Dirty Air

[HurriCrane Racing]

Being new to the NPWDRL, I'm trying to improve and hopefully become competitive some day. What I have noticed is that my cars are a good .02 faster alone than when there is a car directly next to it. I have two lane test track and this just amazes me that the turbulence could have this great of an impact.
How do you pros compensate or minimize the impact of dirty air?

 

[3phase]

From what i have found around here is ......be in front.
I will look for the thread.
Here

 

[HurriCrane Racing]

That would be interesting but it seems that most cars drop very close together. It's the flat that separates the great builders from the rest of us also rans. I've noticed that one of my fastest cars can get unstable if there is a car running near its' right rear wheel. Just kills the times.
Wonder if sloping the body edges would cut down on this effect? Or is this just an indication that my drill job could have been better?

 

[GravityX]

Stay in front! /images/boards/smilies/smile.gif

The GEE fenders help. Getting the car as stable as possible. Minimize wheels gaps, optimize weight placement and get the oil process down to an art.

Practice. Practice. Practice.

Practice will define a better car.

 

[HurriCrane Racing]

Built a car with GEE fenders for the first time for the April race. Was able to run tighter gap than with my home made fenders.
We will see if this translates into a faster time. Hoping to average below 3.0 this month. Last month it was 3.0002.

JUst wondered it there was a method for dealing with the dirty air.
I'll keep at it.

 

[IAE Racing]

"Dirty Air" I just say excuse me and keep racing.

 

[Quicktimederby]

Play with the set up of the car. It's kind of cool watching the race videos. The cars that are on the edge of being to loose will usually run good in the red lane than wobble bad in the blue. Those cars that have a little to much steer will slow in the red and speed up in the blue. All do to the cars next to them. The way you set up the car will help minimize the effect of the other cars.

 

[Guest]

Dirty air, dirty water, and throw granny off the cliff!

OK. The NF fenders look cool as heck. Tough to deny it.

They also stiffen the body of the car due to triangulating the structure.

(Who says that stiffer is always better though)

IMHO the NF fenders are much too large to slip thru the air cleanly.

I seriously doubt that one can assault a neighboring car with air without slowing their own car considerably. Think about it. In order to push the air over there that means you had to displace the air initially (slowing you down).

I believe the best one can hope for is for the air to circulate as freely as possible under, over, and around the car. One wants as little as possible for the air to "stick" to in terms of skin friction etc.

Right before the air leaves the car it wants to be disturbed.

 

[Obsessedderbydad]

Please explain how deflecting air will slow you down. I could see it slow you down if your car was deflecting it at a 90 degree angle, but can't see it slow you down if the angle of deflection is much less than that.

 

[zeebzob]

If you see that big of a time variation when running two cars on yor track, something to consider is the vibration the other car causes to the track. You will want to dampen it as much as possible. Someone came up with the idea of putting Dynamat on the underside of the track and this helps greatly. Dynamat is what car stereo enthusiasts put on the inside of the car body panels to reduce noise and vibration. Dynamat, however is really expensive. It would probably cost a few hundred bucks to do your track. A much cheaper alternative is to go to Lowes or Menards or Home Depot. Go to the roofing section and find a product called Peel and Seal. It's a thick adhesive backed strip of aluminum foil. It's 6 inches wide so you just cut it to 3 inch stips, 7 feet long and put it under the track. You can do a two lane track for probably like 30 bucks.

P.S. The reason this is not a good choice for cars instead of Dynamat is because it's an asphalt based adhesive and when it gets hot, it smells and gets gooey, but unless you have you track out in the sun, it should be just fine. It's what I have on my track.

 

[Guest]

Please explain how deflecting air will slow you down. I could see it slow you down if your car was deflecting it at a 90 degree angle, but can't see it slow you down if the angle of deflection is much less than that.

