Hole through middle of car. Aero benefits?
 

I realize this sounds like a whacky idea BUT...

Would it work and how much benefit would it give?

I got the idea from this joke CFD by trebuchet03

This would actually be a fairly simple and easily reversible mod for my van if it gave enough of a benefit.

Do it! It would be fun just to see, I think :)

hole
 

Yeah,it's pretty whacky.GM actually released an artist's rendering of an COE 18-wheeler in the 1980s,which depicted an enormous hole between the driver's compartment and running gear below,with streamline sections supporting the upper structure.------------ As far as I know,this is as far as it' gone.No claims were made about the concept.So you and Treb are not alone.-------------------------- The twin-boom Tarf,by Taruffi(?) had driver in one boom and running gear in other,and wing-like spars connecting the two,with Cd 0.10 claimed.I think the polar-moment-of -inertia would limit a vehicle like this to the track,where it operated.----------Some solar racers have used this layout but the didn't make it into the winner's circle.------------------------ The design is a shoe-in for donut-shaped motorists.

Theoretically though, it would work, correct?

Air from the high pressure region in the front would rush to fill the low pressure in the back with little restriction other than surface friction. I guess it would have to be a pretty direct path. I would think this would be even better if it was the radiator duct but then it would have to be insulated in the summer.

I suppose it wouldn't be a huge change but it's an interesting thought experiment.

This might help fix an existing vehicle if the interior room is not needed, but if you pursue the idea, you wind up with a stove pipe with all surface drag and no useful volume.

Bicycle Bob -

Would an inline fan help make a smaller diameter pipe useful? For the purpose of the conversation, assume the cost of running the fan is free.

CarloSW2

If you can postulate a free fan, you can rewrite the economics of almost anything.

Bicycle Bob -

I know, but I want to know if the "aero" will benefit first.

If the system was workable, then you could run the fan off a battery?!?!?!

CarloSW2

The aero can benefit to the point the regular engine becomes redundant - just see a jet aircraft. The battery power is not free - it makes the alternator draw power from the engine.

Hi,

If this idea was used to ventilate the interior of the car, then it would have that benefit, as well as filling in the low pressure in the back. The Aptera does essentially this exact thing.

Even though if you have the back window open in an SUV or truck, air comes in...

Different concept entirely than what's being discussed here.

This site needs a NASA engineer with the keys to a wind tunnel.

MadisonMPG -

You're telling me. My Dad's a retired NASA engineer, but he doesn't have the keys, :( .

CarloSW2

that hole is like the tunnel of a non-transverse drivetrain. One of the reasons all exotics have it..the tunnel, not the hole. the tunnel where the driveshaft goes.
the middle of a belly pan (the very sqaureness a car revolves around for its precision) gains different engergies and physics at different air flows and temps. The tunnel and driveshaft in a normally mounted drivetrain aid in the peace of the body, as well as a bit of the hole you drew. I am no engineer, but I am a car rebuilding lunatic speaking my own language. this hole you drew exists for normally mounted engines. One of the silent and invisible reasons it is simply desirable by more than hotrodders, it creates and maintains comforts not many mention, it cannot be described. It is called physics. The drawback to the tunnel, is when it ends. It is always before the rear end and stuff immediately gets hung up on the sides..this is the silent drawback to normally mounted engines..the rear end gets ripped apart sometimes in a few short years (like all subarus known to man) and embarassing steel breaks like in an old dogde dart..yes the cars killed themselves with physics, the tunnel and energies of elctrical, heat and chemistry explode out the other side of the driveshaft tunnel at the back end and underneath the car.
This problem goes back to over 20 years ago for me, a a 1978 delta 88 I drove broke both tail ends of the frame...I have been analyzing ever since. The most comfortable cars ever. non-transverse is my vehicles for the rest of my days. big or small, they are simply beneficial, the hole through the middle of the car is close enough with the tunnel and a driveshaft. :)
the height of the hole through the car, its like you are humoring a hinda civic with a brick wall called a vtec engine in front of you. The compression of keeping it under your feet is another benefit for you and the body, the hole is going to find something nasty on many occasions.

would it at best be equal to reducing the frontal area of the car an amount equal to the smallest section of the pipe running through the car? or is there some benefit that i'm not catching on to? if it was very small of a pipe, i wouldnt think it would have any more benifet than the removal of an outside mirror... if it was very sizeable you'd be looking at removing seats for the space. then you might as well remove all the glass and cover the lower section of the interior with sheet metal like some race cars do.

Exactly the question I was thinking about. Does the fact that you are moving air from the highest to the lowest pressure area give you a greater/smaller/equal effect as the same frontal area reduction taken from the outside of the vehicle?

I could easily get a ten inch pipe (78 sq/in area) through if I really went off the deep end and did this. It would have to give me the equivalent of more than half a square foot off the frontal area

Amen brother.

Speculation here:

I think at high speed, there would be a choking effect, that would not allow you to realize the full A reduction.

Based on what I know about fluid dynamics, which admittedly isn't as much as several others on this site, the "pipe" as it were, would have to be completely straight. Any taper in the front of the pipe would cause further compression of the flow as it was pushed into the "hole". Any expansion in the pipe after the entrance would allow the flow to expand accordingly, thus slowing it down, causing a back-pressure effect.

The pipe itself would contain it's own boundary layer, which also cuts down on the net A deduction, albeit minutely.

Er... no, the Aptera doesn't do that. Maybe to a teensy fraction of a degree of this idea... but then would just about any car qualify as the cabin air intake is in a high pressure zone and the exhaust in a low pressure zone?

IIRC this exact topic was hashed out at GS.

