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

[grantsfo]

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.

This post has been edited by grantsfo: Nov 3 2007, 11:18 PM

[BahnBrenner914]

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.

[chris914]

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. (IMG:style_emoticons/default/biggrin.gif) 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.

[grantsfo]

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. (IMG:style_emoticons/default/biggrin.gif) 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.

[jd74914]

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.

[chris914]

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.

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

[chris914]

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.

Sorry, no I haven't.

[sean_v8_914]

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)

[sean_v8_914]

Elise, Exige Enzo too.

[jd74914]

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?

[chris914]

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?

That was a typo. It should have been FloWorks.

I fixed that and some other things that were made late at night.

[jhadler]

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.

Because they're not allowed to use them. RTFR.

As for actual numbers? I can't tell you first hand, but I can tell you that some of the SM and SM2 people I know have measured 75-150 lbs of downforce. That may not sound like a lot, but it's enough to warrant changing of the spring rates, and noticeably effect the handling of the car...

Then remember wieght of a Mod car. 100 lbs of downforce on a sub 1000 lb Mod is huge differnce.

Yeah, and remember that the A-Mod cars are pulling 3+ lateral G's at an autox on a good surface. The doors slammers are no where near that.

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.

Geez Grant...

Simple. The cars that are really taking advantage of these wings (and not all of them are actually utilizing these wings to their full advantage) are already on the ragged edge of neutral handling. The intent of the wing is to have a car that rotates super well at lower speeds (slaloms), and isn't excessively loose at higher speeds (sweepers and fast transitions). A little extra "dynamic" weight in the back can help get that little bit extra. Otherwise, you either have a car that is planted in the fast stuff, and pushes in the slow stuff, or a car that carves the slow stuff and is a handfull in the faster stuff.

Grant, talk to the big dogs who are doing this. You live in the Bay Area, you run with SCCA from time to time. Go up and talk to Andy or Vic some time about the wings, you might find that these people really do some considerable research and testing on these cars.

-Josh2

[914Mike]

...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

Actually NO fan anymore, the motor just has aluminum fins, so the question becomes: which way does the air flow easiest? Factory setup had a big fan to suck air in from the top, out the bottom, aided by the little flaps, which create a low pressure area for the air to flow into.

What happens without any fan, i.e. no suction from the top? Does the top create a lower pressure at the engine grill (lower than the small drop caused by the underbody flaps) and reverse the airflow? (IMG:style_emoticons/default/confused24.gif) If this is the case, removing the flaps would mean more airflow, right?

[jhadler]

Actually NO fan anymore, the motor just has aluminum fins, so the question becomes: which way does the air flow easiest? Factory setup had a big fan to suck air in from the top, out the bottom, aided by the little flaps, which create a low pressure area for the air to flow into.

What happens without any fan, i.e. no suction from the top? Does the top create a lower pressure at the engine grill (lower than the small drop caused by the underbody flaps) and reverse the airflow? (IMG:style_emoticons/default/confused24.gif) If this is the case, removing the flaps would mean more airflow, right?

Uhm... First off, no fan equals no engine... Just a lump of metal...

As for air flow? Probably wind up with a pretty stagnant flow in there. Low pressure on top combined with low pressure below equals very little flow.

-Josh2

[914Mike]

Uhm... First off, no fan equals no engine... Just a lump of metal...

As for air flow? Probably wind up with a pretty stagnant flow in there. Low pressure on top combined with low pressure below equals very little flow.

-Josh2



Right, no ENGINE. I have a 156V 3-Phase AC MOTOR... Air Cooled via aluminum fins, NO fan. (IMG:style_emoticons/default/beer.gif)

[Katmanken]

Hey!

Thanks for the big shot of the different versions with the HP gain or loss.

I think it's fricking awesome that a 2 HP gain is obtained by simply adding vertical slots to the sail panels.

That's most of the maximum 2.4 or so HP gain from the slanted rear window AND the rear wheel covers. All from a simple area mod......

You ought to have somebody model that area in more detail with a few other versions. We ought to get more engine cooling AND more HP from the slots.

Wonder what rounding the sail panels inward at the rear would do? Better air flow around the cab??? Curving or rounding the sail areas in combo with the slots???? That might funnel air into the grill area. Combo of sail slots and a wing gives what kinda flow????

Spring loaded flaps in the sails to move with the flow and open up to get the free HP at speed?????

Replacing the flat sails with tubing to make a tubular rollbar having the sail panel profile????.....

Hmmmmmmmm.... (IMG:style_emoticons/default/idea.gif)

Plenty of juice left in this for more projects

Ken

[Katmanken]

OK boys,

I'm priming the pump....

Here is 2 free ponies AND better cooling.......