OK gang. We've had a lot of conversation. Now I'm kinda curious how many of you have whacked your wing already, am planning to whack your wing when you get around to it, thought very seriously about it, would consider it or think this whole concept is kind of....uh..... just plain whacked. Tell me more!

Paul Barrera
'91 $4

 

Whack the damn wing already. Worst case scenario your 928 will handle like every 911 on the road.

They seam popular so it cannot be all that bad.

 

+1

 

ugh! just read the first part.

 

I'm late coming to this thread, but I gotta say: If you want a wingless 928, you gotta earn it. It aint easy owning an OB. The rest of em just don't look right.

-T

 

Wow lot of good disinformation sprinkled in here. I might as well add to it, since I'm not an aerodynamicist either(I stayed in a Holiday Inn once though).

First, airplanes don't require engines Jim. Most have engines, but they'll fly just fine without provided you can sacrifice lift for airspeed, usually in a rising column of air.

Second, the aero kits on cars are much more than just the wing. Look at the blue car in post 200. Start at the front, and notice the valance, now just around the lower wheel wells there is a flared treatment. If you're really sharp you've seen the strakes along the roof line, just inboard from the door/roof line. And of course, the massive wing. For further reading, lookup the BMW Batmobile - awsome display of aero equipment.

Next, I believe that any car maker, including Porsche would add a 'feature' to the car to improve sales. This also goes for the S4 wing. It was the eighties, Peter Max posters, KC & the Sunshine band, tie-dye, etc. If a massive wing would help sell the car, and maybe improved the Cd, then toss one on there.

Take a look at a 1990 or later 928GT. You'll find all the little gizmos that you would expect to find. It has the valance or air dam front that does two jobs. It creats an area of low pressure under the engine bay, and it scoops air around the side and outboard of the wheels. The cute, but nutty cooling doors on the grill, which only help until at high speeds when they could do some good, then they open to cool the engine, Doh! Behind the front wheels you'll find that plastic fender flare treatment again, and it's also on the front of the rear wheel arch. Notice it's not on the back of the rear arch, hmmm, bet they could have done more there, but didn't want to affect the clean sweep of the rear pickup behind the wheel. Then - The Wing. And it's a big booger for such a small car.

Someone mentioned the Lamborghin Countach. It's very true that the Countach is quite a bit faster sans wing. The wing on the Countach is strictly for looks, it has no aero benefit, and sadly a rather large detractor at very high speed. The same cannot be said for the 928. While it won't do much for downforce, that's not why it's there. Think about an aircraft wing. The bottom is a smooth surface chord-wise. On top, it has a gently curved arch surface chord-wise(front-to-back). Now, the aircraft wing is designed to aid in 'lifting' the plane up, while the wing on a car is used to do just the opposite, to hold the car down. So we expect to find the top of the 928 wing flat(true) and the bottom curved(true, but subtle). Thus being used to suck the air downward and keep the hiney planted.

HOWEVER; you say! The 928 wing doesn't provide much downforce. Right! And why? Because of it's AOA, or angle of attack. As Mark discovered, there's plenty of downforce available if the AOA is raised a few degrees. This is a very tricky area. Anyone remember the ultimate wing guru Jim Hall(Texan)? Google Chaparral and Jim Hall and you'll have fun reading for a while. Anyway, he had a moveable wing(banned now, too effective) that he could change the AOA for nice and smooth on the straights, or quite steeply pitched when reaching and driving through a corner.

What happens if you go too far with AOA? Well, just like an aircraft wing, it stalls. Not in the engine sense, but an airfoil stall means that the smooth barrier of air that flows over the wing and allows it to do those wonderful things becomes corrupted, and the air simple falls away from the surface at AOAs over about 16-20 degrees.

So, how does the wing DO those cool things like reduce Cd? You would think that adding surface area, even though slight would increase Cd, but nope, it's job is really working on the air both in front of the wing and behind it. Wanna argue about the effects in front of the wing? Watch a bird soar along a ridge sometime. Do they float behind, or above the highest point, or do they float out in front of it quite a way? That's right, the air flowing over the hatch is disturbed significantly by the wing. This is what we're trying to accomplish at the back of the car. We want the air, which has been our friend at the nose, and over the roof to now 'go away' smartly and not cause a area of low pressure or suction at the back. This is also why those kammbacks are so successful, the air is broken cleanly away from the body, and the turbulence is desirable for us(not so much for the car directly behind though).

