Aerodynamics

[mshekleton]

As I was reading some of the older posts about splitter and wings I thought I might bring to light some of the misconceptions about aerodynamics and discuss some modifications.

One of the most popular aerodynamic modifications is the spoiler or wing. The intent of a spoiler is to "spoil" the turbulent air coming off that back of the body. It's main purpose (other than looking cool) is to increase to aerodynamic efficiency of the car. A wing is designed to utilize fast moving air to produce downforce on the rear of a car (like an upside-down airplane).

And downforce is good, right? Maybe. In a front wheel drive car, downforce on the rear levers up the front end actually removing traction from where you need it to be. Rear downforce has the advantage of combating oversteer. Unless you have a major oversteer problem on your hatchback, this is probably not a good thing. This is where the front splitter comes into play. A front splitter is designed to produce downforce on the front of your car. Just as the car can be aerodynamically unbalance using just a rear spoiler, a super aggressive front splitter with no rear spoiler can produce oversteer. A proper high speed vehicle should be aerodynamically balanced. It should have both a rear spoiler and a front splitter both tuned to the desired high speed understeer/oversteer specifications. Most high speed vehicles are pretty evenly balanced with a small amount of understeer.

So before purchasing that giant wing, remember that you would probably benefit from a front splitter first (since the Yaris loves understeer). Also, If you're driving your Yaris fast enough to need these aerodynamic components I might also suggest purchasing some life insurance with your wings.

[127.0.0.1]

Be sure to include real facts and data please:

* air velocity through the test section
* direction of airflow
* direction of airflow approaching a surface
* dye, smoke, or bubbles of liquid introduced into the airflow upstream of the test
* pressures measured with beam balances
* pressure distributions and using multi-tube manometers to measure the pressure
or pressure paint, and wake survey


Otherwise, yer aerodynamic discussion and how it applies to the Yaris just might
be a load.

[mshekleton]

Sure, I can talk about some of these topics... but no one is turning their Yaris into an indy car. But If you want to hear it, let's begin.

Aerodynamic testing is a complicated process. It involves wind tunnel testing, modeling and prototyping, and computer modeling. Here are some basic definitions:

Coanda Effect: A moving stream of fluid in contact with a curved surface will tend to follow the curvature of the surface rather than continue to travel in a straight line.

Bernoulli's Principle: Fluid moving at a higher velocity over an object produce less pressure than fluid moving at a slower velocity.

Winglet: A winglike structure at a wingtip set at an angle to the plane of the wing designed to reduce drag by its effect on wingtip vortices.

Gurney Flap: A very small bent angle attached to the wing's trailing edge. It produces more downforce by increasing the vertical airflow deflection.

Laminar Airflow: The smooth, continuous movement of one layer of gas or liquid over another.

Turbulent Airflow: Fluid regime characterized by chaotic, stochastic property changes.

Manometer: A liquid column hydrostatic instrument used to measure variations in pressure or vacuum near to that of the atmosphere's

Particle Stream: Typically smoke or dye used to visualize the effects of moving air in a wind tunnel.

Force Balance: A sensitive instrument attached to a model in a wind tunnel which is used to measure lateral force vectors and rotational forces (yaw, pitch, and roll).

Vortices: Airflow with a rotational element.

Airfoil: A structure shaped to produce lift when moving in air.

Aerodynamic Chord: The imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil.

What would you like to hear more about?

[SilverBack]

Good thread and I'll keep this in mind when I finish Auto-X and move up to road racing, but:

Originally Posted by mshekleton

(since the Yaris loves understeer).

Not always. The rear-end actually wants to swing around and induce oversteer while entering corners. Balancing the throttle with this oversteer actually keeps the car in line and even helps you corner just a little faster, which makes splitters and spoilers unnecessary at up to some 60 MPH. Also, I'm sure you agree that the Yaris can't reached speeds past that range due to the fact 1) it's painfully underpowered (unless you own the 300HP Garmobile) and 2) not all tracks can give you a long enough straight-away to reach speeds that can effectively induce downforce up to the next corner. 2¢.

