Tag: Subaru

Wing Logic Dual Element

In the previous article, I mounted a Wing Logic wing to Steve Leo’s WRX. He’s been pretty happy with it, but I’ve been wondering about adding more rear downforce. An excess of rear downforce can make a car boring to drive, but it also improves braking, high-speed stability, and requires fewer corrections when you lose control. So while more rear downforce might ruin the aerodynamic balance, if the driver goes 2 seconds faster, let’s call that a better car.

If you want more downforce from a Wing Logic wing, you can increase the size of the Gurney flap by duct-taping down a piece of angle aluminum butted up against the built-in 1/4” Gurney flap. And with the larger wicker, you can add a little more wing angle. But you’ll soon hit a point of diminishing returns, and shortly after that, the wing will stall out. I haven’t run a full sweep on this wing, but I’ll guesstimate that a Gurney flap 1″ tall (very draggy) and an angle of attack around 11-12 degrees is the limit.

If you still need more downforce, the easiest way to do that is add a second element above the main wing, set somewhere between 25-35 degrees angle of attack (in relation to the main wing). Unlike the single wing, the double wing won’t stall because of the slot between the wings; Air shoots through the gap at great speed and this keeps air attached to the underside of the upper wing. Thus you can run more angle on the upper wing, which effectively increases both the chord and camber of the entire wing, without flow separation.

If you have a 9 Lives Racing wing, they can sell you a dual element wing for around $440 (with shipping). The kit includes the upper wing, plus adjustment brackets that go inside the standard end plate, plus little brackets that go in the Gurney flap slot. It’s a clever arrangement that’s easy to install and remove. I tested the double wing in a wind tunnel, and came away really impressed with how well it worked.

If you have a Wing Logic wing and you want a dual element, you’re shit out of luck. There isn’t a similar kit available, and I have yet to see anyone cobble something together. I wonder if the reason for that is because some people believe (incorrectly) that you can’t put a dual-element wing on top of a wing that has a Gurney flap? There was a recent discussion of this on the Professional Awesome Facebook group, and it seemed like most of the people said you should cut off the Gurney flap, or a dual wing won’t work with a Gurney flap on the lower wing, or that Gurney flaps only work on the top wing. That’s horseshit.

You can absolutely put a Gurney flap on the lower wing. Two research papers (James C Moss , and later F.M. Catalano and G. L. Brand) concluded that adding a Gurney flap to the main (bottom) element of a dual-element wing added downforce and improved L/D ratio. By fiddling with the Gurney flap height, overlap, and gap, they increased lift by 12% and increased L/D ratio by 40%.

But before you go adding a Gurney flap to your double wing, you should know that the authors only got those results after tons of experimentation. The height of the Gurney flap, the distance (gap) between the wings, and the overlap between the wings all need to be set correctly to get the most out of it. Knowing all of this, if you’re going to put an upper element on a Wing Logic wing (or any wing with a Gurney flap), you’ll need to be able to adjust the upper wing’s X-Y-Z coordinates for angle, gap, and overlap.

If this is all too much work for you, go and buy a 9 Lives Racing Big Wang and add The Deuce double element kit. It’s already set up with the right overlap and gap, and is simple to adjust for angle. The performance is excellent, and you will not be disappointed. Tell Johnny I said hi.

But if you’re a DIY-or-die kind of person (ahem, guilty), or you have more time than money, then maybe putting together your own dual wing how you want to spend a day. If that’s the case, read on and I’ll walk you through how I made a dual element for a Wing Logic.

Assembling the upper wing

I make wings rather than buy them, mostly so that I can experiment with different shaped airfoils and construction methods. My S1223 is a torsion box, and my MSHD is a foam core with fiberglass. But neither of those construction methods works great for a wing with a much smaller chord and less thickness. So rather than build one from scratch, I bought a couple cheap extruded aluminum wings on Amazon for $35 each. You can sometimes find them cheaper, and my friend Bill Fischer of Garage Heroes in Training once bought one of these wings and got a box of 10 for the same price.

Cheap extruded wing from Amazon, eBay, etc.

I’m not exactly sure what the airfoil is, but it looks a bit like a Wortmann FX 72-MS-150A. With a cL of 1.8, this is decent, but not what I’d call an ultra-high lift wing. According to my Car Wing Comparisons article, the airfoil outperforms the NASCAR used for in their Car of Tomorrow for a hot second.

Airfoil Tools is a great place to research wings.

These cheap extruded aluminum wings are strong and light. They have two internal semi-circular spars that run the length of the wing, and provide a lot of stiffness. These supports are also tapped with M8 threads and do double duty fastening the end plates. While I might wish for a different shaped airfoil, the entire design is lightweight, sturdy, and inexpensive.

