Flat Bonneville-type spoiler

[Pendragon]

Originally Posted by brucepick

Thanks Frank. I think you're saying the rear edge of spoiler should meet the aero template line? I'm thinking, if it extends beyond that line (which represents a curved plane) that would be detrimental? And of course if it doesn't extend to meet the line, it doesn't intersect.

This is just my opinion, but the "aero template" calls for a device that is rather larger than what I believe is being discussed here and certainly larger than the ones used in the 200 + MPH Bonneville cars.

The idea is also somewhat different in that these extensions are being used to move the separation point further to the rear and attempt to provide a more orderly transition than is typical of rounded surfaces on the rear of cars done created by stylists.

Airflow under the car was also addressed on the Bonneville cars. They had full length belly pans and one of them had the rear of the belly pan angled up with strakes not entirely dissimilar to those used on F1 and other race cars to provide some downforce and move air into the "hole in the air" made by the car.

Anyway, I think it impractical to attempt to fabricate an extension which actually intersects the "aero template". Besides, there is nothing which demonstrates that the particular "aero template" shown in the forums is any more accurate than any other.

[California98Civic]

Originally Posted by EVDRVR

Have you considered attaching a spoiler using commercial suction cups to test your design? Here is a link to one particular brand, many are available. Industry swings plate glass through the sky with these things so I feel that following reasonable cautions and a safety strap you might find them useful.

Wood's Powr-Grip Co., Inc. | Vacuum Cups | Mounting Cups | 3" Concave Vacuum Cup with Threaded Stud

Rated for 15lbs and about 1.5" high, it would certainly be a way to secure the item without tape. But if you look at my cardboard spoiler test a couple posts back you might see that such a suction cup could be overkill. Thanks for the idea though. -j

[cfg83]

brucepick -

Originally Posted by brucepick

Thanks Frank. I think you're saying the rear edge of spoiler should meet the aero template line? I'm thinking, if it extends beyond that line (which represents a curved plane) that would be detrimental? And of course if it doesn't extend to meet the line, it doesn't intersect.

That's what I would say. But you have to overlay the template correctly with regard to the center of roof camber.

CarloSW2

[California98Civic]

Originally Posted by cfg83

brucepick -



That's what I would say. But you have to overlay the template correctly with regard to the center of roof camber.

CarloSW2

Here, attached is the overlay for the spoiler I preliminarily tested last night and plan to test again soon, more rigorously. The line in red is what I built. The line in black is an alternate I am considering. The inconclusive test showed a possible 0.45mpg improvement at 52mph.

[UFO]

^^^ Nice job with the overlays. I wonder if someone has a New Beetle profile laid over in that aero template, I'm curious where the Beetle flat spoilers would have to extend.

[scottoriou]

I was able to sneak another test in before the weather changed. I believe the improvement is due to the warmer temps than what I had the other morning. I did an average of 52.1 MPG. I left with a tailwind at 10 mph and came back and the headwind was 13 mph. My run north was 56.3 with the tailwind which I was super happy with. Only to turn around and head into the wind to get 47.8. 47.8 into a headwind is still better than my previous best (before spoiler) of 47.5 with no wind. So the average is 52 thereabouts. I cant say its proven to make an improvement yet but the trend is headed that way.

[brucepick]

scottoriou,
That's definitely a nice trend.

California98Civic,
I have this idea that the airflow won't follow a curve without having a physical shape there for it to follow. I'm guessing there's a separation point as it tries to follow the downward curve of roof + rear glass. After separating, I think it would continue in a straight path if not otherwise influenced.

So for the airflow after the roof, I drew a blue line tangental to the final roof curve, starting just before the rear glass. Then a 2nd blue line which would be a spoiler that meets that line.

Both the earlier red and black lines come close to the blue line I added. The red line meets my blue one just about perfectly; the newer black line extends through it just a bit.



What do you folks think?

[brucepick]

I looked at a bunch of oem-looking spoilers, in the large parking lot at work today. They all seemed to follow my idea in post above:

I could sight from a point behind the car, where I would be in line with the line of the roof just prior to the rear glass. Depending on the car, I had to be 10-20 feet behind it, crouching down. And I found the rear edge of the spoiler meeting that sight line.

One exception was a Porsche that had a double wing, like a biplane, with about 2" gap between them. The lower wing was positioned as I described, the upper one wasn't.

[cfg83]

California98Civic -

It looks good to me. Hopefully, aerohead will chime in.

CarloSW2

[California98Civic]

Originally Posted by brucepick

I have this idea that the airflow won't follow a curve without having a physical shape there for it to follow. I'm guessing there's a separation point as it tries to follow the downward curve of roof + rear glass. After separating, I think it would continue in a straight path if not otherwise influenced.

So for the airflow after the roof, I drew a blue line tangental to the final roof curve, starting just before the rear glass. Then a 2nd blue line which would be a spoiler that meets that line.

Both the earlier red and black lines come close to the blue line I added. The red line meets my blue one just about perfectly; the newer black line extends through it just a bit.



What do you folks think?

I think I don't know, but thanks very much for working with my image. One problem with my overlay is its resolution, the scale of which is not precise. Even with the image, I cannot be sure of placements, angles, lengths and such. What you say sounds plausible. I think I'll have to just improvise like a musician: get a feel for something that "works" and then try it and see.

Your comments make me think of an image MetroMPG posted on this site some time ago: http://ecomodder.com/forum/member-ae...-kamm-back.jpg

The airflow here has begun to disperse, scatter after separating from the tail end. Maybe that demonstrates your point. My understanding is that the long flat spoiler *might* allow such flow to briefly reattach (to the spoiler) and separate from the tail of the spoiler cleanly, reducing vortices, the wake, and the drag effect of the more steep rear window. That's what I think I am doing, based on what I read here on this site. But a little knowledge is sometimes a dangerous thing... !

I scoped out a test route today on a section of freeway closer to my house. It will allow me to try 60+/- speeds at a steady 16.1 throttle for 6.2 miles each way. All I need now is a clear and still day.