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.