Flat Bonneville-type spoiler

[aerohead]

Originally Posted by California98Civic

I was just studying these template again, this time with a well drawn image of my coupe from the 1998 Honda service manual. It looks like the highest point on the car is just ahead of the center pillar. Got freeware in the form of Paint.Net and used Aerohead's template from this site and made this workable image of my car. It does seem I would need a much larger spoiler, no? Would it even be legal?

The CHP might get you on a safety violation.Don't know.Any un-suspecting pedestrian,cyclist,etc.,might not be vigilant enough to realize it's sticking out there.Slice and dice!
When CAR and DRIVER streamlined the Pinto back in '74,they gave the rear spoiler a 30-degree up-kick to add more 'virtual' length to it.
The Bonneville type foil is also used in drag racing ( both away from the general public ).As others may have mentioned,the flow will burst off here in clean separation,the low pressure base drag is communicated under the open plate creating low drag down-force.
When you consider that some of these cars are experiencing power-induced wheel-spin at 300+ mph,you can see the need for down-force.
The other thing is that above the foil,there is nice laminar flow for the drag chutes to catch
It appears that the long length of the horizontal foil,necessary to approach the 'Template' line cuts into its attractiveness,compared to a 30-degree foil of low drag and much shorter length.

[California98Civic]

CHP might get me, but maybe not if I mark the tail somehow... a long thin strip of reflective orange tape? I just estimated a couple forms that I might build. One extends straight out by 28 inches from the plane and angle of the trunk (not gonna do that). One extends 24 inches at a very modest angle from the trunk (might try that). The last picks a stronger angle and extends 35 inches from the rear window, across the trunk and 20 inches further. I'm gonna have to build one of em... I'll figure that out later...

[aerohead]

Originally Posted by California98Civic

CHP might get me, but maybe not if I mark the tail somehow... a long thin strip of reflective orange tape? I just estimated a couple forms that I might build. One extends straight out by 28 inches from the plane and angle of the trunk (not gonna do that). One extends 24 inches at a very modest angle from the trunk (might try that). The last picks a stronger angle and extends 35 inches from the rear window, across the trunk and 20 inches further. I'm gonna have to build one of em... I'll figure that out later...

Cal,if you have a scan gauge you could do a quick cardboard and duct tape prototype and quick test to check its performance.If you like the results,then do a nice one.
Also,Pep Boys and most auto parts stores carry high-conspicuity reflective tape,by 3M.It's designed to be SEEN.Check it out.If the Chippies see that,at least they'll know you're thinking of others.

[Pendragon]

As you have observed, "the template" frequently suggests impracticably long afterbodies. If using "the template" at all, I would be inclined to use an abbreviated form of it. I would establish a line of the angle of departure of the roof line just in front of the rear window and then find a parallel line which is tangent to "the template" at that point and then move it forward until it was in place over the rear of the roof. This would place the area of clean airflow closer to an achievable afterbody. Even so, "the template" simply does not suggest a realistic option in my view.

The reason that I surmised that a five or ten degree slope on the trunk lid extension would be a more balanced choice than the thirty degree one suggested is that the steeper one becomes more of a wing or spoiler and I think that the down force generated at highway speed would be sufficient to unbalance the car and might generate more net drag (including increased front end drag) than the benefits could overcome. The objective, after all, is to reduce total drag.

Another example of a small "flip" is the Honda Civic Hybrid. On a car which has gone to the trouble of utilizing a (standard equipment) underbelly and wheels that suggest they were designed to both reduce (unsprung) weight and aero drag with the concession of some ventilation for the brakes, I do not think Honda would have installed the trunk lid "flip" purely for styling reasons on a car that is supposed to compete with the Toyota Prius. The idea, I think, is simply to catch enough of the disturbed airflow in the region to establish some degree of order to the airflow. Sure, something larger might have doe slightly better, but this is a car to be used as everyday transportation and Honda are know to be conservative in their styling.

If we take a look at the '99 Honda Civic HX, there is absolutely nothing remarkable about it aerodynamically, but it achieve rather good FE because of other optimization. (Note: Another thread remarked about the continued high price of this car. I saw a national average of around $5,500 for one with less than 150k miles so I guess its FE is being valued in the market place.)

Originally Posted by California98Civic

I was just studying these template again, this time with a well drawn image of my coupe from the 1998 Honda service manual. It looks like the highest point on the car is just ahead of the center pillar. Got freeware in the form of Paint.Net and used Aerohead's template from this site and made this workable image of my car. It does seem I would need a much larger spoiler, no? Would it even be legal?

[Pendragon]

Here is a link to a post about a Bonneville Honda Civic that topped 200 MPH. As you would guess, there is absolutely nothing stock about the engine, but there are pix of the front and back end showing some fairly conventional, but apparently effective, aero mods in addition to an under body pan. Take a look at the rear wing. It looks to me to be a reasonably easy to duplicate design.

[Edit] P.S. Here is an image of another shelf spoiler of a Bonneville Civic

[California98Civic]

Originally Posted by Pendragon

Here is a link to a post about a Bonneville Honda Civic that topped 200 MPH. As you would guess, there is absolutely nothing stock about the engine, but there are pix of the front and back end showing some fairly conventional, but apparently effective, aero mods in addition to an under body pan. Take a look at the rear wing. It looks to me to be a reasonably easy to duplicate design.

I have been seeing those little "flips" all over town now. But I think I need something bigger for this purpose. And I agree the rear spoiler on that "Bonneville Civic" looks easy to mimic. I think the trunk lid is the key to securing the spoiler ultimately. I could create little flaps in the spoiler that close into the trunk lid. The supports featured on the Bonneville Civic could rest against the lid, or under it, without adhesives or drill holes anywhere. Cool pics, btw.

Oh! And aerohead, thanks for the tip on the tape... I'll check it out for sure.

[brucepick]

Here's the Bonneville Civic.
Seems to me the spoiler is angled down towards the rear. An important point, I believe. Looks like the viewing angle is about even with spoiler angle so you barely see any of its surface, just the rear edge. And you can tell from the view of underbelly that the camera position is near ground level - that is, looking up at the wing area.

[Pendragon]

Originally Posted by brucepick

Here's the Bonneville Civic.
Seems to me the spoiler is angled down towards the rear. An important point, I believe. Looks like the viewing angle is about even with spoiler angle so you barely see any of its surface, just the rear edge. And you can tell from the view of underbelly that the camera position is near ground level - that is, looking up at the wing area.

I have yet to find a pic that shows this spoiler from above so that you can determine its shape. I think that it is probably not that different in result than that of the Hondata Acura

Hondata Car

which also made 200+ MPH runs (as well as some class runs below 200 MPH. There is some video on YouTube which shows them spinning out after deploying the drag chute at the end of the run. I am just guessing, but it is probable that they had the rear downforce at the absolute minimum for the speed run. When the weight transfer to the front occurred, the rear tires were no longer able to provide adequate traction for control.

Fun, huh?

[Frank Lee]

Those wheelwells are sure nicely stuffed!

[darcane]

Originally Posted by Frank Lee

Those wheelwells are sure nicely stuffed!

Yeah, space savers with full moons and front runners are a good combo. Inexpensive and lots of people have run over 200 with them and they look good too.