My C4 aero... revisited.
12-22-2009, 09:01 PM
#1
Race Director
Thread Starter
My C4 aero... revisited.
I was looking through a bunch of pictures from this past season and found something pretty interesting. I would love to hear what some of you guys have to say about it...
If you remember a while ago I had a discussion abut my C4 feeling aero unbalanced. A vast majority seemed to say that the Greenwood stuff was of little or no aero value.
If you look at the close up of the nose you can see that the center part of the nose is pushed down a fair amount over what it is normally. I actually went out this afternoon and stood on the center part. I weigh 200+ and it took every bit of my weight to get it to bow down that far. With that in mind it seems to me that it does indeed have a fair amount of downforce causing it to bow. Anybody care to chime in?
Normal...
At speed...
If you remember a while ago I had a discussion abut my C4 feeling aero unbalanced. A vast majority seemed to say that the Greenwood stuff was of little or no aero value.
If you look at the close up of the nose you can see that the center part of the nose is pushed down a fair amount over what it is normally. I actually went out this afternoon and stood on the center part. I weigh 200+ and it took every bit of my weight to get it to bow down that far. With that in mind it seems to me that it does indeed have a fair amount of downforce causing it to bow. Anybody care to chime in?
Normal...
At speed...
12-23-2009, 09:13 AM
#2
Melting Slicks
What you are seeing is stagnation pressure. That is, air is entering the inlet faster than it can get out, so it is damming up and that is causing high pressure. Note that all the surface other than what is sticking out as a lower lip is seeing an equal pressure upward, so other than the couple of inches of lip sticking out, that isn't covered by the area above it, there isn't any real downforce added. If you didn't have the lower lip, there might be more lift, there is also pressure under the nose ahead of the spoiler, so there is a lot more going on than can be just addressed by the fact that the lower lip is bending down.
If you look at the uncovered lower lip, at 75 mph the difference in pressure is about 1/10 of a psi. If the opening is three feet across and you have about 5 inches of lip uncovered, the net downforce is on the order of 18 pounds. Not a lot, but it is something. If you go up to 100 mph you get about .17 psi or almost twice as much, so you can see that there is a benefit. Without a real measurement of the lift and the interaction with the spoiler below you really don't know much about it.
If you want big downforce in the front, move the spoiler forward all the way to the front of the car, and that will make a big difference. Since it is way forward of the front wheels, you will likely need a lot more rear downforce to get it back into balance.
If you look at the uncovered lower lip, at 75 mph the difference in pressure is about 1/10 of a psi. If the opening is three feet across and you have about 5 inches of lip uncovered, the net downforce is on the order of 18 pounds. Not a lot, but it is something. If you go up to 100 mph you get about .17 psi or almost twice as much, so you can see that there is a benefit. Without a real measurement of the lift and the interaction with the spoiler below you really don't know much about it.
If you want big downforce in the front, move the spoiler forward all the way to the front of the car, and that will make a big difference. Since it is way forward of the front wheels, you will likely need a lot more rear downforce to get it back into balance.
Last edited by Solofast; 12-23-2009 at 12:02 PM.
12-23-2009, 10:18 AM
#4
Race Director
Thread Starter
What you are seeing is stagnation pressure. That is, air is entering the inlet faster than it can get out, so it is damming up and that is causing high pressure. Note that all the surfae other than what is sticking out as a lower lip is seeing an equal pressure upward, so other than the couple of inches of lip sticking out, that isn't covered by the area above it, there isn't any real downforce added. If you didn't have the lower lip, there might be more lift, there is also pressure under the nose ahead of the spoiler, so there is a lot more going on than can be just addressed by the fact that the lower lip is bending down.
If you look at the uncovered lower lip, at 75 mph the difference in pressure is about 1/10 of a psi. If the opening is three feet across and you have about 5 inches of lip uncovered, the net downforce is on the order of 18 pounds. Not a lot, but it is something. If you go up to 100 mph you get about .17 psi or almost twice as much, so you can see that there is a benefit. Without a real measurement of the lift and the interaction with the spoiler below you really don't know much about it.
If you want big downforce in the front, move the spoiler forward all the way to the front of the car, and that will make a big difference. Since it is way forward of the front wheels, you will likely need a lot more rear downforce to get it back into balance.
If you look at the uncovered lower lip, at 75 mph the difference in pressure is about 1/10 of a psi. If the opening is three feet across and you have about 5 inches of lip uncovered, the net downforce is on the order of 18 pounds. Not a lot, but it is something. If you go up to 100 mph you get about .17 psi or almost twice as much, so you can see that there is a benefit. Without a real measurement of the lift and the interaction with the spoiler below you really don't know much about it.
If you want big downforce in the front, move the spoiler forward all the way to the front of the car, and that will make a big difference. Since it is way forward of the front wheels, you will likely need a lot more rear downforce to get it back into balance.
That actually does make a lot of sense.
12-23-2009, 10:47 AM
#5
Le Mans Master
On a side note....had a little fun with your car yesterday (yeah got a little slow at work). Didn't know if you'd want the graphics in white or black, so I just left them whatever color they were for ease of photoshopping.
12-25-2009, 05:20 AM
#6
Safety Car
