Mark Anderson

so like this?

Jerry Feather

No, Mark, I guess my answer is "not really." Those pictures seem to show something that is a very exagerated version of the S spoiler whereas my spoiler is more of an abreviated version of only part of the S spoiler, hence the word "bikini."

Too, my Bikini Spoiler is intended to accomplish the deletion of the Rear WS wiper, and the one you show clearly incorporates it.

Interesting picturtes in any case.

Alan

Mark - the only part that doesn't look good to me is at the top of the hatch where it just ends and the chrome hatch trim becomes visible. Seems an odd transition.

Alan

Jerry Feather

Yesterday I was able to glue up most of the body pieces onto the backbone. When the glue cured fairly well I did some shaping of the body.

Today I glued up the remainder of the body pieces and have it layed up curing now. When these additional pieces set pretty well I'll do some more shaping.

One additional thing I did with a lot of the epoxy was to rebed some of the under side of the Spoiler in an effort to try to capture more of the edge formed in the hatch by the transition from the bevel I'm working with to the outer surface of the hatch. I want to have all of that edge captured in the final version of this Spoiler mainly for fitting purposes.

I'll be making some molds off of this wooden buck of the Spoiler out of fiberglass and resin, probably three segments in total, so I'll soon need to be sculpting this thing to the final finish. What I'm going to use is some Bondo and then simply sand it to finish like it was an auto body part. Then I'll probably primer and finish paint it in order to take a real smooth mold off of it.

If I have it that far done I think I'll bring it to SF 13 with me. Or, maybe I'll bring it in whatever state it is by then.

Jerry Feather

One thing you are going to notice about this Spoiler is that I am locating it a bit farther aft from where the S spoiler is located. One result is that it nearly covers up the key hole to the hatch. What I'm going to have to do is cut a significant recess in the back of this buck to allow access to the hatch lock. Given the location and the relative lack of much thickness to this Spoiler, that is going to result in nearly cutting the backbone and much of the body in half. Therefore I will not be able to do that to this buck until I have it nearly finished and even then only after I have figured out a way to stiffen the buck so it will not break in two.

To do that I think I am going to cut with my router a couple of groves in the buck and then bed some aluminum or steel bar stock in them across the center. That should give it enough strength to stay together for the mold making. Then, I'll probably be laying some bar stock in the finish versions of this spoiler in order that the fiberglass versions will not break in half also.

Jerry Feather

This epoxy resin that I am using takes about 4 or 5 hours to cure enough to work without it changing shape. Then it takes overnight to get fairly hard, but to be hard enough to be sandable it take about two days. Even then, if I am using it for the finish surface, it takes a cure with the heat gun to get hard enough to sand to dust without gumming up the sand paper.

After two hours on this present cure I was able to work it a little without it running, so I used some of the drips to fill in some of the small voids that are inevitable in this kind of project. By later this afternoon I'll be able to take the Spoiler off the hatch and try to get it to near final finish, at least the finih level suitable for the bondo application. Then, in the meantime I need to go get some bondo.

While that was curing I was able to get some time in on the Gas Cap Separator and the Pawls I am working on. See the other thread in a minute.

Jerry Feather

The epoxy set up enough for me to work on the shaping a little bit more. First I squared off the foreward extensions so they fit within the paramaters I had in mind and then I rounded them off to near the final shape I have in mind. Here are the pictures to show this process.

I used my 4 inch disc grinder/sander with a 36 grit sanding disc and carefully sculpted with that. It is fairly easy to use on the outside of cuirves, but much more difficult on inside curves.

Then I put the buck onto one of my S4 rolling tubs so you can get a better idea of the size or perspective, particularly since Mark, and I suppose others, are having some difficulty in envisoning just what this Bikini Spoiler might amount to is terms of size. I hope these pictures help.

The last couple of pictures show how the lock is mostly covered up and then I have marked in the area that I will have to dig out for key clearance.

UncleMaz

Looking good Jerry.

Jerry Feather

In looking at the pictures it occurs to me that I may very well want to taper the approach or leading ends of the two extension more that I have here. They seem a little too blunt for me now that I study them. I'll work on that a little later. The rest of it seems to have just about the right amount of sweep or angle to the flow of air, but then, I don't have almost any idea of what the air flow might be like in this area of the car.

One thought I have had is the idea of putting little winglets on the ends of this Bikini Spoiler, but then I don't think they would be of much advantage since I don't think the car is generating vortises (sp) in this particular area, like the wing tips of an airplane. They might look pretty cool, though.

