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Old 02-08-2011, 07:05 AM   #71 (permalink)
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idealistic

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Originally Posted by SvdM View Post
So if I understand this correctly, he DID run faster because this mod helped more high pressure air to the back of the car into the low pressure area, thereby reducing drag?

Now it sounds like most posts here are theorising about almost eliminating the low pressure completely, but even reducing it by say 5% would be beneficial.

I (thus) still thing that ducting higher pressure air from the back of the radiator through a well made ram-air system, running parallel to the exhaust in the tunnel (not to increase FA) to the back, could be a positive rather than a negative, especially at highway speeds.

Yes / No
the ghias nose would begin bobbing at 120, an unpleasant occurrance at best.
i had my stock 71 VW fastback (similar round nose) up to 100 on one of the endless bridges in FLA and it was beginning to move around a bit!
as is common in elmo and b-ville depleted uranium is added anytime there
is a lack of traction as well as for suspension tuning, rather than designing
suspension for the intended purpose. the lead didnt do doo doo. and the turboed l4 rabbit gasser in the back where a modest air cooled engine used to be still had plenty of punch. therefore the implementation of the duct.
did he go faster because of drag reduction? invariably yes, by how much -
dunno. did the duct move air - hell yeah! eventually it allowed him to get up to 160MPH!

most cars have transmission tunnels whether utilized for their namesake or not. however clean airflow is always obstructed by lots of stuff.
exhaust pipes, cats, resonators, brackets, heat shields e.t.c. on a FWD
and a driveshaft, mounts, flexplates, u-joints e.t.c. on a RWD.
its very busy under there. now purposely route additional air through there and
your exhaust pipe will be cooled even more. 200f air coming off the back of your radiator is cool compared to what is inside your exhaust system especially once it has gone through a catalytic converter. also your radiator air will mix with ambient air along the way considerably cooling it. racers go through considerable lenghts to keep their exhaust pipes as warm as possible for max efficiency/power. some cars exhaust systems approach 20'. lots of potential for loss there. which is why most boneville rigs vent their exhaust right behind the front tire...

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Old 02-08-2011, 07:31 AM   #72 (permalink)
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proposed duct

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Originally Posted by Piwoslaw View Post
Exactly. I've thought about making a duct that would transport air from the high-pressure zone in front of the car to the low-pressure zone behind it, but then decided that there would be plenty of drag in the duct, and it wouldn't be doing anything that's not already happening under/around the car. Generating compressed air will have an even lower efficiency.
this duct you were planning on running, what was the cross sectional area like? what size were you intending it to be and where were its pickup and exit points going to be? was it to be used in conjunction with your beautiful kammback?

project groovy will eventually be outfitted with such a duct but in the meantime development will take place on my 80's rabbit which has an 4cm x 25cm oval opening inside the dashboard on the passenger side which is essentially the outside intake for the heating/ventilation air.
unfortunately by the time air has made it to this oval it had to turn downward and squeeze through vents below the windshield and then make another 90deg turn into the duct which would go to the rear window.
lots of resistance. the rear glass window would be replaced with acrylic
which could easily be modified with holes and slots.
of course this would be in conjunction with a kammback.

what were your thoughts?
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Old 02-08-2011, 04:20 PM   #73 (permalink)
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Henri Coanda

One of my aviation books had some info on Coanda.
Henri Coanda,Romanian inventor,built,and presented an aircraft of his design in Paris,1910.
The aircraft was powered by a 50-hp engine directly coupled to a centrifugal compressor.
The compressor developed 450-pounds of thrust,not enough to propel the plane.It never flew.
In 1911,Coanda presented a second aircraft of 150 hp turning a conventional 4-blade tractor propeller.This plane also failed to fly.
In 1912 Coanda relocated to England where he would work for Bristol Aircraft.
Coanda had great gifts with airframe ingenuity and construction.
Coanda is a cult figure among UFO conspiracy circles,and claims are made to the efficacy of disk aircraft constructed in late WW-II Germany which exploited the Coanda 'effect.'
PS I quickly ran the drag force for an 18-wheeler of Cd 0.70 and 95 square feet of frontal area at 70 mph at standard temp and baro pressure and came up with 957 pounds of aero drag.Using the centrifugal compressor,over 100-hp would be required to create an opposing air jet to cancel the drag.More to compensate for rolling resistance.
Reshaping the back of the trailer would accomplish the same thing with zero horsepower,although,certainly,it opens up other issues.


Last edited by aerohead; 02-08-2011 at 06:23 PM.. Reason: add data
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