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

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.

They 2007 report says that they tested CFD models @ 32 m/s . . . thats about 70-75 mph guys.

the flow path is the relevant info.

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.

Now if they could determine the optimum height, surface area and location of a wing, that would be useful to the track folks.

Click to view attachmentPlease steer your students to test something like this.

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.

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.

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.

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

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.

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.

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.

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?

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

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

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.

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

I'm getting in on this thread a little late, but for you non-believers that think wings don't work at low a/x low speed, you are full of horse-hockey. Have a look at some of these cars....

Yea...

Those wings "MUST" be just for the bling factor.....

Those guys just spent all that money and engineering for looks....


Claytonious

There is a ratio for a wing's height to its depth that is used for low speed down force. I used it when I designed and built my wing. Joe is right (for once) that wings absolutely make a difference, that is why they are closely regulated.

Here is a quote from a A-Mod designer/builder:

"In regards to wing design for autox, the problem is finding a profile that is efficient for low-speed applications. Most of the profiles out there for airplanes and race cars are all designed for higher speed. For low speed applications, you need a "thick" body relative to the wing's cord (measurement from leading edge to trailing edge). The goal is to find a profile that approaches 20% in that ratio."

Ken. That statement was half-joke. But only half. It was used as a transitional statement into the subject of formula car tech, and their expenditures in developing better aerodynamics in different angles.

And "slab area" doesn't matter as long as everything you calculate uses the same variables. What does it matter to you or anyone else to know the exact resistance. It doesn't. But as long as you apply the same equation to every car you consider, you'll have accurate data for improving the design.

Besides. I've been blown over 2 lanes by crosswinds before in my 914. 914s are lighter and have MUCH less traction than most cars. That's never happened to you? WTF with your statement?!?

Chris...................

Be nice dammit.

Da old man.

ok, jumping in, no areo background and for the neophytes out here like me..would a package like the below work??? do any of the pieces work???

operating arena 80-140mph

front spoiler for flared car ( member vendor)
air tabs at back of targa ( work??)
sheridan 4 or 6 in blade spoiler

what are the cheap$$ jap wings that work and that will hold up to speed
(ricards ??) Does it have to be above the targa ala gt class pca cars??

My wing was not cheap and it is NOT a "RICER" wing. Got to APR Racing. Find the GT wings.
They may look the same but there is significant differences in the shape of the air foil that make mine provide down force and recude drag

Yes if you have a 914 the wing MUST be even with or better yet above the roof line to provide any benefit.

Not sure why I am trying to convince ou guys. Maybe if I was racing against you I would just tell you "yea it's just for show" Don't spend you money here.

Never mind that nearly every class champion in STS, SM SM2 XP and most of the Mod classes had wings. and thier cars go significantly faster than 50 MPH on course.

didnt mean it as a shot, just alittle toward styling, I have your wing booked marked, but compared to gt racing at a $1000.00 just for the wing and about $1500.00 mounted yours be cheap!!!

Again, I like yours just checking on use, autocross vs track, and effectiveness..

Sorry for the shorthand, I don't like typing much..


http://www.aprperformance.com/index.php?op...4&Itemid=44

$340-570.00

Huge differnce in pricing, hence my questions.....By the way I do believe you even used the ricer like wing back when you first posted about the wing way back when . Again did in no way mean it as a shot... performance parts are perfomace parts, I'll look any where to save a buck on something that works..

ohh and one last edit, look at the engine in my avitar,,,,,subie with the tranny, I can't but go ricer!!!

my wing a ling your wing a ling, won't you play with my wing a ling. those HUGE wings do work at lower speeds but look at how ridiculously large they need to be.

wind resistance is non-linear

someone flip that turtle. the underside of the 914 has some area of improvement under the engine to where the air exits at the rear bumper valance/ air brake. we could benefit from a belly plate diffuser ala Exige or Enzo...not just a flat cover but a channeled diffuser where the channels increase in size as the air exits. sorta like a funnel flowing in reverse. this would reduce relative pressure

the primary confuddlement is in wing vs spoiler. a wing is more effective at lower speeds than a spoiler, however, since wind resistance is non linear, the wing must be HUGE to work well at low speeds. a huge wing becomes a huge drag at big track speeds. the wing MUST be in clean air above the path of air flow that has been modified in direction by the car passing thru it. notice how high the wing is on the slower cars. notice that it is much lower on faster F1 cars. notice the severe angle of attack on those wing monsters as compared to the less extreme angle on the faster F1. notice also the the wing airfoil is inverted so it wants to fly towards the ground.

in summary: no answers are absolute here. the answers are strickly dependent on the use of the car

somebody make us a belly pan

I agree, the wing must be suited for the application. In aircraft design, low speed 45-70mph the chord of the mean camber or thickness of the wing is on a curve that the slower it is effective, the thicker it will need to be. The real problem is that when lift is created (negative lift for this application) you also create Parasitic drag, now decreasing your top end speed.