[mshekleton]

Originally Posted by SilverBack

Good thread and I'll keep this in mind when I finish Auto-X and move up to road racing, but:



Not always. The rear-end actually wants to swing around and induce oversteer while entering corners. Balancing the throttle with this oversteer actually keeps the car in line and even helps you corner just a little faster, which makes splitters and spoilers unnecessary at up to some 60 MPH. Also, I'm sure you agree that the Yaris can't reached speeds past that range due to the fact 1) it's painfully underpowered (unless you own the 300HP Garmobile) and 2) not all tracks can give you a long enough straight-away to reach speeds that can effectively induce downforce up to the next corner. 2¢.

Hmmm, my Yaris understeers but I think it's because of all the suspension work. I guess the only way to get your Yaris going fast enough is if you can get the handling down so you minimize the speed loss in the turns. But I agree with you.... for all practical applications, the Yaris doesn't need a wing. That's pretty much my point. But I've done a lot of aero work so I figure I could talk about it if anyone cared to listen.

[lilredrocket]

What is your alignment setup?

[mshekleton]

Originally Posted by lilredrocket

What is your alignment setup?

Umm... no idea. I'm bringing it to the shop for an alignment once I get all the issues worked out. I'm trying to stuff big tires in it without rubbing (checking out some fender flares as a possibility). Haven't touched the alignment since I bought it though.

[Cosmonaut]

aren't spoilers a source of drag and therefore reduce aero. effic. ?

[mshekleton]

Originally Posted by Cosmonaut

aren't spoilers a source of drag and therefore reduce aero. effic. ?

Cosmetic spoilers reduce efficiency. Functional spoilers are intended to reduce turbulent flow and extend the length of the laminar flow.

[d1nzfe]

ah, lets talk about underpanel!
sites selling claims it increase downforce!

[cali yaris]

1. Yes, spoilers are a source of drag. However, the benefits can often outweigh the small amount of drag they create. 1. downforce for more traction (high speeds only). 2. airflow redirection (keeping dirt off the back window for example).

2. Underpanels, diffusers and other smooth surfaces under the car speed up the air. If the air going under the car moves faster than the air going over the top, a vacuum is created underneath. This is exactly the same as downforce. It's also exactly the way a plane's wing works, but upside down.

[cali yaris]

In a front wheel drive car, downforce on the rear levers up the front end actually removing traction from where you need it to be.

Lots of misinformation in some of these posts. Go look at your Yaris. While the point is true in general, the position of the Yaris rear wheels makes the difference in front negligible. I know this firsthand and yes, I've driven fast enough to feel it (130+ mph, so far).

Since this is a Yaris forum, let's be clear what car we are talking about (when relevant) when making points about aerodynamic effects.

[d1nzfe]

anyone tried to make the underbody as smooth as possible yeah? other then front underpanel?

[cali yaris]

the midsection is pretty much fine as is. The rear could use some work, but will require some interesting bracket arrangements to work very well. I sell a front underpanel of our own design (but close to the BeatRush version). Test cars reported +1-2 mpg increases, so we know it has an effect even at "normal" speeds.

[kngrsll]

i think the biggest benefit to this car now would be to smooth the airflow under the car. It isnt fast enough to warrant a bunch of downforce creating devices. I think the best thing to do would removing drag.

Personally, i think the biggest gains would be: vent the rear bumper, create a rear diffusor, and finally a front splitter. I think a little chin on the front splitter would be a little helpful

[lilredrocket]

Originally Posted by mshekleton

Umm... no idea. I'm bringing it to the shop for an alignment once I get all the issues worked out. I'm trying to stuff big tires in it without rubbing (checking out some fender flares as a possibility). Haven't touched the alignment since I bought it though.

Why have you put on coilovers and not aligned your car?... Thats the first thing you are doing wrong. Get an alignment setup on hw you drive your car and what you do with your car. It will make it handle alot differnetly and get rid of that understear problem you are having.

[TLyttle]

I don't know for sure, but I suggest that the sedan is a better place to begin. The shape of the body (I think it is also lower than the 3-door, reducing frontal area, also important) gives a better departure angle for the air, possibly offset by the extra weight of the sedan.

As far as wings, spoilers, and all that frippery is concerned, the differences for most owners is cosmetic. Long experience has shown me that just a slightly better driver can more than offset any advantages wings/spoilers/diffusers may make. Drag is a larger concern than presented here, and you can prove it to yourself simply by coasting with and without said additions.

[lilredrocket]

The sedan is actually lighter than the hatch