Track Day Report - Gainesville Test Course - 01/08/11

What a day! After some mishaps early on in the morning, I have gathered some good results.  I got there late, at around 9:00am.  Fortunately they hadn't started the drivers meeting or anything yet.


Conditions: 52 degrees at 10am, 65 degrees at 12:30pm.

• Changes from previous event:
• Tires a bit more worn
• Hi-Kick Racing design front splitter and rear spoiler (Both 7")
• Airtab® Vortex Generators
• Passenger seat was still removed

Session 1

Spoiler at the third highest setting and tire pressures at my 36f and 31r, I went out.  Two bad things happened here.  I a lot of oversteer due to lack of rear downforce, and I was putting my brakes through hell.  Months before, I had replaced my Hawk Black pads to Axxis ULT pads, which were rated "track worthy."  The brakes got spongy after a lap or two, and I could smell fumes from outside the car.  I did a few more laps and I pit back in.


Fastest Time: No laptimes were recorded because I messed up the settings on my laptimer.


I went home and changed the pads back to my worn down Hawk Blacks in a hurry. They had about 20% of life left in them.  Took me an hour to drive, change, and drive back.  I arrived at noon, and asked Grant to drive my car.

Session 2

I adjusted the spoiler to its second highest setting.  No other changes were made.  I went right back out and did a few more laps than the last session.  Handling balance was a bit better, but I was still loose around transitions and kept scrubbing off speed with the end kicking out.  Two problematic areas were the transition between turns 2 and 3, corner exit at turn 4+5, and after the second apex on the chicane at turn 7.  I decided to pit in after a short cool-down run before I boiled my brake fluid.


Fastest Time: 1:02.8
Average Time: 1:03.3

Session 3 - Vortex Generators (Airtabs®) 

I taped four vortex generators in the middle of the rear edge of my roof.  Both had the same laptimes.  Its hard to quantify the exact effect but comparing the best sector times between the VG run and the non-VG run (session 2) in the constant radius turns (turns 2 and 3), the VG installed car seems have slightly higher average lateral acceleration.  My driving in this session with the VGs is also much more consistent.  Furthermore, the car felt more stable.  Objectively speaking, it could be just because I was more used to the car, but I really think it was the VGs that made the difference.  I didn't adjust my driving very much in this run and I drove much cleaner.  I will make a separate post about my experiences with the Airtab® vortex generators.


Fastest Time: 1:02.8
Average Time: 1:03

Grant's run

Grant driving my car

Because I missed out on a lot of track time changing my brakes, I asked Grant to do a short stint.  I dropped the rear tire pressures about 1.5 lbs.  He says he can go faster with a few more laps and even faster with a better driving position.  Grant barely fits in my car.
Benchmark time was 0.4 seconds faster today than his last record of 1:01.8.  His time was 1:01.46

Session 4

With VGs installed, spoiler at second highest setting (man, I need to number the positions), and rear pressures the same as when grant drove the car, I did a 1:02.1. Woohoo! Personal record.  Some of its due to better driving, some of it is due to lower temperatures (should be about 5 degrees lower than my previous record) and some of it is due to the aero mods I put on my car.  The tires have been aging each event, but I guess the changes to the car and driving made up for it.

Driving Notes

Even if I dive-bomb into the chicanes, turning in early and hitting the initial right-side apex allows me to bleed off speed and properly later-apex the left side apex.  Mimicking grant's driving, I accelerated off of that apex into turn 9, but I have to make sure I am positioned correctly on the far left side of the track in order to make it into turn 9 without coming out too wide.  Smooth inputs with steering and throttle are critical in order to not oversteer in turn 9 entry.  This is even more applicable because my car is more neutral.


With aero mods, I can get on the gas way earlier than usual; carefully dialing in throttle allows very good acceleration off of turn 9. Trail-braking into turn 1 and 4 works very well also.

Conclusions

I can say with good definiteness that the front and rear aero mods and the Airtabs® had a net positive effect on the performance of the car.  Top speed of today was 1.5 miles higher than my past top speed, even with a lot of fuel in the car.  Even if I account for the cooler temperatures, this is pretty good.  This means that putting down more power with the increased aerodynamic grip on the exit of turn 9 overcame the drag penalties of my splitter. Vmax: 75mph!

Some more pictures from the event. Pictures seem to be of all Mazdas today!

By the way, I attended the 24 hours of Lemons in PBIR as a crew member. I'm still working on the report; stay tuned!

Aerodynamic Modifications to the car

The LOHP Miata (AKA Brokecore car) received aero mods this winter. It was a long overdue project that I finally got around commencing. I haven't track tested this yet, but I will make an update on it after my track event this weekend.

So what did I make? I made a splitter and spoiler on my car. I went through two spoiler designs because of aesthetic reasons. Ironically, the uglier one worked better. I still have that one if anyone wants it, but your car will look like the Corellian Corvette from Star Wars.

I tested them on the freeway up to 80mph, which is about 7mph faster than my maximum velocity at my home track. They held up fine. The splitter scrapes every once in a while when I drive around town, and the spoiler flutters a bit around the edges but it won't affect the durability at all.

Here is the picture of the modified car:

Links

Front Splitter build

Rear Spoiler build
Test Results

Laptime improvements will be at the next track report.

