Aero dynamics question ???
 

I understand how a Turbo tail or (tea tray) would work, also a Carrera tail ,do to size and down force,..But what makes the Ducktail and the newest design of the 964 wing work,...are the Duck tail and the 964 tail designed to keep the cars more stable at high speeds only now,..and has little to do with the downforce anymore,Their so much smaller than the TT and CT, is it due to the evolment of aero dynamic testing or is it the wider wheels and tires ...how does the smaller tails acheive the same result per-say,I want to put a 964 wing on a narrow body 77' and I'am now curious as to how the old versus new compare,..Thanks Frank

Don't bother with all the work to put a 964 wing on a 1977 911S. Just go with a Burzel- ducktail. The 964 is heavier, more complicated, and prone to failure. The only reason they did the retractable thing was for looks at low speeds (to not disrupt the body line)

The Burzel evolved as an early attempt to tame the rear end lift and high speed instability as the factory prepared to race the 911 in the Sports Car World Championship. They added a small wicker bill like what was used on numerous earlier cars like fiats and examined the effects in the wind tunnel. They saw how it trapped the turbulent air at the engine cover, aiding cooling, reducing lift, and cleaning the tailights. They moved it around and enlarged it into the Burzel. To compliment it, they made the front RSR spoiler for anti-lift and the oil cooler.

In only a few months, the factory engineers moved on to develop the "Mary Stuart Collar" spoiler that was on the 1973 911RSR Targa winner. This was developed a little further into the IROC spoiler and then to the Whale Tail and Tea Tray.

A parallel development was the prototype 911 2.1 liter Turbo RSR. This used a similar front air dam to the IROC, though with more air-dam effect and better brake cooling. It used a full-blown rear wing like a 917, practically. This was deemed ugly by Norbert Singer and the head engineers so they painted it black to disguise it and the rear window extension that ruined the 911's lines but made great downforce. Ths wing was outlawed in the silhouette formula so they toned it down in width and went for a biplane design more similar to the 930's wing.

A fiberglass IROC tail with matching front spoiler would be best for the track. A ducktail and early S/RSR air dam would be great for the street. Make sure you balance the front and rear.

The downforce only starts with the GT2 style wing that serious track guys use with a spoiler and upper wing element. The later RSR 3.8 wing, late Turbo, GT2, GT3 Cup, all work well but would require a good bit of work to adapt to your car.

Aero
 

well I have a duck tail on it now with just a stock front valence ,..which i'm soon to install a chin spoiler...she's a tad squirly at 80 MPH plus for some reason, it is lowerd aswell and it still is not as planted as I think it should be ??? Thanks Frank

I have a ducktail and IROC front. I love the look. It feels stable to me but I mainly do the tight twisty roads.

Make sure your rake angle is right and if you need more stability, I would go IROC front and rear. It would fit well on your car and lighten the load. Consider a fiberglass rear bumper to replace the unfathomably heavy impact bumper on the stock vehicle. The Turbo tails with rubber surrounds are very heavy as well. This will improve handling through better weight distribution.

The chin spoiler should help a lot, as would a Euro ride height/alignment+corner balance. The more of these tricks you do, the better it should handle.

No aero expert here but reading through posts it's dangerous to have a tail, regardless of style, and no front spoiler. If you think about it that makes sense. The weight is in the back then you add a tail for further down-force. With nothing up front to keep it planted I can understand why she feels unstable. You can use a front spoiler without a tail for the same reason you shouldn't do the opposite, all the weight is back there anyway to keep it planted.

here is the data for the street configs from circa 1970 . circa 2000.

Note, they can be improved by proper chassis setup

http://forums.pelicanparts.com/uploa...1213183164.gif

http://forums.pelicanparts.com/uploa...1213183183.gif


http://forums.pelicanparts.com/uploa...1213183197.gif


http://forums.pelicanparts.com/uploa...1213183219.gif

its interesting to note the accedental nature of the discovery of how to reduce 911lift, someone accidentally left the lid partially raised during a wind tunnel test and noted the improved aero #s
http://forums.pelicanparts.com/uploa...1213183236.jpg

Now there's an expert!!!!!!