Rear Wings

[1stlsx]

In terms of how I classify it? Or in terms of performance?

The answer is yes. The gap underneath is why I'd say you could call the one pictured above a wing. It also allows for pressure recovery on the rear/underside surfaces which reduces drag.

Am I correct in looking at the model that this gap has been omitted? this would generate different results correct?

 

[Famine]

I usually go by whether or not the majority of the part is isolated or connected to the car when you take 2D slices oriented length wise along the car. A wing would be a 3D extension of an airfoil with its own stagnation points while a spoiler would be an extension of the car.

Since there's air all around the part on the rear of the MR2, I'd say it could be wing. I've never really seen a solid definition separating one from the other (except for aircraft).

In automotive terms, a wing has to produce a net force effect downwards (not in terms of the car, which may still produce a net force effect upwards) that, if running a fixed angle, increases in magnitude in proportion to the road speed.

A spoiler merely exists to spoil airflow - which could be in terms of reducing undesireable lateral forces (particularly so if they're not proportional to speed) or by moving the separation zone rearwards (perhaps for reasons of fuel economy), particularly in the case of reducing drag from turbulent air ahead of it caused by separation from the rear screen. They can reduce lift, which isn't necessarily the same as producing net force downwards as it's the change in shape of the car body that reduces lift, not the device itself producing airflow-proportional force in any one direction.

The MR2... "accoutrement" doesn't produce a net force downwards (pretty much nothing on road cars did in the 1980s - just about the only exception was the Escort RS Cosworth) so it's not a wing. It does spoil airflow (and might reduce lift), so it's a spoiler.

In terms of how I classify it? Or in terms of performance?

The answer is yes. The gap underneath is why I'd say you could call the one pictured above a wing. It also allows for pressure recovery on the rear/underside surfaces which reduces drag.

I'd agree that wings need to be separated from the body to function as wings - but spoilers can also be separated from the body and not function as wings. Like the MR2 above

 

[Exorcet]

Am I correct in looking at the model that this gap has been omitted? this would generate different results correct?

Yes, however the effect is minor compared to the other inaccuracies in the model. My goal was to measure the size of the separation bubble behind the driver area.

In automotive terms, a wing has to produce a net force effect downwards (not in terms of the car, which may still produce a net force effect upwards) that, if running a fixed angle, increases in magnitude in proportion to the road speed.

Alright, I can accept this as a good definition.

The MR2... "accoutrement" doesn't produce a net force downwards (pretty much nothing on road cars did in the 1980s - just about the only exception was the Escort RS Cosworth) so it's not a wing. It does spoil airflow (and might reduce lift), so it's a spoiler.I'd agree that wings need to be separated from the body to function as wings - but spoilers can also be separated from the body and not function as wings. Like the MR2 above

Well now that we're settled on a name, mentioning it in posts should be a bit easier.

 

[Keef]

Just for reference, this:

is a spoiler, not a wing. Wings can be (and usually are) both, but spoilers are just spoilers. And that's just a spoiler.

It's a wing. Technically, an airfoil. It's separated from the body of the car with airflow both over and under it. As you said, it's both a wing in and of itself and a spoiler in its use to modify the airflow over the car.

This is a spoiler:

It's purpose is to spoil the function of an airfoil. Airplanes use them to descend, slow down, roll, or some combination thereof. Cars use them to decrease lift, increase stability, increase downforce, etc, because cars' natural profile is similar to an airfoil.

 

[Famine]

Unless it produces downforce (proportional to road speed) by virtue of its own shape, it's not a wing by automotive definitions.

 

[GDII]

$600 NZD will get you a set of OEM Bilstein struts from Toyota. That will make your car much more stable.

Start off with good suspension and brakes. Semi slick tyres will be next. Unless you are pushing out 400hp + aero mods will be not be much help and will just cost lots. You could spend that money other places to gain speed.

