aero-mods,installment#9(internal drag)
 

Note from Darin (admin): this installment is part of a series posted by Phil (aerohead) about the effectiveness of various aero mods - usually with quotations and citations to source data.

See the Aero mods data index here.

End note.

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More debris from the library. As always, it's a mixed bag spanning a few decades. The numbers should stand on their own merits, as they come from the big-boys. My own tidbits are courtesy, Southern California Timing Assoc., official timers for all F.I.A. land speed records. Images will come later, sorry! Many of the vehicles can be found through GOOGLE Images.

There's not a lot of info, so this will go pretty quick. Thing is, people have thought about these things and "looked into it". As George Santayana said, "those who refuse to learn from the past are doomed to repeat it." There's no reason why any ecomodder should waste time going down a trail that's been thoroughly flushed out.So here we go,and I hope it helps.

Internal-Drag

1938, windtunnel tests on the Adler/Jaray (on the car lots in Germany) demonstrate that blocking the grille achieves a 15-percent drag reduction, dropping the Cd from 0.38 to 0.32.

Walter Korff, in his recipe for a Cd 0.21 passenger car suggests that an idealized cooling system,with airtight inlet and outlet ducts properly positioned, can cut drag by 7.7-percent.

1963, Kelley and Holcombe, of GM suggest "The ideal circuit for an engine-radiator internal flow system requires a smoothly edged, clean intake opening that leads to a completely enclosed diffusing duct, permitting the velocity energy to be converted to pressure energy with low losses, minimum pressure drop across the radiator, and is directed into a contracting duct that exits the air at a convenient low pressure. It should be possible to accomplish the engine cooling job with little or no net loss in an efficient system."

1973, CAR and DRIVER's Pinto picks up an added 0.40 mpg with an optimized grille-block.

April, 1975, C and D's aerovan Dodge picks up a 3-percent drag reduction with optimized grille-block.

1975, Dr.Alberto Morelli designs all the best features into the cooling system of the CNR "banana-car", cooling system losses are cut to 0.008. Morelli observes losses in production cars up to 0.1. On CNR, an air-tight 4:1 diverging inlet duct, and four, air-tight converging exit ducts are positioned on the car such that air bleeds into surrounding air at same velocity.

1986, Fiat windtunel studies of large-scale models show cooling system drag at 6.9-percent. Sealing the system only cuts drag by 1.2-percent, as upper-body drag increases.

1987, Bridgestone/Firestone Test Track, Fort Stockton, Texas,U.S.A., In closed-course, l and speed record attempt, GM tapes-off cabin ventilation NACA inlet to minimize aero drag. Driver, A.J.Foyt, can only tolerate 5-laps in the car at a time before being overcome by alcohol fuel vapors.

July, 1991, Bonneville International Speedway, Wendover, Utah, the Phil Knox, 1984 HONDA CRX, 1.3-liter experimental streamliner : air-cleaner deletion returns no measurable improvement to top speed ( internal-internal flow).

Hucho publishes that cooling system drag can me minimized to 2-percent,drag as high as 10-percent has been observed.

General note, all NASCAR teams use the Korff/Kelley-Holcombe/Morelli/American Aviation P-51 air-tight divergent inlet duct. Kamm and others, since the 1930s have used critically-cited exit ducts for the exit flow. Ford and GM PNGV cars use rear, quarter-panel heat-exchangers to dispense with front grilles altogether, for sub-Cd 0.17 bodies. The Olds AEROTECH uses "ideal" heat-exchanger inlet and outlet ducts, borrowing from aviation oil-cooler technology and probably has no drag at all due to thrust from expanding air mass.

Cooling system drag constitutes about 12-percent of overall aero drag and its been demonstrated that it can be eliminated. Its under the hood and out of sight, but its something to think about.

Another great post with some valuable stats. Thanks for digging through the stacks.

And Phil: good news! The forum upgrade did in fact include individual photo galleries. I will be testing it out, then importing the MaxMPG images to your gallery.

