spoiler angle

[mod88s]

What spoiler angle do most of you run? 12" spoiler crate car but would like to hear what yall run.

[RCJ]

65 degrees on an 8 inch

[turtle1hp]

That is a loaded question. You are trying to achieve as much down force as possible which will require more angle, at the same time it will affect aero balance. I have run 80 on short stop and go tracks and 45 on large momentum tracks. You can tell you have to much when the car doesn't want to turn into the corner off of the straight away or you have to slow your corner entry to get the car to turn off of a straight line.

[A ron]

Something I noticed this weekend at our local track crate class: all the cars except one had 12" spoilers 60ish degrees and it had a 6-8" spoiler almost straight up. He ended up 2nd but pretty much usually dominates running that small straight up spoiler. Any thoughts?

[turtle1hp]

Hmmm... Maybe the shorter 90* spoiler still creates the higher pressure area on the rear deck without the parachute/dragging effect of the larger 12" spoiler.

[Matt49]

The spoiler is essentially a Gurney flap for the much larger airfoil/wing which is the entire car body at attitude. Or at least that's the way I like to think of it.

[a25rjr]

Anyone remember when Ronnie Lee won all those Nesmith races at BRP? He was the first to switch to the 8" spoiler that week!

[MBR Performance]

These cars already have a ton of rear downforce with a 8" spoiler then add 4 more inches with limited horsepower makes no sense.

[mod88s]

So back to the original question, how much angle would/do you run using a 12" spoiler? I realize there are alot of variables but just wanting to know what yall run

[powerslide]

These cars already have a ton of rear downforce with a 8" spoiler then add 4 more inches with limited horsepower makes no sense.

So do you shorten the deck to the min and then keep the big spoiler?

[RCJ]

I would try a 12" at 45 to 30 degrees .Trying to get the same downforce as an 8" but with less drag.

[dkibel]

So I made a quick and dirty table and graph of the down force that occurs on the wing. The velocity will only change the magnitude of the force. You can look the graphs and find that an 8" spoiler at 50* will have the same force as a 12" spoiler at 30* and so on. If you guys would like to see a proof of the calculations I would be more than happy to provide them. Essentially you will have the same drag between the two spoilers if they are matched to their corresponding angles like the example I mentioned above. The biggest thing is matching that condition to the track condition and not nailing the back of the car down to the ground too hard. The advantage to the 12" spoiler is that you can build more down force with it but you are limited on the down force or adjustment you can take away.

[Matt49]

Aerodynamics can get complicated but I'll make a long story as short as possible.
If you have an 8 inch spoiler at some angle and you are getting a downforce of X and a drag of Y, and then you put on a 12 inch spoiler and set it at the angle that produces a downforce of X, I can almost guarantee that the drag will still be Y.
There are ways to reduce drag without changing downforce (negative lift) but spoiler angle isn't one of them. If you want reduced drag without losing downforce, the best thing you can do to your car (legally) is keep straight sheet metal on it.

[dkibel]

Not quite, the difference in 4 inches will make the air that much harder to recover. Esentailly a spoiler does create downforce but it is also designed to aid in airflow recovery. If you are making your air have to travel an extra 4 inches downward to recover to its inital state, you do create drag because you get a high pressure region behind the car and a low pressure region on the spoiler/ decking which acts like a vacuum slowing the car down. If you want to reduce drag absolutely yes keeping your sheet metal straight helps but also thinking about trying to make the air flow smoothly behind the car (when it exits the quarter panels) helps a bunch. Of course this really only comes into play when we are talking about 1/2 mile tracks.

[Matt49]

I think we're saying the same thing dkibel. Speaking of quarter panels...take the LR quarter panel off and see how she does. It's been done before.

[dkibel]

I think we're saying the same thing dkibel. Speaking of quarter panels...take the LR quarter panel off and see how she does. It's been done before.

This man has it all figured out. haha

[RW57]

On my son's car with maybe 350 up we started with the spoiler at probably 45 degrees car was always tight getting in one nite for the hell of it I laid it back as far as it would go probably at 30 degrees car was much better getting in and thru middle.

[RCJ]

How did you arrive at those calculations?

[dkibel]

Using bernoullis equation (basis for all of fluid dynamics) you can find that Pressure= (1/2) * density of air * Velocity^2 . Once you find the pressure that is on the wing you can easily find the force on the wing, for this calculation pressure is essentially a constant or a multiplier in this case since we are only solving for the difference between the 8" spoiler and the 12" spoiler. Then you can find that Force= Pressure * area. This will just find the force on the wing. We want to find the correlation to angle so when you have flow over the spoiler you will have a vertical and horizontal component. To find the down force (in the vertical direction) DF=F*sin(angle). Typing this out on a computer is quite hard to explain so im doing the best i can. A degree in engineering really helps show the results behind the theories on these forums. If anyone needs further explanation feel free to pm me.

[turtle1hp]

Matt49 What exactly does happen when the LR quarter is removed? I was actually thinking about making it shorter on a car that we run that has a closed rear section. In hopes of lowering the pressure under the car while the body is rolled through the corners.