IIRC I put forth that if one has the luxury of all that interior room they are willing to sacrifice, they'd be far better off chopping the top.

Yup. And you know why that is of course ??
( Surely )

On a related thought -
If you opened the back ( passenger compartment) windows of the SUV, as well as the tailgate window, you might find that there would be some sort of airflow through the cabin that changes the wake in some way.
Since you have a mess of seats and other obstructions in the pathway of the air, ... who knows, it might even be worse. I would think the turbulence would tear the air all to hell and make it even worse ... but who knows ?
It would be an interesting and extremely easy, no modification experiment.
( Except maybe folding down the seats to make a cleaner pathway for the airflow. )

Anyone here have an SUV with a tailgate window that goes down ?

( Just be sure and put the windows up when stopped - carbon monoxide !! )

I think we already talked about this sort of thing in another thread ( The SUV with a back window open topic )


SO ... back on topic. :thumbup:

This seems to suggest that it should indeed work... provided (naturally) that you don't add to the total frontal area.

F Ducts: How do they work? | F1 2011 | Formula One technology | Racecar Engineering | Race car technology explained
2010-formula-one-technology/

I don't see how that applies to non-winged vehicles.

And I don't think the idea has merit.

Correct me if I'm wrong, but as far as I see it they're simply talking all fancy and engineering-like about stalling the wing, but in effect all they're doing is filling a low pressure area with air from a higher pressure area, thereby reducing the drag (and it certainly sounds like this was their goal).

I think whether it's a wing or not is slightly irrelevant for drag reduction purposes. It just so happens that since they're F1, have a lot of equipment and knowledge, it pertains to the rear end of a high downforce wing.

I think the idea does have merit, but whether or not it can be accomplished with significant improvements on an every day vehicle will depend on how much 'free' space one might be able to find without increasing the FA.

The first sentence on your link says it all: "When McLaren’s F-Duct system first appeared in pre-season testing it was hailed by many a a true stroke of genius, a classic example of out-thinking the regulations."

"Out thinking the regulations." Race cars are built to a set of rules and this tech is designed to get around those rules. Street legal cars are built to a different set of rules so even if, and it's a big IF, this idea worked with these different rules there are likely easier and better ways of getting to the goals we have. And speaking of goals, race cars are also built for different goals than ours. :turtle: Who here wants to pull 5 gees in their car? :confused:

Ducts have drag; if you have excess interior room you are better off chopping the top or some such.

@ai_vin
I don't know what 5G has to do with the this... you'll note they used this F-duct system for the long straights to reduce the overall drag of the vehicle. For them it was for top speed, but for Joe Ecomodder it'd be for better fuel economy.

@Frank Lee
I agree, less FA would always win above this. I don't really see this working on many vehicles as components are too tightly packed under the floor. And who'd want to cut a hole through their car inside the cabin, apart from perhaps some die-hard ecomodder with an older cheaper car. I do think there is a lot of scope in perhaps an older pick-up or something similar, since they seem to have a lot of open space between components.

Now lets imagine this older pick-up has already been modded with a flush underbelly from something like coroplast, but now you take it off, stick a pipe or two linking the high pressure front (maybe just aft radiator) to the low pressure back in some space you can find under the chassis and stick your coroplast underbelly back in its original position - hence not increasing the FA. Where one might have vented some of this air out the wheelwells, now you channel it down the smoothest pipe(s) you can make to the back.

Surely this can help and would be easier than fabricating a chopped roof. But yes, I understand how it'd probably not be worth the trouble unless you have a lot of free space to work in that might otherwise have been blocked off.

Higher pressure engine compartment air vents to lower pressure areas anyway... otherwise it wouldn't flow.

Interesting to think about pickups though...

Wouldn't it be easier to prevent the high pressure via body mods than to cut a freaking hole in your car? In America we can do virtually whatever we want to our cars without consequence. We aren't under draconian FIA rule and I see no reason to go to these lengths for such a small increase. The only time it could possibly be worth it in my opinion is on an already aero'd out car like the Aero Civic.

This is the proverbial "high hanging fruit" that we not only need a ladder for, we need to rent a helicopter to grab it from the very top of the tree. Sure it's fruit and it's on the tree, but unless you've eaten every other apple in the orchard and are still hungry, why do it?

Exactly, race cars are designed with elements that produce negative lift for going around corners at high speed, but downforce also produces high drag. This tube only reverses some of this at the cost of extra internal drag in the pipe itself.

Here's a friction loss graph for ducts... All you have to do is subtract the loss in the duct from the benefit of reduced pressure at the rear and compare that to an unmodified car... Easy!
http://docs.engineeringtoolbox.com/d...-diagram-2.png

Think of the great safety benefits for people following. They could see through you to the car ahead which would give them precious seconds reaction time in a panic stop.

Think of the utility of transporting long straight things like unicorn horns and the like. ( are they horns or corns?) Although that would negate some of the benefits.

Pretty easy to try on a hatch back, block open the trunk a few inches and open the sunroof. The red on top of the roof would blow in and out the back

Or just cut a few holes on the firewall. The area right under the windshield is supposed to be a high pressure area, if you could duct that with some 4" PVC through the transmission hump to the back you would be set

I was thinking about doing something like this on my vw kitcar. The car has nothing under the hood except the gas tank and I was thinking of sealing the whole front of the car so air moves around the car and not through it. This would not give anyplace for the hot air from radiator to go so I was thinking of venting the hot air into car during the winter and having the hot air flow between the floor and the bellypan the rest of the time.

The car was setup to have ducting running from the front of the car under where the radiator would be into the car for fresh cool air.

That sounds like my red clay truck design, would you by any chance know where I can get a photo of that?