible. how do i know? i am glad you asked. cycled in traffic for many years. during the winter it is easy asses - especially if lightly dressed. on a bicycle you are quite sensitive to temperature specifically temperature fluctuations. imagine this if you will,
balancing behind a car at a stoplight which has its tailpipe pointed backwards.
awaiting the moment the car "launches" as SUV jockeys love to do, you do the same, providing you posses the skill and power to stick to the object for as long as you can. while feeling the air that has rushed around the car and joined with exhaust gases it is imperceptible to notice a temperature difference from the ambient air.
lets move up into diesel territory. 22:1 compression of a normally aspirated low compression diesel vs. 9:1 for an engine using spark plugs and a fuel which was specifically formulated not to combust.
the diesel dumps twice the air out the back! add a turbo running 15 psi or perhaps 30 on a modded engine. hmmmm!
pack in behind a pickup running that much boost and although they almost invariably have exhaust pipes pointed to the side or an angle now you can begin to feel the heat. on a large truck (class a and b) 3 atmospheres of boost are not uncommon and if somebody did their homework on aftercooling and decided utillize air to air charge cooling instead of using engine coolant you are actually feeding your engine oxygen molecules instead of hot air.
now you have something! however, this phenomenon only happens during periods of high boost. at crusing it once again becomes negligible besides big rigs and a lot of pickups shed their exhaust out the top. now if you consider
the enormous wake a large truck leaves behind everything gained by what i mentioned above and running the exhaust to the very rear pointed into the wake zone it all becomes peanuts again. UNLESS of course turbo chargers are re-utillzed to produce boost at all times instead of just being on demand power adders!!

if approached a like a complete system, carefully integrating all airflow related components such as always on engine cooling fans (which can use up to 50 horsies! on big rigs) various other heat exchangers of which i counted no less than EIGHT on a 2007 super duty, integrating airflow from all other componentry which sheds heat, the best up to date body aero design and naturally all external aero enhancements and bolt ons available to date,
high pressure relief ducting, and of course proper exhaust augmentation which is FINALLY being exploited - quite beautifully on F1 racers. along the way targeted CFD and finally wind tunnel verification. throw in some FE based driving clinics, because quite frankly the truckers i rode with drove
just like truckers speak

i feel tremendous change could be affected with careful approach and design
but one will have to STEP OUT to make it happen.

i know bigevilmart would buy 10mpg rigs

[max_frontal_area]

Originally Posted by DonR

Old Suburbans that had roll down glass in the tailgate exibited the same properties. Kept you cool too. As far as asphyxiation goes, Most trucks & SUV's have the exhaust turned to the side for this reason. A simple clamp on extension with a 90 degree bend should keep you consious.

Don

carbon monoxide, (CO) bonds to your hemoglobin PERMANENTLY!!!
the only way you can get rid of it is by doing a Floyd Landis oil change!
be careful playing with a gassers exhaust!