|
|
-
Not trying to get in the thick of things here, but I think what Brian is mainly trying to say is there has to be air under the car in the first place to be sucked out to create the downforce/vacuum. Not necessarily air flowing under from the front.
-
You would be correct.
I can clearly see there is no point to further discuss this topic some people can't think past their old philosophy s
-
 Brian stepped in it the moment he said "wing" and used it as an example.
We will not be able to stop air from entering the car from the front. Air is present as we are not working in a vacuum. No body is arguing against that. However, you shouldn't think that increasing air flow under the nose helps with down force on a latemodel. Seal that nose to the ground best you can and still be able to cool the car.
Ghopper
-
Where did I imply you should try to increase air under the car?
Im pretty sure I said you cannot have down force without air under.
-
In order to generate an aero force, there has to be a pressure differential betwen the air above the car and air under the car. When the pressure above is higher you have down force. The other way around and you have lift.
But the idea is not to flow more air beneath the car which would cause higher pressure resulting in more lift. The idea is to speed up the airflow that already exists under the car, reducing its pressure(Mr. Bernoulli's Law) to help aid in downforce. Its the whole reason they use diffusers on F1 cars & redirected exhauast gas flow to help evacuate air under the car, and they've even used fans.
-
I'm going to move past the whole "air under the car" aspect because I think we're agreeing but perhaps not having a common understanding of the "why" that makes it work.
Moving on...
I think one thing that gets lost in all of this (remember the discussion was about pinning down the RF) is that it does a lot more than just seal off the nose to help create vacuum under the car. Because we are also hiking the LR up with shocks and bars, having the RF down in combination with the yaw that the car travels in, creates a drastic change in the angle of attack of the decking and the roof. The decking is a huge amount of surface area so presenting it at even a slight angle of attack is going to generate considerable downforce. The same can be said for the roof. I also think getting the nose out as far as the rules will allow (lessening the angle a bit) will maximize the downforce/drag ratio.
Has anybody ever thought about putting vortex generators right at the curve where the angle of the nose goes on to the hood? I'd be interested in knowing how much flow separation there is in this area to determine if vortex generators would be at all beneficial.
That being said, I think you could probably find something in most rule books that wouldn't allow something like a vortex generator even though it might not come out and call it that.
-
Last edited by FlatTire; 01-31-2014 at 09:52 AM.
-
Be careful comparing a 1400 to 1600 pound, depending on the year, F\1 car capable of reaching over 220 mph with a completely purpose built belly pan used with in some cases with mechanically driven fans, plus varying degrees of perimeter controlled sealing of the surface it operates on that is smoother than almost any highway, while on a suspension that's total movement is closer to a go-kart than any late model dirt car, in conjunction with anti drag designed into it along with dedicated wings to a late model dirt car weighing 2300+ pounds with NO belly pan or wings operating at half the speed, while yawing, lifting, bouncing on a almost infinitely variable surface. As for Bernoulli's Law, while correct in as far as it goes, is not detailed enough to support the precise calculations required for engineering a purpose built race car with it alone. Sorry for the run on sentence.
-
Matt49, vortex generators, open sail panels, an angle here, a bump there. I now go to my corner and say no more.
-
FlatTire, Brian: The moment anyone says Wing or Bernoulli they are implying air speed differential to create a pressure difference.
We all agree that we want this pressure difference on our DLMs that builds downforce. I want to focus on the nose part of this discussion as it applies to the thread topic. The roof can be more closely treated as a wing, so you can Bernoulli that.
Dirt Noses: The "splitter" designed into all of these dirt noses is not speeding up any thing....Especially if you are using the something like the valence kit for the MD3. It does make a nice big surface to take advantage of the high pressure built up at the front of the nose.
My neighbor works for TotalSim (http://www.totalsim.us/). Maybe I can pick his mind for more ideas. We kicked around crunching some numbers if I had better CAD or 3D scan of my car, but in all reality that would still be cost prohibited.
Ghopper
Last edited by Ghopper; 02-01-2014 at 09:07 AM.
-
-
Lets talk about this nose situation, why is the "splitter" surface of a late model nose above the air dam/skirt/valence? Should it not be below instead like every other type of race car that uses a splitter?
