There really can be a lot...
There really can be a lot learned from spending some time in the wind tunnel. We were lucky enough to be able to tag along with Menscer Motorsports when it visited the A2 Wind Tunnel in Mooresville, N.C.
I know what you're thinking, Come on, a Dirt Late Model in the wind tunnel. . .are you serious? But before you start blasting us for having Cup envy (a term where race teams do things just because they see NASCAR Sprint Cup teams doing them), take a moment and put down your pitchforks and torches, and have a read about what we learned from tagging along with a Dirt Late Model team on its trip to the wind tunnel.
To better understand the data we learned from having a Dirt Late Model in the wind tunnel, you need to have a crash course in aerodynamics, and understand a few terms that we'll be mentioning throughout the article.
Dave Salazar from the A2 Wind Tunnel defines aerodynamic drag as a force in the opposite direction of the vehicle's forward movement. Drag will increase as the speed of the vehicle increases. You need enough power to move the air around the vehicle, and at low speeds drag isn't too much of a concern. However, as the speed increases, so will the aerodynamic drag on the vehicle. It will increase by approximately the square of the speed increase. What that means is, if you double the speed of the vehicle, you will increase the drag forces on the vehicle by about four times!
So, imagine that your drag force is 70 pounds at 50 mph. Then the drag force at 100mph would be close to 280 pounds. What makes this important is that the horsepower required to overcome drag is dependent on the speed as well. HP=Drag Force x Velocity. This means as the speed increases, the horsepower required is now approximately the cube of the percent of the increase in speed. Every time the speed doubles, the horsepower required to overcome the drag forces is increased by about eight times!
The guys at Menscer Motorsports...
The guys at Menscer Motorsports were ready for the tunnel, they brought adjustable tie rods that allowed them to put their car at ride heights as well as different hoods, spoilers, fenders, and more.
A byproduct of the development of downforce is drag. However, the two don't necessarily correlate with changes in magnitude. You'll see a perfect example of this later with the rear spoiler on the Dirt Late Model. You see, the aerodynamics of the Dirt Late Model body, or any racing body for that matter, are extremely dependent on every factor of that body. What I mean is this, if I change a rear spoiler to gain rear downforce, I could increase or decrease the front downforce because the air-flow across the front of the car is affected by the new rear spoiler angle. In essence, the airflow across every part of the car can be influenced by changes to any part of the car. This is specifically where wind tunnel testing could benefit teams.
The guys at A2 Wind Tunnel (A2WT) were gracious enough to let us tag along when Menscer Motorsports brought its Dirt Late Model into the wind tunnel. The numbers that were recorded really caught us by surprise. Out of respect for Menscer Motorsports, I won't be able to share all of the downforce numbers, but I will be able to show where we saw gains and where we didn't.
The key to having a successful test at the A2WT is to be prepared and the guys from Menscer Motorsports were. They had pulled the shocks off the car and put the car at normal ride heights using adjustable length rods. This meant that the car would not change its ride or pitch attitude as a result of the 85mph wind that it was going to feel. We could run our tests over and over again without having the numbers being skewed by changes in the car's attitude.
Once we strapped the car down and centered it, we were ready for our first run. The baseline run would show us our first downforce numbers for the front and rear of the car, along with side forces and drag. The results came back and what amazed us more than anything was that almost 70 percent of the downforce was being made at the rear of the car. When compared to a sleek Sprint Cup car, the Dirt Late Model produces a ton more drag, however the downforce numbers are much higher than a Cup car.
We had to square the car inside...
We had to square the car inside of the tunnel, since it would be strapped to a set of monitors that would feed the A2WT computers with all of the data collected.
Dave Salazar from A2WT is...
Dave Salazar from A2WT is getting ready to run the first baseline, this will provide a way of looking back and seeing how much downforce we've gained or lost from our adjustments.
The next thing to do was to put the car at race attitude because, as I'm sure a lot of you readers have already concluded, a Dirt Late Model will never sit that flush when traveling near 100 miles an hour. The guys of Menscer Motorsports were ready and after a few adjustments the car was almost hiking the LF inside the wind tunnel.
The incredible thing was that even with the car at attitude, the downforce numbers actually increased. The biggest jump we saw was the increase in the side force numbers. After we ran the car at attitude, we then put it back to ride heights and started to work toward evening out the car's downforce numbers.
The goal would be to attain a front-to-rear downforce balance closer to 50-50 by trying to increase the downforce at the front of the car without affecting the rear too much. Plus, we need to remember the reason why the bodies are designed with so much rear downforce is because of the need for better bite off the corners. You need that much downforce to be able to help accelerate better.
Another interesting fact that we came across was how much horsepower we would need just to overcome the drag being produced. Remember from earlier, as the speed increases, so will the drag. We'll need roughly eight times the amount of horsepower to overcome that drag. What we found out was that to achieve a top speed of 135 mph, we would need roughly 400 horsepower. "This is a huge number for you guys," says Salazar. "Now we know that we don't need to be concerned with reducing the amount of drag." This is because no matter how much downforce we create we'll always have an abundance of horsepower to be able to overcome that drag."