There is a black SW20 turbo in NZ which has a GT wing but that is raised up almost above roof level. That car has quite a bit of power.

If you wanted to go really crazy you could install a flat bottom and proper rear diffuser. But that would involve wind tunnel testing to get a design that actually works.

 

[Exorcet]

Unless you are pushing out 400hp + aero mods will be not be much help and will just cost lots.

Not true. What may be true is that the kind of aero mods that will help at low speed/power aren't as easy to find (I don't know, I've never looked at off the shelf aero parts). You can make aerodynamic parts for pretty much any speed or power though. They might go against Husky's desire for subtly however.

If you wanted to go really crazy you could install a flat bottom and proper rear diffuser. But that would involve wind tunnel testing to get a design that actually works.

That could yield big gains without being overly obvious, and it does not strictly require a wind tunnel, but I would bet that they would be more expensive if they're even easy to get at all.

You also need to be careful with them because of ground effect.

 

[Keef]

Unless it produces downforce (proportional to road speed) by virtue of its own shape, it's not a wing by automotive definitions.

I don't care about the automotive definition, I care about the fluid dynamic definition. A wing is a surface which produces lift. Even a completely flat panel will become a wing when introduced to a relative wind or flow at an angle. And downforce is a nonsense term that is only used by people who don't operate in three dimensions.

That aside, upon inspection you'll find that this MR2's wing is cambered quite a bit, as was the small wing on my mom's Corolla.

And like I said, even if these were flat planks aligned with the standard wing's chord line they would still have an angle of attack and produce downward lift.

 

[Famine]

I don't care about the automotive definition

Pity, because we're in the "Cars in General" forum. If it's about cars, the automotive definition is kinda important.

And downforce is a nonsense term that is only used by people who don't operate in three dimensions.

Like... cars?

Romain Grosjean being a notably exception, obviously.

downward lift.

If "downforce" is nonsense because it's limited to the two dimensions cars habitually move in, lift is a nonsense term because it's limited to fluids. Of course this particular patch of semantics helps the topic and the poster none - lift is just force perpendicular to the direction of travel in fluids. If the lift is downwards it's a downwards force... Thus it's perfectly cromulent to talk of downforce in this application - and even if it weren't, I used the term "a net force effect downwards that, if running a fixed angle, increases in magnitude in proportion to the road speed" earlier, which is significantly more accurate.

Dude's looking for a spoiler for his car, not a wing, because what came with the car is a spoiler, not a wing - bolt it onto a secure base in a wind tunnel and it won't generate a net force downwards in proportion to road speed. The automotive definition is fairly important because it changes what product he buys in relation to what effect he wishes to achieve.

If he gets a wing for his car he significantly changes the forces operating on the car and can achieve the exact opposite of what he's looking for - or much more of what he's looking for than he'd wish. He could conceivably destroy his fuel economy by introducing an earlier separation layer along with the massive increase in drag (if he gets pylons big enough, the frontal area too) and generate more lift over the car as a whole - and at least on the front of the car, which is suboptimal if you like turning.

 

[Punknoodle]

 

[Exorcet]

Dude's looking for a spoiler for his car, not a wing, because what came with the car is a spoiler, not a wing - bolt it onto a secure base in a wind tunnel and it won't generate a net force downwards in proportion to road speed. The automotive definition is fairly important because it changes what product he buys in relation to what effect he wishes to achieve.

Strictly speaking, it's an airfoil like shape, and Keef pointed out the camber. Stand it alone in a wind tunnel and it will probably generate downforce (assuming I'm not totally off on the shape) and it will grow with speed.

Typically spoilers on a sports car turn the flow upwards which makes it hard for them to avoid generating some downforce, and you can't avoid having the force grow with speed unless it's zero.