Aerodynamics: Summer project

Aerodynamics Project

I've been reading "Race Car Aerodynamics" by Prof. Joseph Katz. A thing about Dr. Katz; he is a professor at the San Diego State University. He was a professor while I was at the FSAE program also. Sadly he did not participate in the project. However, he is the authority on race car aerodynamics. Very detailed book, goes into how to test and collect data, how to do CFD simulations, wind tunnel testing, as well as calculating values needed. Of couse, it has a very comprehensive overview of aerodynamics in general and how it effects cars. And a basic section on how it has been applied in car technology. Alas this isn't a book review. I really recommend people to read books on whatever topics they are interested in. Speaking of which, please recommend me any low-priced books on composite fabrication.

This summer I am going to try and make a fiberglass air dam, ABS front undertray, front splitter, vortex generators, rear undertray and rear spoiler. I will probably get to only a couple of these projects. 

Explanation of Aerodynamic Concepts

Drag

     Let me explain what happens as you push the car through air, for those readers who never thought about aerodynamics. Its not all that much important when we are in the entry-level of this track hobby.  I will be using extreme laymen's terms so you techy readers, please forgive me.

     As air flows over a surface, it tends to stick to the surface. Air particles stuck on the surface pull other air with it, slowing them down. The layer of air that is slowed down in relation to the ambient air velocity is called the boundary layer. This friction contributes to total drag in the form of skin drag.

     Airflow likes to follow surfaces. Take any streamlined shape. Flow re-attaches in the end part of the shape, because airflow likes to follow surfaces. Wings are an example of such shape.

     Lets take a shape of the side mirrors. As airflow splits along the front half, the abrupt edge of the surface separates the airflow. As air tries to converge, it goes into a turbulent state and a slight "vacuum" state will exist as the airflow caves in to fill the void left by the mirror. This creates a negative pressure area, which pulls on the mirror that is trying to move forward. This area can be very long behind a moving vehicle. The airflow created by such vehicles are called wake flow. This is the most major contributor to drag. The drag created by this is called form drag. This sort of drag exists behind your canopy, mirrors, behind your car, doorknobs, and any other part of the car sticking out into the airstream.

Lift and Downforce

    Following Brunelli's principle, an increase in fluid velocity is accompanied by a decrease in pressure. Lets go back to the wing example. As the airflow's cross section gets "flattened" by the curvature of the airfoil, it is forced to go faster. The same reason water from a garden hose moves faster when you put your thumb on it. As this travels faster, it creates negative pressure on the top of the wing. This is what creates lift.

    The airflow over the car is generally faster because it is more streamlined. In contrast, airflow under the car is slow because it has to deal with all the junk hanging out of the bottom. Airflow is slowed down. There is less pressure above the car and more pressure below the car. Result is net positive lift. Your tires stick better when there are more forces pushing the ground and the tire together. All you have for this at this point is your cars weight. The positive lift will decrease the force of the car's weight, resulting in less traction.

Race-car applications

    My goal, and everyone else's goal is to reduce the positive lift in the car. This is achieved by reducing the pressure differential as much as possible. If you can accelerate the air under the car faster than the air over it, then you can even achieve net negative lift, also known as downforce. This is why you see race cars with smooth undertrays and side skirts. Not just for looks.

    A more effective way to reduce net lift and add downforce is to add an inverted wing in the areas it is needed. A wing can create much more downforce than what you can do under your car.

    My goals for this project is to reduce lift and drag. I will do this by accelerating airflow under my car and promoting smooth airflow over the car.

Upcoming projects

Fiberglass air dam

    The fiberglass air dam helps divert air upwards over the car, and less air under the car. This reduces the effects of the bottom of the car has on airflow. It also works in conjunction with an air splitter to create downforce, but for that explanation please read the section on air splitter.

    My design will be very simple. Flat, vertical air dam. The major design consideration is probably going to be bracing it properly, so it will not flex much and won't damage more than the air dam itself when you go off track.

Vortex Generator

Simple vortex generator to keep boundary layer attached to the rear roof and deck. The air's momentum is what separates the airflow. Vortex generators twirls the airflow into a vortice. This dissipates the momentum of the airflow, allowing it to stay attached longer. You can see vortice generators in airplane control surfaces, race car undertrays, etc. The Mitsubishi Evolution has them in the rear part of the canopy. My vortex generators will look like that.

As far as the design of the generator itself, I used published, public information to come up with a design. The design consideration will be figuring out how to optimize the positions of the generators and how far they need to be apart.

Splitter

    Whenever air hits your car, there is a pressure zone created. This can be any place on the car where air "piles up" The most major pressure zone is probably the nose of the car. When air hits the front of a car, there is a stagnation point where the air velocity reaches zero. This air pressure exerts forces in all directions. The splitter is necessary to utilize the downward force of the pressure zone, and also traps more air in the area. The air dam promotes this effect.

    Another function of the splitter is to "split" the airflow and create cleaner air going under your car.

    It will probably be made out of foam sandwich fiberglass. It will be adjustable slightly, but I will have to figure out how to properly bolt it in to the undertray without shattering it.

Front Undertray

    Its going to be a simple, mushroom shaped piece of plastic that bolts onto the bottom of the car. I just need to make sure its strong enough not to flutter on the track and break itself off, and make my splitter work with the undertray.

Final Note

As usual, my projects will be as low-cost as possible and easy to follow. Well, I hope they are usually easy to follow. Please correct me if anything I said here is wrong!

Photos

Porsche GT3 in wind tunnel - speedhunters.com

Marine Corps AV-8B Harrier vortex generator

Mitsubishi Evo vortex generator

Ford Fusion Sprint Cup Car front air dam and splitter - K&N Filters website
RE-Amemiya front splitter and canard assembly