This is a serious question, I do not mean this as a joke. Okay, reading through some parts catalogs, I have noticed that some companies sell bumper shell reinforcement kits. It would seem these devices allow holes to be cut in the bumper to let out air that would otherwise become balled up in the scoop-like shape of the rear bumper cover. These seem to be intended for drag-racing applications. I don't know if they require the removal of the rear bumper impact-absorbing material, or bumper structure. I was thinking that perhaps such collection of air would create a high-pressure zone at the rear end of the car which would cause lift at high speeds. Would ventilating the bumper cover and installing some sort of metal bracing to retain the structural integrity of the bumper cover be of any benefit to reduce drag and lift at the rear end of the car? Any thoughts of making a flat cover-like apparatus to connect to the rear bumper cover from the rear subframe to prevent air from getting up there at all?

~Chris P.

 

I'll take you seriously. I wrote up some such in my 2002 Plan and Andy and I have talked about it a fair amount too. If you look at the back of that swoopy TVR V-12 that gets into Autosport every so often you'll see that what part of the rear bumper area that isn't handled by the diffuser is cut and filled with wire mesh for just the reason you'd think. I'm not going to sacrifice any protective structure and don't think you should. I've thought about that area from the rear tires back too - it just depends on what's possible. Obviously any object you put into that area should rise toward the rear - assuming the frontmost portion doesn't collect any air on the topside.

What about venting the open window pressurized drivers compartment too - assuming for all of this that there are no rules forbidding it.

My plan includes videoing with remote camera observing smoke emitted at the front of the car as I drive at test speeds - poor mans wind tunnel.

Scott, who has trouble thinking like air....he's looses his train of thought....

 

I picture Scott climbing out of the driver side window with a lit cigarette at 100 MPH.

 

scott, what about the old sk00 method...piece of string (yarn?) tapes all around the car.

yoshi - who saw this on a really old car design vdo *shrugs*

 

I remember seeing videos of the Soviets using it on their nuclear sub models when doing fluids testing. I can't even imagine how you would comfortably get smoke underneath your rear tray. Also, I'd imagine there is quite a bit of turbulence back there, and it would all just diffuse anyways.

 

I was gonna see if I could get Jonathan to come down from BC to help me, but he'd probably want to use a phatty....."come on, you gotta exhale dude".

Yeah, I know about tufts, but I like smoke better. If you tape tufts to your surfaces you can see what's happening there, but that leaves questions about other areas that can only be answered with rods and more tufts and I think it would be a whole lot easier to process the visuals if you use smoke. And I'm prepared to be pretty crude about this...I'm not going after the last iota. Oil spots are useful too - this months Sportscar (SCCA) has an article on aero that covers some of this.

Scott, who likes threads like this....but after a pretty steady diet of red meat they seem pretty tame....

 

I cant seem to find the website where I saw a pic of it...but at Portland last year, one of the SVWC Preludes had just that... where the lic plate should be, there was a hole, screened off, as big as the plate was.

 

It might turn out to be a magical mystery tour, but I'll try it.

One of the neatest things I ever saw was a really heavily steaming manhole cover where the cloud was being driven thru by traffic. I spent a fair amount of time watching different vehicles pass thru it - it was truly fascinating. A similar sight was watching LMP cars on the wet banking in Las Vegas. I am very committed to a simple visual approach - especially since it's all I'm practically capable of using.

Scott, who hopes to see something in the smoke behind his kaa....oh no! it's the face of evil!.....

 

Not sure where this came from.

When I went to Indy for a visit with Formula SAE a few months ago, they had (if I remember correctly) 1/8 scale carbon fiber mock ups of Indy/Cart cars. They said they typically don't use smoke very often because they have accelerometers, yaw/pitch meters, but he said they actually prefer to use <u>bubbles</u> of all things. Since they have to recirculate their air, the smoke makes everything a mess. They also said the bubbles are very neutral in the air.

PS-Even the tires are made out of carbon fiber, and they had cute little caliper mock-ups with ducting and all.

 

hmm... if you got really bored, you could have a smoke generator machine connected to a power inverter running off the DC electrical system of your car. run ducting to wherever you would like to place smoke and voila! Have a friend videotape it and you've got some aero analysis.

 

It might also be possible to make a quick-n-dirty tube manometer (pressure guage) out of a long piece of aquarium air hose. Build a water level but putting water tinted with food color in the tubing. Both ends of the water will be at the same level, unless the air pressure at your "test end" (placed in the area that you want to check) is higher/lower than at the "observed end" (placed inside the car maybe?).

Of course, this only provides you with qualitative differences between the two ends and your "observed" end might well be the one that changes! You also have to deal with having someone look at the tube while the car is moving (mark its level when stationary) and too great a pressure differential might just suck the liquid out of your tube.

If it DOES work, you could do a test with the bumper cover on, then one without it completely (test end in the same place) to get some kind of baseline. You then have to "map" the pressure differences somehow, intuitively determining how pressure differentials might influence drag where, if they are over some area = force.

Of course, you could also just do coast-down drag tests. If you can't detect any significant change in the time it takes to coast to a stop from, say 60 mph, the chances of that aero change panning out into seconds on the track are pretty darned small.

Have fun!

Kirk

 

http://www.autospeed.com/A_1065/page1.html

Just thought this was relevant and worth posting.

 

I was think about Scott brought up about the pressure in the cabin the other day, and I was trying to think of ways to relieve the cabin pressure at high speed, and if it would even do anything... I was thinking of cutting holes somewhere in the rear of the car, but the rear licence plate sounds looks a great place... Might try it...

Damnit, this is Corey (honda318dx)


[Modified by urbanlegend21, 2:52 PM 12/27/2001]

 

I am waiting for the first light snow to fall here in Charlotte.

ITR rear wing videos (side view) will be taken.

Will

 

The cabin already has a pressure vent. It is on the LR underneath the bumper. Honda put it there so you don't have to SLAM the last door shut. Also helps with flow through venting to reduce possibility of exhaust fumes building up inside.



Friends following me on highway have mentioned it "flapping" around while at speed.

 

Yea, I have 2 vents on the sides of my trunk... But they are small and will not let enough volume of air pass through them, well, not as much that flows through both windows.. I think putting a hole where the licence plate goes is the way to go to help release the pressure/turbulence inside the car...


[Modified by Honda318dx, 12:00 PM 12/28/2001]

 

Personally, I wouldn't have the sack to punch holes out in the body of the car. I have been thinking about purchasing a Lexan rear window and cutting out vents in it. Most race series do not allow this, however.