Aerodynamics of a bug

[Blizzard]

I wanted to do the same as you are making at the moment. But I did not like the look of all the loose pieces put together. The plate on top of bumper, bumper itself, the Kamei spoiler and the splitter plate. Thats why I bought a Remmele front bumper and I am adding polyester extensions to fill the gaps on the sides and on top between bumper and bonnet/front fenders. The end result will look completly different than yours. I bought the bumper in Hannover on the firtst of May but I am not finnished jet. (still talking about it instead of finishing the thing.

This,



has to look like this when it's finnished.



Seeing youre work motivates me again to do something myself.

[Wally]

Originally Posted by Blizzard

I wanted to do the same as you are making at the moment. But I did not like the look of all the loose pieces put together.

I agree, it would be much nicer if everything was 'one piece', but not everything fits as we want to (you know this just as well as I do I think unfortunately) or is available in the first place.
So we make something ourselves

No I see the doctors car again, I see some resemblance, but the form really came as I was duplicating Rummenholls bumper plate and the extensions just seem the most logical thing to do as an opportunity to add some downforce.

Seeing youre work motivates me again to do something myself.

If for nothing else, that good in itself

[Steve C]

Hi

I just saw a photos of a VW fun cup car, they have an interesting front air dam and they may have had access to wind tunnels for the design or at the very least some designers with aerodynamic experience.

Steve

[judgie]

what you need to remember with the fun cup cars is that theres a rad in the front of the car, heance the big vents in the valance and bonnet.
not sure how well they would work as the as the splitter/side planes look like they would be a very turbulant area.

the quattro above is the way i was thinking for my 03 race car but with a slightly more rounded wing to suit the shape of the bug. will have a splitter on rather than the lip that the rally cars had. been playing with drawings on a bug and its just working out how to do the back end to match in with the differnat front end.

[al_kaholik]

Dump the beetle and just buy one of those! Amazing I jest but it has got to be tempting.

[chug_A_bug]

Originally Posted by al_kaholik

Dump the beetle and just buy one of those! Amazing I jest but it has got to be tempting.

[Jadewombat]

Got a few speedholes punched in the fenders. I drove it this morning and it does seem to help already, the car felt more planted to the road on the highway. Gonna try to get the fender flares mounted before tomorrow's autocross race.

[aartjan]

Porsche did introduce their 2012 model 911 GT3 RSR today. With the 48mm increased width compared to last year, they relocated the engine intake and did some 'drastic' modifications to the shape of the rear fender.

2012




2011

[72marinablue]

Originally Posted by Jadewombat

Where did you get those!?!?!?!

[proughj]

Originally Posted by 72marinablue

Where did you get those!?!?!?!

I asked the same thing he said datsun 260z

[Wally]

Thanks AJ!

I like the ducktail of the 2011 model better BTW :-)

[Jadewombat]

Yep, made for a Datsun Z 240/260/280 car. I just guessed as those cars came with 15" rims and the curve of the fenders looked roughly the same as a bug. I got them off eBay. Various sets are about $110-150 new. These cover 2 3/4" width, actually mounted on the bug I'd say closer to 2" or less extension. Read the shipping time before you bid on a set, I didn't look closely but the auction I won could ship in 11-14 days--meaning I think he waits until gets enough orders then lays the fiberglass.

Anyhoo, I didn't have enough time to mount them before the autocross. I did one this afternoon and it does fit pretty well.





Just trying to think how I can taper out the transition of the lower edges smoother with the fenders, especially the front. I don't plan to run this car on the track regularly (maybe once, if that), I autocross it mostly and don't plan on putting a front air dam on either as my driveway is pretty steep. I do drive it to work about once or twice a week. I'd like to fab something to at least cover more area where the tire is exposed under the fender here, just send the air down and out to the side of the wheel. Thoughts of something I could use already made to adapt to the car again?



Next thing, related to the above about not running a front air dam. I do have a lower carbon fiber shield I made for the underside to close up that gap between where the underside of the front apron and the sway bar exists, or where the stock air-conditioning would be normally.



I've done some testing with a generic manometer to see what the readings were (a tube of water mounted at 30 deg. on a board). The slotted vents on the front apron are open. So my results are:

At 65mph:

Underside of the front of the car, tube outlet mounted just behind the front sway bar
--With the CF shield pulled -.25" of water
--Without " " " pulled -.1875" of water

which stands to reason. The shield installed guides more air under the car as it smoothes out the underside. But...

Underside of the front of the car, tube outlet mounted below the spare tire wheel well (or in other words, mounted on the top side of the front sway bar)
--With the CF shield pulled +.1875" of water
--Without " " " pulled -0.125" of water

which I was not expecting at all. That whole area on the underside of the wheel well, but above the sway bar with the shield becomes positively charged. The only way I can justify this would be it helps keep my front brakes cool, but is this creating a significant amount of drag? Would I be better of blocking those vents? I think if I block off the vents though this would send more air under the car and create more lift though, correct? Whew.

[proughj]

when you mounted the fender flares how much of the original fender did you need to cut? could you take a pic with the flare removed or a pic of the underneath wheel well

[Gerrelt]

@Jadewombat: Maybe you results can be explained by a smaller boundary layer under you car (that would be a good thing).
See the picture and text in this link: An overview of vehicle aerodynamics (start reading at the previous page).

[Jadewombat]

Thanks for the link, that helps to visualize it a bit better. Maybe I need to block off the vents and try retesting?? I took another couple of photos, in this photo the area just behind the vents I was getting a positive pressure reading with the shield installed meaning it was a positively charged (high pressure) area.



Here where I'm pointing on the underside of the sway bar I was getting more negative draw meaning more air was being directed on the underside with the shield in place.



As for the fender, I didn't cut anything. I just lined up the front and rear edges as best as I could while matching the curve of the fender lip. I could still cut it if I get ambitious but this is also a dual-purpose car. I plan to rallycross with it at the next event here. My off-road and snow tires match the fenders just fine so there's not really a need to cut it. What I'm getting at is autocross--flares installed/wide tires, rallycross--pull the flares off and change the rims/tires. In case you can't tell, this ain't a show car. Gonna paint the flares silver to match the underside of the car:



With off-road tires:


The bug is my play car, just trying to have fun with it on a limited budget and power (and time to invest) constraints. My bus is a different story though, just came home from the paint shop today:



That link said a lot of drag created from the spinning wheels, what about something like this? Not this exact overpriced piece, just something like it on my front end of the bug: