New lower air dam for 2017 Chevy Full size van

[Vman455]

Originally Posted by aerohead

There's been a bit published about airdams since 1960, when Chevrolet Division of General Motors introduced it to the motoring public.

There's been some published on air dam research, yes. The most recent article I have was published by Ford engineers in 2018, testing air dam depth and curvature on the 2015 F-150.

Nowhere in the literature, however, does the rule "air dams should extend as low as the lowest-hanging component under the car and no lower" appear (that I've read, anyway). The Ford paper points out that drag reduction depends on the pressure on the backside of the tailgate--which changes with air dam shape and size and cooling air inlet shape, size, and flow rate! It's tremendously more complicated than the "rule of thumb."

[freebeard]

The Ford paper points out that drag reduction depends on the pressure on the backside of the tailgate--which changes with air dam shape and size and cooling air inlet shape, size, and flow rate! It's tremendously more complicated than the "rule of thumb."

Back in the day, Porsche learned that when they added a spoiler at the top rear, they had to balance it with an air dam at the lower front.

[EcoVan]

Here's a side shot of the air dam/valance so you can see its shape. The upper portion mostly follows the curve of the bumper and the dam is actually the lower portion.

And yes, I know that aero design is very complicated... I've read Huchos' book along with studying NASA's 1970's Van research that lead to the Aerodyne and other aerodynamic semis, amongst other sources. In the last 10 to 20 years it seems like the whole auto industry is finally taking the subject seriously and instead of just making cars look aero, they are making them actually more efficient. Using air movement to improve aero ( such as the air curtains over wheel wells) is a big step forward.
However, if you take a look at these vans, it doesn't look like GM has done much with these vans since they were introduced. There is nothing to indicate any design work done on the bottom side, the wheel wells , the rear or just about any where else other than maybe the grill inlet and the addition of a small air dam under the bumper in the later years. The rounded edges front and rear are probably the biggest asset of the current design. There isn't even a rear "spoiler" to help air flow fill in the huge wake of the rear end. The body is essentially unchanged since its introduction in 1996, with the exception of some front end changes. Around 2003 the body was moved to a much heavier truck chassis.
To me it looks like it wouldn't take much to make big improvements to this vehicle... alot like the motorhomes. In fact this is a motorhome/ box truck chassis.

[aerohead]

Originally Posted by Vman455

There's been some published on air dam research, yes. The most recent article I have was published by Ford engineers in 2018, testing air dam depth and curvature on the 2015 F-150.

Nowhere in the literature, however, does the rule "air dams should extend as low as the lowest-hanging component under the car and no lower" appear (that I've read, anyway). The Ford paper points out that drag reduction depends on the pressure on the backside of the tailgate--which changes with air dam shape and size and cooling air inlet shape, size, and flow rate! It's tremendously more complicated than the "rule of thumb."

1) We'd be compelled to accept Ford's data, as specific to this particular vehicle.
2) A review of my sources, of which presented drag tables derived for the specific test vehicle, all indicated for 'sweet-spots', where drag curves for both airdam drag, and underbody drag intersected, constituting the configuration of minimum total drag, as a function of airdam vertical 'size,' just as with streamline bodies of revolution vs fineness ratio.
3) Wolf Heinrich Hucho's 2nd-Edition textbook's very first drag curve ( Figure 4.80, page 166 ) demonstrates the phenomena.
4) Anyone interested, would be free to examine the particulars of each test vehicle represented in each SAE, or other sourced articles, and pay particular attention to the dimensional relationships of each.
5) The take-away is: as the airdam is introduced, drag is initially reduced up to a certain 'length', at which it nulls out, after which, drag begins to increase again, and at some 'length', the total drag exceeds the OEM drag for a non-airdam configuration.
6) The caveat is presented by Lieutenant Nathan A. Williams, in his September, 2003 Master's Thesis, in which he investigates airdam 'length' all the way to the road surface ( this would never be examined by an automaker, as they are constrained by SAE 'approach' angles of 16-degrees ).
7) The lowest total drag for his 1997 Dodge RAM 2500 airdam configuration occurred @ zero ground clearance.
8) Anyone interested, could take his data, plot it on a Cartesian X-Y grid, and statistically determine where the drag ' trend-reversal' occurred on the pickup.
9) This would constitute part of the vast amount of empirical data which establishes the ground rules for fluid mechanics, aerodynamic engineers must respect in seeking aerodynamic solutions with off-the-shelf technology, as Hucho admonished readers to take away from all data from all sources, across all time.
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10) Wolf H. Hucho cautions us about 'adding frontal area', when pursuing any vehicle aerodynamic modification. I have deferred to his education and experience, plus empirical evidence within the rest of the literature I'm in possession of.
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11) I agree with you 100% with respect to 'testing.' The qualifier would have to do with taking what's already 'known quantities' as a 'first-principle', 'first-approximation', which includes the caution about aggravating frontal area ( It's gotten me two speed records and multiple mpg records so far ).

