IndyCar – Thoughts on the 2012 Dallara Aerodynamics
We’ve now seen the new 2012 car in both its road course trim and its oval trim. The road course package was tested at Mid-Ohio last month the Monday after the race there. This past Tuesday, test driver Dan Wheldon shook the car down in its oval trim at the Iowa Speedway. Perhaps it would be better to call it its short oval trim, as the car was still fitted with a multi-element front and rear wing and looks very much like the road course package used at Mid-Ohio. Regardless, the media were invited in to have a look at the car during the testing session’s lunch break and Bill Zahren of pressdog.com was there and snapped a series of great close-up shots of the car. You can view all of Bill’s photos on his Flickr site.
As I looked through the P-Dog’s photos, I started to think about what aero bits were ready to go and which were still in need of development, which were likely to be effective, and which were perplexing to me by appearing to be hindrances to efficient air flow. I’ll go through each element and share my thoughts on them and point out notable bits in Bill’s photos that he’s most graciously offered up to the rest of the IndyCar blogging community.
When I first heard that Dallara was chosen for the sole manufacturer of the 2012 IZOD IndyCar Series chassis, I was disheartened. There were many other designs that, if we were going to be stuck with a single manufacturer, were far superior aesthetically and that brought a broader partner base. Swift really seemed to be the strongest contender, in my opinion, but they had no desire to move their already well-established base of operations in California to Indianapolis. So, we got Dallara, and the “hologram” they showed at the unveiling was uninspiring to say the least.
This year they brought two concept variants out for the public to see live and in person at the Indianapolis Motor Speedway during the Month of May. What we saw at Mid-Ohio and what was tested at Iowa was the oval car concept utilizing a road course wing package. It’s been made clear, that alternate aero packages that were initially part of the 2012 concept will have to wait until at least 2013, and because of that, I don’t expect that we’ll see the road course concept that was displayed at IMS ever appear on the track in 2012. What you see in Bill’s photos is likely what we’ll see for the duration of the season.
There are many who will be quick to criticize this new design simply because it is in essence a spec car. There will be no variation from team to team next year. However, when you look at this car on its own merits, separated from the politics of the environment in which it will race, it’s a pretty curvy, sexy looking car! It doesn’t look like any other car out there in motorsports, and it’s much easier on the eyes than the current Dallara.
There are some notable difference between the oval concept and the test car. Notice that the test car lacks a shark fin on the engine cowling, as well as the fin-like guide elements on the plank outside of the side pod. Another difference is that on the concepts, the mirrors were molded into the main part of the chassis, whereas on the test car the mirrors are mounted via more traditional stalks. Very often, cool looking aero bits and appendages don’t really do much to increase the efficiency of a design unless there are other restrictions in place. The reason why we saw so many barge boards, winglets, and other aero bits on F1 cars until recently was because of the larger restrictions on what was allowed within the technical regulations. A clean car design up front means that you don’t need all those little bits and protrusions poking out all over the place, and the 2012 test car looks very clean and sleek.
At first glance, the front wing looks to be a standard multi-element wing similar to that utilized in a wide variety of formula car series, including a channel outside of the endplate to help redirect air around the front tires. The current front wing assembly places the endplate flush with the outside edge of the wing, which is also flush with the outside face of the front wheel. This means that the airflow over the front wing is then subjected to the aerodynamic chaos that is the spinning front tire. Directing the airflow to avoid the wheels as much as possible has always been a goal of aerodynamicists faced with the difficult task of making the best of an inherently drag and turbulence inducing open wheels have as minimal of an impact as possible.
The wing on the concept car also included this outside channel feature, but there are significant differences between that design and the wing currently being run on the test car. First, rather than being mounted on struts that protrude downward from the underneath side of the nose cone, the wings angle downward from the sides. It’s reminiscent of one of my favorite aircraft of all time, the F4U Corsair. The nature of the main plane and the two trim elements are nearly identical, otherwise.
