Spoiler angle

[racingobserver]

First off if this has been discussed on this board several times I appologise. We run mainly IMCA modifieds, but get the chance to run a latemodel a hand full of times each year. We are suffering from an overall loose/lacking forward drive off of the corner. I havnt put an angle finder on the spoiler, but was curious how much angle guys on here run. I was thinking of standing the spoiler straight up. How much affect does this have on the cars?

[rocketdent]

I saw in a magazine where after so many degrees the spoiler becomes more drag than downforce. I cant recall number?? Anyone know? Id guess 60's?

[MasterSbilt_Racer]

I think it is much lower than most people realize. I think it is quite a bit less than 60.

[Egoracing]

Speedway magazine had a dirt late model in a wind tunnel several years ago, the whole car is designed to create a vacuum under it and the spoiler actually increases or decreases where the rear decks pressure is and actually varies nose down force more than it creates drag. Even with the spoiler straight up and down the pressure on the deck is increased farther forward on the deck. The worst drag on the car was the drop at the front of the deck where the hood ends. On some old cars that was 3 inches tall. The higher spoiler angle also caused the car to decrease the negative pressure area under the car as the air rolling over the spoiler actually went under the car at the rear the same way that air going over the pickup cab drops into the bead and creates a rolling low air pressure area but without the bottom of the bed in there it just pulls over the back and rolls under.

[latemodel86]

I know this is off topic from the thread title, but what you're saying Ego, is that the drop decks cause more drag than you think and it's adviseable to have a deck flush with the hood? I have a "newer" car with a drop deck on it, and it's probably a good 3". On the other hand, I have I guess what you would call "fins" built around the opening of the driver's box, probably 4" tall, to help send that air to the spoiler. I guess what I'm asking is, do those fins make up for the drag on the drop deck by sending air to the spoiler than what it would if I didn't have those fins built around the driver's box? Or am I missing the whole concept?

[C10]

Ever look at a spoiler on a pro stock drag car? Nuff said ...

[billetbirdcage]

Just to clear up what may be some confusion: Any time you increase down-force your going to increase drag, that's just the nature of the beast.

There are going to be times where you can increase down-force with only a minor increase in drag and other times where the increase in drag is much higher all the way to where you may only add a couple pound of down-force but add several points of drag coefficient.

So what you should be looking at is the added down-force worth the added drag?????

Seeing how a typical late model body has an average drag of .XX (doesn't matter the actual number, just know this is an average Drag on a LM body). Now take in the fact that with this average number (.XX) that it only takes around 400HP to make the car go 120MPH (this has been published in different articles over the years). How often are you running at those speeds and with only 400HP?????

The general consensus among people that do aerodynamic testing is that with the given drag and power ratio of a LM, that any extra down-force is more then worth the added cost in drag. If you were running a large track where handling/down-force wasn't an issue and HP/speeds where low/high enough then removing drag at the cost of down-force could be an advantage. However this just really doesn't happen in the dirt LM world.

To answer the OP question: Around 70 degrees is where the ratio of drag/down-force, really starts to go heavy drag for diminishing returns on the down-force. That doesn't mean that the back of the car has less down-force with 80 degrees the 70, it just means you may have added twice the drag to gain a 10% gain in rear down-force.

[Egoracing]

Ever look at a spoiler on a pro stock drag car? Nuff said ...

They make a TON of down force BUT they are designed for well over 100 mph AND the back of their cars are closed in.

[Egoracing]

I know this is off topic from the thread title, but what you're saying Ego, is that the drop decks cause more drag than you think and it's adviseable to have a deck flush with the hood? I have a "newer" car with a drop deck on it, and it's probably a good 3". On the other hand, I have I guess what you would call "fins" built around the opening of the driver's box, probably 4" tall, to help send that air to the spoiler. I guess what I'm asking is, do those fins make up for the drag on the drop deck by sending air to the spoiler than what it would if I didn't have those fins built around the driver's box? Or am I missing the whole concept?

They did a lot in the article, put tapers on the rear of the tubes, the rear of the seat to the deck, made the dash drop go away, and changed shape of some of the components and front fins and hood to nose changes. The single biggest thing was the dash drop, getting rid of that was MUCH better than tapering all of the tubing AND tapering the seat to the deck. That little drop creates an area of low pressure that creates a large amount of drag in that area. It was right after that article that Rockets came out without that drop.
All they used for the changes was cardboard and tape but to get rid of that drop they use a 4-5 inch flat piece across the area and it made a difference.

[Aerotech/Dominator]

http://www.circletrack.com/ultimateracing/ctrp_0908_dirt_late_model_in_wind_tunnel/vi

Hi guys --- go to this Circle Track wind tunnel test done by Jeff Smith ..... Thanks Dominator Race Products !!http://www.circletrack.com/ultimater...l/viewall.html

[latemodel86]

Thanks for sharing, learned a lot from the article.

[MasterSbilt_Racer]

I think everyone is making this drag arguement too simplistic. Drag does limit your top speed, but it isn't always correct to say that it doesn't matter as long as you have reserve horsepower to still reach some top speed.

That drag is a force in the opposite direction of the car's motion. Force is equal to mass times acceleration. That drag is limiting your car's acceleration up the straight. If you have plenty of grip to get off a slow, paperclip tracks corner, is the downforce at high speed advantageous vs the drag you have added that cripples your acceleration off the corner?

[Egoracing]

Hi guys --- go to this Circle Track wind tunnel test done by Jeff Smith ..... Thanks Dominator Race Products !!http://www.circletrack.com/ultimater...l/viewall.html

That was a good article but the Speedway article was MUCH more descriptive and showed more as they were the one doing the testing. I have not been able to find any info on line about their test though.

[dualdj1]

That drag is a force in the opposite direction of the car's motion. Force is equal to mass times acceleration. That drag is limiting your car's acceleration up the straight. If you have plenty of grip to get off a slow, paperclip tracks corner, is the downforce at high speed advantageous vs the drag you have added that cripples your acceleration off the corner?

Yeah that's it right there. On a momentum track, where you keep it wound pretty well, as long as you have enough hp to reach top speed, you can add drag ok. much different beast (all around, not just drag) when you're talking stop and go tracks.

[700horsepower]

The pro stock drag race cars spoiler is designed to create lift on the back of the car reducing drag not increasing drag. That is why it goes straight back horizontally. A funny car on the other hand uses a huge spoiler and spill plates to add huge down force (and necessay drag) but they have 8000 horsepower to use up. Top fuel cars use wings proper to increase down force with the least amount of drag. I think the top fuel cars generate somewhere in the neighborhood of 4000 lbs of down force on a car that weighs less than 2000 lbs (also using 8000 horsepower)