If you were to use a wing it would have to be tuned specifically for the application for optimum benefit. Hence the $$$$$.

The real solution would be to have a variable camber wing that was controlled by air pressure. This would be the easiest way to regulate the mean camber. The Helio courier is an excellent example of simple application of this concept, it is low tech, yet does some really incredible things. This aircraft has slats that drop down below 55 and when the air pressure is greater than 55 they roll back, buy airpressure. This allows the aircraft a minimum speed of about 30 mph, and it can cruse at 165 mph. With the exception of the top end these are the speeds that you would be operating at, and I bet the benefit of the changing geometry at about 55mph would also benefit.


http://www.stolaircraft.com/
http://www.bush-planes.com/helio-courier.html

For what it's worth.

Just a few somewhat random thoughts to add to the discussion:

Sean is right, "wind resistance" is not linear. Aerodynamic forces (drag, lift, downforce, all of the above) function as a square of the speed. In other words, double the speed and aero forces quadruple.

When you are looking at a various race cars for examples of things to try, keep in mind that the wings on those things are very tightly restricted by the rule book. Even those humongous billboards on the A mod cars are restricted (If I remember correctly) in the overall area and number of elements. Most of time what you see on race cars are not the ultimate solutions to an aero problem, but the best solution they can come up with and still be within the rules.

I did a study once looking at low speed wings in an autocross application. I found that a 6'span, 1' chord wing with the proper airfoil and camber (Very similar to the wing Paul has built, by the way) could produce as much as 45 pounds of downforce at 30mph. Doesn't sound like much, but last time I looked they time autocross down to the thousandth of a second... A small advantage is still an advantage!

Very, very generally, downforce helps in the turns, drag reduction helps in the straights. Look at where you spend most of your time on the track and in most cases an increase in drag in exchange for more downforce is a good swap. The only place I know of where minimum drag wins races is at Bonneville...

Suit on; flame away...

Hmm, now that might make a good fluids and controls project for the students.

Another couplea thoughts:

Airplane wings operate at almost constantly changing angles of attack (Chord angle relative to direction of travel), and have to be designed to operate over that wide range. Race car wings operate at fixed angles of attack and can have airfoils designed more specifically for those angles.

Most places we race won't allow any movable aero devices like the slats on a Helio, but some don't say anything about it. As I recall autocross rules (PCA, anyway) only mention "spoiler/wing" and say nothing about movable bits.

Hmmmm...

Early race car wings were actuated by the brakes. Hit the brakes, and the wing flopped down. Let off, and the wing went straight. Easy.

Also, I have pictures of 356s in the 60s with wings mounted on the front trailing arms and tied to the body. When the suspension moved up (the wheel starts to leave the ground,) the wing exposes more surface area and holds the wheel to the ground. Easy.

Thank you! I'm glad someone else understands this.

I agree w/the belly pan idea.

I know that there are books out there that I could use, however, I didn't ask for book recommendations. I was hoping someone knew of a web site that had this info instead of me having to waste time searching for it.

Not quite so easy... I don't know of any that worked off of the brake. One reason is that the wing going "straight" when you let off the brake minimizes the downforce just when you need it most; right when you're trying to accelerate through the corner.

Mercedes had an air brake mounted behind the cockpit of their LeMans cars in 1955 but it was hinged at the rear and operated only as a brake and not in any kind of (intentional) downforce producing capacity. A couple of cars in the original Can-Am experimented with aero braking, but all of the ones I'm aware of used a separate panel rather than the wing itself.

The wings on the various Chaparrals were connected to a pedal on the left side of the floor where the clutch would normally be (They used an "automatic" transmission with no clutch). The driver controlled the wing using high angle for braking and cornering and flattening it out for the straights.

Most of the movable wings were connected directly to the suspension and were designed to increase angle of attack as the suspension extended, just like you described on the 356.

Sorry to go on so. One of my favorite subjects!



I'd like to see those. Post 'em!

You know what they say:

The bigger the wing, the bigger the $&^%....

This guy must have REAL issues...

Well... You're right about the "no downforce when accelerating through corners" problem. But the tech was banned by numerous race organizations. Including the modern FIA.

But now we have the ability to rig a moving wing to a linear actuator and wire up a time delay circuit. Something like 1,5 seconds of braking switches the wing into downforce position and it will stay there for the next 2 seconds after letting off the brake. BAM! Downforce throughout the whole corner.

I love amatuer aerodynamic discussions.