The second major difference is in the design of the channel outside of the wing endplate. On the concept car, the rear cap was a curved and smooth transition from the endplate to the outer edge of the outside channel of the wing, helping to divert air around the front tire. On the 2012 test car, there is simply an abrupt wall placed at the rear of the wing. This unsubtle approach, while perhaps offering less drag than allowing the air to strike the tire unimpeded, is far from ideal, and is an area that could easily be developed by teams and aero kit manufacturers in the future. Dallara may also bring a cleaner design to the final specification for the car. For now, the solution looks clunky and slapdash.
Rear Wing and Rear Diffuser
The rear wing of the test car at first glance doesn’t seem extraordinary, or substantially different than what is on the current car. That is until you look under the traditional rear wing and notice a sub plane mounted just behind the gearbox, below the rear attenuator and above the rear diffuser strakes. This element is not present on the current Dallara, but is an element seen often in many other formula car designs including Swift’s Formula Nippon and 2012 IndyCar concepts.
This plane appears to serve as the attachment points for the rear wheel bumpers. There is a Gurney flap at the trailing edge of what appears to be a flat plane, so the surface will produce some downforce, but not as much as it would if the element were for properly airfoil shaped. A traditional secondary rear wing element would be part of the primary rear wing assembly, which you can see attaches at the top of the gearbox, and would aid in getting the air to exit past the engine cowling at a higher angle thus allowing air to exit more freely from the diffuser. This is one area where I think a lot of ground can be gained in the development of downforce with minimal addition of drag.
As an aside, it’s interesting to note that the wing geometry on the test car is set to the maximum downforce configuration. Thus it is absolutely no surprise that Wheldon was able to get the car to run flat around Iowa in only 15 laps. Many expressed immediate disappointment in that, hoping that drivers would again have to lift going into the corners of short ovals like Iowa. I wouldn’t give up hope on that just yet. Keep in mind this is testing. Dan isn’t going for speed records or a pole run. Keep the car stable first of all. Work on finding the speed later.
The inclusion of a rear bumper will have many raising the argument that this isn’t a truly open-wheel design just as they did for the Delta Wing concept. I will respectfully disagree with that viewpoint. The inclusion of these devices just aft of the rear wheel might have been able to prevent some of the horrific airborne incidents we’ve seen in IndyCar over the past few seasons such as Mike Conway’s season-ending crash at Indianapolis in 2010. These elements are hollow in order to allow the air flowing over the rear tires to exit smoothly. With the test car not being painted, but simply left in its natural carbon fiber weave state with a few decals stuck here and there, we can easily see that the rear bumpers are carbon fiber. I think this is a mistake. Yes, carbon fiber is very light and strong, but it is also very brittle and expensive. These rear bumpers are going to get bumped, and often! When carbon fiber is struck too hard, it doesn’t bend, it doesn’t yield, it fractures and disintegrates into extremely sharp shards which are quite good at puncturing tires.
Carbon fiber, given its strength, is an ideal material to use in structural elements of the car or where aerodynamic loading might cause flexation beyond the limits of the technical regulations. These rear bumpers are neither structural nor aerodynamically loaded, thus they do not necessarily need to be fabricated out of carbon fiber. A better solution, in my opinion, would be to utilize the material that the Delta Wing concept will use extensively in its body work, Tegris. I wrote a piece about the benefits of Tegris over carbon fiber back in April of 2010 when the Delta Wing group announced their partnership with Milliken, a major manufacturer of the Tegris material. Tegris is a layered polypropylene composite weave whose construction is very similar to carbon fiber, except that the material is completely recyclable, more flexible and less brittle, and costs about a tenth of what carbon fiber does to manufacture. In this era of cost-conscious motorsports, it seems reasonable to utilize an innovative material like this where ever one can, and these rear bumpers seem to be an ideal place for it. As it stands now, I see a lot of punctured tires and expensive parts-shopping excursions in IndyCar’s future.
