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.

[dkibel]

Essentially when you take the whole fender off you are creating a high pressure point right behind the driver. This is act like a vacuum at high speeds trying to turn the front of the car at high speeds. With all of the bars on the chassis being exposed on the bottom of the car there is enough turbulent flow to create a large low pressure zone underneath the car. Im interested to see what matt has to say about this! Side note, this is probably one of the most interesting threads ive been apart of!

[Matt49]

I can't speak for a closed rear end car but SOME of this still applies. The key to downforce is to create high pressure above the body and low pressure under it. The LR quarter panel is part of the low pressure discussion. The more air you can prevent from going under the car (by sealing the nose to the track) and the more air you can get to escape from under the car (open rear end), the lower the pressure will be under the car = more downforce. To understand the importance of the LR quarter panel in all of this, it is important to understand how the bodies are constructed. The rules state the body can be 76" wide (max) above the rear axle and 72" wide (max) at the spoiler/end of the rear deck. The rules also state that this taper must be even on both sides but this rule hasn't been enforced in decades and almost everybody builds their bodies so that the right side is flat and all of the taper from 76 to 72 is in the left side. Now think about the car's angle of attack (yaw) on the race track and you can begin to see how the LR quarter panel is kind of "holding" a lot of air under the car...this is bad. Several years ago, some touring guys cut the LR quarter panels so they were only about 6 inches tall and they were bad fast. The sanctions quickly wrote new rules to make that illegal. Lucas Oil has a rule stating that the quarter panel must be at least 27" tall without plastic and 31" with plastic.
If you just look at recent pics of some of the touring guys cars you can see that most of them run the LR quarter panel as short as possible with the plastic trimmed more like you would be accustomed to seeing on the right side.

[billetbirdcage]

I can't speak for a closed rear end car but SOME of this still applies. The key to downforce is to create high pressure above the body and low pressure under it. The LR quarter panel is part of the low pressure discussion. The more air you can prevent from going under the car (by sealing the nose to the track) and the more air you can get to escape from under the car (open rear end), the lower the pressure will be under the car = more downforce. To understand the importance of the LR quarter panel in all of this, it is important to understand how the bodies are constructed. The rules state the body can be 76" wide (max) above the rear axle and 72" wide (max) at the spoiler/end of the rear deck. The rules also state that this taper must be even on both sides but this rule hasn't been enforced in decades and almost everybody builds their bodies so that the right side is flat and all of the taper from 76 to 72 is in the left side. Now think about the car's angle of attack (yaw) on the race track and you can begin to see how the LR quarter panel is kind of "holding" a lot of air under the car...this is bad. Several years ago, some touring guys cut the LR quarter panels so they were only about 6 inches tall and they were bad fast. The sanctions quickly wrote new rules to make that illegal. Lucas Oil has a rule stating that the quarter panel must be at least 27" tall without plastic and 31" with plastic.
If you just look at recent pics of some of the touring guys cars you can see that most of them run the LR quarter panel as short as possible with the plastic trimmed more like you would be accustomed to seeing on the right side.

https://photos.smugmug.com/WORKING/Dirt-racing/Screven/Screven-Ga-Late-models-Feb-3/i-cJtcBZs/0/XL/IMG_1635-XL.jpg

[billetbirdcage]

http://oi52.tinypic.com/2d9adjq.jpg

http://i229.photobucket.com/albums/ee1/NGates84/OOO.jpg

[zeroracing]

So what would they do if they passed a new rule? Your allowed to trim the LR as much as you want, you cannot run any covers, and back to 2015 suspension rules... Be interesting to say the least.

[RCJ]

I don't think your calculations take enough real world problems in to account.The amount of force at the contact patch of the tire is what I'm think about.Let me get some measurements from my car to explain better.

[dkibel]

My calculations were purely based on how much down force the wing would see. I was just trying to get to the point that everyone could see the correlation between wing angles and heights. I'm sure i could find out exactly how much weight was on the tires but i would need to know the geometry, percentages, wheelbase at full hike, a model of the acceleration and deceleration (if you wanted to see how much force it would give at any given point), so on and so forth. Actually, that would be an interest project this weekend.Thinking about those pictures it actually makes a lot of sense. Pretty cool stuff.

[billetbirdcage]

So what would they do if they passed a new rule? Your allowed to trim the LR as much as you want, you cannot run any covers, and back to 2015 suspension rules... Be interesting to say the least.

First sorry about the huge pictures and messing up the screen size on page. Also for getting off topic on this but I gotta say something about the rules deal.

I think I been clear on how I feel about closing the box but that is another story. The problem is enforcement and the consistency of what is checked and what isn't.