This could be a factor for you crate Late Model guys though, if you're only pushing near 400 hp. Then, you might want to look at getting the body as low to the ground as possible and reducing the amount of drag.
Putting the car at attitude...
Putting the car at attitude shows the type of downforce we are creating when the left front wheel is almost off the ground.
Next we reduced the speed of the wind to 40 mph and were able to see how the air was traveling around the car by doing a smoke-wand test. We don't record any data during this test but we were able to see exactly how the air travels over the body. What we were able to determine and see was where the "dirty air" was being produced. We could see that the air traveling across the center of the hood wouldn't actually ever get to the spoiler, but the air flowing over the right and left sides of the spoiler is where all of the downforce was made.
Help increase the front downforce To help increase the amount of front downforce, the team tried a variety of different changes to the front end including different hoods, fenders, and more and we found a few gains. One of the most impressive gains was found by simply taking a 90-degree piece of aluminum and running it horizontally across the front fender (as shown in the picture on the previous page). This seemed to help the front downforce numbers. Don't get too carried away though on how tall the piece is, a 1-inch piece did just fine. If you go too much larger it will actually start to hurt the rear downforce numbers by deflecting too much air away from the roof and spoiler.
The other adjustment we tried which seemed to help was installing a carbon-fiber air-filter cover. This piece helped both the front and rear downforce numbers.
Rear Spoiler Now, the rear spoiler is where we found some really good information. A small rear spoiler change can affect how the car handles drastically. A good example of this is the gurney bracket that was attached to the rear spoiler. The flap is only a couple inches wide and it helps hold as much rear downforce as possible. What we did was take the gurney flap and turn it around backwards to where it faced the direction of the wind just to see if we lost downforce. We found that we lost 100 pounds of downforce at the rear of the car. Someone asked, "Is that a big change?" To which Dave responded, "Well if your driver can't feel 100 pounds of change, you need a new driver."
These bodies produce a ton...
These bodies produce a ton of downforce, but 70 percent of it is coming from the rear of the vehicle. In order to gain front downforce, the team added a 90-degree piece of aluminum across the hood. It made a big difference on the front downforce numbers.
This carbon-fiber air filter...
This carbon-fiber air filter duct not only increased our front downforce numbers but we saw an increase in the rear as well.
What we found out with the...
What we found out with the rear spoiler was a simple, minor change could cause huge changes in the rear downforce numbers. But what surprised us was the rear spoiler, if tilted too far up, would cause an increase in drag, but a decrease in rear downforce.
The smoke-wand test allows...
The smoke-wand test allows us to see how the air was traveling over the car.Notice once the wind gets to the air filter cover, it splits toward the passenger-side of the vehicle--providing a more direct hit on the spoiler. This is why we saw an increase in the rear downforce with this piece.
We also found that all rear spoilers have a stall point where they stop producing downforce at the rear of the vehicle. For instance, we kept making small changes to our adjustable rear spoiler where we would raise the angle about 10 degrees, do a test and then raise it some more. When we got to a certain higher angle, all of a sudden we lost rear downforce.
At first we thought the bolt wasn't tightened and that the rear spoiler had slid back to its original height, but we noticed we still had recorded an increase in drag. The team found the stall point of its rear spoiler. This goes back to what we'd talked about before--increasing drag will not necessarily increase downforce. Even though the spoiler was causing more drag for the entire car, it wasn't increasing the downforce for the rear of the vehicle.
Now with all the downforce...
Now with all the downforce numbers that Menscer Motorsports has, it will know how big of an adjustment it's making when it tilts the rear spoiler, or if the team attaches a new roof. This is why time in the wind tunnel is beneficial.
The point of all this is not only to prove that you can benefit from spending a few hours in the wind tunnel, but also to show you that simple changes can go a long way in affecting the handling of your car. This also gives you options when at the track. Menscer Motorsports now knows that if its driver has a complaint, the guys know how much downforce they can expect to add when they make a small rear spoiler change. I'm not saying that in order to win you have to spend 5 hours in the A2WT, but it could go along way in helping you end up in Victory Lane.
The A2 Wind Tunnel (A2wt)The A2 Wind Tunnel (A2WT) in Mooresville, N.C., was designed with the grassroots market in mind. The A2WT has been open for almost three years now and it has seen a wide variety of vehicles come through its doors. It has seen everything from Karts, Bicyclists, and ATVs to Dirt Late Models, ARCA, and USAR Pro Cup cars. Pricing for the A2WT might seem a little outrageous at first, $390/hr. But when you compare that to its big brother, the Aerodyn Wind Tunnel, which services the NASCAR Sprint Cup teams and charges $1,590/hr., it seems relatively inexpensive, even a bargain. And unlike its competitors who make you rent the tunnel for the entire day, the A2WT requires only a two-hour minimum.
The key to having a successful test at the tunnel is to be prepared when you unload the car. As you can see in the photos, Menscer Motorsports was ready for the test, it brought different hoods, spoilers, fenders, and so on. Each time the team made a change, it was able to see exactly where and how it changed the downforce numbers.