Aero ideas....

[timcole421]

Hi guys, have been doing a lot of reading on the subject lately. It seems like the aero stuff has a minimal gain, but it is also free speed and worthy of some thought....I have to design a new body anyway.

The only real "rule" we have on the bodies are the front nose cannot be wider than the front wheels (why this is determined by a variable like track width, I have no idea.

What is a "double skinned roof"?

We have no rules regarding roof size, rake, etc. Would a flat roof with considerable rake be the best way to go? Some of the roofs out there now are borderline stationwagon, and look ridiculous. Is there a benefit to lowering the RF corner of the roof?

Should the roof and rear sail panels be as large as possible? Should the sail panels be at as much of an upright position as possible?

We have to run a tail piece, which means the rear quarters need to taper in to meet the tail piece width. Is there a preferable side to bring the rear of the quarters back in, or should it be balanced?

We aren't allowed fully enclosed interior tin. We can have 18" in from the door on the same level, then it has to drop down to the trans tunnel level. I am assuming a slope down would be preferable to straight down? Would a "flap" built up between the hood and interior panels help clean up some of the turbulence? Is the drop interior a benefit?

Just looking for info to better design my bodywork. Thanks in advance!

[kevpow]

Aero...

Well the idea of aero is great and does indeed offer free speed. However, there are many misconceptions concerning rake and the gains that are offered. Many times a raked roof will create drag instead any aero advantage help. Keeping the roof as low as possible is the first part. Believe it or not, in the wind tunnel, a reverse raked roof has created the better aero effects. Higher in the front, lower in the rear. It quickly guides the air to the spoiler instead of it having to "find" the spoiler. The drag created by a raked forward roof would help on a long track and would help to plant the car but it would have to be by design for that purpose-downforce. Most Sat. night local tracks arent long enough for aero downforce to come into play other than the back spoiler. Most is created by mechanical downforce such as shocks and springs. As for the quarter panels, you will gain better aero effects by skewing the quarters to the right side. The more air that can get to the right side of the spoiler the better and more stable the car will be getting into and through the corners. If there are no rules concerning body sides, you can invert the longer parts of the side of the car on the right side. Kind of like a snow plow. Basically the whole right side of the car becomes a spoiler. Make sure you have open sail panels(windows). The more the air can flow "through" the car the better. And last but not least, I would make some sort of spoiler or lip at the (not a nice word)(not a nice word)(not a nice word)(not a nice word)pit entrance. If youre not able to raise the interior floor, this will help direct the air over the roof and not create a downward turbulance inside of the car. Hopefully this helps.

[timcole421]

Great ideas....a lot to think about. Thanks! Any other ideas?

[Matt49]

These are just my opinions and my reasoning for them. I'm no aero expert and have never been in a wind tunnel.

1) The roof HURTS downforce as a whole because it is keeping air off of the spoiler. Ask anybody that has run a topless race and they will tell you the car has more downforce without the roof. That being said, I would keep the roof as flat from front to back or possibly put a bit of an arch in it (just a couple of inches) so that the air coming off of the back is directed toward the spoiler might not hurt.
2) Do what you can to keep the air going OVER the car and not under or around it. The new style MD3 nose sides help with this. Also tapering your front fender tops so that they are higher on the outside and lower toward the hood. And run a valence under your nose to keep the air going over the nose and not under it.
3) Keep the right side of the car as flat as possible (taper in on the LR after the wheel). Keeping it flat will give you aero side bite though the corners.
4) Cut a window hole in the right side sail panel to allow more air to the spoiler when sideways through the corner. Leave the left side window hole closed to direct more air back toward the spoiler.
5) Use a good aerodynamic hood scoop. You'd be surprised how much the breather disrupts the air that might otherwise have a smooth pathway back to the spoiler. But with the fact that you can't run a flat decking, this may be a moot point.

Again, just my opinions...I don't claim to be an expert.

[MasterSbilt_Racer]

I will make only one comment on this. Any air that goes over the roof will not make it down to the spoiler.

[Egoracing]

If you are going fast enough to feel air moving you can gain from aerodynamics, tracks 1/4 mile in diameter can generate enough speed to add a BUNCH of down force. Need proof? Take the nose off of your car and try to drive the same speed that you normally do.

