harris

is the Cw drag coefficient the same with or wthout raised back spoiler???


harris

Dock

Hard to say. The raised spoiler does develop lift (downward vectored in this case), and lift causes induced drag. But the parasitic drag of the raised spoiler versus the parasitic drag of the lowered spoiler also has to be taken into account. The increased induced drag generated by a raised spoiler could be offset by a reduction in the parasitic drag...but maybe not.

harris

and for my knowledge what is the Cw of our car?

Jean

I would guess that the way to know it is by comparing vs. the C4S, which is basically the same body and tire sizes but without a wing, what matters more than the CW , is the CW x A , which is the surface.

996 TT:
Cw: 0.31
A: 2.00 (Sq.m)
=>CwA: 0.62

996 C4S:
Cw:0.30
A:2.00
=> CwA: 0.60

harris

Hi Jean,
not excactly but this is also good info...!!!!thank you very much!!!

the comparison was between 996TT with low spoiler Vs 996TT with high spoiler

Woodster

I will bet you $100 that the Cd is lower with the spoiler down than up.

My car went faster in the Texas Mile with the spoiler fuse pulled.


I do not know the exact answer though.

MK

Jean

You are welcome!

But you got me confused....
You are not going to get a better estimate unless you put it in a wind tunnel. This is very accurate info.

If the difference in CD with spoiler (996TT) or without spoiler (996 C4S) is 0.01..

=> the difference with spoiler up or down must be somewhere in between 0.00 and 0.01, we are talking totally irrelevant numbers here. At 200 mph that would represent a loss of 12hp difference, and at 125 mph that is only a 3 HP difference.

Remember that the C4S and the 996TT share the exact same body so you should look at a C4S as a TT but with the wing down...almost.

If you are trying to establish loss in acceleration at high speed, then you can add to this increase in drag, the downforce that the wing produces in the rear and consider it added weight on the body mass, which is:

996 Turbo: incremental 13lbs of downforce at 125mph
996 Carrera: somewhere 22 lbs of lift at 125mph (don't have the info handy but this is whatthe 997 Carrera S has)

A difference of about 35lbs..again almost irrelevant.

What will change is your downforce and car stability at speeds.

Dock

Almost the same body...different front spoilers, plus the Turbo has the intercooler intakes on each side.

detailjohn

If you wax your spoiler, you'll gain 2 miles per hour down the quarter mile.

RdRunner

And here is a Yellow one....