In the Hot Rod article this month about wind tunnel testing, under "things that don't work", it says that beyond about 45 degrees, additional windshield rake generally doesn't reduce drag. The bulge I speak of apparently is an attempt to make the center part of the hood an effectively very highly raked windshield. Do you have any reason to think this feature reduces drag?
The reason I ask is not because I suspect that it increases drag, but because it moves the center of pressure way forward, counteracting all the effort you've made to move it back. I've seen a video that suggests a little extra stability might be useful for the car.
I am aware that it is absurdly presumptuous for a wannabe like me to ask you such a question.
A good question and one I don't have a for sure answer for. I was interested in the 45 deg. thing in the Hot Rod article. Surprised me, but I guess it is kind of the teardrop shape thing where the blunt part at the front that is pushing thru the air is fine as long as the taper at the back is less, like the 6-7 degrees PorkPie mentions to allow the air to stay attached and fill in behind the car.
The main thing the hump is up there for is to clear the 871 blower. I wanted at first to extend the air inlet snout all the way along the top of the hood and out in front of the car. Then Tom brought up the center of pressure thing that you are talking about. So a compromise was made to take it to where it is now. And yes it does move the center of pressure forward. That and the traction issue that resulted in the near spin last year on the second run resulted in the 800 lb. weight increase. Before the spin we already were over 200 lbs. more than the year before in hopes of helping with the CP/CG that you mentioned. It obviously wasn't enough
. We will take another 300-400 lbs. with us this next year in case we need it.
Finally the scoop could have been a few inches lower and presented more of the top of the windshield in the middle to the air, but I still feel the shape we have is better than doing that. It would be interesting to have the wind tunnel time and see for sure.
I think the car is pretty aero as it has run 241 on what I believe is less than 700 HP at the crank. We have talked about the possibility of a new nose for 2008. A longer nose would help to move the CP back also and the longer wheelbase should also help.
So like I said most of this is gut feelings and no hard facts.
One last thing as I don't know what pictures you are looking at, but.....
In the first year 2004 we didn't have a blower and were running fuel....
Now of course we do have a blower and needed to modify the hood.
c ya,
Sum