The Poor Man asks: Active Aero -- and Split Wings

[Jack Olsen]

I just read about a group of MIT guys who have developed a computer-controlled active wing system that uses accelerometers to raise or lower each half of a rear wing independently of the other based on whether the car is turning, braking, or both.

Here's video of it in action. Their website is here.

First off, I think they're kind of missing the point using it for autocross, where speeds are so slow that any aero is a pretty minor factor. And my gut tells me the split wing idea is somewhat misguided. Even though the outside wheel will always be doing the vast majority of the work in a corner, I can't see how it would hurt anything to be increasing downforce on both of the rear wheels at the same time. Drag from a wing just isn't much of an issue in track driving.

But I'm no expert -- and there are a lot of guys who are smarter than me on this board. So, in my ongoing quest for sloppy and cheap alternatives for my home-made rear wing, I thought I'd solicit opinions on how it might be possible to rig up something like this without a computer, maybe using two or three inertia switches to activate a wing when braking or turning, but to let it flatten out when I'm on the gas and pointed straight.

Can anyone think of cheap parts that could be re-purposed for raising and lowering the wing and/or inertia type switches that could be adapted for this application?

I've got my aluminum and glue waiting in the garage.

[Geronimo '74]

Split wing looks cool but I agree, with the supports being so close to the centerline of the vehicle, I don't think they are able to divide the pressure to one side of the vehicle.
But I'm no expert either.

[gtc]

My first thought for this: Couple the motion of the wing to the rear sway bar links. The wing would move anytime the body pitched or rolled.

It probably wouldn't be very nice looking....

[Elombard]

Waht about just using the brake light switch and a TPS to trigger it. Would that be a problem in left foot braking??? I am sure they would of thought of that.

I wonder if it changed there lap times in that car? Seems like you would have to be an awfully good driver, able to set very consistent lap times to measure a difference with the moving wing vs a stationary wing.

[Chuck Moreland]

some 917 variants had active wings. If memory serves it was tied to the suspension mechanically.

I think the advantage of the split wing is the ability to reduce body roll without additional spring rate.

[safe]

Originally Posted by Chuck Moreland

some 917 variants had active wings. If memory serves it was tied to the suspension mechanically.

I think the advantage of the split wing is the ability to reduce body roll without additional spring rate.

908s, before active aero devices were baned.
I've recently read "Racing Porsches" by Paul Frere from 1973.
Porsche used linkages from the rear suspension arms to control separate wings or flaps. Apparently the stabilizing effect in curves from the split wing was more on the academic side...

[Paulporsche]

I think Jim Hall had movable wings on the Chapparals of the mid 60s. They would turn them more vertical for cornering and braking (kind of like some 50s Mercedes race cars, I think) and then trim them out on the straights.

[304065]

Jack,

Yes, the early 917 had the rear wings linked to the suspension. They later made them fixed. The old racing Gullwings used a flap that was basically the entire rear turtledeck, this would flip up at 90 degrees under braking. Frightening in the days of vented drum brakes.

The whole thing seems dangerous as hell to me and I tell you this as a veteran club racer and aerobatic pilot. Part of driving fast is PREDICTABLE behavior of the car under a variety of conditions-- if you were successful in engineering movable aero elements I think that would add another layer of complexity that would make it hard for even the best to react.

I think you are right that the MIT guys (smart as MIT alumni may be ) are on the wrong track with active aero aids at low speeds. Where this stuff really makes a difference is above 100 MPH, at least if you believe the factory data.

The only thing I can think of that might be acceptable would be a wing support that articulated fore and aft and had some sort of linear spring tension holding it forward. At low speeds, the wing would be held at a fairly negative AoA, but under an air load would pivot backward to be less negative (never positive even with the front suspension on the rebound stops)-- as long as it was linear you might get a slight pitch change as the car went from low to high speeds. Again, I'd be too afraid to try it.

[Quicksilver]

The big point that John makes is the predictability. I'm trying to imagine the actions that you could see from the rear end being tossed around in a "Geeze, can I recover?" situation.

I think the one action you could do that would be useful is to flip it up under deceleration forces. You would want it actuated from the g-forces though. If you actuated it from the brake system it would be flipped up no matter what under braking. Remember that the opposite of 'ground effect' is 'sky effect' which is what you will see if you spin the car. (A friend used to have a picture someone snapped of him spinning his little Renault sports racer with ground effects. The body was ripped off and about 150 feet up in the air. Sky effect...)

Predictability is even more important after the excrement hits the rotating ventilator!

[Patrice911]

I will think that if you mount the wing on hinges and spring that you will achieve what you want.
At high speed the higher downforce will move the wing flatter and at lower speed the angle will change trying to keep the downforce kind of constant being balance by the spring. So instead of a downforce that increase with speed you will have a downforce that will increase to a point and then remain fairly constant until the flatter angle is reach and then start to increase again as speed go up. So you should reach the maximum downforce at lower speed or at the same speed then if you mount the wing fix at the higher angle of attack. The hard part will be to figure out the hinges setup and the spring force.
There is some reason why movable wing are ban in racing.
I will be making my own wing soon. I’m starting from the bottom up. I got the support bracket to attach the upright done. I need to do some kind of support attach to the body that will transfer the force of the bracket attach to the ducktail directly to the body that no extra force are applied to the ducktail, next is the upright and the wing.
Nice idea to add to my wing project.....

[Won]

The active aero on 908/917 (images found elsewhere on the board)




You guys should see a proper A/Mod autox car, those things are made up of mostly wings with some rubber and an engine

[Reaper930]

I'd like to see a wing that had a greatly increased angle of attack based upon brake modulation etc. So high speed braking can be more stable with a "air brake" if you will.

