Active rear wing

[kverges]

You guys need to go to a drivng school where they teach weight transfer, which, by the way, in steady state is independent of body roll.

I personally think the concept is sound and the idea of more downforce on the inboard side in a corner would not be to affect body roll, but weight transfer. The inside tire has much less load and ability to bear more load without getting to the point where the ability to bear lateral grip diminishes due to vertical load is a factor. Tires do not have infinitely increasing lateral grip as a function of vertical load, they get nonlinear with higher vertical loads. In addition, it would take weight off the outside front tire, so the extra donwforce in rear would be less likely to just cause a huge push due to lack of comparable aero grip in front. That said, I might prefer twice the downforce over both rear wheels.

But if I understand the controller properly, you can set up any change in angle of attack as a function of speed and g's, so you could have the wings work in tandem or not and see what difference it really makes. I thnk it is a great idea! If the price is sensible I am going to try it on my project car.

[steuspeed]

Cool video on Chaparral 2E

YouTube - Chaparral 2E walk-around from WINDING ROAD Magazine

[R'elise Me]

Originally Posted by xtn

The split wing idea is silly. It must be the product of somebody with an engineering mind but not enough sense.

Lets say, for purposes of discussion, that the full wing at full deflection, traveling at 100mph, produces 100lbs of down force. Doesn't matter if those numbers are way off; this is just for purposes of discussion. So lets assume that you're getting 50lbs of down force on each rear tire.

So why, oh good golly why, would you want to only get your 50lbs of down force on the inside tire? Why wouldn't you want the extra 50lbs of down force on both rear tires? Why wouldn't you want to increase the grip of both tires? Giving up down force on either side only reduces your maximum overall grip level.

I can only guess it's an ill guided attempt at reducing body roll? Body roll by itself doesn't hurt a dang thing. In fact Carol Smith advocates springing your car as softly as possible, providing for as much travel as possible, as much as you can without encountering bad behavior caused by geometry restraints, such as bump steer, undesirable camber curves, etc.

The times given for various configurations suggest the slit wing is the best, but I'm willing to buy a cheap steak dinner for anybody who can prove there were not other variables involved, or that indeed the seller of this wing didn't intentionally massage his numbers.

xtn

I think you're discounting the fact that any one car can only use so much downforce at each axle, so if you can direct 100% of that to the inside wheel, you are getting more benefit than if you apply 50% to each wheel. In theory at least, the split wing accomplishes that, and from a visual perspective it appears to be a very agressive shape so I would think that it could in fact develop as much downforce on 1/2 the wing as most wings can over the entire length.

[Rei]

Yea sure so who's going to be the monkey to try it first. I would like to see what people really think about it in real world experience. The concept does seem valid but I still have my issues with it.

[Pestodude]

I'm confused. Does the wing activate by computer based on brake, gas, and steering inputs or is the driver constantly pushing buttons while he's driving to manipulate the wing? Unless you're a former F1 driver, that seems like a lot of stuff to be trying to do (along with driving the car) on a track.

[xtn]

Originally Posted by R'elise Me

I think you're discounting the fact that any one car can only use so much downforce at each axle, so if you can direct 100% of that to the inside wheel, you are getting more benefit than if you apply 50% to each wheel. In theory at least, the split wing accomplishes that, and from a visual perspective it appears to be a very agressive shape so I would think that it could in fact develop as much downforce on 1/2 the wing as most wings can over the entire length.

Sure, there is a limit to the down force that a given spring can take before it bottoms out the suspension on that corner, or to how much down force a tire can take before its deformation causes big problems.

But I think that's irrelevant here. I hardly think that particular wing is going to cause either of those problems, at autox speeds, if you let it develop as much down force as it can on the outside tire as well as on the inside tire.

xtn

[Riddlefox]

The yellow '01 BMW M3 in the video is Vic Sias'. He took third this year in Street Mod at Nationals. I would assume that he would be able to turn fairly consistent lap times..

One of the designers of the system posted up on NASIOC about it. Apparently, it's triggered off of accelerometers (lateral / longitudinal), so no need to twiddle with it in the cockpit - though you can tweak how much it triggers for a given g-loading back in the paddock.

Active aero?! - NASIOC (designer's post is #30)

[R'elise Me]

Originally Posted by xtn

Sure, there is a limit to the down force that a given spring can take before it bottoms out the suspension on that corner, or to how much down force a tire can take before its deformation causes big problems.

But I think that's irrelevant here. I hardly think that particular wing is going to cause either of those problems, at autox speeds, if you let it develop as much down force as it can on the outside tire as well as on the inside tire.

xtn

I wasn't refering to the limits of the springs or tires. I was refering to limits of manageable aero drag as the inevitable compromise for wing induced downforce. Drag is not really an issue at autox speeds. On the track, particularly with low HP cars like ours, fixed wings are always devised as a compromise between drag and downforce. Active wings have long been the solution to that problem, but they were banned in most classes decades ago.

In the case of the Exige, for instance, the downforce is cut back to very little to avoid causing the drag our little motors can't deal with. It took the S to render any real advantage in that body style.