The wing has a 4.7” chord, which is larger than the upper element 9 Lives Racing uses. A rule of thumb is that the upper element should be about 30-40% the chord of the total wing (combined chord of main and second element), and this second element comes in at 32% of the combined 14.7”, and that’s right in the ballpark.

Wing profile and center support.

The longest of these cheapo wings I’ve found is 135cm (53.3”), and so if you want a bigger wing than that, you’re going to have to figure out a way to join them together. Welding is the obvious solution, but I didn’t want to rely on skin strength alone, I wanted to add an internal support as well.

M8 stud is threaded into both sides.

I cut threads into one of the wing holes and installed a M8 stud, bottoming it out on the threads. Then I tapped the same hole on the other wing. I sandwiched a little bracket between them, which will be used to hold up the center of the wing, and then twisted them upon each other, essentially threading the two wings together.

Both halves threaded together.

I took the wing to a local fabrication shop and they charged me their hourly minimum of $80 to weld it up. So that’s $150 for the upper wing, all in. I’m sure the welding could be done cheaper, especially if I was doing several wings at the same time.

Welded all the way around, and pivoting on the center support.

Double wing end plates

To mount the upper wing to the lower, I’d need to make new larger end plates that hold the ends of the upper wing. The top wing also needs to be able to adjust for angle, gap, and overlap, and because it fits inside the end plate, it’s kind of an end plate within an end plate situation. I made the inner plates from 9mm plywood because I needed to countersink the 8mm hardware into the ends. If I used 12 gauge aluminum, the bolt heads would stick up proud and keep the wing from changing angle.

Maximum angle for a second element is typically around 40 degrees, measured from the bottom element. But at this angle, the upper wing risks flow separation. A safer bet is to set the upper wing to 35 degrees, which should provide nearly the same downforce as the maximum angle of attack. I traced all this out on the end plate (a No Parking street sign, per my usual $1-per-pound source at the metal recycler).

I always lay out the chord line parallel to the upper edge of the end plate, this makes it easy to set the angle of the wing. I’m also mocking up the position of the upper wing.

I first made the maximum downforce 35-degree setting, and to this I added a low-drag setting of 25 degrees. I don’t see needing any more adjustment than that, because I can always rake the entire wing to adjust between the high- and low-downforce settings. If I want less downforce, I’ll just remove the upper wing and run it as a single. From there I can tune wing angle and Gurney flap height as I would any other single element wing.

Upper wing pivots inside of end plate. You can see the forward hole, which increases overlap and gap. The gaps are larger than you’d have normally, because of the Gurney flap.

The completed double wing weighs 22.8 lbs total, and so the upper wing added only 6.2 lbs, including all of the things required to mount it. That’s pretty light, and it feels quite sturdy. Eventually I’ll lighten the main wing by milling out slots and wrapping it with carbon fiber. But more on that DIY project when I’ve liberated the wing from Steve.

Completed wing.

Data?

This section is supposed to be filled with A/B testing data, including vital details about the ideal gap height for a dual-element wing that has a 1/4” Gurney flap on the bottom wing…. but instead it’s filled with a pissy rant.

Steve and I had a full test day planned, which involved him setting a few laps and then coming into the hot pits, where I could quickly change the main and upper wing angle, gap height, and swap between single vs dual wing. But despite an entire day at Watkins Glen, we got shit all of nothing. The problem is the same as the first time I did aero testing… Watkins Glen.

The weather is always variable, and the first session was wet and made data irrelevant. In the second session, a McLaren (620R?) dumped it’s coolant and oil on the first lap. This sent four cars into the T11 wall, and the cleanup crew onto the track for a lengthy stint. In the third session, again on the first flying lap, a Corvette stacked itself in Turn 2, requiring a full session of cleanup. And in the fourth and final run of the day, a BMW M2CS decided to get some new baby-blue racing stripes in T10. In the end, I don’t think the Advanced/Instructors run group got more than 15 minutes of track time the whole day.

Now this is the same run group I would have been in if I chose to drive that day. The two people I was with (Steve and Gregg) were the first two cars through the oil. Steve was going slowly because the McLaren directly in front was misting oil on his windshield. Gregg went through at speed and saved it like a hero. But he has a ton of experience at WGI and has proven many times over that he can save a spin.

Gregg saves it and avoids the wall. The next four cars don’t.

Well, if I was out there, I would have certainly been passing both of them in the session, which would have made me the first car through the oil. Dodged a bullet right there, I did! (I’m kidding about passing them; I drive like a grandma on this track.)

And this is why I seldom drive Watkins Glen, even for free. There are so many other tracks that have runoff, sand traps, and slower speeds, and are much safer as a result. Where I find enjoyment is pushing the car to the limit, and I’m not going to do that here, it just doesn’t make sense, financial or otherwise. My understanding is that some track day insurance companies will no longer cover cars at Watkins Glen, and I can’t blame them for that.

