Quote:
Originally Posted by bitmap
I'm wondering which aero modification would be the most beneficial for this hatchback. And no, boat tail is not an option as all vehicle modifications are forbidden in my country and it has to look OEM 
On the left is a base model with no aero.
In the middle small trailing edge extension is added as can be seen on almost all modern production vehicles nowadays.
On the right spoiler is added with small gurney flap on the top to make angle between top of the roof and top of the spoiler as shallow as possible.
This design was quite frequently used in the 80's (Kadett GSI, Audi 100 wagon, Car and Driver Pinto) and is proven to work but nobody uses it anymore.
Is it because trailing edge extensions are better at lowering drag, or is it in fact superior solution and manufacturers abandoned it only because it might not look "cool" enough for today's car buyers? |
From drag tables published by Hucho,the Soda's rear slope may be so steep as to create a squareback type wake,which includes the entire rear face of the car.
To get to a 'fastback' wake,the upper tip of your lower spoiler would have to create a roof-to-spoiler angle of about 25-degrees.Even with this,you'd be creating vortex drag.And your separation line remains essentially the same,so your base pressure of the wake would be constant.
Just to begin with,you'd need to extend the roof out as Kamm recommended,and this is illegal.
A complete side photograph of the car would be helpful.
There's about 7-criteria involved in deciding an 'optimum' rear slope.The more information the better.