If someone is braking from high speed and the brake pedal is half depressed, the wing would increase its angle of attack creating more downforce on a lifting rear end. This would have great use on the track I would imagine.

[Peterfrans]

the bugatti veyron has this. http://nl.youtube.com/watch?v=I3Hlv7ySshM at 2:00

[Reaper930]

Yes the idea I'm proposing is used on the Mclaren F1 - so how can we adapt that to our cars?

[911-32]

I think the control part is actually fairly simple if you distill down when you actually want the wing in low drag (ignore the split business for a minute and concentrate on Olsen level simplicity - no slight intended). The only time you really want a low drag wing is on the longest straight (or perhaps 2 longest straights on some tracks) - on short straights it won't make any real difference, in corners you always want high drag/downforce and braking you want high drag/downforce. For control you have a button on the steering wheel that the driver operates to move the wing to low drag. You hit the button as you come on to the longest straight and hold it down until you brake. At that point of release, the wing returns to its high drag/downforce position and stays there for the rest of the lap (or until the next long straight). The default setting is high drag/downforce and the wing returns to default as soon as you take your thumb off the button. Captures probably 80-90% of the benefits, its simple and has limited driver error possibilities. Actual control of the wings is probably electric motor, but thats beyond my competency - I'm an ideas man like Jack.

[Patrice911]

Here 2 drawings of a possible hinges and spring setup I came up with in relation to my previous post.

[Patrice911]

Originally Posted by 911-32

For control you have a button on the steering wheel that the driver operates to move the wing to low drag. You hit the button as you come on to the longest straight and hold it down until you brake. At that point of release, the wing returns to its high drag/downforce position and stays there for the rest of the lap (or until the next long straight). The default setting is high drag/downforce and the wing returns to default as soon as you take your thumb off the button.

Fairly quiet at work today.

Instead of holding the button, one can do a latch function that will hold the wing down until you touch the brake. The brake light signal can be used to reset the latch and the wing will go back up. That way you don't need to hold the button down all the time on the straight.
With 2 relays, 3 switches, a motor with a cam that should do it.
The only think with that is that you need to remember on each lap to push the button when coming on the straight.

Here a schematic






Push button is push, relay K1 come On, K1-2 will close and relay K1 is self latching ON. push button can be release.
K1-1 close also, activating the motor after half a turn switch S1 open, motor stop, wing is down.
Brake is applied K2 come On, K2-1 normally close contact open deactivating K1, K1-1 return to normally close contact, motor is activated, after half a turn S2 open motor stop, wing is up. System ready for next activation.

[Jack Olsen]

Thanks, guys. These are interesting responses. I can think of two things I don't like about the spring idea. One is that there are two over-120-mph portions of my home track, and one requires maximum downforce (exit of turn 8, Willow Springs) while the other would be better with none at all (the second half of the front straight). The springs wouldn't be able to tell the difference between these two corners, and the wing would flatten out in both instances. Also, I'd think the rapidly-changing conditions a wing goes through in high speed corners and hard braking would likely produce a bouncing effect in a spring-supported wing. Dampeners could address this, but I don't think the weight and other trade-offs would be worth the gains.

It seems like it makes sense to have the default position of the wing be high-downforce-high-drag, with the occasional straight-line moment where you'd want to back it off. The idea of any kind of a trigger makes me a little nervous, though. It's a new thing to have to do when I'm out on the track, and it's already pretty hard keeping up with everything else.

I'd think a back-off trigger for the wing could come from there being no lateral inputs from an accelerometer-type switch combined with there being a positive signal from some kind of speed sensor. But that adds two kinds of complexity, and if a brake- or lateral-g failed to let the wing return to its agressive angle, you could conceivably be asking for a lot of trouble in the next kink-type turn or braking zone.

Essentially, eliminating the user-activated switch creates the same problem. No, my idea is slightly worse -- a long straight could turn your wing off without your knowledge, and the brake or lateral-g sensor could fail to turn it back on. With a manual switch turning it on at least you would know that it's killed your downforce before the brake or lateral-g switch failed.

It would be nice if there were a mechanical way to have it relax the wing only when you're going straight and accelerating. But it's hard to work that when you need a quick response -- there are lots of individual instances of straight-ahead acceleration that are too brief to warrant taking the downforce off.

Maybe a dead-man type of switch makes the most sense. You can back the wing off by holding a button down, but as soon as you release it the wing goes back to its aggressive angle. Maybe a foot-activated button would be the way to do this, since your clutch foot is (mostly) free on long straights.

But I'm talking myself in circles. I still haven't come up with a clean and simple answer. Having the wing turn on every time I clutch on a straight seems like a bad idea.

Ideas?

Patrice's switch is better than anything I've come up with.

[jtfreels]

FYI, Jim Hall used the pedal option in the high winged Chaparral, won at Brands Hatch in .... 1967. Honestly I don't remember which way the pedal worked, but I think it was as you describe, the pedal was used to "flatten" the wing on the straights.

Not a split wing though.

Jay

[arerrac]

Wasn't Ferrari accused of having a "moving wing" on their '06 F1 car.

I seem to remember that it would just lay down at high speeds. No mechanical or electronics gadgets, just constructing the wing composites to react to the air going over it at slow vs. high speeds.

I found the following on a UK F1 blog from May '06

"The moving parts are the rear elements that make up the wing, they 'bend' so that the gap between them becomes smaller. This was accentuated by the Ferrari's easily topping the speed traps at San Marino."

something to think on.
-W