[aerohead]

Originally Posted by EcoVan

Here's a side shot of the air dam/valance so you can see its shape. The upper portion mostly follows the curve of the bumper and the dam is actually the lower portion.

And yes, I know that aero design is very complicated... I've read Huchos' book along with studying NASA's 1970's Van research that lead to the Aerodyne and other aerodynamic semis, amongst other sources. In the last 10 to 20 years it seems like the whole auto industry is finally taking the subject seriously and instead of just making cars look aero, they are making them actually more efficient. Using air movement to improve aero ( such as the air curtains over wheel wells) is a big step forward.
However, if you take a look at these vans, it doesn't look like GM has done much with these vans since they were introduced. There is nothing to indicate any design work done on the bottom side, the wheel wells , the rear or just about any where else other than maybe the grill inlet and the addition of a small air dam under the bumper in the later years. The rounded edges front and rear are probably the biggest asset of the current design. There isn't even a rear "spoiler" to help air flow fill in the huge wake of the rear end. The body is essentially unchanged since its introduction in 1996, with the exception of some front end changes. Around 2003 the body was moved to a much heavier truck chassis.
To me it looks like it wouldn't take much to make big improvements to this vehicle... alot like the motorhomes. In fact this is a motorhome/ box truck chassis.

1) GM's corporate policy, historically, is not to 'innovate' with shareholder's money.
2) GM is in the business of making money.
3) One of GM's business operations has to do with manufacturing automobiles.
4) Historically, automobiles burn fossil-fuels.
5) Historically, GM's parent company was also in the fossil-fuel industry.
6) Aerodynamic efficiency threatens fossil-fuel profits.
7) GM has been concerned with 'look-alike' automobiles since 1926.
8) GM 'invented' style obsolescence in 1927 ( Law of the Paris Dressmaker ).
9) GM lets other automakers take risks.
10) If a competitor has a success with some innovation and some GM committee agrees that GM should 'compete' technologically, then one can expect to see an innovative feature appear on a GM product.
11) As of 1987, GM 'produced' a vehicle of Cd 0.089.
12) GM's Aerodynamics Laboratory 'Knows' about low aerodynamic drag.
13) GM's Pontiac Trans Sport van was Cd 0.30.
14) GM's 1992 HX-3 hybrid van was below Cd 0.29.
15) We are not constrained by committees who may value fossil-fuel profits to nameless shareholders ahead of aerodynamic efficiency.
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16) Since aerodynamic drag is governed by frontal area and shape, and frontal area isn't negotiable, on a practical modification basis, we're left with 'shape.'
17) If you were to mimic what NASA did to their Ford Econoline, it would not be unreasonable for you to experience their drag coefficient. I un-knowingly did what NASA did in 1980, and pushed my VW Transporter, from 27-mpg, to as high as 34-mpg. If I'd had access to a fifth gear, I might have seen better.

[EcoVan]

This is the specific starting point I have kept in mind when adding an air dam.... don't bring it below the existing outline of the vehicle. This air dam/valance appears to do that. The front cross member is still below the air dam and the lowered sides cover the tires and the front suspension just barely. Remember this airdam is suv sized.....about 9 inches above the ground in the center and about 7 1/2 on the edges just as it is on the Suburbans and Tahoes. It's huge by car standards, but to scale. From observation, this limitation seems to be very common in the newer aero design of SUV's. Most appear to round the bottom leading edge and either have no air dam or a small flexible one and then tire spats. Even many cars were going that direction until we started seeing built in splitters at the bottom of the leading edge. With SUVs, I suspect this design was in part to allow larger approach angles. My wife's 2007 Jeep GC was designed with an easily removable 4 inch air dam so extreme approach angles are possible when off roading. This my other current aero/MPG project which it seems Jeep left all sorts of room for improvement...not unexpected since its chief design goal was off road capability. However, the manufacturer's have wised up ( and forced for higher MPG standards) since most SUV's are never taken off road, so now many manufacturers produce a specific off road model without much of the lower aero equipment.

There is only one covering under the vehicle.....between the lower crossmember and another higher one that is forward. This probably helps aero but it's reason for being is probably to protect the belts from water and mud splash. This is similiar to the front skid plate on Jeep GC's, it acts as a skid plate but also prevents mud from begin thrown up into the front of the engine, particularly on the v-6 vehicles as there is about 12 inches of open space between the engine and the radiator. I heard various reports when removed, highway MPG drops.
The rest of the underside is an open frame and open wheel wells.

For the Full size Express vans, they are not subject to MPG regulations, so there is not much effort put into increasing mileage. The main design goal is for them to be able to take as much abuse as possible and carry and tow large amounts of weight.

