wing performance specs?

[reflexx]

Anyone have downforce specs on various toyota and aftermarket spoilers?

I'll start... toyota supra stock wing, 65lbs @ 100mph

[ToyotaTechGeek]

man, does anyone have a wind tunnel??? LOL

[reflexx]

i built a small one, so i'd need a small copy of the wings to test them

[ToyotaTechGeek]

cool!!!

[mr2greasemonkey]

if you are really testing wings, you should also plot drag in comparison to downforce of the wings.

[jus7o]

I think the wing is for looks.

does it really serve any function?

also could it possible give you bad gas mileage?

when I get one (aw11) im taking it off.

[Sylvan]

Originally Posted by jus7o

I think the wing is for looks.

does it really serve any function?

also could it possible give you bad gas mileage?

when I get one (aw11) im taking it off.

Let's look at a hypothetical scenario. Say you were designing an aftermarket wing. If you pick a good low-speed airfoil, (say, Selig for example) which can achieve a lift coefficient over 2.0 at the right angle of attack. Now if you were able to position the wing to grab clean air and make it around 4 square feet in area, you can get the following kind of numbers: (made an Excel spreadsheet cause I'm a nerd)

~ 75 lbs of downforce at 60 mph.
~ 200 lbs at 100 mph.
~ 400 lbs at 140 mph.
just for the heck of it it would be ~ 800 lbs at 200 mph but we don't need to worry about that, do we?
So on and so forth.. (lift is proportional to the square of velocity).

So what would 200 lbs of downforce at the rear wheels do for an MR2? Well, say we have a 2800 lb car with 60% weight on the rear axle (pulled this out of my ass, dunno what it really is). So around 1700 pounds on the rear axle. Let's say on a good race day your tires are giving you a coefficient of friction of 1.0.

Now with our snazzy downforce at 100 miles per hour, the road is feeling 1900 pounds from the rear tires. Since we are using awesome tires we have 1900 pounds of grip at our disposal. So at the rear axle this gives us about 1.1 g's possible (1900/1700). So for all that work we gained a potential .1 g of acceleration in the rear. Yippee! Would that keep you from spinning out? Dunno, probably not unless you had an extremely well dialed-in suspension and you were a good driver.

Note that all the above assumptions about the wing and tire performance were very generous, so real-world performance would probably be significantly suckier. Then of course there will be extra drag, which would affect miles per gallon a bit, but would help with high-speed braking a bit, too.

So, I think most wings are just for looks. To really get a good functioning wing, it has to be big, and should probably use some sort of multi-flap which would look like an F1 wing and would probably get you laughed at in the In-n-Out drive thru.

I'm pretty sure most of the downforce in high-end cars and competition cars comes from the underbody aerodynamics, not the wing.

[Tycoon788]

AHHHH MATH!! lol good work tho

[Mike_E_P]

wow!!! i...i.... didnt catch a word you said...Jk

[mthreat]

Originally Posted by Sylvan

So at the rear axle this gives us about 1.1 g's possible (1900/1700). So for all that work we gained a potential .1 g of acceleration in the rear. Yippee! Would that keep you from spinning out? Dunno, probably not unless you had an extremely well dialed-in suspension and you were a good driver.

I'd love to hear from some experts here, but I was under the impression that it wasn't about getting the extra grip for acceleration, but rather for stability. Here's my thinking:

At low speeds, the wind resistance is very low (since it's an n^2 thing, as you mentioned). So the rear tires aren't having to "fight" the wind too much, and traction is fairly even all around. However, at higher speeds, say 100mph, the air resistance is actually a factor, and the rear tires (on a RWD car) are having to "push" harder against the air. Taken to the extreme, it would be like pushing against a brick wall, and the rear tires would just spin, causing loss of traction. The air doesn't exert as much force as a brick wall, but the loss of rear-end stability is still there, so when you go to turn at 100mph, your rear end is less stable than it was at 50mph.

Is my thinking correct? I've never really read an explanation, but that's the only thing I've come up with on my own. Any Formula 1 wing designers in the house?

[Sylvan]

Originally Posted by mthreat

I'd love to hear from some experts here, but I was under the impression that it wasn't about getting the extra grip for acceleration, but rather for stability. Here's my thinking:

At low speeds, the wind resistance is very low (since it's an n^2 thing, as you mentioned). So the rear tires aren't having to "fight" the wind too much, and traction is fairly even all around. However, at higher speeds, say 100mph, the air resistance is actually a factor, and the rear tires (on a RWD car) are having to "push" harder against the air. Taken to the extreme, it would be like pushing against a brick wall, and the rear tires would just spin, causing loss of traction. The air doesn't exert as much force as a brick wall, but the loss of rear-end stability is still there, so when you go to turn at 100mph, your rear end is less stable than it was at 50mph.

Is my thinking correct? I've never really read an explanation, but that's the only thing I've come up with on my own. Any Formula 1 wing designers in the house?