[Matt49]

If you are going fast enough to feel air moving you can gain from aerodynamics, tracks 1/4 mile in diameter can generate enough speed to add a BUNCH of down force. Need proof? Take the nose off of your car and try to drive the same speed that you normally do.

A buddy of mine tried to convince me that the spoiler didn't do much on small tracks so I cut a 1'x4' piece of plywood (same surface area as a 8"x72" spoiler) and we hopped in the bed of a truck and tried to hold it in the air at 45 degrees while going 50MPH down the road. That'll make a believer out of anybody!!! Don't try this at home by the way...this was after one too many adult beverages. Lucky not to be roadkill.
The nose is WAY more surface area than the spoiler and gets much more "clean" air.
These cars are light. ANY amount of downforce makes a difference.

[LM14]

Your open interior is a deal killer for many reasons. Close off everything you legally can. Make the back edge of the interior a smooth transition to the rear deck. Radiused is better than a square corner.

Long track, make a curved roof to dump air on the spoiler. Short track use a straight roof raised at the rear. A lip along the sides of the roof will also help trap air on the roof to guide it.

Use short side roof panels on the right to get air moving across the spoiler in the corners, long roof side panel on the left to trap that air on the spoiler. Don't use spoiler braces in the middle, it just disturbes air. Use a 1/4" rod on the right side of the spoiler for the brace instead of a flat panel so air gets on the spoiler in yaw.

Bloomquist used to run a double panel roof. There was a panel below the bars to smooth the air. They actually had a hole in them to fit the top of the helmet in.

Just things we've tried.
SPark

[racer69]

EGO and Matt are very right along with some other stuff said above. I just caught tons of static for my asphalt car! lol

Like said above....keep air out from under car. Keep valances as tight as rules allow. Frontal area needs to stay at a minimum. Direct all possible to spoiler.

And speaking of spoiler watch angles. Many use way to much. Try what we all done as a kid. roll down the window and stick your hand out. Come on you know you still do it!!! I do! But this time change the angles and notice the downforce on your hand. At a point the force becomes lighter with more angle. Try it!

At an amusement park recently me and my daughter rode the big swings. Hooked so they dont twist. When we got up to speed I had her stick her hand straight forward fingers away from her. She watched me to see lol. And we would turn our single hand left and right like a tiny rudder. Next thing ya know we was turning completely backwards against the force of the chains. Got kicked off too.....whoops! But when you think small gains only on a small track.....think again and think bigger!

[timcole421]

Awesome discussion, this is going to be a lot of fun to work with! PS, this is actually a 3,000 pound car on 8" tires if that changes the discussion much. However, the body will be modeled roughly after a dirt late model which is why I brought the discussion up here.

We recently ran a "run what you brung" race which is what led me to believe -any- way to use the air to your advantage would be worth it. We were over 1.5 seconds than the track record, fastest lap of the night, heat win from sixth, and feature win from fifth.....my first ever feature win, and all with a very badly running/misfiring engine all night. We ran a big lexan board like the late models, it definitely wasn't horsepower that made us dominant.

[Egoracing]

Skirts if you can use them as low as you can get them and keep them on the car, Then make the front as wide as you can and make sure the front side of the wheel opening is wider than the rear of the wheel opening and as much as possible. This difference will help generate a low pressure area to pull down on the car. Watch a late model idle thru the pits. The car generates enough of a low pressure area under the body even at that speed that it lifts dirt up when it drives over it. Then watch the other classes and you will notice that not nearly as much dust is pulled up when they drive by.

[hall99]

Very good points, I lost my spoiler about 5 or 6 laps into the the Topless 100 at Batesville this August I tried to stay out and couldn't even come close to keeping pace ending oup pulling off as soon as the next caution came out. I knew it would hurt me but it really dropped me off the pace.

[FlatTire]

Shhh.........those LUCAS Oil officials are reading this.

The more aero knowledge that gets out there, the more teams follow suit, which all leads to sanctioning bodies writing rules against all of it. Just something to think about.

[hall99]

LOL! Funny they came on the radio and told me ease into the corner on the restart because my spoiler was gone... I thought great I already new I didn't change my car enough for the feature now this!
Really I was impressed with the Lucas Oil people over the weekend.

[RACR_73s]

I just read an article in Circle Track...Areodynamics for Dirt Racers. It has some of the same things listed here plus some other thing to consider. I thought it was informative, but I have little to no experience with areo. Give it a look in the Jan. 2013 issue.