The nature of any car has an area of low pressure develop just behind the B pillar. This can be messed with significantly by changing the shape, angle, size, and slant of the rear window. In the 60's, Several US cars had abrupt even back slanted rear windows that looked kooky. The man behind the development was a noted aerodynamicist Gordon Buehrig, who also designed the 1936 Cord 812, which has an amazingly low Cd for a car of it's day. since the motoring(Porsche) public wouldn't go for a reverse slant, or even a Kammback on the 928, they had to live with the poor shape that caused a fair amount of drag.

The Wing was an effort to fix that problem, and the spoilers that go before it could be optional because they didn't work even remotely like the wing does. The spoiler has almost no effect on the air in front of it, past about 15cm or so. All the effects of the spoiler are to break up the air behind, and cause the turbulence to work it's way along the top ridge of the car, destroying some of the suction. That's why that spoiler is canted so high, it has no significant AOA, because it's not SUPPOSED to be aerodynamic. The Wing however, is supposed to be aerodynamic and operate as a pressure valve just as Bernoulli postulated so long ago.

So, hope you've enjoyed this little trip, several other things to note, that make a lot of difference in air, as opposed to mechanical friction. The air drag increases not in linear increments, but at the square of the velocity. A barrier of moving air on a smooth surface creates something called 'laminar flow' which reduces drag significantly. It is hard to induce, and is fickle to maintain. That's one reason why your car gets worse fuel economy in rain, no laminar flow anywhere on the body. There is no such thing as 'vacuum'(outside the noun discribing a Kirby or some such) only varying degrees of pressure. In the 70s, an F1 team named Tyrell designed a 6-wheel car, with 4 tiny front wheels to minimize drag. It didn't do well, but not related to the wheel configuration.

if you want to take the wing off an S4 or GTS, it won't make much difference at highway speeds. Perhaps a slight decrease in fuel economy if you do a lot of freeway driving due to the reduced Cd. The removal of the front belly pan is probably just as costly, as it doesn't take advantage of the front air dam pressure reducer. The air from the engine bay is just shunted down there, and probably makes a nice pressure bubble right under the firewall area. If you really want to be frugal, tape up all your body gaps, remove the wipers, use one aero mirror only, and keep your speed just barely above the speed needed to stay in high gear. The engine will be less thermodynamically, and mechanically efficient, but the aero drag savings will offset that many-fold.

 

Wow - thanks Doc!!


So....how about those OB owners with the S spoiler who add an S4 wing to the hatch?

 

Wow, Doc, that's some interesting write-up!!! Thanks for putting this together!


Some of them go to Hell.




Hell, MI, that is.

 

Doc, You haven't a clue as to what the hell you are talking about!..........KC and the Sunshine Band were a complete manifestation of the mid 70's disco era! They were pretty much washed up by the time the 80's came around! Peter Max was a popular artist in the 60's and early 70's and Tie Dye, was from the 60's!!!
Get your facts straight before you start preachin' the gospel!!

 

Keith... the disclaimer is is posted in the first line of the first page...
Perhaps living through the 60's does something to one's recollection of what was 'goin' on'...??
BTW, *Van Halen is reuniting & planning to tour...again... Hmmm, from mid 70's-80's, 'IIRC!'

We now return to the previously OT'd 'whack or don't wack the A$$' thread.

Kim

*music world info provided, as a renne bene - 'fee free!'

 

From 68-83 is all a blur. I think I was in the Army, and I know I attended college, but everything else sort of floated on by - sorry. What about Devo? Weren't they 80? Whip it, whip it good!

 

Hey now, I don't have "duel" wings on my car. The 81 is stock & the 79 has a nice smooth bare ***

 

Devo and their red flower pot hats in the video. Whip it good.

Wish I can remember for my life where I saw the picture of turbolators(eddy current generating wedges) stuck behind the door and at the back of the roof of a 924. The vortices generated by the small wedges help encourage the airflow to "part" from the round butt of them front engined Porsches. Air trying to wrap back around the butt is what I gather to be the force we call drag.
I don't think we get laminar flow at the slow speeds our land crafts achieve.
Slow when compared to real aerodynamic bodies like powered aeroplanes.
Think those aerobactic gliders can beat our cars on speed. And those things don't got any Hp save for the pilot yanking on the stick.

I stayed at a Holiday Inn in Waterford for the ALMS race. Not sure how smart that was since they suffered a water valve malfunction and there was water pouring out the side of the hotel at 2am.

Whack that butt. Hit it hard enough and you've got a Kamm-Tail.

 

Holy crap, Doc! Impressive post. Not so impressive response here... sorry.

 

Still respect me or did I go too fast, too furious? Hate to think it's starting to look ricer, but I just dig it. Wack the wing and have fun with it! Think my look will be better once it's painted solid black....until I add the yellow checkered graphics..