Hi,

A great example of this type of cooling is the Britten V1000 motorcycle:
http://www.nzedge.com/heroes/images/jkb-bathurst.jpg
The air enters in the small ducts in the nose of the fairing, and the (small) radiator is located under the seat, and the hot air exits out the duct "stinger" at the tail of the motorcycle.

This motorcycle is totally amazing btw: custom engine (producing 165 horsepower at 12,400 rpm -- with no need for counterbalencers) is a stressed member (it IS the frame, really!), the front and rear suspension are carbon fiber girders with the suspension travel provided by linkage, the wheels were handmade with a "skin & bones" carbon fiber structure, and the aerodynamics (dubbed "torpedo over a knife edge") was unusual and ground breaking.
http://www.nzedge.com/heroes/images/jkb-queenstown.jpg

Hi,

Another tie-in with this thread is the Crower 6-stroke engine:

http://en.wikipedia.org/wiki/Crower_six_stroke

Once it warms up, it injects water into the cylinder, which expands as steam, producing a second power stroke, and cooling the engine at the same time. There is no need for a radiator, or a cooling system, as such...

Wow.

pretty cool. I believe indy cars also use the engine as a stress member. Totally changed my thinking when I found out.:o

maybe this will help illustrate things a bit

(I will try and get option B setup on my car)

http://www.killrobot.com/images/rad_air.gif

version C
 

Version C is what Walter Korff,and the GM Research Labs guys were promoting back in 1963.This is also what Morelli did with the banana car,although he had exits underneath too.Kamm pioneered the principle in the 1930s,and this allowed the flow over the roof of the car to be good enough for the K-car form to work.Great image,thanks!

Be sure to read the AUTOWEEK article at the link further down the page.

“Especially an 18-wheeler, they’ve got that massive radiator that weighs 800, 1000 pounds. Not necessary,” he asserts. “In those big trucks, they look at payload as their bread and butter. If you get 1000 lb. or more off the truck…”

Offsetting that, of course, would be the need to carry large quantities of water, and water is heavier than gasoline or diesel oil. Preliminary estimates suggest a Crower cycle engine will use roughly as many gallons of water as fuel.

And Crower feels the water should be distilled, to prevent deposits inside the system, so a supply infrastructure will have to be created. (He uses rainwater in his testing.) Keeping the water from freezing will be another challenge.

The wiki article already mentioned that keeping the water out of the oil will be a big problem. It will be a HUGE problem. You can add piston rings, but that adds friction to be overcome. Any steam that gets by will condense in the oil, which will then have to be filtered out.

This (digitaldissent) is close to an idea i had a while back. It's a theory so here goes!
Hypermiling doesn't work an engine hard does it? So remove the radiator and install a custom built (tubular?) heat exchanger that the engine air intake draws air through. As it draws its air through the heat exchanger, the engine coolant is pumped around like in a radiator, cooling the coolant and warming the air to the engine. Then in the space the radiator was in, re-build the belly pan so it slopes up in front of the engine, to the underside of the bumper, thereby creating a pointy front end on the car and hopefully improving aero. The new "radiator" will need cool fresh air to maximise cooling and so that the air going to the engine isn't flaming hot! So an intake in the nose is used.
Does any of this make sense? I suppose the idea came about because of the drag a radiator places on a car. I thought maybe i could remove the rad. Then how was i going to cool the coolant? Simple: stick a radiator in the air intake. Does anyone here have a grasp of the approx heat output from an engine and how much of that heat could be directed back into the engine safely via the air intake?
This might not work at all but we've got to keep trying right?!
Maybe i'll try it before i de-commission the civic next year....

ollie

do a search on Smokey Yunick and look at some of his engines :thumbup:

vtec-e:

Engines typically reject equal amounts of energy through the drivetrain, exhaust, and cooling system. This is pretty typical of the "30%" efficient internal combustion engine. That means that if you are utilizing 80 kW to maintain speed or to accelerate your vehicle, at that time you must be rejecting 80 kW of energy through cooling or your engine will heat up until you require less power.