But I also understand that many of you like the combination of high speed and steel walls; you feel it gives you focus or commitment or whatever. Good for you. But the reason i have no data or wing gap information is because someone else also felt that way, and lost their focus or commitment or whatever.

Mounting a Wing Logic wing on a Subaru WRX STi

Wing Logic makes a satisfactory wing at a great price. It doesn’t come set up for any particular car, and so you will need to do some DIY fabrication. You’ll have to figure out things like how to mount the wing securely in the correct location, and then you’ll need to drill the bottom mounts for a range of useful angles, and then weld the bottom mounts to the wing.

It takes some patience and know-how to figure it all out, and if I’m being honest, 90% of people will cock it up and do a sub-optimal job, losing some of the wing’s performance in the process. If you buy a ready-made kit from 9 Lives Racing, AJ Hartman Aero, and other reputable companies, you’ll get an easier install and better performance straight out of the box.

But if you know what you’re doing, a DIY wing like Wing Logic or 9 Lives Racing’s new Express kits, can save you some money. Or if you have a car that doesn’t have a ready-made kit available, then a DIY solution is the only game in town.

I tested a Wing Logic wing in the wind tunnel vs the industry standard 9 Lives Racing Big Wang (Wing Logic versus 9 Lives Racing), and found the performance was similar. Wing Logic’s wing has less camber, and so it makes less downforce for a given area, but it’s a physically larger wing (9.2” vs 10”), and so the performance ends up being quite close. 9 Lives has the edge in weight and performance, and so if you’re racing in a series that limits the total wing area (GLTC, SCCA TT Nats, etc), or if you care about two pounds (high up, at the polar end of the car), then 9 Lives is a better choice. For the track rat or hard-park poseur, it’s a wash. I have plans to radically lighten the wing by milling it out into a skeleton, and then wrapping with carbon fiber, but that experiment will have to wait until the end of the track season, because I no longer have it.

Steve Leo is making a foam composite dual element, and while that process takes place (for fucking forever) I loaned him my 65” Wing Logic for his Subaru WRX STi. He didn’t have any wing mounts for it, but he had a spare trunk, and I said bring it over and I’ll figure something out.

Because I had already tested this wing on a Miata, the wing has brackets welded 41” apart. Ergo, I’d need to put the same spacing on the Subaru trunk. As luck would have it, that put the wing mounts right on top of the hinges, which is a sturdy area with some extra thickness and support in the metal frame. Also as luck would have it, the hardware would now be in the way, and I’d have to work out how to allow the trunk to close.

But first things first, to place the wings on the surface of the trunk, such that the wing is braced against side to side movement. I went to the Lowe’s racing department and bought a couple feet of 1” angle aluminum. I cut this into four pieces to make brackets, and sandwiched the Miata wing stands between them.

But I couldn’t put bolts through the top of the trunk and nuts on the bottom, as the nuts would be in the trunk gutter – this would cause interference and keep the trunk from closing. So I installed the hardware upside down, with countersunk 6mm bolts going through the underside and nylock nuts on top. It’s maybe a little less attractive, but this was the only way I got it to work.

Countersunk bolts of differing lengths install from the bottom.

It took a bit of head scratching, but I figured out how to install all 12 bolts from underneath. It took bolts of different lengths, which I’ve noted in the previous images in case you want to give it a go. It all came out surprisingly sturdy, and probably more rigid than you’d see on most cars. You can grab the wing and shake the car side to side, and the wing mounts don’t move.

Angle aluminum brackets on the trunk hold the wing stands in place. It’s very rigid.

The only thing I wasn’t terribly happy with is that the wing is too far forward. The rule of thumb is to overlap the trunk by 1/4 of the chord. So on this 10” wing, 2.5” should overlap the trunk, and 7.5” should be over the bumper.

How important is that? Well, I tested a Civic coupe in the wind tunnel, and moving the wing from on top of the trunk to the ideal rearward position resulted in less drag and more downforce. Usually you get one at the expense of the other, but this was a win-win. I would have liked to do that for Steve, but I didn’t have any more aluminum stock to make another set of wing stands, and he needed this done ASAP.

We got super lucky with the setback distance, any closer and the wing would hit the roof when the trunk was fully opened. I’ll take that as a win and optimize the wing stands at some later date.

By a stroke of luck, the trunk can open fully and the wing doesn’t hit anything.

Data?

Steve reports that the wing is working really well, but through some bad luck, we have had the devil of a time getting comparative A/B data. He’s used the wing at Watkins Glen, Lime Rock, NYST, and Pineview Run, and while we have data from those events, it’s not the kind of back-to-back data that tells a compelling story.

By the seat of the pants, the Wing Logic setup works better than the VSC rally wing he had on there previously. But the Wing Logic single wing doesn’t work quite as well as the Wing Logic dual element he tried this week. Wait, what?! Dual-fucking-element Wing Logic? You can read about that in the next post.