1. At the Show-Me, there was a car that was told 3 times to take something off the LR over the whole weekend. He didn't, it wasn't until the final A feature that they supposedly made him or finally got him to take whatever they didn't like off.

2. Another guy asked a Tech official (it was not schwallie) if he could run what he had on his car. It was a split birdcage which is clearly defined in the rules as Illegal. The Tech guy told him, he was fine because everyone was trying stuff and they couldn't keep up with all of it so as long as it only had 2 (non compressible) links on the LR they where fine with it.

SO WHAT THE HELL IS THE RULES?????? Is it what is written in the rule book or what the tech guy said or just what they going to check that day, I'd really like to know.

I'm leaving out a bunch of stuff because it's not my place to call out guys, throw anyone under the bus, or ETC: but I just want to know what the MOTHER F'ing rules are.

End of my rant

[billetbirdcage]

They write 2 pages of suspension rules, when the can't or more importantly won't enforce the body rules they have. Half of the cars have more then 1" of rise or drop on the right side body line, which is clear as day in the rules as NOT LEGAL

[MBR Performance]

Off topic but related to billet's rant. What gets me is they say no split birdcages yet the option to split them has been around for a long time. Stupid

[turtle1hp]

I can't speak for a closed rear end car but SOME of this still applies. The key to downforce is to create high pressure above the body and low pressure under it. The LR quarter panel is part of the low pressure discussion. The more air you can prevent from going under the car (by sealing the nose to the track) and the more air you can get to escape from under the car (open rear end), the lower the pressure will be under the car = more downforce. To understand the importance of the LR quarter panel in all of this, it is important to understand how the bodies are constructed. The rules state the body can be 76" wide (max) above the rear axle and 72" wide (max) at the spoiler/end of the rear deck. The rules also state that this taper must be even on both sides but this rule hasn't been enforced in decades and almost everybody builds their bodies so that the right side is flat and all of the taper from 76 to 72 is in the left side. Now think about the car's angle of attack (yaw) on the race track and you can begin to see how the LR quarter panel is kind of "holding" a lot of air under the car...this is bad. Several years ago, some touring guys cut the LR quarter panels so they were only about 6 inches tall and they were bad fast. The sanctions quickly wrote new rules to make that illegal. Lucas Oil has a rule stating that the quarter panel must be at least 27" tall without plastic and 31" with plastic. If you just look at recent pics of some of the touring guys cars you can see that most of them run the LR quarter panel as short as possible with the plastic trimmed more like you would be accustomed to seeing on the right side. That is what I was thinking. The idea of shortening the quarter panel "should" help direct flow from under the car when it is in yaw through the corners. This should help to increase the pressure differential on the deck surface. JMO

[7uptruckracer]

So where can I find split cages?

[Kromulous]

Speaking on Aero, and the Rules...

I see a lot of cars, with the right-side sheet metal, mainly the door area dished in, concave. In the rules it clearly says flat. If you look at Bloomers car it is dished in big time.

I am guessing its trying to duct the air up and over the car, and not under.

The LR thing is interesting, tin snips are out and ready LOL.

Also side panels, whats the thoughts on closed or open? seems like alot of guys are running the really big and open panels now.

[Matt49]

For sail panels, the ideal scenario would be open on the right and closed on the left. Open on the right to allow more air on the rear deck and spoiler when the car is in yaw and closed on the left to direct air onto the spoiler.
Most rules state that the sail panels must match (open or closed, not one closed and one open)

[MasterSbilt_Racer]

Speaking on Aero, and the Rules...

I see a lot of cars, with the right-side sheet metal, mainly the door area dished in, concave. In the rules it clearly says flat. If you look at Bloomers car it is dished in big time.

I am guessing its trying to duct the air up and over the car, and not under.

The LR thing is interesting, tin snips are out and ready LOL.

Also side panels, whats the thoughts on closed or open? seems like alot of guys are running the really big and open panels now.

I think the concave issue is that you will have more volume of air against it, than if it was flat. It will hold the car from sliding to the outside more when yawed and headed up the track. Air is a fluid.

[RCJ]

Finally got some measurements.From the contact patch of the tire to the tip of the spoiler (c-t) with 8"at 67 =68.5 .With 12'' at37 =73c-t.My thought is that with both spoilers set to give the same mathematical downforce the extra 4.5'' will give more leverage.I also thought the 12'' would be higher too.The higher an object is typical gets it in better air flow creating more force.The overall height from the ground was very close to the same at 67 and 37.When the l/r when up on the bars the c-t grew by 6 or 7 ''.