I don't think this will work, because you will be rejecting heat to air that will then circulate through your engine. This will return a substantial portion of the heat to the engine block, plus hotter air is less dense and will greatly diminish power, not to mention the decreased volumetric efficiency created by pulling air through a heat exchanger.

More gains are to be had by utilizing advanced lightweight radiator designs, appropriate ducting, electric water pumps and fans, and you'll be less likely to blow up your engine.

Thanks MechEngVT. I kind of figured it might be a bit much but didn't have the figures to test the theory. Ah well, back to the drawing board...

ollie

Problem is, you have to design the system to handle the worst case, which might be for instance climbing over a Sierra pass on a hot summer day - something I do quite often, as it happens.

I drive an Insight, and have a ScanGauge which is usually monitoring coolant temp. (I run a partial radiator block most of the year, taking it out for climbs in spring & fall.) On level ground it will maintain its 195F thermostat temperature, unless it's pretty cold, so you could get away with a size reduction akin to my block. On a long climb, though, temps can go to 208-210F. With a smaller radiator, they'd go even higher.

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Something I've wondered about is whether the heated air could be exhausted at strategic locations in order to reduce drag. It seems you'd have a mild ramjet effect, since the air going through the radiator is heated, and so expands. Some of the diagrams seem to be taking advantage of this, but is there anything more explicit?

Yes, and although it doesn't look like it in the diagram that's exactly what setups B and C are attempting to do. In diagram B, it's showing the ducted expansion air exhausting around the front tires which can disrupt the turbulence that exists without a wheel skirt.

In setup C the idea is to take high pressure air from in front of the air dam, duct it through the radiator, and duct the warmed air out through hood-top vents into the low pressure area that typically develops above a car's hood. In a lot of racing applications the nose is blunt with a flat hood (stock cars, touring cars, side pods on open wheel) rather like a lot of production vehicles. This generates a low-pressure zone on top of the hood and causes frontal lift. Extending front air dams and installing chin splitters helps counter act this by reducing air flow underneath the car, but as shown in diagram C ducting the stall pressure air from the nose through the cooling system and injecting it into the low pressure zone will equalize the pressure. I'm convinced this is the most effective method. I've seen it work in a small-scale open wheel bike-engined car where designs A and D had caused repeated overheating issues, a switch to design C in a side pod with a smaller radiator produced reliable driving for hours on end. Granted this was in a vehicle that never saw above 50mph for more than 2-3 seconds so aero was not much of a factor the cooling performance worked very well.

DIY hood vent
 

I'll go with option C and I'm thinking to make hood vent like this guy http://www.240sx.org/links/installs/hood/hood.htm
http://www.240sx.org/links/installs/hood/hood12.jpg
What do you guys think about this mod?

I would guess that you'd also need an underbelly pan to close off the downward flow?

I sure wish I had a good CFD program, and some accurate numerical models of car shapes...

I have installed my belly pan few weeks ago. Now it's time for my hood vent mod. I don't know yet how wide should I cut opening and how much to open. I guess radiator width and an open an inch. Need some advise, please.

Anybody with advice please.

Here's a good shot of "option c" on the Ford GT:
http://www.rsportscars.com/eng/artic...t_heritage.jpg

The intake opening on the front vs the hood exhaust opening seems to be roughly equivalent. Also seems to have a much gentler slope where it returns to the over-hood flow than that Nissan.

Once I get the time/money/space/balls to play under my hood, I'd probably go for "option B".

Per Hucho et al, that vent would work best if moved forward about a foot. Air incoming at the highest pressure stagnation point on the nose, then drawn out at the lowest pressure point right about at the leading edge of the hood.

This will also draw off that pesky under-hood hot air, keeping the intake manifold cooler, for better performance.

