Cd and blunt front ends

[ECONORAM]

Originally Posted by winkosmosis

The other day I saw a Boxster at 65mph with the rear spoiler popped up. Apparently lift does matter at normal speed.

I would not be so sure. I recall when the VW Corrado was brought to the USA, VW changed the functioning for the rear spoiler so it would deploy at 55 mph, instead of the normal 90 mph in Europe. With our low speed limits, an auto spoiler that doesn't deploy doesn't do much for sales appeal.

Aerohead, I also find it interesting that more gain resulted from the tail work than from the front end work...

[fidalgoman]

Simply put in aerodynamics the more turbulent displacement you create, the more energy you impart into the air stream. Some of it is the whirls, eddys and vortexes created and some of it is from air displacement. That air drug along with the car due to skin friction and form drag.

If you look at an airfoil shape you will see a smooth rounded curve that creates even acceleration of the air up to about the 1/3 chord point (1/3 from leading edge). Then since the air has been smoothly accelerated out of the way it will tend to fall evenly back into line as long as there is a smooth transition (not too sharp an angle) without too much turbulence, back into the hole the car just made in the air. The air can only fall back in so much before there is seperation of flow. The process is called by some the pressure recovery section of the airfoil and it is the most critical area in reducing drag. The kind of drag we are dealing with in our boat tails is mostly pressure recovery. Just look at the solar racers and you can see the clean flow lines.

[texanidiot25]

Originally Posted by Christ

I'd be interested in the actual numbers produced at 65MPH by that car... Just cuz the "engineers" programmed the BCM to put the spoiler up, doesn't really tell me that it's anything more than a nicety.

Fun thing about this spoiler- you can pop it up and down at what ever speed you want, but it's programmed to pop up at 65-70 I believe. Road testers say at higher speeds (tracks) it does keep the rear of the car planted. In my mountain road driving ('08 Boxster S), I couldn't hit speeds fast enough to tell, but at 50mph on some wicked roads the car had MORE than enough mechanical grip, you have to get pretty crazy to make good use of the spoiler. However, maybe there's some fuel economy plus since it's a drop-top, not being a totally ideal shape.

[aerohead]

Originally Posted by texanidiot25

Fun thing about this spoiler- you can pop it up and down at what ever speed you want, but it's programmed to pop up at 65-70 I believe. Road testers say at higher speeds (tracks) it does keep the rear of the car planted. In my mountain road driving ('08 Boxster S), I couldn't hit speeds fast enough to tell, but at 50mph on some wicked roads the car had MORE than enough mechanical grip, you have to get pretty crazy to make good use of the spoiler. However, maybe there's some fuel economy plus since it's a drop-top, not being a totally ideal shape.

Driving in the slow lane at 124-mph,on the unlimited speed portion of the Autobahn invites an appreciation of spoilers,as the biggest Benzs, Bimmers,and lightweight Porches blow by on the left with abandon.And this is on wet,rainy, April roads.