Presented by Nine Lives Racing
1 2
klodkrawler05
klodkrawler05 Reader
11/2/18 1:43 p.m.

Oh one other note, If you spend some time building a splitter out of plywood there's a fairly good chance it will be far more robust than the factory underbody cladding. Our splitters (I believe we're on #4 now) have survived some very heavy shunts going off track and protected the much more valuable things above them. The flimsy plastic undertray BMW provides would've been destroyed.

z31maniac
z31maniac MegaDork
11/2/18 2:50 p.m.
AnthonyGS said:

Good call on the undertray.  If you dad add aero keep in mind wings work a lot better than spoilers.  Spoilers add drag and a smidge of downforce.  By comparison wings add scads of downforce and a smidge of drag.  You don’t need math, wind tunnels and a lot of conjecture to figure it out.  Chapparal figured it out from the humble surroundings of Midland, TX.  My dad crafted very effective aero parts in the shop without the aid of a calculator or wind tunnel too.  I used to put rear wings on slot cars when I was a kid too amd they work great.  That was long before I learned about Reynold’s numbers too.  

I wouldn't testify in court, but I think you are mixed up on this one. The way I understand it is that spoilers reduce drag (and reduce lift, not generating downforce), and that wings add lots of downforce at the expense of drag.

That's why F1 cars run much smaller wings at high speed tracks to REDUCE drag and increase top speed. Then at slower speed tracks like Monaco run the highest downforce package (largest wing) of the season to create as much downforce as possible, ignoring drag, because it's a much lower speed track.

stafford1500
stafford1500 HalfDork
11/2/18 2:54 p.m.

Spoilers and wings both add drag and downforce. They make the air do things it does not really want to do and that work equates to drag.

There is less drag increase with a wing compared to a spolier for the same amount of downforce, due to how the devices make the downforce.

The case of F1 cars is a trade-off of straight away speed Vs cornering speed. They simulate everything to figure out what the best trade-of is going to be fo reach track. This is the case for any/every professional series. The level of simulation is the main difference.

Robbie
Robbie UltimaDork
11/2/18 3:06 p.m.

what about the front 'scoops' (I don't know the technical term)? For example on the gt40 air comes through the grill and out the hood in large quantities. Does that create much down force? Seems like it would.

I know there is a radiator in there usually heating up the air, but still.

z31maniac
z31maniac MegaDork
11/2/18 3:14 p.m.
stafford1500 said:

Spoilers and wings both add drag and downforce. They make the air do things it does not really want to do and that work equates to drag.

There is less drag increase with a wing compared to a spolier for the same amount of downforce, due to how the devices make the downforce.

The case of F1 cars is a trade-off of straight away speed Vs cornering speed. They simulate everything to figure out what the best trade-of is going to be fo reach track. This is the case for any/every professional series. The level of simulation is the main difference.

I guess I'm thinking of the long, low-angle spoilers lower powered cars tend to use on road courses to reduce drag versus trying to add downforce, compared to AutoX classes where the spoiler is nearly straight up like an air brake to add downforce in classes where airfoils are prohibited.

sleepyhead
sleepyhead Dork
11/2/18 3:28 p.m.

it all depends on the car and the implementation

wings will almost universally add drag, just because of the struts and the wing shape, plus what ever drag due to circulation that the wing is creating ("making the air due what it doesn't want to do")

There are some limited scenarios where a spoiler will reduce drag (even one sticking straight up, albeit fairly small in height) because it's moving the stagnation point and increasing the circulation, which is causing flow that was detached from the rear window to now attach to the rear window.

although, that observation was on cars from the 70's.  Then again, we've started to see similar with the small "add on" strips added to the top trunks of hybrid models.

One of my favorite professors always responded to design questions of "should we do that?"  with:  "well, you certainly could... whether you do or not is up to you.  It's your design, after all."

stafford1500
stafford1500 HalfDork
11/2/18 3:52 p.m.
z31maniac said:
stafford1500 said:

Spoilers and wings both add drag and downforce. They make the air do things it does not really want to do and that work equates to drag.

There is less drag increase with a wing compared to a spolier for the same amount of downforce, due to how the devices make the downforce.

The case of F1 cars is a trade-off of straight away speed Vs cornering speed. They simulate everything to figure out what the best trade-of is going to be fo reach track. This is the case for any/every professional series. The level of simulation is the main difference.

I guess I'm thinking of the long, low-angle spoilers lower powered cars tend to use on road courses to reduce drag versus trying to add downforce, compared to AutoX classes where the spoiler is nearly straight up like an air brake to add downforce in classes where airfoils are prohibited.

There are more effective ways to reduce drag than extend the length of the car with a decklid extension. Such an extension is still likely to make downforce based on the pressures above and below.

 

For Robbie: The top exit radiator does generally make downforce, but mostly front downforce. It also provides a more 'simple' design to take care of engine heat without having to model the entire underbody.

 

SleepyHead is right that a lot of modern cars are getting widgets added to control airflow. Most (but not all) are directed at keeping the wind noise in the cabin to a minimum. Some are for flow conditioning around the rear of the car to reduce drag. Both of those are high on the list of making new cars better for the general customer base.

One of my professors was often noted for saying "It Depends!" to nearly any question about how/why to do anything.

Snrub
Snrub HalfDork
11/2/18 4:30 p.m.
Dusterbd13 said:

This thread gas sent me back down the rabbit hole of research of miata aero for the challenge car.....

This doesn't apply as much to a G35 that you may want to look half decent, but the easy stuff is:

Cut vents in the hood - see FM pressure picture/diagram. I cut slits in the hood, hammered underneath against a metal tube against the hood to get aero efficient flares. Cut down the rear bumper, etc. Run a roof of some description, or DIY. Tuck the fender at the rear of the front tires. Create a "crusher" style front air dam (google) with wood splitter. A successful V6 MR2 team in Champcar DIYed their rear wing. DIY a diffuser.

AnthonyGS
AnthonyGS Reader
11/2/18 5:50 p.m.

Lot’s of good explanation going on.  I may have oversimplified a tad, but I’m just a poor ignorant white dude from west TX.  Out there they say “‘pends on,” which sounds just like penzon.  

 

 

Robbie
Robbie UltimaDork
11/2/18 6:19 p.m.

This guy has made some pretty cool YouTube videos on vehicle aerodynamics.

https://youtu.be/quDLzxmJl5I

 

1 2
Our Preferred Partners
pdEpsVW2FAMKPvndIv8vyHKYS8HHbgXpW0QMcwDdOCfZkWPcCD4TzTH7pi5hD3nF