My Porsche 944 Turbo is similarly shaped, and its turbo intercooler is under a header panel between the pop-up headlights, so I plan such a vent to extract air in similar fashion.

@holypaulie

you should check out autospeed.com

they did some articles on hood vents. wich where pretty well researched
if you want to get it all right you should measure the pressure in different locations under and on the hood to see where the vent needs to be, finding the right spot is much more important than getting the right shape i think .

also this may show your car has other areas like the wheelwells wich you might (also) use to your advantage

low pressure spot
 

Thanks for the info lunarhighway. I've just find out the best spot it would be close to the upper grill. Look at the picture, the blue color is low pressure area, green is high pressure and red is the highest pressure area.http://us1.webpublications.com.au/st...1/2162_6lo.jpg

Hi,

Here's another example:

http://upload.wikimedia.org/wikipedi...s_Elise_S1.jpg

I think the location differs depending on the SHAPE of the nose?

Methinks inlet at red, outlet at purple, or put the vent about a foot forward of where it's shown on that picture of the 240SX.

Do I have my low pressure color (purple) wrong?

Otto you are right.
Here is a picture showing where I am going to make a cut on my hood. I think that's the closest I can get. If I move more down to middle, my exhaust manifold will rust after rain.
Upper grill block and half of the lower one is already blocked(pic is not showing my car)

Under the hood
 

I could cover additional exhaust manifold with thin aluminium to protect from rainhttp://photos.ebizautos.com/6234/3075479_23.jpg

My Westfield Seight has a fully ducted nose cone rad with ducted outlet onto the top of the nosecone. Its a really smooth transition with an angled rad and does work very well.

The rad has a pre & post glassfibre moulded duct that bolts onto it. Something like the attached drawing

A pic of the outlet herehttp://www.seight.com/images/david/car1-eng.jpg

AXMonster, I think the little drawing with your previous post is one of the better ideas. I think that's how all the production heat extractor hoods are set up.

Why not do a cowl flap? That's what NACA designed for reciprocating aircraft engines such as B-17, B-29, etc.. In other words, put a hinge on the leading edge of the rectangular piece you cut out, and control its upward deflection with a cable or just let Mother Nature set the angle as a consequence of pressure differential below and above the flap. Do internal exit ducting with Coroplast or similar to make a smooth exit path. You want the exiting air to be as parallel to the slipstream as possible, i.e., point it to go smoothly back over the hood. The only downside is that such heated air may be drawn into the cabin via the vent inlets of the high pressure area just in front of the windshield, but that won't amount to much if you are not racing.

When parked, the cowl flap sits in flush position with the same contour it now has, and keeps the rain out.

That's what I plan for my Porsche 944 Turbo, which has a well engineered intercooler inlet, but they sorta forgot about the outlet. Stock, the cooling air is supposed to find its way somehow down and out the bottom of the engine bay past various obstructions to flow. Ungood, especially since heat rises. I figure that in addition to sucking the spent intercooler cooling air out, it will also draw off radiator and underhood air, with otherwise heat soaks the engine. BTW, this reduces nose lift on the car, as undercar flow and pressure is reduced, and the flap also acts as a lift spoiler for the hood. So, she rides a bit lower, less drag from that and less lift on the nose for better high speed handling. Win, win, win.

For a hinge(s), I'm considering those nylon ones used on RC model aircraft from a hobby shop. Gonna fix it in position on the underside of the sheet metal BEFORE I make the cut. That way, I know the flap alignment will be perfect.

What do you think?

I see your are very creative and I think that's interesting idea.
PROS:
- fixed rain issue
- reduced front lift
- better radiator air flow
CONS
- more cutting
- require ducting
- require holes for hinges
- less airflow at low speed or traffic
How to mount those hinges to the flap without drilling a holes? How to prevent flap falling inside (down) ?

Epoxy or JB Weld is your friend: no holes to drill. Ducting via Coroplast and duct tape, or aluminum foil tape. With push-pull cable (from bike shop) adjust cowl flap angle. Add (with JB Weld) small lip to keep flap from falling down. Cut one more slot beyond the 3 you were already gonna cut.

