multiple air dams??

[kach22i]

Originally Posted by Ladogaboy

The only thing I could see is two "mini dams" to direct air away from the rear tires.

Yes, like the side skirts on a semi-truck which are inboard at the leading edge.

Not exactly a second air dam, but perhaps doing what the original poster of this thread had in mind. The way sc2dave describes it will not work, Frank Lee spells this out pretty well.

FAQs on Trucks

[shovel]

I've been having a hard time finding a photo on google, but Amigos (or something like them?) had an air dam behind the rear axle...

[aerohead]

I've not seen nor heard of it being done.SAAB has has some interesting plastic bits under their cars,but I think it was more splash control than drag reduction.
RV motor homes and buses sometimes have a rubber or bristle splash control panel which spans the rear behind the rear wheels.

[rollercoaster]

Some mid 80's Dodge Daytonas had side skirts from the factory, but not sure just how much they help?

[expensivehobby22]

If the bottom of your vehicle is flat bottomed, then yes, an aero feature in the middle of the underbody can be beneficial.

-It can deflect flow that has crept in behind the front tires, or around the front airdam back out from under the car before it hits the rear tires, axle, etc
-It can stop crossflow in yaw, ie air coming in from the left of the vehicle and impinging on the right rear tire

So, it can work in the right situation. However, it's probably simplest to add small, local tire spats in front of the rear tires, or skirts along the sides.

[pjbgravely]

I have been thinking about this too. I plan to extend my belly pan all the way to the rear but what do I do with the rear axle? I was thinking about spats on either side of the drive-shaft in front of the axle.

I tried an air dam in front of the front tires on the front belly pan but it didn't do much and affected high speed stability.

[Rokeby]

The Inter-web is thick with big-rig aero ideas/aids.
Here is something that seems like it is what is being contemplated here:



Aerodynamic add-ons reduce fuel consumption of semi trucks by 7-12%

SmartTruck

[Sven7]

Originally Posted by expensivehobby22

If the bottom of your vehicle is flat bottomed, then yes, an aero feature in the middle of the underbody can be beneficial.

-It can deflect flow that has crept in behind the front tires, or around the front airdam back out from under the car before it hits the rear tires, axle, etc
-It can stop crossflow in yaw, ie air coming in from the left of the vehicle and impinging on the right rear tire

So, it can work in the right situation. However, it's probably simplest to add small, local tire spats in front of the rear tires, or skirts along the sides.

If the bottom of the vehicle is flat, a spoiler/dam would just add drag. Why push air away from a smooth surface? Add wheel strakes instead and it'll be ideal.

[expensivehobby22]

Originally Posted by Sven7

If the bottom of the vehicle is flat, a spoiler/dam would just add drag. Why push air away from a smooth surface? Add wheel strakes instead and it'll be ideal.

See the post above for one example of what I meant. I didn't specifically mean an airdam.

What I meant was a device in the middle of a flat floor that manages the air that creeps back in under the car behind the front wheels or the air from the front of the car that flows between the front wheels. It can either be shielding the rear axles or directing the air back out around the rear tires.

Sorry for not being more clear.

However, I do agree that in most cases tire spats will give you asignificant bang for the buck/effort.

[99metro]

I have thought about a mid-car air dam. I would be concerned about adding turbulence under the car and creating a bad exit vortex. One idea I am toying with is an air dam that works with the wind instead of pushing against it. Sort of a resistive self-moving air dam. I am leaning towards exit air mods rather than a front dam.

Aero obviously changes the faster you go. I have heard that some new car is coming out with aero panels that only come out over a certain speed. Don't remember which car it was.