Anyone care to publish actual measured downforce and drag created by those huge double wing Mod cars at 40, 50 and 60 MPH from a wind tunnel? Look at surface area of those wings - I havent seen a heavy production AX car that has a wing that comes close to that surface area. Then remember wieght of a Mod car. 100 lbs of downforce on a sub 1000 lb Mod is huge differnce. What are you guys making at 50 MPH with those wimpy wings on your 1400 to 3500 lb cars? So rather than attributing wings to performance to National class drivers choice why not offer some emprical measure data? Becuase somone uses a wing doesnt mean its effective. They may have a belief that wing is effective on their bigger car.

Downforce created by wimpy little wings and spoilers I see on most production cars that AX in my opinion dont offer much at speeds below 60 MPH. And where is the front wing on 914's? Why bias an already rear heavy car with even more downforce at the back end? Youre only lightenting the front end if you dont have effective areodynamics up front. Like a 914 needs a lighter front end at speed? That blue mod car has its big wing in the right place.

I dont think either side of this postion have offered much to support their use or non use of wings for AX. I just havent seen anyone offer data other than the "fast guys" use em.

Alright, reading through all this stuff is really getting my ideas going. Aero is a complicated thing and if you want to get better than a rough (and sometimes its really rough) estimate, you have to do some specific testing.

this whole discussion is really pushing me to do my senior design project (fall 08 to spring 09) on different mods to the 914's aero. I believe my Uni has some CFD software, and we definately have a windtunnel. So we can keep debating here, but I think if I decide to do this, I'm going to solicit your ideas and we'll have a full-blown technical engineering smorgasboard of info and tests for this specific application.

I will most likely be sponsoring another student group project spring 2008.

FloWorks software is more complete but also takes more to setup.
http://www.solidworks.com/pages/products/c...osfloworks.html

VisualFoil software is a good basic package
http://www.hanleyinnovations.com/racecarpack.html

Most wind tunnels don’t offer high enough speeds to simulate real word speeds. It’s all about the Reynolds numbers. We have a water tunnel that gives you better Reynolds numbers but still not real world speeds. 100 mph in the tunnel does not equal 100 mph in the real word.

That is why we had the students doing as much testing as they could using our wind tunnel, water tunnel, dye visualization water tunnel, G-Tech meter, and yarn testing to show that the computer analysis would work for the given applications.

The last year’s group looked at as many 914 variations that they could find then came up with several designs of their own. Because there has always been so little information in the 914 community in regards to the overall aerodynamic characteristic of the 914 they have been mostly looking at its drag coefficients. Last years Student Presentation Poster shows what they found. http://www.cassidy-online.com/porsche914/a...aids/index.html

I’m going to have next years group look at the downward effects of the aerodynamics of the 914 and how it performs on larger tracks. Who out there would be willing to have the students come take measurements of their large rear wings in SoCal? I know there is a few out there. The goal would to be 1st to model what is out there then try to design improvement that would be more efficient. I want them to look at how much downward force do you need to keep the 914 stable at high speeds in a straight and how much force do you need to keep the 914 stuck to the ground when cornering.

Curious did you model any down force calculations for rear mounted wings at 50 MPH?

Also interested if you would want to give somone challenge of seeing what works best for a 914 without a winshield (ginter screen). I'm thinking of mounting a wing on top of my targar bar as I'm not confident a reat mounted wing will be as beneficial as a wing mounted mid ship.

Chris, have you ever used Fluent? Some guys here are trying to learn it to theoretically test out spoiler/body configurations for our FSAE car.

Not at 50mph. But they did a few big wings.

I added a new bigger picture showing all of the different comparisons.

http://www.cassidy-online.com/porsche914/a...aids/index.html

Sorry, no I haven't.

like Mugz said...random thoughts... from an amateur aero lugnut

to increase the speed of my car on the straights, I invert my skivies. the outward seams direct the flow of my mojo. it works because I tell myself it does.

the rulebooks of where we race will be the ultimate factor in wing config.

I have seen the dirt oval sprint cars running a midship mounted wing. it is huge and works well.

I have also seen good wings mounted too low in teh "dirty air

nobody has mentioned that a car is kinda wing shaped and inherently creates lift. the lip spoilers my not create down force but they do minimize the lift the cars body shape creates.

NOW BACK TO THAT BELLY PAN. Grant please comment on this concept: the farther back you go under the moving car, the more air gets trapped under a dirty (not smooth) underside. I submit that this creates a higher pressure area toward the rear , higher pressure than the front. perhaps this is why the "Big Dogs" successfully run a big wing in the rear.

holly crap. the SCCA rule book

check out the back of the GT
http://www.burdford.com/brochures/05GTSB.pdf

several cars have a rake in teh stance to decrease rear air pressure. f1 cars also use this principal (and a belly pan diffuser)

Elise, Exige Enzo too.

One more question. It says in the 2007 piece that "A 3D computer model was created using Solid Works and the computer analysis was done using Solid Works." What feature on Solid Works allows this flow testing/visualization to be done?