How to cut? Dremmel tool? Laser? Router? Hi pressure water jet? This would require a practice run on a scrap piece of metal, using tape to protect the paint surface. Properly done, you would only need to use touch up paint to color and protect the edges after the cut, to prevent rust on the exposed metal edges. Probably best to remove the part from the car and do the work on a bench. Probably worthwhile to ask somebody who does custom body work for input, or artist who works in sheet metal. Probably best to position the hinge on the cut line before making the cut, to make sure all is in perfect alignment after the cut.

Thank you very much for details Otto. Your plan require good skills, a lot of work and spent some money. Too much hustle more me, though. I don't know if is worth it.

http://www.240sx.org/links/installs/hood/hood3.jpg

Those cuts across the support members look like they will take away a lot of the strength of the hood.
It might actually bend the hood if someone slammed it shut too hard.

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http://www.240sx.org/links/installs/hood/hood13.jpg
That looks like a screen mesh inside the vent. If it is, surface turbulence on the mesh might restrict air flow. I would try it first, without the screen.

Those are observations of a novice. Likely to be wrong. :eek:

Cheers,
Rich

limited space
 

Today I have checked my underhood and I can tell there is not much room. On the left side is air intake resonator, on right is air conditioning pipe. Maximum width that I can make a cut and bent it down freely is about licence plate width. I marked on pix where bent would be. Is that enough for efficient working vent ???:(

How about installing a cowl induction scoop? (it's like a backwards air scoop).
http://www.showcars-bodyparts.com/AM...-scoop-135.jpg

Might even be able to mount it so it keeps out the rain..

http://www.hawkinsspeedshop.com/cate...1107scoop1.jpg

I wonder how they would effect aero drag. I guess more front area.

I'm not sure. Since it's sitting in front of the windshield, does it really add to the frontal area?

The main selling point is, these things don't intrude down into the engine compartment
and I think (at speed) they may actually suck air out.

It would be nice, if one could use the intake and hood-hole size to balance the amount of air flowing out of the vent, so it matched the speed of the air flowing around the outside of the cowling..

Cowl hood scoops are supposed to provide pressurized air to the carburetor inlet at highway speed. The transition between the flat hood and the rather vertical windshield of old muscle cars created a very high air pressure at speed, and the cowl scoop took advantage of this to provide a "cold air" intake with a little extra pressure on it. These do not work well to vent hot air at highway speed.

I have seen pictures of tri-5 shoeboxes run at the Silver State classic road rally with tons of aero tricks to try to keep the front wheels on the ground above 100 mph. Some of those folks cut a wooden block for each rear corner of the hood that's about 3/4-1" high and slam the hood on them. The raised rear corners of the hood bleed off underhood pressure as they are further from the stagnation point in the center of the windshield and the gap runs parallel to the air flow. Placing a side- or rear-facing outlet near the windshield will have to be done with care, and probably by moving it far toward the sides of the car.

The cowl induction 'scoops' (Output vents?) I've seen on the web look pretty low profile.
http://images.buyautotruckaccessorie..._SpCm_Cowl.jpg

If I were to install one on my CRV, I would place it close to the nose,
in order to suck the air out of the area behind the radiator.
The one in this picture seems to be too far back.

Rain isn't going to be able to get directly to the engine, and if you made a small rim around the hood hole and drilled some small drain holes in the cowl, that would drain off any water that ran inside the output vent..

About 60% of the fuels energy,at any given load, is lost to waste heat.About half of that heat goes out the tailpipe,the other half into the cooling system.As to how much can go back into the inlet tract,I don't have a clue.Charge density would suffer at some point,with power falling off.The PNGV cars were moving the heat exchangers to the rear quarter-panels,ala Ford Probe concepts.As to the "pointy" nose,the body of research suggests we can do as good with less radical architecture.