Nicole

Please allow me to point out the obvious: The fact that Porsche tested this style spoiler does not automatically mean it worked very well...

I personally don't find it very attractive on the otherwise rather organic shape of the 928.

Jerry Feather

Actually I don't either, Nicole; but maybe fortunately not all of the 928 community happens to have your and my good taste.

The Fixer

Hey Jerry,

Looks like it is shaping up nicely and made me think of an airplane as you started.

Your Wing Design:

Incredible Craftsmanship, Great Looking Wing and Great Idea to use the factory mounting holes (if you are).

That said and with due respect, to my eyeballs your design looks like it will create drag , but then again I can only guess.

It's smoother transition actually can be deceiving and create unwanted drag rather than chop the air off from the little i know.

Mark's looks correct to my eyes.

RS Ducktail:

With my design I first started shaping the exact angle of the stock S Spoiler (as noted in my thread) used on my car from the factory, and elongated it

for down force.

At the same time I looked at the shape, angle and height of the ducktails designed by Porsche.

The ducktail angle looked identical to the S Spoiler's from what i could tell. The height is different and the extra lip at the top (on Ducktail) was to help create down force.

My RS Ducktail is extremely light (1.75 lb) and extremely strong. It is shorter than what was used on a 911RS because it can be due to the 928 having a better shape and higher rear end, any higher would create unwanted drag.

Road test:

When on the road again and somewhere safe, i will see how fast it will go. If it won't hit the top speed it is supposed to, we will know you were right and i was wrong, but i highly doubt it. I'll use video as proof.

If it creates the drag you say, it will be considerably slower. I will test this before the motor enhancements (euro intake) are made.

The Porsche ducktail on a '70s RS 911 was in fact a very good shape to counter lift as tested. The taller ducktail on the RSR created usable downforce and won many races, beating the Prototype Class routinely.

But, in the end there is no way anyone can determine whether a wing does what it is intended without doing controlled tests as you know.

You can only guess.

Landseer

944-esque

Jerry Feather

Matt, Thanks for your compliments and for your analysis.

When you get to test your car on the open road, when it hits whatever top speed it will hit, you will not have a clue about what effect your spoiler has on that.

Neither your spoiler, nor mine, nor the factory ones on so many S cars, is a wing. This thing did not become a wing, in my opinion, until the one they put on the S4 and later 928s.

The purpose of a spoiler is to spoil the airflow over the top of the car. The body of the car is actually a lifting body, so the faster it goes to more lift it generates. If the flow of air over the top can be spoiled it will kill some of the lift. Unfortunately, the devise they tested on the prototype, as shown by Nicole and many others, the devise they put on probably about 30,000 S cars, the ones you and I have made/are making, and the one Mark has shown, does just what was intended, and that is kill the airfow. The ideal place to have put such a spoiler is probably on the top of the car. I think the reason they put them at the rear is to hopefully convert some or all of the drag created into a negative lift or downforce, as it seems to be called, at the rear of the car where it will be most effective.

I think the reason they finally went to the S4 wing design is to better utilize the flow of air to create the negative lift, but without so much of the drag.

Your and my wind tunnel is going to be the interstate highway, and we are both extremely limited in the kind of equipment that might be utilized to fully test our creations. However, one thing that we can do is what is called "tuft testing." I think I will try to do some of that with my creation, if I ever put it on one of my cars. I'll have someone drive next to me and take pictures or video of the tufts as they flutter around and/or streamline in the flow of air around and over the spoiler at speed. I think that will give some idea of what might be taking place, but then again, as you say, it will only be a best guess.

Yes, I am devising this spoiler to cover up and even utilize the original S4 wing mounting points and the Rear Window Wiper holes, all for mounting. My idea with this spoiler is to provide a plug and play for the S4 and later guys who wish to delete the wing and wiper but don't want to fill the holes and paint the hatch. I'm not sure what it is going to amount to for the S car guys or even the OB car folks.

My design still does almost nothing for the guys who were looking for a seamless plug to fill the wiper sweep void in the S spoiler, even though that is where the impetuous for this project was generated.

Jerry Feather

Nicole, I think that the fact that the factory tested the little spoiler as shown in the picture and then put it and the additional side extensions on the S version of the 928 for about 6 years, actually tells quite a lot about the success of it.