how bad are big vans are aerodynamically

[racprops]

Originally Posted by aerohead

* NASA took a circa 1977 Ford Econoline, of approx. Cd 0.50, and got it as low as Cd 0.238.
* I modified my 1970 VW Transporter, and went from Cd 0.43, down to an estimated Cd 0.331.
* The Toyota T-100 went from Cd 0.5016, to as low as Cd 0.195, depending on configuration.

Nice BUT what did all that do in MPG improvements, from start to converted.

Like from say 15MPG stock to??

Or the VW transporter or the Toyota T100. What was the changes, not drag effects...but MPG?

Rich

[aerohead]

Originally Posted by racprops

First need more info on Rockettail

Second my van already has vortex generators.

Third ground effects.

So bottom line how much MPG improvements can these aero mods give, in a percentage of MPG improvement.

Rich..

Here are few pictures of my van:

I don't think we can say definitively.
1) I know only of a Naval officer's Master's Thesis on a Dodge Pickup, which investigated an airdam as low as your's.
Extending down even with the belly returned the lowest drag.
2) Deeper than that only increased drag, however, if extended to within one inch of the pavement, it indicated the lowest drag. For racing only. Very conditional!
3) CAR and DRIVER found an airdam they tested to be most effective when it wrapped around the leading edge, extending as close as possible to the front tires, closing the gap.
4) The deep rocker panel extensions are an unknown quantity. Typically, for passenger vehicles, they extend no lower than the belly.
5) And then you have the big-rigs using deep skirts below the semi-trailer, and these are laboratory developed.
6) Extending the panels, picking up behind the rear wheels would help ,maintain a flow surface which currently does nor exist.
7) Aeronautical engineer, Gary Wheeler, who invented AIRTABs, developed them originally for a notchback car, to assist in flow reattachment. As the van has no structure behind it onto which separated flow could attach, I've never understood how they could function as installed.
8) Drag reduction is from pressure recovery. Pressure recovery is from attached flow decelerating on a diminishing cross-section in the direction of flow.
9) There's no surface like that.
10) 'pinching' the wake, if that actually happened, wouldn't have any affect on base pressure.
11) Hucho said, boat-tails and box-cavities are the only devices known to actually reduce drag.
12) No 2-D, 'aeronautical' devices ever reduced drag in 3-D flow.

[racprops]

From: Phil Knox's aero-modded 1970 VW van https://ecomodder.com/forum/showthre...-van-8675.html

OK HERE is some real numbers:

The standard baseline tank - mpg over 3668 miles of testing was 23.795 mpg,at a steady 55-mph( the Federal National Speed Limit).

With addition of all-season steel radial tires and bellypan,and after 981 test miles,the tank mileage was 26.136 mpg(a 9.83% increase)

With addition of boattail and cardboard rear wheel skirts and 589.4 test miles, the tank mileage was 30.187 mpg ave..

RAC So all that work give an increase of 6.392.

I can add propane booster and see an est. 20% improvement….on that VW that would be 4.75 MPG or a total of 28.554.

I have been able to add 15% to a 2000 Mercury Grand Marques that got 30MPG pure Highway 65MPH by leaning it from 14.7 TO 16.4 at which it reached its peak MPG and started losing at higher settings.

This car on a hard run from Phoenix to CA at 85 MPH got 24/25 MPG and once in CA at 80MPH got 26MPG Stock 14.7 as I was unable to set it up to smoothly switch from 14.7 to 16.4 so did not run it changed. IF I could that could have been 28.75 MPG at 85MPH and 29.9 at 80MPH theoretically.

Add the propane booster and see an est. 20% improvement so 34.8 MPG….just two mods.

IN a full sized 4 door Ford 4.6 4 speed auto running a 3.27 rear end and could do better with a 2.73 rear end.

Back to Chevy Vans: Page two:

The Chevy should react like any other bread box on wheels.If you can find the FLOW-IMAGES thread,you'll eventually see the Cd 0.16 "van" that Klemperer came up with in 1922 which remains a "benchmark for low drag today.That body would give about a 33 % mpg increase at 55-mph,more at faster speeds.


CAR and DRIVER attempted a full-size van aero-mod in the latter 1970s.Their bellypan was of no benefit unless painstaking detail was applied.


Your fan delete is one which is well known of and proven benefit.


I would mimic the front of any modern van or pickup if you can.

Smaller mirrors have shown measurable results.


One and a half feet length of boat tail gave me 4-mpg.