One of the major design initiatives of the 2012 chassis was the inhibition of wheel-to-wheel contact between cars. This type of contact has lead to a number of very serious incidents including Kenny Brack’s horrific crash at the Texas Motor Speedway which ended his open-wheel career. The before mentioned rear wheel bumper is part of that solution, but the extension of the underwing out beyond the side pods is the main device that will prohibit the interlocking of competitors’ wheels. This is really a great idea, although I wonder if the edge of the plank will offer enough resistance to a wheel of a car running at speed, or whether that wheel will instead climb on top of the exposed underwing and result in the same wheel-to-wheel contact we’ve seen before. On this, I will have faith that such a situation has been tested and examined already. It may be that in such a situation, the proximity of the front wing prohibits penetration deep enough for a wheel to ride up onto the plank.
One nice feature about the underwing extension is that it appears that the outside edge and wrapping around to the leading edge in front of the radiator intake is replaceable by removing a few bolts. However, it’s also worth noting that this element, although not structural, is also carbon fiber. This would be another excellent opportunity to utilize a lower-cost, less brittle material such as Tegris. There is a significant amount of horizontal surface area in front of the radiator intakes, and it will be interesting to see how teams and sponsors utilize this area. While it may be tough to see from the typical camera angles at a natural terrain road circuit, many of the angles at a street circuit or at an oval where the camera is on a scissor lift or similar type of platform would give a very nice view of this area.
Fuel Fill Valves and Vortex Generators
One thing that struck me as odd about the 2012 test car were the fuel fill valves and one particular vortex generator. The car being tested at Iowa was presumably in oval trim. If that’s so, then one should never need to have a fill valve cutout on the right-hand side of the vehicle. Yet, there it is, plain as day, on the test car. For a road course car, it’s obvious that you need to have the ability to provide fill access from either the left or the right depending upon the circuit, but unless we start running clockwise around ovals, the fill should always be performed on the left-hand side of the car. The only thing that I can figure is that the right-hand cutout is there for balance. There is no flap over the fill valve, so that void space is exposed to the airstream. Formula 1 had a simple flap that opened as a driver came into the pits and closed as the driver exited. If one wanted to provide a sleek and efficient design, it seems to me that such a turbulence inducing element as an open fuel fill valve would be undesirable and that some type of flap solution would be deployed. My preference would be for a triple element, spring-loaded valve cover that a fueler could push a nozzle through easily and that would close up as the nozzle was removed.
As I was looking at the picture above showing the right-side fill valve cutout, I noticed a vortex generator mounted just above the cutout. Normally, vortex generators are placed in front of aerodynamically tricky parts of a vehicle that can’t be substantially altered, such as the driver’s cockpit. If you look at most open-cockpit cars, you’ll notice one to three small fins mounted on the fuselage just forward of the cockpit. The point of this is to create a vortex that covers the cockpit and serves as a pseudo-surface for the rest of the airstream to flow around and maintain a more laminar profile. It’s interesting how adding just a little bit of turbulence in just the right place can save a lot of turbulence generated downstream. In the case of the yellow vortex generator shown above, there’s nothing downstream to indicate its necessity. Above the left side fill valve, there are two antennae that would have a similar effect, so perhaps its back to my thought on the existence of the right-side fill valve cutout and the right-side vortex generator is there to balance the left-side antennae.
I know that this has been a long discussion, and if you’ve made it down this far, you deserve serious congratulations! Keeping my final overall thoughts on what we’ve seen of the 2012 car thus far brief, it’s sexy! I like it! The car is sleek, curvy, easy on the eyes, and looks to achieve the goal of providing a safer, more comfortable car for the drivers. Yes, I’ve nitpicked on a few things here and there, but that’s really all it is, nitpicking. I’m a scientist, that’s what I do. Also keep in mind that this is a test car and won’t necessarily represent the absolutely final version of the car we’ll see compete in anger next season. While I doubt very much that Dallara will suddenly move to a lower cost polymer composite as opposed to carbon composite for its non-structural elements, I do think we’ll see some aerodynamic refinements throughout the Fall and Winter. My only genuine complaint would be that this is the car we’ll see everyone race next season. As cool as the car may be, it’s still a spec chassis with spec aero, suspension, turbo, ECU, and gearbox. I’d love to return to the days in which teams would “roll their own”, but let’s face it, those days are gone. Let’s just be happy that the car we will see in 2012 looks to be substantially better than the vintage racer we’re running now.