Why not drop the splitter surface lower so its closer to the race track and get rid of the blunt air dam/valence/skirt.
You could even move the leading edge further forward.
-
We can't control our splitter height as well as asphalt cars to design our application the same way. NASCAR splitters can generate better down force a small distance off the track because they can work in the correct range of heights to apply your Bernuolli skills. In that case, sealing the nose by putting the nose ~2mm off the ground can stall the air vs ~10mm and have measurable down force changes. They also have a very different body cavity after the splitter and are usually at speeds 2x what we are driving at.
Since we cannot play in the same spitter game, we need to look elsewhere. The dirt valence is a durable solution to minimize air under the nose and not rip it off on our highly variable dirt surface. But if you can get it lower, you should have more area to generate the high pressure on top. It would have to be better, as long as you don't rip the nose off racing.
Ghopper
Last edited by Ghopper; 01-31-2014 at 12:57 PM.
-
 Originally Posted by FlatTire
In order to generate an aero force, there has to be a pressure differential betwen the air above the car and air under the car. When the pressure above is higher you have down force. The other way around and you have lift.
But the idea is not to flow more air beneath the car which would cause higher pressure resulting in more lift. The idea is to speed up the airflow that already exists under the car, reducing its pressure(Mr. Bernoulli's Law) to help aid in downforce. Its the whole reason they use diffusers on F1 cars & redirected exhauast gas flow to help evacuate air under the car, and they've even used fans.
Ding ding ding we have a winner!!!
-
Look at what was done with a splitter here:
http://www.katechengines.com/street_...a%20report.pdf
The video of this car in the wind tunnel is on youtube if you care to see more.
So which one of you nose manufacturers has done your home work like the company I mentioned above and tested your product and collected actual data?
-
"Matt49: I think one thing that gets lost in all of this (remember the discussion was about pinning down the RF) is that it does a lot more than just seal off the nose to help create vacuum under the car. Because we are also hiking the LR up with shocks and bars, having the RF down in combination with the yaw that the car travels in, creates a drastic change in the angle of attack of the decking and the roof. The decking is a huge amount of surface area so presenting it at even a slight angle of attack is going to generate considerable downforce. The same can be said for the roof."
Totally agree and have thought the same thing. Just take a look at all the dirt on dirt pics from out in Tucson. The faster cars have got the noses glued down, the spoiler/deck is up in the air more so than ever before to take full aero advantage of whats there. The front suspension trend isn't the only reason these cars are tighter than ever before.
Now we gotta figure out how to get air to the center of the rear spoiler to better utilize that. I think hpmaster alluded to that with his open sail panel comment.
Sometimes I think it would be smart to take a year off racing and just go test. You guys got my wheels turning........thanks.
Last edited by FlatTire; 01-31-2014 at 03:18 PM.
-
The reason I brought the F1 car was not to compare the two obviously different cars. I brought it up to compare the F1 car to Brians example that with no air under the car the whole thing turns to drag. There is far less air under an F1 car than a DLM. So I thought his drag issue was bunk.
-
Sorry off the subject just a bit. Does anyone sale a good open sail Panel ? I can make one but do not have the right tools to make it rigid enough . Any help ? I believe it is very important to this subject.
-
Keeks. Post 54
True f1 cars have less air under them , let's say less room for air, which is why they use the exhaust and various air inlets to blow air into the diffuser at the rear. This adds volume to the diffuser which aids in increasing the air speed under the car. The faster the air moves the more air volume that passes under the car. There is more downforce generated by increasing the air speed under the race car than both of those wings combined . This I learned from a very good aero engineer at lotus. One of the key rules in f1 pertains to the diffuser. Very critical to handling
Last edited by Brian Gray; 02-01-2014 at 09:14 AM.
-
You can test this by taking a piece of paper and laying on a table. Just blow air across it horizontally you will find some interesting results
Posting Permissions
- You may not post new threads
- You may not post replies
- You may not post attachments
- You may not edit your posts
-
Forum Rules
All times are GMT -5. The time now is 11:30 PM.
|
|
Senior Member
Reply With Quote
Bookmarks