Another drag racing question
 

Hello all, I asked about our new race car body for next year. photo here

http://i26.tinypic.com/mm525s.jpg

Just found this link of another body with a 'shark fin' spill plate on the rear deck. What would be the benifit to using this type over the usual 2 at sides???

Thanks!

not much if any,

it may be more stabel in a straight line on a calm day but could be affected more directly by cross winds (i'd have to see it though). Also if its a centre rib design it won't stop the side spill from and aerofoils you add to the re deck - thus reducing their effectiveness.

p.s. where are you based in england?

Totally understand the straight line part but normally they have two, on the sides rather than one in the centre. Some of this design of body dont have any....meaning i am guessing that its a pretty good design?

Based in Essex (near to Benfleet)

Dude, it could just as well be a poor design. Just cause someone builds it does not mean they knew what they were doing. In aerodynamics, you'll find that even people with a large amount of knowledge have a hard time connecting the dots and coming up with solid answers due to the complicated nature of the art/science. If you have only seen one example of it, and the guy is not the one who won your class championship, I'd guess he either thought it looked cool, or, he has some theory he is testing out.

As far as drag racing aerodynamics in general, in my mind, I see it as a balancing act. Anything you put on your cars body is going to create some type of drag which will slow you down aero wise. But if you are able to create more down force with it, and can put more power to the tires, overcoming the drag and then some, then there is a benefit for you.
I think the trick is to create just enough down force on the rear tires to keep them from spinning at full throttle while going down the track. Too much down force is drag and slows you down, too little, and you spin the tires.
Directional stability is obviously a concern for safety, so aerodynamics can play a large role here if things get unsorted from mid-track on when you are at high speeds.

Here is a little reading I found for you, I'm sure what I'm saying is nothing new to you.

Aerodynamic Tips & Tricks from Hot Rod Magazine

Good Luck and be Safe!

That is a good point could well be, well there have been lots of these bodies made, I think its just preference as some have no spill plates (like were going to run) some have two side plates, some have this one in centre, so I think its more of a personal thing.

Were going for none as this body will be 1000% better and more stable than our last and no spill plates means little bit less drag.

1 or 2
 

I didn't find a link to the other car with shark fin.
Here's my guess :
The single fin adds to directional stability,as it helps keep the aerodynamic center of pressure behind the center of gravity.It does nothing to enhance the performance of the rear deck.
With the double spill-plates,their name describes their function,preventing the higher pressure air from moving in a spanwise direction and spilling over the ends,spilling into the lower pressure regime underneath,and in so doing,creating attached vortices which can produce significant drag.
Also,the spill-plates also act as weather-vanes,like the shark fin,and if you start to go sideways,their dirty Cd 1.11 helps to re-center the car through high,separation-induced drag.
If they don't do it,you go for the parachutes as fast as you can!

Strange, unless it was removed?

Thanks very much for help everyone, just gives me an idea why they use them or one. We going for none. The body itself is great and a huge amount better than our old body below so it will go straighter!

http://i29.tinypic.com/21jwx1y.jpg