mark kibort

Just got back from testing the new splitter expansion and boy, im glad I did. Just 1" added to the prototype splitter Ive been using makes a huge difference. Those of you that have followed my progress, have seen the thing grow an 1" at a time. now up to 6.5" width.

I ran it last week up to 100mph with no issues, but decided to see what happens at 120mph and video tape it too! man, wait until you see this. I have pictures at 130mph with nothing like this happening, as far as I could tell, but at 120 with the larger splitter, it goes haywire! it flapped around like a cloth flag in a breeze and bent downward. I also measured pressure with my sunx sensor.
50mph .04psi
60mph .08psi
80mph .12psi,
120mph .24psi. Only .24psi at 120mph! from my last posts on the ram air subject, we know that the potential at 160mph is near .44 psi . on a 300sq" surface, thats near 150lbs, but most of its effect is not so much pressure on the splitter, but the air not going under the car, and being routed to the sides. Also,there is a differential pressure I measured when putting the pressure sensor under the splitter. there was actually .04psi vaccum measured , but that could have been due to the curvature of the splitter when deformed.

More testing next week with the new cable supports. If there is more deformation, Ill will do some reinforcing of the splitter with some CF honeycomb sheet I have.

enjoy. video to be posted from todays experiment later

1st picture is before test run with pressure sensor near support strap
2nd picture is after the return with the sensor fed through the splitter to get underneath pressure readings
3rd picture is the sunx sensor reading .006psi.
4th picture is the set up wth 3 added support cables.

mark kibort

Here is the video

http://www.youtube.com/watch?v=ah1nFtInXkU

a4sfed928

How do you know what percentage of your reading is dynamic verses static pressure with the tube pointed forward like that?

mark kibort

I had it pointed downward for the test to make sure the readings didnt get any "ram" effect. actually pointing down can reduce the pressure, reading by air running over the opening. If you are looking at the slight forwad look of the tube. Ive done the tests in that area enough times to show that its orientation is not critical. backwards, down, up, in closer, out farther, etc. the pressure in the nose area is all pretty uniform. the splitter allows for that pressure to build over a much greater area.

a4sfed928

Just wondering as I was inolved in many types of pressure testing and errors are easy to induce with sample tubes like that, but it sounds like you have done your homework.

mark kibort

I found as long as it wasnt pointed forward, the results are pretty much the same. what have you found,and with your experience, what would be the best way to get to get the most accurate reading? im thinking pointed just slightly rearward 100degrees backward.

I think after watching the video, its time to stiffen the splitter up a bit. It was amazing. It almost liquified at 120mph without the supports. Ill do another run with the supports and see what we see.

Thanks

mk

AO

Obviously it needs to be stiffened or supported or both.

Isn't the idea to "split" the air so air doesn't spill under the car - thus preventing the creation of lift? Allowing the splitter to hang down and collect air would do more harm than good in my mind.

mark kibort

Yes, thats the idea, but the more you get from going under the car the better, but, my splitter failing was not the shape it is supposed to be. it failed and the pressure distorted it and it bowed to the ground. still effective, but not as effective as if it was straight out. you want it as low as possible, without scraping. mine is about 3.5" off the ground when flat and level.

Ill need to stiffen this up a bit. as a note, everything was fine until I put an extra 1" on the splitter. amzing how that little change effects things.

mk

Vlocity

Mark,

What does your splitter look like underneath? Does it extend back well under the car like the one I built or is it just at the leading edge?

Mine is also about 3 7/8 inches from the ground to the bottom edge.

Also, what do you think the net effect of my diffuser is based upon what you have seen with yours?

Luckily, I think mine is way over built and I can't imagine that I am getting any deflection.


Ken

mark kibort

The underside is more about drag. sure good to have it flat, but I use the air flow underneath for cooling of the oil pan. thats my oil cooler the defuser part would come through complex channels as you dont have toward the rear and exiting wtih a higher pressure blast out the back. you are not going to get anything more than ambient under the car. (More meaning vacuum). the differential pressure is what you are after. actually, turbulece under the car would lower the pressure, but at a cost of drag. you want a higher pressure than you normaly have over the car. normally, there is a huge vacuum over the front of the hood, lifting the car up like a wing. remove the air that spills under the nose and route it to the sides and through the radiator and hopefully out the hood vent, and you are doing all you can do for downforce. there is some ground effects that can be achieved with a totally flat bottom, but it has to be real flat all the way to the back. (witih optional channels for defusing air flow)

mk

mark kibort

Look what i found on the web....


http://www.pts106.com/FB%20Aerodynamics%20Splitter.htm

S4ordie

Not only does it provide some sound technical insight but it does so using the 928 as an example. Perfect.

Someone should start a 928 racing thread where things like this can be posted and kept in one easy to search thread.

danglerb

Speaking of racing, what are the racing class rules for splitters?

mark kibort

most have it limited to the body shape lengths. In ITE, its fairly unlimited. Ill have to look what Porsche rules say. Ive seen some pretty radical splitters out there. It will interesting to see what they limit the length to.

Slantnose!

That was a pretty wild video...hadn't seen one like that before.