A receiver-hitch cargo box might serve you as a foundation for such a mod,with quick-on/quick-off capability.


This is something "hard to park" curbside and better suited to long highway excursions.

Too much work for LITTLE gains…

Thanks for the info gentlemen.

So in conclusion I will stick with engine and drive line mods and a few other mods to the fuel system and so on as they can really add up.

[aerohead]

Originally Posted by racprops

Nice BUT what did all that do in MPG improvements, from start to converted.

Like from say 15MPG stock to??

Or the VW transporter or the Toyota T100. What was the changes, not drag effects...but MPG?

Rich

At the time, we had the 55-MPH National Speed Limit. And engineers said that an 10% drag reduction would translate to a 5% improvement in MPG.
Some Universities continued to use this relationship into 2012.
My Volkswagen went from an average 23.795-MPG, to 26.136-MPG with the addition of all-season radials and a full belly pan.
Adding 18-inches of boat-tail and cardboard and duct tape rear skirts pushed mileage to 30.187-MPG, average.
Highest observed fuel economy was 35.6-MPG.
The HONDA CRX HF went from 52-MPG to 65-MPG and a high of 82-MPG.
The Toyota pickup went from 25.14-MPG @ 65-MPH, to as high as 39.9-MPG at the same speed, on Regular Unleaded.

[racprops]

Originally Posted by aerohead

At the time, we had the 55-MPH National Speed Limit. And engineers said that an 10% drag reduction would translate to a 5% improvement in MPG.
Some Universities continued to use this relationship into 2012.
My Volkswagen went from an average 23.795-MPG, to 26.136-MPG with the addition of all-season radials and a full belly pan.
Adding 18-inches of boat-tail and cardboard and duct tape rear skirts pushed mileage to 30.187-MPG, average.
Highest observed fuel economy was 35.6-MPG.
The HONDA CRX HF went from 52-MPG to 65-MPG and a high of 82-MPG.
The Toyota pickup went from 25.14-MPG @ 65-MPH, to as high as 39.9-MPG at the same speed, on Regular Unleaded.

Originally Posted by aerohead

At the time, we had the 55-MPH National Speed Limit. And engineers said that an 10% drag reduction would translate to a 5% improvement in MPG.

Some Universities continued to use this relationship into 2012.

My Volkswagen went from an average 23.795-MPG, to 26.136-MPG with the addition of all-season radials and a full belly pan.

RAC note that on a Chevy Van a belly pan was nearly impossible to get to do anything.

Adding 18-inches of boat-tail and cardboard and duct tape rear skirts pushed mileage to 30.187-MPG, average.

RAC A gain of 6.392 MPG…

Highest observed fuel economy was 35.6-MPG.

The HONDA CRX HF went from 52-MPG to 65-MPG and a high of 82-MPG.

RAC a nice 13MPG Gain.

The Toyota pickup went from 25.14-MPG @ 65-MPH, to as high as 39.9-MPG at the same speed, on Regular Unleaded.

And the Toyota gained 14.76.

I am disregarding your highs as I am not throwing in readings of taking a Toyota and a Hyundai from 32MPG an getting readings of 60 and 70 MPG using Hydrogen systems as we could not do them twice…Yes a unicorn….but it happened on two cars (out of 14) and one drove home complaining to us about ONLY getting 62 MPG on two fillups…after we saw 72 on one drive test.

Rich

[cRiPpLe_rOoStEr]

There is always some compromise between form and function, no wonder most vans are not the greatest example of aerodynamics.

[aerohead]

Originally Posted by racprops

And the Toyota gained 14.76.

I am disregarding your highs as I am not throwing in readings of taking a Toyota and a Hyundai from 32MPG an getting readings of 60 and 70 MPG using Hydrogen systems as we could not do them twice…Yes a unicorn….but it happened on two cars (out of 14) and one drove home complaining to us about ONLY getting 62 MPG on two fillups…after we saw 72 on one drive test.

Rich

I get your point.
Please bear in mind though, that we have data on every tank of fuel, for the entire 415,000-miles of driving, since it was purchased new in 1994.
Under NO circumstance did the 'naked' truck ever experience mpg excursions ever approaching 39.9-mpg. Which leaves one to ponder causality.

[cRiPpLe_rOoStEr]

[aerohead]

I'll guestimate Cd 0.80.

[cRiPpLe_rOoStEr]

Sure it's a brick, and the 67hp naturally-aspirated 2.9L Diesel 3-cyl engine wouldn't be of much help.