Aerodynamic Aids - What a drag, What’s your drag? Options

[chris914]

Have you made changes to your 914 body or are you thinking of it?

Here are a number of computer models comparing different body modifications to the 914 and the effects that they have on the cars aerodynamic drag.

http://www.cassidy-online.com/porsche914/aerodynamic_aids

[TeenerTim]

Interesting but the 2006 report doesn't address the problem they were given. No testing comparing with and without the spoiler was done. It does confirm what most people know that top on and windows up is the most aerodynamic configuration. The 2007 study is much better but the actual results are too blurry to read. Without that data it really doesn't help much. To truely be useful the test should have been done at multiple speeds. I think most people would agree there would be little to no effect of spoilers at 20 or 30 MPH.

[BahnBrenner914]

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[jd74914]

They 2007 report says that they tested CFD models @ 32 m/s . . . thats about 70-75 mph guys. (IMG:style_emoticons/default/smile.gif)

[sean_v8_914]

the flow path is the relevant info.

[chris914]

Over the past three years, three different student groups have worked on this as their student projects each year, with various emphases.

The 1st year’s group worked on creating the basic test tunnel models with the after market model spoilers and setting up the computer model for testing.

Their main findings were that the small rear spoilers do almost nothing.

The 2nd year’s group worked on comparing the test tunnel results to real world results and computer modeling.

Their main findings were that computer models could be used to model the real world results.

The 3rd years group looked at creating a number of different computer models and looking at the effect on drag.

Their main findings showed that the shock car is pretty good in regards to drag.

If I continue with a forth years group, I may have them place their emphasis at looking at the aerodynamic effects of the 914 on a large tracks.

[TeenerTim]

Now if they could determine the optimum height, surface area and location of a wing, that would be useful to the track folks. (IMG:style_emoticons/default/beer.gif)

[Joe Ricard]

Please steer your students to test something like this.

[wbergtho]

I think most people would agree there would be little to no effect of spoilers at 20 or 30 MPH.

The only time aerodynamic aids will make an appreciable difference are at speeds much greater than autocross speeds. To make it worth your while, I would think you'd need to on a big track going between 50-150MPH or greater. The aero info is interesting and I'm not trying to be negative...you just won't make much use of aero aids on an autocross track. Use your points for suspension upgrades.

[Joe Ricard]

Our slowest courses are 50 MPH.
I'm keeping my wing as is my competition. if it didn't work then why is it specified in the rules for size location and such?


Got a point with suspension though. No substitue for more mechanical grip.

[chris914]

I think most people would agree there would be little to no effect of spoilers at 20 or 30 MPH.

The only time aerodynamic aids will make an appreciable difference are at speeds much greater than autocross speeds. To make it worth your while, I would think you'd need to on a big track going between 50-150MPH or greater. The aero info is interesting and I'm not trying to be negative...you just won't make much use of aero aids on an autocross track. Use your points for suspension upgrades.

Yes that is true. If you read my introduction on the web page you can see why I was testing my original front spoiler at all.

Also a lot of the testing was done for speeds of 75mph to 120mph to help people that run their cars on large tracks.

And it is useful to know the flow path as Sean pointed out even at lower speeds.

[jhadler]

I think most people would agree there would be little to no effect of spoilers at 20 or 30 MPH.

The only time aerodynamic aids will make an appreciable difference are at speeds much greater than autocross speeds. To make it worth your while, I would think you'd need to on a big track going between 50-150MPH or greater.

I gotta disagree. The big dogs in SCCA autox have found that wings -do- in fact make a difference, even for fast door-slammers in autox. Joe is taking his cues from people that have invested the time and effort to find that aero works for autox. But there is no way you'd want to take an autox aero setup onto the big track without some changes.

-Josh2

[BahnBrenner914]

This has got me thinking of my ME/Aero senior design project. Joe Ricard, I might just help you if you help me. My Uni has a subsonic windtunnel that goes to 150mph+ , plus I want to do racecar/F1 aero one day, so it'd be a good resume builder.

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[alpha434]

Mr Hadler is definitely correct.

It's simple fluid dynamics. There is an accurate formula for calculating wind resistance of an infinite size, flat surface here someplace (looking around my desk), the equation indicates that wind has a strong effect even at very low speeds. And on a similar subject, crosswinds. There's trouble for slab-sided teeners everywhere. Current "F1 level" development uses a very special wind tunnel to see the effects of crosswinds at odd angles of the car, and aerodynamics under turning too.

It's a big deal. And as more and more about aerodynamics is commonly understood, the more entry-level racers will be using it's more advanced principals. And the more we will see in street technology. It's the next big thing for us.

[Air_Cooled_Nut]

So does anyone have EQUATIONS that one could plug in values to get a rough estimate of x (x=top speed or hp or weight or...whatever is trying to be figured out)? Variables like weight, hp, frontal area, Cd, gearing (this would be real nice!), speed, etc.

I understand aerodynamics isn't simple stuff but aren't there algebraic equations that could give ball-park values?

I'm looking for equations, not web pages that output the results.

[914Mike]

I'd like to see some studies done on the airflow through the engine compartment, with and without the underbody spoilers, with and without a large fan on the engine...
My '74 no longer has a fan on the (air-cooled electric) motor to create suction on the topside, so should I remove, keep or reverse the little flaps? (IMG:style_emoticons/default/confused24.gif)

[chris914]

So does anyone have EQUATIONS that one could plug in values to get a rough estimate of x (x=top speed or hp or weight or...whatever is trying to be figured out)? Variables like weight, hp, frontal area, Cd, gearing (this would be real nice!), speed, etc.

I understand aerodynamics isn't simple stuff but aren't there algebraic equations that could give ball-park values?

I'm looking for equations, not web pages that output the results.

http://www.amazon.com/Aerodynamics-Hp1267-...720&sr=1-23

http://www.amazon.com/Race-Car-Aerodynamic...7760&sr=1-2

http://www.amazon.com/Competition-Car-Aero...7760&sr=1-1

[jhadler]

...so should I remove, keep or reverse the little flaps? (IMG:style_emoticons/default/confused24.gif)

The little flaps underneath the car on the edge of the bulkhead? Keep 'em. They were put there to improve down flow out of the engine bay. Doesn't matter if you're using a crank driven fan, or an electric one, you still need to get rid of that heated air.

-Josh2

[alpha434]

Frontal profile X Cd = Drag Efficiency

Wind speed X wind density (should be a constant for your area)= resistance

Resistance X drag efficiency = total resistance on the car





EDIT: Gearing starts to get a little harder. Most of figuring race car aero IS reducing that frontal profile and reducing that Cd.

But you're going to need to calculate acceleration rate in X gear in a vacuum, and then apply total resistance that you calculated earlier.

[Katmanken]

Hunhhhhhh??????

Chris, according to you "the equation indicates that wind has a strong effect even at very low speeds. And on a similar subject, crosswinds. There's trouble for slab-sided teeners everywhere."

In reality, the teener may be slightly slab sided, but it's a damn small slab. That's a heck of a difference from an "infinite" slab.

Less surface area means less side force (Pressure times AREA), and, the car is so low the pressure doesn't exert as large a rocking couple as most cars.

So WTF with your statement?????

Ken