So I'll ask you this, if you had a lead weight under the car that you could shift from side to side, wouldn't you want to shift it to the inside wheel on turns and the center of the car on straights? I know I would. If you do too then wouldn't you want a wing to do the same if it could? That would render all the advantages of that lead weight without the obvious weight disadvantage.

The questions of stall speed and reaction time may indeed negate the value of this design, but like so many technological advances that have been shunned as some sort of heresy against commonly accepted principles, this design may deserve more merit than some of you are willing to even entertain. At the very least I would credit it as an interesting prototype that further R&D can improve. I'd like to see more data on this and even test a car with and without (or perhaps at zero lift, conventional fixed position and fully active).

On the practical side, I would expect the split wing to perform to some benefit over a single wing, but I imagine it will never see any sanctioned racing due to restrictions.

[xtn]

Originally Posted by R'elise Me

I wasn't refering to the limits of the springs or tires. I was refering to limits of manageable aero drag as the inevitable compromise for wing induced downforce.

I know you weren't refering to the limits of springs or tires. I pointed them out as the only limit, because during a turn, at least until you're well into the exit side, unwinding and trying to accelerate with everything you've got, I'd take the full down force on both sides. During the turn, the pros of down force outweigh the cons of drag. So yes, adjustable is good, but no, the split wing idea seems pointless.

Originally Posted by R'elise Me

In the case of the Exige, for instance, the downforce is cut back to very little to avoid causing the drag our little motors can't deal with. It took the S to render any real advantage in that body style.

What? It is my personal experience that an S is not significantly faster around a track than my NA. A couple miles per hour better on a longish straight, but that's it. The wing size, profile and angle of attack is the same. Assuming the tires and suspension are the same, what advantage of the body style is the S benefiting from? It's benefiting from some extra horse power, but that's it. It's not taking any better advantage of the body style.

Originally Posted by R'elise Me

So I'll ask you this, if you had a lead weight under the car that you could shift from side to side, wouldn't you want to shift it to the inside wheel on turns and the center of the car on straights? I know I would. If you do too then wouldn't you want a wing to do the same if it could? That would render all the advantages of that lead weight without the obvious weight disadvantage.

Yes I would prefer the weight be on the inside because it has mass. The down force created by mass is subject to lateral G force, and the resultant force vector during a turn would not be directly down towards the asphalt over the inside tires. The idea of moving it to the inside is because the resultant force vector would point down and out, resulting in some net down force on both sides of the vehicle. Down force from wings is not subject to that lateral G force. It pushes straight down towards the asphalt all the time, and as such I would want both sides of the wing pressing down on both my rear tires during a turn.

xtn

[Riddlefox]

Down force from wings is not subject to that lateral G force. It pushes straight down towards the asphalt all the time

Does it? Even when the car's body is rolling in a turn?

[xtn]

Originally Posted by Riddlefox

Does it? Even when the car's body is rolling in a turn?

Well no. Of course it remains parallel to the vertical axis of the car. Sorry to be inaccurate on that point, however my logic still stands; it's is much, much closer to vertical than the vector of force created by a mass of ballast weight.

xtn

[apk919]

Neglecting the "split" part of the design... active aero is standard on a number of Porsches as well. IIRC, Jaguar had a LeMans racer in the 50's which used active aero for braking, and not downforce... the entire engine cowl turned into a air brake.

[apk919]

Originally Posted by xtn

The down force created by mass is subject to lateral G force, and the resultant force vector during a turn would not be directly down towards the asphalt over the inside tires... Down force from wings is not subject to that lateral G force. It pushes straight down towards the asphalt all the time, and as such I would want both sides of the wing pressing down on both my rear tires during a turn.

xtn

Originally Posted by Riddlefox

Does it? Even when the car's body is rolling in a turn?

Originally Posted by xtn

Well no. Of course it remains parallel to the vertical axis of the car. Sorry to be inaccurate on that point, however my logic still stands; it's is much, much closer to vertical than the vector of force created by a mass of ballast weight.

xtn

If the car's body is leaning, the aero force vector leans too. It's perpendicular to the spar of the wing. That's how airplanes turn, by the way... (in addition to use of the rudder). So body roll reduces the vertical component of aero force, and creates a small lateral one (toward the inside of the turn).

The overall force vector of the car's mass does change from the pure vertical when a car is cornering, but the magnitude of the vertical component is constant... it's only the lateral component that changes. The weight distribution on the tires does change though... but the sum of the vertical components still equals the car's mass, regardless of whether it's cornering or not. Now, if the corner was banked or cambered, and not flat, that's another story.

[MikeP]

I don't think the split design makes a whole lot of sense. Depending upon where you are on a track, you tend to either want as much downforce as you can get or you want the least amount of drag. The only situation where you'd want an intermediate condition would be in a full throttle corner where you'd want to reduce drag and downforce to the point where you're close to the limit of grip. If you're in any corner where you can't use full throttle, the only thing that will help you go faster is more downforce. On a straight, of course, you simply want the least drag. Because of that, you would tend to either want both panels angled for max negative lift or both angled for minimum drag.

Another thing about a split design: getting the same amount of downforce with two panels at different angles of attack as a single panel of the same span will necessarily generate more drag. This is because of the induced drag that will be generated between the panels when set to different angles of attack and therefore different lift coefficients.