airdam vs screen bellypan
 

I've been running a screen belly pan for about two months now... I think I'll try an extended airdam and rear wheel dams for two months and compare numbers. I am cautiously optimistic that the dams will out perform the screen.

Throw caution to the wind! Just be optimistic. :)

What kind of ideas do you have for the rear wheel dams?

Phil:

Did you make the belly pan yourself or can they be bought?
Do you have any pictures to show us of it installed on your vehicle?

Lapointe told me that he knew of it being used on a Mecedes vehicle. I do not know the year or model.


Paul

I have Photographs in my garage the rear wheel dams are made of 20 gauge steel and will be painted to match the car. The airdam has not been decided as of yet but I am leaning toward lawn edging since it it urethane and has a stiffening tube in it.

Are you setting up the rear wheel dams to be perpendicular to the direction of travel,canted to force the air out from under, or back under the car? Just curious on which way you're thinking or if you have some insight that you've seen before on it.

I was thinking slightly canted out but I'm open to ideas and suggestions. the ones I've seen have mostly been perpendicular to the flow. I'm going to keep looking in the gallery for a bit before I install anything.

My bet is that perpendicular is optimal because it extends the forward surface area presented by the wheel, lowering the pressure behind it in a more balanced way.

Canting it one way or the other risks creating larger eddy currents than might exist with perpendicular placement. Of course that may or may not be moot depending on how the airflow is behaving around the rear wheel to start with, but I suspect that most vehicles have a fairly balanced, albeit turbulent flow at that point, negating any benefit of directing the airflow one direction or the other.

In other words, like a Gurney Flap, the real goal is to impose a little more energy into the airflow to aid in seperation and reduce the amount imparted into it later.

what I've seen on insights and prius's flat to the flow is good angled back/down to match the tire is best. I'll go flat first since they are cut and bent already and I'll see what happens

interesting, is there any reason for using a screen over some other smooth surface?

also, what are your plans for the front air dam? are you worried about increasing your frontal area or are you matching the frontal area?

the air dam hopefully will not increase the frontal area at all. I used the screen to see if a uniform but not smooth (golfball esque) surface would make for improved underbody aerodynamics. 2 months with the underbody VS 2 months with airdams is the experiment. My postulate is the airdams will outperform the screen however I think possibly the difference will fall in the noise of tank to tank variances.

well the air dams are installed but in a bout of laziness I left the bellypan. I will keep logging my milage and see if there is an improvement in milage. The immediate thing I noticed is that with the dams in place the car is eerily devoid of wind noise, Similar to when drafting a big rig.

That doesn't sound surprising to me. Ever heard a screen whistle in a high wind storm? No doubt, it's not the quietest under body material one could use. ;)

yea i was going to say that air passing through screens is ridiculously turbulent, but i was uncertain of the behavior of air passing over the screen. so is there any empirical data supporting the belly screen?

well without the screen the best I ever got milage wise was 25 and change this tank is looking like an easy 30+mpg

I think the screen idea is a very valid one logically. While it has a high degree of permeability, the turbulence and eddys that can pass through it are minor compared to the normal rough contour of car underbodies. I'm also thinking that it could work better in terms of not requiring as smooth a belly pan, as the perforations create a very active boundary layer from airflow that is laminar, allowing it to better follow transitions.

my main problem with the screen is being aluminum it tears quite easily and has torn free about three times now. quite annoying really. now the wind noise there was a significant drop from no screen to screen then it dropped to almost none with the dams.

Belly Pan Ideas
 

With my new coming vehicle I plan on using a belly pan. What do you do with the exhaust? Do you cover the exhaust system with a pan and wrap it in heat wrap? Will it make the floor pan so hot the carpet will melt? Or do you build the belly pan up to it and leave it exposed? I also thought about puting cone shaped pieces like you would find at a Home Depot for chimney vents around the muffler for the aerodynamic bullet effect.

I plan on a full under body belly pan and maybe cut out the middle section of the rear bumper to aim and let the air out from underneath to merge with the air over the top of the vehicle. Either that or cut some 3 inch holes in the back bumper to release the air trapped by the rear wheel wells and the lower lip of the rear bumper.

I also plan on sealing up the front, panning the lower part of the front chin and making sure the front wheel wells are sealed and rounded to make corners as aerodynamic as possible. Also taking the side of the vehicle and rolling the pan to meet the edges next to the doors. Essentially as aerodynamic underneath as the top of the vehicle.

I just read somewhere that a Hummer has 5 times more drag than the average vehicle. Aside from the fact that the Hummer is a box, the underside has differentials hanging down, a transfer case, and all sorts of open frame work. Unlike the Aptera which is a Jelly Bean or rain drop, it kind of reminds me of a Cessna without wings, but if I can get one for under 20 grand, I feel a hole in my pocket forming. Before the Aptera I know I will have to buy a regular car and transform it, honestly I can wait to put the car on 4 ramps and start cutting belly panels. You ideas?

with a metal screen belly pan the exhaust heat can escape unfettered if you go for an enclosed pan you will need some venting to let the heat out.

heat wrap + dd = rust.

and the winner here is ....... the airdams

three tanks consistently over 30mpg without trying the screen netted 30+ but required all the hyper miler techniques. the airdams didn't.

Air dam looks very nice. :thumbup:

I'm taping up the Focus' lower grill for a trip. We'll see how I do.

Thanks for the write up!:thumbup: :thumbup:

I'm just curious if you tracked average temperature with those tanks? Seems to me like even a difference of 10 degrees could amount to a significant difference.

On my belly pan, the covering under the exhaust system is aluminum flashing. I designed it so there is an air flow running from the engine compartment through the enclosed exhaust tunnel to keep it cooled. Its been in place for almost 2 years without problems.

Why not use both alu. screen and coroplast?
 

The aluminum screen is cheap, fireproof, breathable, and apparently pretty easy to install. Does not rattle or boom like sheetmetal. So, use it around the hot spots like mufflers and exhaust pipes, to let hot air be drawn out by Venturi effect. Also, being a superb heat conductor, it will very efficiently dissipate heat from any point of contact with a muffler, etc.. Even though porous, the screen will still go a long way to reduce improve form drag, i.e., streamline or smoothly cover otherwise gross aerodynamic shapes such as leading edges of mufflers, etc.. Porsche uses perforated screen as an engine cover on its latest high performance mid-engine car, the Carrera GT.

Coroplast everywhere else practicable.

thank you for the pics.. lol