Underbody aero

[kulluminati777]

been done? or thought of





or maybe like a radiator air diffuser or something...

[Ryan]

http://www.mx-3.com/phpBB3/viewtopic.ph ... t=diffuser

[onlytrueromeo]

^For a total underbody diffuser, ryan you are correct.

For a front only one, there can be benefits seen outside of the purely aerodynamic drag aspect.

I have looked into creating a front underbody diffuser to decrease the air pressure in the engine bay. Why? Because this would increase the airflow that goes through the radiator. More flow = better cooling. Especially if you are running a turbo / FMIC the benefits of this will help considerably.

I can't find the thread right now, but there was a discussion on a different site where an engineer explained using a properly placed reverse hood scoop and an air pressure gauge with an underbody diffuser. He was able to double the amount of air that passed through his radiator like this.

[Daninski]

Fowljesse is the under body aero man. Search his post last year, he built the badest one of all.

[Mooneggs]

yeah Jesse used one of those big election signs under the front of his car

http://www.mx-3.com/phpBB3/viewtopic.ph ... 26#p500026

[fowljesse]

Bad is correct! It worked great, and kept the rain water out completely. It went away in the wreck, though. Next election time, I'll grab enough for the complete underbody!

[Josh]

I have made my own in the past. I think with the MX there are benefits to be had from a front and rear diffuser.

Years back I think it was Lexus, BMW or one of the higher end brands of cars designed a golf ball inspired under carriage that cut down on noise and increased the flow reducing the drag.

I am making one now for the MS front bumper to the Rad, and will be making one for the entire front under carriage out of Fiberglass.

This was going to be the final body piece for my RX8 had I not sold it. this is designed by knight sports.



My goal will be to add vents in key areas to help with flow from the engine bay, and also funneling the air from the front fog light inlets to the the wheels. The one on the right side will funnel into the fender well where the filter will also be.

[kulluminati777]

dude you HAVE to take alot of pics and put that project in your worklog

[Ryan]

The dimples on a golf ball are only effective because the golf ball rotates. Unless you're driving incorrectly, a dimpled undertray is an error in logic, or a brilliant marketing scheme, I'm not sure.

a FG undertray is undertray suicide.... unless you make it half an inch thick.


If you all do decide to cover up the front, make sure you leave a fair gap close to the firewall to allow flow out of the engine bay. The cowl is in what is called a stagnation point, which is a point of relatively high pressure, which will not draw air out as quickly as the fast moving air beneath the car.

for a rear undertray, cover it all up. All you get under there is messy flow with no need for it. Just leave enough to cool your exhaust (so it doesn't turn your gas tank into a hot tub)

[wytbishop]

There isn't a great deal of gains to be made under the car. By cleaning up the airflow there is a (small) bit of mileage to be had but you will not be able to create any downforce. Ryan's right though...you potentially have a real problem with flow through the engine compartment if you enclose the bottom.

There are a lot of good topics on forums around the interweb about aerodynamics. Here's a good one...

http://forums.turbobricks.com/showthread.php?t=135617

[Nd4SpdSe]

The dimples on a golf ball are only effective because the golf ball rotates. Unless you're driving incorrectly, a dimpled undertray is an error in logic, or a brilliant marketing scheme, I'm not sure.

Dude, you need to watch some tv:

http://dsc.discovery.com/videos/mythbus ... imyth.html

[Ryan]

Yay mythbusters!

In principle, the idea is bulls---.(skin friction is a minor factor for drag in cars... most is from the partial vacuum created behind it) In reality, who knows. Lol. 3 MPG is an impressive increase... for adding a couple hundred lbs of clay to your car. I wouldn't call that a carefully controlled scientific experiment, but aside from mumbo jumbo, I have nothing tangible in response. Interesting.


Thoughts:

Drag is caused by partial vacuum, partial vacuum is caused by flow reversal, flow reversal is caused by seperation.
The dimples stimulate a turbulent boundary layer. Turbulent boundry layer is less prone to seperation, although has higher skin friction.

Ideally, Mythbusters should have done this again, but only dimpling the roof, rear window and trunk. I think they would see their best results then.

[mikeinaus]

on the dimpled vs smooth surface thing. i saw a documentary on tv a few years ago about some racing company that was trying to develop a dimpled type of vinyl wrap for race cars. in the video i saw they took a porsche 911 turbo and did a few laps/test conditions, then wrapped the car in this dimpled vinyl and ran the same tests. in every test they went threw they saw an improvement in lap times and whatnot. i know lap times arnt the best measure of performance as there is too many variables but it was interesting none the least. the whole show could have been biased and a load of crap but its an interesting idea.

[_-Night-Shade-_]

Yay mythbusters!

In principle, the idea is bulls---.(skin friction is a minor factor for drag in cars... most is from the partial vacuum created behind it) In reality, who knows. Lol. 3 MPG is an impressive increase... for adding a couple hundred lbs of clay to your car. I wouldn't call that a carefully controlled scientific experiment, but aside from mumbo jumbo, I have nothing tangible in response. Interesting.


Thoughts:

Drag is caused by partial vacuum, partial vacuum is caused by flow reversal, flow reversal is caused by seperation.
The dimples stimulate a turbulent boundary layer. Turbulent boundry layer is less prone to seperation, although has higher skin friction.

Ideally, Mythbusters should have done this again, but only dimpling the roof, rear window and trunk. I think they would see their best results then.

Sounds like hindsight bias to me. Eat your beret Ryan! ;D

There isn't a great deal of gains to be made under the car. By cleaning up the airflow there is a (small) bit of mileage to be had but you will not be able to create any downforce. Ryan's right though...you potentially have a real problem with flow through the engine compartment if you enclose the bottom.

You will always create downforce any time you accelerate the air underneath the car and reduce the air pressure, via the Ground Effect. In fact that is one of the primary reasons why diffusers and splitters are used, along with aerodynamics. Definitely not for fuel economy, even if that may be an added benefit.

http://en.wikipedia.org/wiki/Ground_effect_(cars)

[wytbishop]

You will always create downforce any time you accelerate the air underneath the car and reduce the air pressure, via the Ground Effect. In fact that is one of the primary reasons why diffusers and splitters are used, along with aerodynamics. Definitely not for fuel economy, even if that may be an added benefit.

http://en.wikipedia.org/wiki/Ground_effect_(cars)

that's true...but just closing off the underside of the car is not going to accelerate the air passing under the vehicle. Airflow accelerates as it passes over a wing, for example, because the shape of the wing causes it to travel farther than the air passing under the wing. In order to maintain constant flow rate, it must accelerate. Cars which create downforce are shaped on the bottom so that the air passing under the car must travel farther...i.e. an iverted arc...or tunnels are used to create vortices...etc. Just making the bottom of the car smooth will not achieve this at the ground clearance that the MX-3 has, but it will reduce turbulence around the wheels and reduce resistance, improving fuel economy a bit.

If the car was lowered to say 30-40mm ground clearance you'd get some ground effect...but you'd also be wiping your a-- on the pavement.