If he gets a wing for his car he significantly changes the forces operating on the car and can achieve the exact opposite of what he's looking for - or much more of what he's looking for than he'd wish. He could conceivably destroy his fuel economy by introducing an earlier separation layer along with the massive increase in drag (if he gets pylons big enough, the frontal area too) and generate more lift over the car as a whole - and at least on the front of the car, which is suboptimal if you like turning.

Well technically even with your/the automotive definition, a wing could make anywhere from 0+ to 20 tons of downforce so it won't necessarily destroy the handling on the car. However I doubt he'll build his own wing, so he's limited to what's for sale, and I'm not familiar with the range of performance available from aftermarket wings.

I guess maybe this is the time for a simple question. How stable was the car before the spoiler(?!) was damaged? That would probably be a good indication of whether it is the problem or if the suspension is (though suspension should be in order before you go looking for wings anyway).

Following up to Famine's point on stability, automotive spoilers don't just combat lift, but lift oscillations, which can be more dangerous than lift itself. A curved edge may not have a steady and consistent flow separation region




The spoiler on the MR2 may be trying to rectify that more than augmenting lift in any significant amount.

 

[Luminis]

I just wanted to say this:

I'm not the OP, I don't need a wing/spoiler and I'm not half as well versed in terms of defining what's what - but dang, this is quite the informative stuff on automotive aerodynamics. Keep on enlightning me, pleaase 👍

 

[JrDarknes]

I just wanted to say this:

I'm not the OP, I don't need a wing/spoiler and I'm not half as well versed in terms of defining what's what - but dang, this is quite the informative stuff on automotive aerodynamics.

I swear O_o. Reason why I like this forum, learn a lot of stuff just by reading threads.

 

[Keef]

Pity, because we're in the "Cars in General" forum. If it's about cars, the automotive definition is kinda important.Like... cars?

Romain Grosjean being a notably exception, obviously.If "downforce" is nonsense because it's limited to the two dimensions cars habitually move in, lift is a nonsense term because it's limited to fluids. Of course this particular patch of semantics helps the topic and the poster none - lift is just force perpendicular to the direction of travel in fluids. If the lift is downwards it's a downwards force... Thus it's perfectly cromulent to talk of downforce in this application - and even if it weren't, I used the term "a net force effect downwards that, if running a fixed angle, increases in magnitude in proportion to the road speed" earlier, which is significantly more accurate.

Luckily air is a fluid and is what cars travel through which seems to necessitate aerodynamic terminology. Obviously we both know what lift is and that it works in any direction. My argument is that when you put an airplane upside down it doesn't create what an aerodynamicist would call downforce, nor when banked would it be called kind-of-upward-and-sideways-at-the-same-time-force. If you drove a car upside down would it wouldn't be called downforce, much less rounding a banked curve. The force isn't downward at that point so the term downforce is of no literal use unless the car is driving perfectly horizontal.

Dude's looking for a spoiler for his car, not a wing, because what came with the car is a spoiler, not a wing - bolt it onto a secure base in a wind tunnel and it won't generate a net force downwards in proportion to road speed.

The wing will most certainly create a downward force and simply looking at its side profile is enough to tell. I provided a Corolla wing to illustrate the camber of a very pedestrian application. Whether the car as a whole creates a net downward force is irrelevant. By your justification, the tail of a conventional-wing airplane is a spoiler because it creates a force opposite the main wing and is attached to the same object. That's simply not the case. Earlier I posted a picture of two spoilers, neither of which create any lifting force of their own and both of which spoil the lift of the wings they're mounted to which are the car's body and the plane's main wing. A spoiler simply cannot have flow above and below it because then it will create lift when presented at an angle to the flow and that makes it a wing. I'm sure you realize that air flows both above and below the MR2's wing.

If he gets a wing for his car he significantly changes the forces operating on the car and can achieve the exact opposite of what he's looking for...

It depends on what he's looking for. If he mounts the wing on a bigass pole he'll get a sailboat which is moved forward by generally horizontal lift. If he mounts it curved side up and drives off a cliff he'll get a really crappy glider. If he mounts it upside down he'll have something more aligned with his goals.

