Hole through middle of car. Aero benefits?

[Hermie]

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

[Christ]

Originally Posted by Hermie

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.

[MadisonMPG]

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

[cfg83]

MadisonMPG -

Originally Posted by MadisonMPG

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

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

CarloSW2

[bgd73]

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.

[2000mc]

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.

[orange4boy]

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?

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

I am no engineer, but I am a car rebuilding lunatic speaking my own language.

Amen brother.

[Christ]

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.

[Frank Lee]

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.

[Cd]

Originally Posted by Hermie

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

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.