RAM air Aero Tube

[Tahoe_Hybrid]

Originally Posted by freebeard

The question has become particularized.

30 MPG is a pretty low bar. What vehicle did you have in mind? And what is wrong about the way Aerocivic looks?

2008 tahoe 6.0L it might be possible to get 40 maybe even 45 out of it..
whats his name has been getting 45mpg out of his 5.7L i don't see why not getting 45 out of my 6.0

Someone claimed I could use
MyVoltHold on the tahoe hybrid i would have to get a OBD splitter because i use AFM disabler chip (engine cost more then saving 0.5mpg)

https://ecomodder.com/forum/showthre...tml#post628655

[aerohead]

Originally Posted by Tahoe_Hybrid

i'm just trying to get the mpg to 30mpg which is completely do able without making it look like a aero civic

Without a cannibalistic, powered, high-static pressure air-handler, there's a high probability that air will simply flow forwards, from the wake, to the 'inlet.'
To move air passively you'd need a Bauman scoop to harvest stagnation pressure, and the act of harvesting stagnation pressure would increase underbody drag.
The ductwork itself would amplify surface friction, compared to just letting the air flow to the rear along a belly pan, and slow diffuser.
Nothing's been done for pressure regain, which is the ONLY thing that WILL reduce drag.
The Aero Tube is the stuff of the Unicorn Corral.
Just sayin'.

[Vman455]

Originally Posted by aerohead

Without a cannibalistic, powered, high-static pressure air-handler, there's a high probability that air will simply flow forwards, from the wake, to the 'inlet.'
To move air passively you'd need a Bauman scoop to harvest stagnation pressure, and the act of harvesting stagnation pressure would increase underbody drag.
The ductwork itself would amplify surface friction, compared to just letting the air flow to the rear along a belly pan, and slow diffuser.
Nothing's been done for pressure regain, which is the ONLY thing that WILL reduce drag.
The Aero Tube is the stuff of the Unicorn Corral.
Just sayin'.

For less than $100, you can measure pressure anywhere you want on the car instead of just guessing. That helps with stuff like, oh, maybe siting duct inlets and outlets so air flows through them the direction you want.*

I wouldn't try what OP is suggesting, but if he wants to the tools are available to measure things.

(*For example, I vented my engine bay to my wheel housings last year. But before I cut and installed a vent, I measured the pressure differential between the engine bay-side and wheel-side to ensure air would flow out of the bay and not backwards into it. No guessing required).

[freebeard]

The classic example are those two oval portholes on the hood of an MGA. They were supposed to admit air to the carburetors, but vented the radiator instead.

[Blacktree]

Originally Posted by aerohead

... and the act of harvesting stagnation pressure would increase underbody drag.

Can you explain this in more detail? My brain isn't firing on all cylinders, at the moment.

[freebeard]

aerohead may not post again until Thursday, his schedule changes.

I can only see it if the assumption is that air 'harvested' would otherwise feed the underbody, instead of going around or over the top.

[aerohead]

Originally Posted by Vman455

For less than $100, you can measure pressure anywhere you want on the car instead of just guessing. That helps with stuff like, oh, maybe siting duct inlets and outlets so air flows through them the direction you want.*

I wouldn't try what OP is suggesting, but if he wants to the tools are available to measure things.

(*For example, I vented my engine bay to my wheel housings last year. But before I cut and installed a vent, I measured the pressure differential between the engine bay-side and wheel-side to ensure air would flow out of the bay and not backwards into it. No guessing required).

1) Of course! The Chevrolet Tahoe is a magical vehicle which behaves as a one-dimensional structure.
2) The Tahoe doesn't experience any flow field displacement, accelerations, or pressure variability.
3) When you use your new Pitot-tube and MAGNEHELIC you'll notice that the pressure under the Tahoe, where you're considering your duct inlet, is identical to the forward stagnation point. 'cause it's magic!
4) And now that you have your delta-P, this will immediately inform you of the perfect design of the ductwork itself, plus, accurately predict its new pressure profile, in advance of modification.
5) Presto-chango!
6) It doesn't matter that CAR and DRIVER attempted this type of modification on a DODGE van in the 1970s, only too experience a drag and MPG penalty. Don't let that discourage you. Obviously, DODGE vans operate under different fluid dynamic constraints as Tahoes. And Csere Csaba, an MIT graduate engineer, who oversaw measuring at the Chrysler Proving Grounds, couldn't possibly be trusted for accuracy.
7) It doesn't matter that when I attempted this sort of modification at Bonneville, I experienced a drag and top speed penalty, and then set a land speed record when I covered it up with duct tape and cardboard.
8) But hey, that was only with FIA' officially-sanctioned, Southern California Timing Association measurements, of four decimal point accuracy.
9) Certainly, your measuring techniques will be far more accurate.
10) It doesn't matter that no individual has benefited from a 'ducted' automobile body in the history of automobiles, VMAN455's measuring will carry the day.
11) So go ahead. Take a plasma-cutter and Milwaukee Sawzall to the Chevy.
12) Maybe splurge for a 120-channel data-logger, 120 static pressure ports, and ten miles of Tygon Tubing while your at it.
13) VMAN455 has an illustrious history of mpg and speed records under his belt. He won't disappoint.

[aerohead]

Originally Posted by Blacktree

Can you explain this in more detail? My brain isn't firing on all cylinders, at the moment.

1) In the best case, underbody airflow would pass along a full, smooth belly pan, then decelerate up a gentle diffuser, experiencing pressure recovery, and injecting higher pressure air, vectored into the base, directed into the wake, for an overall base pressure increase, overall reduced pressure drag, overall reduced drag.
--------------------------------------------------------------------------------------
2) Extending a Baumann scoop into the flow below the body, to harvest ram-air to pressurize the 'duct', would rob air from the downstream belly and diffuser.
3) Since the duct has more wall surface area than the belly pan where it would otherwise flow, you've introduced surface friction at an average duct velocity, with a Cd 0.003 coefficient of surface friction drag ( for a perfectly-smooth ) surface, and total wall area of the interior of the duct.
4) There will be viscous shearing losses within the air itself as it decelerates in the duct system.
5) The lowest drag Baumann scoop is Cd 0.05. Along with its projected frontal area. CdA. Which increases the overall frontal area of the vehicle. A step backwards.
6) A NACA submerged-inlet ( preferred over a scoop ) would not be a candidate for use because of the Tahoe's deep, ladder-type frame
crossmembers.
7) On an Audi 100-III for instance, the presence of the scoop(s) could increase drag by Cd 0.015 right where they're mounted, and another Cd 0.025 by destroying the efficacy of a low-drag diffuser downstream. A potential Cd 0.04 drag increase.
8) Add the drag of the flow perturbation, the scoop, aggravated frontal, plus the increased surface friction within the ductwork, and you've shot yourself in the foot. A numericalized guess.

[freebeard]

... and the act of harvesting stagnation pressure would increase underbody drag.

2) Extending a Baumann scoop into the flow below the body, to harvest ram-air to pressurize the 'duct', would rob air from the downstream belly and diffuser.

It must be Thursday. And now we know the stagnation point is below your one-dimensional Tahoe.

[Blacktree]

This conversation is getting confusing. Are we talking about drawing air from the stagnation zone in front of the car, or from underneath? Are we talking about running ductwork through the vehicle, or adding a second floor?

Also, I have no idea what a Baumann scoop is. I tried an internet search, and google showed me a bunch of kitchenware.