 

[Famine]

Luckily air is a fluid and is what cars travel through which seems to necessitate aerodynamic terminology. Obviously we both know what lift is and that it works in any direction. My argument is that when you put an airplane upside down it doesn't create what an aerodynamicist would call downforce, nor when banked would it be called kind-of-upward-and-sideways-at-the-same-time-force. If you drove a car upside down would it wouldn't be called downforce, much less rounding a banked curve. The force isn't downward at that point so the term downforce is of no literal use unless the car is driving perfectly horizontal.

The force would always be downwards, perpendicular to the direction of travel from the perspective of the vehicle...

Interestingly, most car engines would stall if asked to drive upside down for a while.

The wing will most certainly create a downward force and simply looking at its side profile is enough to tell.

No. It's not.

In many instances it is - it's an obvious wing - but not always. Aside from the fact you can't actually see the side profile (the pylons are in the way), simply putting it in a wind tunnel (or scale versions in other media) is enough to tell.

And I can tell you that the MR2 rear wing, on its own in a wind tunnel, provides no downforce whatsoever (though I can't find my source on that one - might be worth grabbing Scaff or Venari). What it does is counteract lift in the vehicle application - it requires the turbulent airflow ahead of it generated by the shape of the car (particularly the separation from the rear screen) to function.

Whether the car as a whole creates a net downward force is irrelevant.

In automotive terms, a wing has to produce a net force effect downwards (not in terms of the car, which may still produce a net force effect upwards) that, if running a fixed angle, increases in magnitude in proportion to the road speed.

By your justification, the tail of a conventional-wing airplane is...

... nothing of the sort because that's not an automotive application.

A spoiler simply cannot have flow above and below it because then it will create lift when presented at an angle to the flow and that makes it a wing. I'm sure you realize that air flows both above and below the MR2's wing.

Is the lift downwards in relation to the car, perpendicular to the direction of travel?

If not, it's not a wing, it's a spoiler in automotive terms. Why do automotive terms matter more than fluid dynamics terms? Because we're talking about an aerodynamic device on a car.

Here's a very obvious example of a spoiler with airflow below it that generates no net lift:

Yes, that's a pallet cutoff mounted flat. It spoils airflow and, I'm sure you can tell from looking at the side profile, will generate no net force perpendicular to the direction of travel and proportional to speed. It might generate quite a bit of drag force and bend the pylons though - at which point the angle might do the job, only in exactly the wrong direction.

It depends on what he's looking for. If he mounts the wing on a bigass pole he'll get a sailboat which is moved forward by generally horizontal lift. If he mounts it curved side up and drives off a cliff he'll get a really crappy glider. If he mounts it upside down he'll have something more aligned with his goals.

And if he gets a wing that generates a net force effect downward in relation to the body of the car that increases proportional to speed, he'll gain effective weight at the back (mass x force = weight), shifting the weight bias rearward and reducing available control on the front tyres unless balanced out with a front wing, affect the shape of the separation layers ahead of and behind it to destabilise the car laterally at speed, reduce the top speed and impact fuel consumption dramatically - generally achieving a car that has a wing, but does the exact opposite of what he wants with a nervous front and rear.

You shouldn't be putting any old wing onto any old car just because it makes downforce. You should put one that has been airflow tested for that application. Of course this has never stopped anyone bolting a wing onto a car before.

 

[Aquarelle]

Just an update on the situation for anyone who cares; I've decided to cut my losses.

I'm selling the car, I went through and thoroughly inspected the car and decided it would be more cost effective to go without while I'm living in this apartment and then buy another car when I have a proper house with a garage.

