Nissan Spec-V: Part 19: Improving Aerodynamics
12/13/2006
Aerodynamics are often overlooked in the construction of a race car. Many enthusiasts purchase an aero kit without really understanding the functionality of the add-ons they are installing. If you are armed with some knowledge, you can modify an off-the-shelf aero kit to greatly increase your on-track performance.
An aero kits adds downforce without adding much drag penalty. By nature, a car’s shape is somewhat similar to an airplane wing: flat on the bottom and rounded on top. Air flowing over this shape creates lift as the air going under the car has a shorter, less inhibited path to travel. Thus, high-velocity air under the car wants to push the car up over the lower velocity air, which is curving over the top, creating lift. Lift reduces traction and creates instability at speed.
An aero kit helps encourage air to flow over the top and discourages the flow of air under the car to reduce the lift and hopefully even give some traction-enhancing downfoce. Most aero kits on the market are designed more for aesthetics than function, so enlisted the expert help of John McNulty of Aerodynamic Solutions and Brian Kono of Afterhours Automotive.
We chose the all-carbon aero kit made by Syndicate Customs. Syndicate Customs also produces a great carbon vented hood. A vented hood is critical for aerodynamics — but we will get more into that later.
Currently, Brian Kono is hard at work modifying the aero kit for best function, a difficult task as he must make the aero kit strong enough to take racing abuse, which can mean off-road excursions, rubbing on curbs and other cars. The kits’ mounting also has to be strong enough to hold up to 300 pounds of downforce that the modified kit can create. The front end of the car also has to be able to be quickly removed to facilitate repairs and to make the car easier to load on a trailer. The aero parts must also be lightweight. Satisfying all of these requirements is a difficult task but presents no problem for a fabricators with Kono’s skills and creativity.
Here is a view of the modified Syndicate Customs airdam. The obvious modification is the addition of a carbon aluminum honeycomb splitter. Also visible is the Syndicate Customs hood with a large vent. We will talk about how hood venting affects aerodynamics later.The first most important part, which is also the most difficult, is to optimize the front of the car for the best front grip. The Syndicate Customs airdam is lower than the lowest part of the undercarriage. This is good, but it is not enough for what we want to do. To encourage the most flow over the top of the car, Kono fabricated a splitter and attached it to the airdam. A splitter is a horizontal flat surface that juts out in the front of the car. It helps force more air to flow over the top, increasing the pressure. This creates more downforce with no penalty in drag.
In these close up photos you can see how the splitter helps force air up over the top by extending the leading edge of the airdam forward.The splitter is tied into a belly pan which helps keep the flow of air under the car straight to reduce drag. The belly pan’s area also helps increase downforce, as the downforce generated is the pressure differential between the top of the belly pan/splitter and the bottom applied over the splitter/belly pans surface area. As you can see, even a slight pressure difference can equal several hundred pounds of downward force.
Kono used honeycomb composite sheeting consisting of an aluminum honeycomb structure skinned with two plies of S-Glass and epoxy resin with one ply of carbon fiber per side. This sheeting is exceedingly strong and stiff for its weight. After cutting out the shaped of the splitter/belly pan, Brian reinforced the leading edge of the splitter with carbon yarn soaked in epoxy resin. This can absorb a very hard blow without shattering.
This aluminum box structure part of the belly pan holds the locating pins, which help hold the belly pan splitter to the car. This is a sturdy mount that can be removed in a matter of seconds.In order to be removable for service, Kono built a box structure out of aluminum to engage guide pins on brackets in the chassis and to tie the belly pan splitter to the chassis with maximum stiffness. Kono also built a jacking point into the structure to make the car easy to jack up with the belly pan in place. Now the whole front can be removed by simply unlocking a couple of Dzus fasteners and sliding the front end forward off of the pins. The structure is also exceeding stiff and strong enough to be stood on.
These three blocks hold the guide pins that engage the aluminum belly pan support box. The center box is also a jacking point that makes it easy to jack up the front of the car without removing the front end.
Here is a view of the splitter/bellypan engaged in the receiver blocks. You can see how the jacking point works from this view.
Here is what the belly pan and splitter look like in a side view. The pressure differential between the top and bottom is what generates the downforce. This part also smoothes the airflow under the car as it is lower than all of the low-hanging parts of the underbody.At the rear, Kono started fabricating a rear diffuser following McNulty’s guidelines. A rear diffuser is a kick up in the rear floor that lengthens the air flow path under the car. This helps cancel out the pressure differential caused by the difference in flow volume at the top and bottom. The rear diffuser helps change the car’s profile from that of an airplane wing that creates lift to an upside-down airplane wing that makes downforce. The diffuser creates the downforce without too much drag penalty, making it a win-win situation.
Kono begins construction of the rear diffuser tunnels. This is part of a vortex generator that will help seal the car’s underbody at speed.
Kono has built the underbody frame to which the diffuser panels will mount to.Stay tuned for future installments as Kono improves our aero kit’s looks and performance.