Your thinking is not necessarily incorrect. I'll try to put it in perspective. Using the drag area (drag coefficient times frontal area) of 7 sq ft (which I extrapolated from a sales brochure for the MK2), at 100 mph the car is getting 179 lb of drag force from the air.

Now back to our assumption of the car without a wing, and also assuming the car itself produces no lift either up or down, thus you have 1700 lb of force on the rear tires and similarly 1700 lb of grip, if our tires/road have a friction coefficient of 1.0.

Using the same spreadsheet it's easy to plot the drag force vs. speed, and it turns out that the point at which the drag force equals 1700 lb is about 310 mph. Now, here we have reached your theoretical brick wall, where the tires are exerting maximum grip just to maintain speed against this incoming air. Any more torque will cause the wheels to spin.

Now, thankfully it's also very easy to plot required power on the same spreadsheet (power required being drag force * speed, once you get the units right). At this speed you require about 1430 rwhp just to overcome wind resistance. This isn't taking into account other resistances, such as rolling resistance from the tire/road interface. So you'd have to be big balling to be making that kinda power.

More realistically, we can look at speeds we might actually encounter. At 140 mph, 132 rwhp is required to overcome the wind resistance. Adding in rolling resistance (which is constant based on the car weight, in this case around 80 pounds for all 4 tires), and you can see that 160-ish rwhp would be required to top out at 140 mph in a MK2. I haven't driven my MK2 to that speed so I can't verify the accuracy of my assumptions.

Back on topic..
I think where the wing might be helpful is in tuning the balance of the car for high speed turns. So you can tweak the under/oversteer with the addition of some downforce in the back, or the front, and it might be just enough to make a difference between under or oversteering. And hey, more grip never hurt anyone.

Edit: when i was talking about "acceleration" that you mentioned above, I didn't necessarily mean speeding up. It would be any kind of acceleration, whether it be speeding up, slowing down, or turning.

[DenverMR2]

whoa that was alot of math filled with alot of info thanks

[mr2greasemonkey]

so what yr sayin is the snow plow on the back of some kids civic aint doing him any good at highway speeds? hehe.

[SpeedballTrix]

"~ 75 lbs of downforce at 60 mph.
~ 200 lbs at 100 mph.
~ 400 lbs at 140 mph."

How do you figure that?

[Sylvan]

Originally Posted by SpeedballTrix

"~ 75 lbs of downforce at 60 mph.
~ 200 lbs at 100 mph.
~ 400 lbs at 140 mph."

How do you figure that?

Remember when I said the downforce was proportional to the square of speed? Well, the formula for the lifting force is 1/2 * air density * velocity^2 * lift coefficient * wing area.

To get force in pounds, you need to use consistent units, in which case standard sea level density for air is about .002377 slugs/ft^3, velocity is in ft/sec (mph * 88/60), lift coefficient is dimensionless and wing area is in ft^2.

So you can plug the formula into your calculator or use an Excel spreadsheet as I did. So if you have speed in miles per hour as your independent variable, the equation would look something like this:

Downforce (lb) = 1/2*.002377*(mph*88/60)^2*Cl*area

And with a Cl = 2.0, and wing area = 4 ft^2, you get the following results:



You can extrapolate the above numbers that I quoted from the graph, or pull them from the spreadsheet as I have done.

[3sgtepower]

I was under the impression that the zone behind the cabin was a low pressure zone and all of the stock wings had little effect on downforce, short of having a wing so tall that it was about the same level or higher than the roof line.

[Sylvan]

You're right, in most cases a wing at the trunk level won't be very effective because it will not be in the free stream. The ideal wing location depends on the shape of the roof and back glass. In this case I was hypothesizing a best-case scenario where the wing did get the free stream air without any low-pressure regions or vortices caused by the flow separating off the roof/glass turning point. It would be nice if I had some CFD software on my computer...

[mopwer]

Originally Posted by Sylvan

You're right, in most cases a wing at the trunk level won't be very effective because it will not be in the free stream. The ideal wing location depends on the shape of the roof and back glass. In this case I was hypothesizing a best-case scenario where the wing did get the free stream air without any low-pressure regions or vortices caused by the flow separating off the roof/glass turning point. It would be nice if I had some CFD software on my computer...

What about using a wing to reduce the turbulence at the back of the car. Hence saving on some drag.

Greg

[Denz]

Altho this thread has been revived from a very long time ago....
The MR2 from the looks of it has a "spoiler" rather than "wing"
I was under the impression that at high speed this 'spoils' the air behind the car preventing suction occurring, this is what you see on the back of BMW's and the like, that very small lip on the boot. Its not just to push the rear down but make sure there is no suction being caused by the air behind the car (this only happens at very high speeds anyway).
But a wing, not seen on street cars generally is for down force to stick the ass down on the road.
Edit, just like to say, who finds it amusing when ricers in FWD cars have huge wings at the rear, forcing the rear down, the front up and making the car loose grip in the front.