I'm still extremely interested in the topic at hand so please don't think this has all been for naught, I'm always eager to learn new things and aerodynamics has always been something that eludes me. (Plus I'll likely end up buying another MR2 when my situation changes)

Just thought I'd let everyone know what I decided to do incase anyone was worried about me driving with the car in its condition (I doubt anyone did but hey)

 

[Exorcet]

Here's a very obvious example of a spoiler with airflow below it that generates no net lift:

Yes, that's a pallet cutoff mounted flat. It spoils airflow and, I'm sure you can tell from looking at the side profile, will generate no net force perpendicular to the direction of travel and proportional to speed. It might generate quite a bit of drag force and bend the pylons though - at which point the angle might do the job, only in exactly the wrong direction.

Actually, maybe that bending is just compensating for the downwash coming off the roof, so the angle of attack may yet be positive. Genius design?

Just an update on the situation for anyone who cares; I've decided to cut my losses.

I'm selling the car, I went through and thoroughly inspected the car and decided it would be more cost effective to go without while I'm living in this apartment and then buy another car when I have a proper house with a garage.

I'm still extremely interested in the topic at hand so please don't think this has all been for naught, I'm always eager to learn new things and aerodynamics has always been something that eludes me. (Plus I'll likely end up buying another MR2 when my situation changes)

Just thought I'd let everyone know what I decided to do incase anyone was worried about me driving with the car in its condition (I doubt anyone did but hey)

I don't even own it, but I'm sad to see it go. Sometimes, you just need to do things like this though.

And if no one cared, they wouldn't have suggested looking at the suspension first. Anyway, I hope you're able to get a replacement soon.

And I don't mean to bother, but out of curiousity, the problems only started after the [insert aero device name] was damaged?

 

[Famine]

[insert aero device name]

The technical term for the above is "BGW". I could tell you what it means, but then I'd have to ban myself.

 

[Aquarelle]

I don't even own it, but I'm sad to see it go. Sometimes, you just need to do things like this though.

And if no one cared, they wouldn't have suggested looking at the suspension first. Anyway, I hope you're able to get a replacement soon.

And I don't mean to bother, but out of curiousity, the problems only started after the [insert aero device name] was damaged?

I'm sad too It was a fun little car but with the cost of parking at this place and the cost of the repair.. it's better to just fulfil my love of driving in the virtual world until I can move. Such is life sadly.

The spoiler was already damaged before I bought it.

The girl just told me that something rather heavy fell on it and that's all I knew, when I bought it I wasn't pushing it hard during the test drive because she didn't seem the type that would be willing to let me get a bit more spirited (under the speed limit of course) and since the problem isn't noticeable at safe road speed I didn't pick up on it.

So yeah, that's why I'm unsure of the effect the damage was having. Like I said I came into this clueless about aerodynamics and I feel a fool now

I'll hunt around my paperwork, I may still have her number. I doubt she'll remember since it's been a fair few months now but it's worth a shot since I'm curious too.

The technical term for the above is "BGW". I could tell you what it means, but then I'd have to ban myself.

This made me laugh more than it probably should have

 

[Keef]

Actually, maybe that bending is just compensating for the downwash coming off the roof, so the angle of attack may yet be positive. Genius design?

This could apply to the MR2 wing also seeing as it is exposed to the downwash off the cars roof. That the wing has a visible negative AOA makes it likely the relative wind makes for an even lower angle which basically guarantees downward lift.

I can't be convinced without a realistic model or wind tunnel results.

 

[Exorcet]

I can't be convinced without a realistic model or wind tunnel results.

If someone could get me a good model, I could try running it (though I won't be able to model it with great resolution of the simulation domain). I don't think I'm going to take the time to model a realistic car. Coincidentally, as this topic came up so did another project that might have more real world results. On top of that using mid-low end version SolidWorks is hard once you've had a chance to use some of the really high end stuff out there. (go PowerFLOW).

 

[Saf1]

I wouldn't worry about deformation due to "narrow" struts mate, you'd have to be going REALLY fast for that to be a problem. Although maybe some chronic deformation over time?