Air dams?
 

What's the general thought about air dams and their effectiveness on road cars from a pure drag reduction standpoint? Anyone have any real world feed back on their effectiveness? I've seen at least one wind tunnel study from the 80s that shows they do reduce drag. Though wondering if today's underbodies are better considered than they were in the 80s, and thus an air dam might simply not have the desired affect.

The consensus I've seen here is that air dams are great for cleaning up the shape, but shouldn't be used to increase frontal area.

Welcome, BTW.

Back in 1983 I put a large chin spoiler on my shortbox 1976 Ford Econline van.

I don't recall it improving gas mileage, but clearly remember it helping in crosswinds.

The van used to wander like crazy in the wind while on the highway. After installation of the massive chin spoiler I could take my hands off the wheel and it would drive straight.

The truck had a lot of miles on it, the whole front end was terribly loose. I even got a ticket after I hit a pothole and it launched me into the curb.

The three on the tree shifter was always binding up too, I had to crawl under it and move the leavers after it jambed up (more than once).

My conclusion, less air moving under the van was a good thing, despite it looking like a brick.

From my experiance air dams work. All of my cars have had very dirty underbellys(aerowise)and have picked up 10-15%mpgs.
96nissan altima,97nissan maxima,98chevy prizm, 04lincoln towncar.

People need to search before posting.

Get off the computer and rest your eyes, better yet go drink some beer with friends.

airdam
 

maybe an airdam even with the bottom of a belly pan,out just ahead of the nose.Which would probably require an 'active' feature so as not to be shorn away on the first driveway ramp.

You can see my air dam test results here.

Actually what I was after is discussion on the topic, it is a discussion forum after all...I've worked in motosports for a bit over a dozen years, gotten to know more than a couple of aerodynamicists, and when I posed the question I got multiple answers. The research says they work, but the available research is more than 20 years old. How relevant is it to today's cars with their much more thought about underfloors?

Excellent work Aveomiller...seems bigger is better...

I'm contemplating a small air dam tucked in a bit from the leading edge and angled slightly. I'll mount it to the small CF underfloor infill I put in last night.

Progress album here:

https://www.facebook.com/media/set/?...3&l=7c1ecda51f

then why didint you post this as your first post?
Come to the table lo0oking like you have done some research and we can save "rolling our eyes".

Heaven forbid your eyes roll out of joint...Sheesh already. The point is to ask a leading inquiry to promote discussion. To move from lurker to participant, stir the sediment so to speak. Done and done. On wards and upwards...

wow, a noobie trying to create discussion.....
How about a noobie using the search function. This is a pretty active forum. we dont need to 'fake' activity.

woodstock74 -

Very clean :

http://sphotos.xx.fbcdn.net/hphotos-...98963118_n.jpg

CarloSW2

why don't you and sven pull the sticks out of your ***'s and be nice. especially since sven doesn't like physics, or discussions; just pretty renderings.

And to keep this on topic; i think they help out cars more then trucks(but that's based more on a car having a low point of 5" off the ground versus 8" or more)

Heck, it's what a discussion / information forum is about.

The search function returns almost the entire site unless you have a very specific search term.
And "air dam" , "belly pan" or even "Kammback" isn't very specific on here ...

It's not fancy, as almost no-one gets to see it, but some manufacturers are applying varying degrees of panelling on the undersides.
Few cars have really smooth undersides, but there's a growing interest to lower drag underneath the car, so we'll see ever more of it.

The usefulness of an air dam decreases as the underside becomes smoother, but it's OK to combine both - one way is an air dam dropping down to the level of a belly pan

We don't get a lot of "general" discussions because each case is different and I think we have a bunch of problem solvers here which excel at tackling specific problems or issues.

There have been several people in the forum claiming large chin spoilers hurt their performance. One of them is in the UK, but I forget the vehicle.

Science
 

Some of the 1st-gen water-cooled VWs were of Hucho's design recommendations,per wind tunnel investigations at VWs climatic wind tunnel.
This was the time of the 1st Arab Oil Embargo and many 'economy cars' had underbodies more akin to today's body-on-frame pickups and SUVs.
Hucho published in 1976 with an SAE paper which included front airdam research.
At that time,for all the cars tested,a drag decrease of up to 15% was possible by utilizing only a front airdam.
From R.G.S.White's research at MIRA in the UK,it was understood that the 'better' a cars underside,the less effective an airdam would be.
FIAT has demonstrated that airdams can increase drag on 'low-drag' cars.
'Airdams' had entered the market in 1966 with GM's 'modesty panel' on their Corvair,after development at the GALCIT wind tunnel at CAL Tech under the direction of Dr.Peter Kyropolous.
In Hucho's 1976 paper they show results from 12-airdam combinations of 4-different configurations on the sloping valance panel of a VW do Brasil 1600X.
The highest drag occured on the vertical dam closest to the front wheels at a depth of 60mm.
A 180mm,45-degree dam (ala Dodge Daytona ) showed no drag reduction at all.
The lowest drag came from a 40mm vertical dam halfway upstream towards the base of the angled dam.
-------------------------------------------------------------------------
Attaching the 'optimum' nose netted a 0.05 drop in Cd.By softening the hard edges slightly they were able to come within 5-points of the 'optimum'.
-------------------------------------------------------------------------
The nose of a 1976 Golf/Rabbit is within 5-points of 'ideal,'as far as zero-yaw is concerned.
This is the reason he basically recommends we blow off the front of the car as far as mods go,and just concentrate on the back.
The lowest cost entry level economy car sold today is a quantum leap,aerodynamically,from similar class vehicles of the first 'oil crisis.'
And there is a very good likelihood that whatever airdam comes from the factory on a new car,has already spent a number of hours of refinement in the tunnel or inside a $billion,neural-net, 3-D, Navier-Stokes CFD program.

