Open spaces in spoilers

Many factory spoilers have open spaces, ie: FiST and FoST.  I thought first it was a Ford thing but I saw another make with the same.

 aerodynamic purpose or something else.

I've always used that as the distinction between a "spoiler" and a "wing".

Aero for sure. Hatchback spoilers I think are just there to change pressures at the back to reduce lift. 

I would love to see a comparison of the spoilers on the back of the ST hatchbacks and the spoiler on the MS3. Different shapes but similar effects. It’s interesting stuff. 

Also, I know very little about aero. Smarter people than me can confirm or deny my ramblings. 

I would guess its just aesthetics. I think most spoilers, wings, and other aero parts are generally not really doing anything until the car is at high speeds, except adding drag. A wing or spoiler designed so that it is effective at high speed, will be ineffective at lower speeds and probably be more of a detriment than anything else.

The Ecomodder website has a lot of material on aerodynamics. It's geared towards increasing fuel mileage, but I think a lot of it could be applicable to racing. They have a lot of info on how spoilers and wings decrease MPG due to added drag.

Couple points: 

Wing (Air foil) vs. Spoiler: Has nothing to do with the open spaces like mentioned.

-A wing is literally an upside-down airfoil that is just that; an upside-down airplane wing. These are devices that generally don't "improve" overall aerodynamics, since they have a large drag trade-off. 

-A spoiler is a device that disturbs localized airflow to improve overall airflow around a vehicle. 

A few errors in the comments so far: 

1. @Freetors That has almost nothing to do with the distinction between a spoiler and wing (see above)

2. @Spandak 

3. @redleg37 Mostly right except for the last part. In a lot of cases, spoilers are an excellent drag reduction device. A good example is blackbird fabworx lexan spoiler (Miata stuff). There's CFD data floating around somewhere that shows quite a benefit in drag reduction at low AOA which makes it very popular for endurance racing series. 

I'm sure there's people that know more. Just an engineer with some free CFD software that I mess around with every once and a while. 

The question was not about the semantics of the device, just what was the purpose of the openings in said device.

They're also trying to change pressure on the rear window so that it doesn't get dirty so fast. You can see this on a bunch of modern minivans and SUV's as well as wagons back to at least the 60's 

I wonder if it works like a wing slot?

 leading-edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading-edge slot is a spanwise gap in each wing, allowing air to flow from below the wing to its upper surface.

In researching my MS3 before I bought it I came across an old video where a Mazda engineer describes the rear spoiler and how proud they were of it and how much lift it prevented at speed. The ST hatchbacks are 10 years newer and I’m sure have even more effective aero devices. 

What I find interesting is comparing performance and non-performance cars of the same model. The standard Mazda 3 has a roof spoiler that continues the airflow right off the back of the roof. Modern cars have the same thing and now they are adding similar pieces to the sides of the hatch too. My understanding is that these create a clean break for the air and lower drag. The performance models have different shapes which are probably higher drag but reduce lift. I’m guessing they work on Bernoulli’s principle by slowing the airflow over the top of the car and then spitting it out into the low pressure area behind the rear window. 

I need some CFD software to play around with. I wish this is what I spent my time doing in Formils SAE instead of suspension. 

In reply to mazdeuce - Seth

 This was my thought.

 Doesn't seem to do much

Appleseed said:

I wonder if it works like a wing slot?

 leading-edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading-edge slot is a spanwise gap in each wing, allowing air to flow from below the wing to its upper surface.

It's probably turning the "Trailing Edge eXtension" into more of a Fowler flap, than a leading edge slot... since it's at the back... although those are both acting to inject higher pressure from the lower surface to reinvigorate the flow over the upper surface of the following element.

in this case it's injecting the faster moving flow from the top of the car under the TEX lower surface, which under normal circumstances is probably closer to stagnant... or even reverse flow.

All of which is to say that they're trying to increase rear downforce for high speed stability... which can begin to be felt at high speeds easily attainable in a variety of jurisdictions

I believe the advantages of the trailing edge extension or Fowler Flap is that they create very little extra drag for the added downforce.

Personally, I like the roof spoiler my Abarth has. It may not add much in downforce, but it serves to extend the roof of the car to decrease drag by fooling the air into thinking the car is much longer than it really is.

I think you're thinking of a slotted flap. Fowler flaps are similar to slotted, except in the fact that Fowlers move backwards before moving down to add wing area. Not a nit-pick, just a clarification. I never thought to link a slotted flap and an automobile wing.

In reply to Appleseed :

That's a fair critique

A while ago I started thinking of cars as the "main element" of a really low Aspect Ratio wing... with a really bad sectional shape (due to various 'human packaging constraints'), and splitters, canards, spoilers, rear wings are just various "multi-element devices".

from this viewpoint, an F1/Indy car wing is more like the aforementioned front slot of yours.  Splitters are kind of like "Krueger Flaps", and "Car Spoilers" are like "divergent trailing edges".

Which actually raises an interesting thought that no ones built a moveable rear wing that acts like a fowler flap... probably because it adds too much of a moment on the chassis/suspension.