Hi ODD,
The way I interpret it is this way.
What one would like to acheive is laminate air flow over the car and avoid turbulent separation.
Apparently flow separation is a source of major drag.
Once the air is separated from the object it can actually reverse direction and cause additional drag.
The car really wants to disturb as little air as possible. It wants to cut thru the air and have the air rejoin at the rear of the car. A visual I like to think of is divers in the Olympics. The judges look for the height of the splash after the diver is fully in the water.
The closer to the front of the car the separation occurs the more drag.

 

[GravityX]

What one would like to acheive is laminate air flow over the car and avoid turbulent separation. Apparently separation of the boundary layer is a source of major drag. Once the air is separated from the object it can actually reverse direction and cause additional drag. The car really wants to disturb as little air as possible. It wants to cut thru the air and have the air rejoin at the rear of the car.

Here are some pictures of objects that may help define what Joe is saying here. The flat square creates a high amount of air separation and turbulence and actually creates a suction. An common example of this is the snow piling up on the rear of the car while driving on a snow covered road, covering the taillights and such.

Obviously the airfoil or wing design is the most efficient out of the three shown here. The wheels share both the sphere and square shape. The side view of the wheel represents the sphere from a 2 dimensional view, in a top view you see the square/rectangle shape. Add the two and you get a 3 dimensional view of the wheel with combined airflow.

The cars ride fairly close together on the track. I'm sure, to a certain degree, the car give off a wake that could disturb the car next to it. How much the car next to it is disturbed by this wake it dependent on design, I would think. But weight balance in the car could play a part in preventing this from happening too, again making an assumption. Wind tunnel testing anyone??? But this would only check air flow over the design and would not consider the weight.

Just thinking out loud.

 

[Kinser Racing]

The vibrations that zeebzob mentioned are a big factor.

 

[Guest]

What one would like to acheive is laminate air flow over the car and avoid turbulent separation. Apparently separation of the boundary layer is a source of major drag. Once the air is separated from the object it can actually reverse direction and cause additional drag. The car really wants to disturb as little air as possible. It wants to cut thru the air and have the air rejoin at the rear of the car.

Here are some pictures of objects that may help define what Joe is saying here. The flat square creates a high amount of air separation and turbulence and actually creates a suction. An common example of this is the snow piling up on the rear of the car while driving on a snow covered road, covering the taillights and such.

Obviously the airfoil or wing design is the most efficient out of the three shown here. The wheels share both the sphere and square shape. The side view of the wheel represents the sphere from a 2 dimensional view, in a top view you see the square/rectangle shape. Add the two and you get a 3 dimensional view of the wheel with combined airflow.

The cars ride fairly close together on the track. I'm sure, to a certain degree, the car give off a wake that could disturb the car next to it. How much the car next to it is disturbed by this wake it dependent on design, I would think. But weight balance in the car could play a part in preventing this from happening too, again making an assumption. Wind tunnel testing anyone??? But his would only check air flow over the design and would not consider the weight.

Just thinking out loud.

Hi Paul,
Yes. That is a great example. I saw this episode on Mythbusters where they examined if a pickup would get better mileage with the gate open. It was rather inconclusive but to see the air circulate in the bed area was instructive.
I would not doubt that the change in pressure between cars will draw them together with the Bernoulli effect.

 

[HurriCrane Racing]

The cars I sent in this month have 3" of steer compared to 4" last month. This will be a good test of QT's position.
My car last month never wiggled a bit. Maybe the steering was holding it back.

 

[Guest]

The vibrations that zeebzob mentioned are a big factor.

Do people ever bolt down the track to eliminate vibrations?
Or incorporate weights?

 

[OPARENNEN]

You may have never noticed it, but DD4H's track (each section) has a 5/8ths piece of a heavy board (not wood, but something else). Purpose was to reduce vibration. My test track is a single lane, so I screwed each section to a 3/4 x 8 inch piece of plywood.
The sound of cars running is very different. If a wheel is out-of-round, I hear it instantly, even if only a single wheel.