As I posted earlier I have had great results, best percentage wise was the Towncar. That car is a body on frame design with a straight axel rear end. The other benifit I have descovered is the cars are more planted at highway speeds and less affected by crosswinds.

For our younger readers, the 1966 Corvair was a rear engine car and a front chin spoiler or air dam would reduce lift.

Well I bit the bullet...

http://www.mulsannescorner.com/pictu...2019.49.59.jpg

http://www.mulsannescorner.com/pictu...2019.50.52.jpg

"Tested" it, went up and down the interstate to make sure there was no buffeting or anything untoward. At very least it isn't hurting. Unfortunately I don't have any better data acquisition at the moment other than the MkI eyeball and tach vs. MPH reading. So initial look showed we're inching closer to 2600 RPM @ 68 mph. Before I started all this 68 was just below 2800 rpm. Now we're just above 2600 rpm. The tale will be the fill up. Though need to look into a ELM adapter for the OBD. Has anyone tried the Torque app for Android? Sounds like a Scanguage for $20 (about the cost of the ELM adapter, the app is free).

I don't know man, I really don't think they're doing all that much tunnel testing/CFD. At least not for the lower tier "econo boxes". If they were we'd struggle to find gains. In my career we'd spend hours in the wind tunnel and be happy to walk out with 1% reduction in drag. But this was on a highly refined race car. People on these forums are finding chunks without resorting to drastic changes (and they're finding huge chunks when they do). This speaks to a fundamental lack of development and refinement. We have to face it, cars are designed these days by accountants and focus groups. Yes, there are the exceptions: where it's profitable and can be used as a selling point.

Woodstock74, that looks very nice.

I agree. :thumbup:

Sporty Modder -

Ibid.

CarloSW2

What's the clearance from the bottom edge of the added air dam and the ground? ;)

What's the clearance from the bottom of the body to the ground? Front to back? ;)

I don't have those numbers (can get them though), but the airdam itself is 3" deep. I went very conservative as a first hit. So what's the thinking, deeper? This weekend's task will be to lower the dam another inch I reckon...

Before you lower the airdam find some dips to drive through. I would hate to see that beautiful piece crunched under the car.

Good point, though I have one of those neighborhoods where there are speed bumps throughout and was good across those, plus my driveway is a bit on the steep side so the lead-in up it is critical. I should have a look at that to see how much more I can go.

all that much
 

A point made by styling chiefs decades ago,was that if $billions were required to push up mpg with a new engine,a few $million could do the same with streamlining.
Since CAFE is measured on a sales-weighted basis for the automakers 'fleet',if these econoboxes ARE optimized for mpg,without affecting styling,then the better mpg here,allows more sales of highly profitable lower mpg designs.
So actually,the bean-counters drive the streamlining based on profit motive,share value to the stockholder,corporate image,marketing advantage,and compliance with EPA regulations.
Sure it's been a slow incremental process but when you consider that the cheapest car sold today could embarrass a Corvette of my college days,there has been advances.
Hucho put an airdam kinda like yours on a VW 1600 and it raised the Cd by 0.04.
There is no a priori knowledge about how any production car might react to any particular modification.We mod at our own peril.
Given market competition I would be very reluctant to presume that any of today's automakers are attaching anything to their cars arbitrarily.It would be antithetical to capitalism.

Once I hit upon the best depth I'm going to convert the carbon extension to something more curb friendly. What plastic would be best for that? ABS? Or some kind of stiff rubber?

chin
 

ABS is great material but will shred or bust in a nasty ground strike.Corvettes,Trans Ams,and New Beetles can't seem to hold onto their's.
I stumbled onto some urethane foam shop floor pad material at BIG-LOTs back in the tool and hardware section.You get about 16 Ft SQ for $15 (US).It's gray in color and has a star-plate kinda pattern on one side.I flipped it and used the smooth side.It bends onto curbs nearly every day for 2-years now and has held up well to the U.V.Since it's a neutral density gray 'color' it goes with any body color.
I've recycled chin spoiler material off Volvos out of boneyards.It had a perfect stiffness vs flexibility.But I really like this foam floor pad.
The plastic lawn edging will do also.I've used it all.
PS,Big Dave has used rubber conveyor belt material to good effect if you can find a local source for that.And it's black.

I'll have to try this material when extending my own front spoiler.

McMaster-Carr, McMaster-Carr, has many different types of conveyor belting. One type is listed as "impact and abrasion" resistant. That belt should make an air dam that will tolerate hitting the road.

That impact and abrasion resistant stuff is $8+/foot. I'm looking at the General Purpose PVC 4" width, $1.62/foot. As this is a "belt" I take it it has a lot of flexibility? When I think of PVC I tend to think of rigid (shatter prone in impact) PVC pipes.

Thought I was going to be clever tonight and lower the airdam another 2"...well, it doesn't clear the driveway. And another 1" doesn't either. So back to baseline. Only have about 1/4" clearance there (it's pretty steep). So I think it imperative to get something with a little impact resistance and I'll be looking at those belts. Need to think of what MkII airdam will be though (always looking to improve...).

I really like the design you have right now. The only thing I personally would do is widen it, go about half way across the tires on each side and call it good.
I dont think going any lower will help.

Problem is finding attachment points beyond the current width. Currently I've attached the airdam to the floor insert I made. I'm thinking MkII might entail attaching brackets to the perimeter of the bumper return. This would move the airdam forward of the current location and would allow me to widen it. I'll have a think.

Can you show /describe how it is attached now?