[EcoVan]

Originally Posted by aerohead

1) GM's corporate policy, historically, is not to 'innovate' with shareholder's money.
2) GM is in the business of making money.
3) One of GM's business operations has to do with manufacturing automobiles.
4) Historically, automobiles burn fossil-fuels.
5) Historically, GM's parent company was also in the fossil-fuel industry.
6) Aerodynamic efficiency threatens fossil-fuel profits.
7) GM has been concerned with 'look-alike' automobiles since 1926.
8) GM 'invented' style obsolescence in 1927 ( Law of the Paris Dressmaker ).
9) GM lets other automakers take risks.
10) If a competitor has a success with some innovation and some GM committee agrees that GM should 'compete' technologically, then one can expect to see an innovative feature appear on a GM product.
11) As of 1987, GM 'produced' a vehicle of Cd 0.089.
12) GM's Aerodynamics Laboratory 'Knows' about low aerodynamic drag.
13) GM's Pontiac Trans Sport van was Cd 0.30.
14) GM's 1992 HX-3 hybrid van was below Cd 0.29.
15) We are not constrained by committees who may value fossil-fuel profits to nameless shareholders ahead of aerodynamic efficiency.
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16) Since aerodynamic drag is governed by frontal area and shape, and frontal area isn't negotiable, on a practical modification basis, we're left with 'shape.'
17) If you were to mimic what NASA did to their Ford Econoline, it would not be unreasonable for you to experience their drag coefficient. I un-knowingly did what NASA did in 1980, and pushed my VW Transporter, from 27-mpg, to as high as 34-mpg. If I'd had access to a fifth gear, I might have seen better.

I see the same pattern at GM and most other manufacturers. They've have no reason to work on the Express van aero as they are making money as it is and it doesn't effect their corporate MPG. They may know aero, at least now, but that knowledge only seems to be used very recently. You look at the 1980's Firebird and Comaro, and Audi's boxy sedans had lower drag. Even the boxy flagship sedan from Chrysler had the same drag as the Firebird, IIRC.

With this van, I think there is easily alot of room for improvement. Starting with a VW, you were probably starting with a much more studied design. I recall seeing that they did quite a bit of aero work ( and crash testing) on the old VW vans from the 60's and 70's. The aero work on the Rabbit presented by Hucho fascinated me and really shows that so much more can be done that just looking aero. Flat faced vehicles can perform just as well as rounded if designed well.

[aerohead]

https://ecomodder.com/forum/member-a...vement-mpg.jpgDefinitely!
All thoughout W.H. Hucho's 2nd- Edition chapter on detail optimization you can 'see' where things 'saturate.'
On some specific modification, you witness drag reduction for a specific range of alteration, say, increasing a radius to a specific body leading edge. Then, beyond some point, no additional increase to this radius returns any additional benefit.
You've reached 'saturation.'
My Volkswagen, stock from the factory, would have been considered 'saturated' at it's nose. And I never touched it. Just the belly, wheel houses, and tail.
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When Don Sherman at CAR and DRIVER aero-modded the Ford Pinto in 1974, he didn't use any radical leading edges. He did go beyond Ford's product 'specification', as he wasn't concerned what 'public reaction' would be, just aerodynamics. This is what 'hooked' me.

[EcoVan]

Its funny, everyone thinks of improving the front end aero, where its mostly the rear , underside and tires where the big gains are. It hard to sell cars with boattails, but the good designers are making virtual boat tails by sculpting the air before it leaves the vehicle. Its refreshing to see good engineers being listened to for a change. I just wish they would figure out how to make lighter vehicles, they just get heavier and heavier. I find it hard to believe that the improved safely features has added 40% or more weight to vehicle designs. An early 70's small block 2 dr Dodge Dart weighed about 2800 lbs, now the Charger, about the same size, weighs close to 4,000 lbs. I wonder what just the bare chassis weigh isfor the newer cars?

I''ll see how far and can get this van with daily driver type changes. Between my business partner and I, we have about 5 in service. I have the only diesel, the others get at best about 15 MPG on the highway. Just getting the time to do it can be tough, but I expect between the 5 vehicles we could save hundreds a month in fuel costs. I figure with my diesel I can probably save about $35.00/month, the other vans about double that.

[aerohead]

https://ecomodder.com/forum/member-a...ed-micro-r.jpg1) If you can get to a cruise velocity and just hold it there, you'll be at your best brake specific fuel consumption.
2) Once you hit traffic, all bets are off.
3) This is why a 'hybrid' version of your van would return 48% higher mpg, according to Emission Analytics, who've tested many hundreds of vehicles for MOTOR TREND Magazine.
4) A BEV version would be about 3.5X higher mpg-equivalent than what you're presently experiencing. And with net-metering, off-peak, you'd be paying $ 0.05/ kWh, or $ 1.97/gallon equivalent. ( that's where I'm going!)
5) In the aero-extreme, towing a net-negative-drag trailer ( empty ) would give you the ultimate in mpg, gas, diesel, or electric.