boat tail for saturn
 

Hello everyone, I want to boat tail my saturn. I would like to just build it off of my trunk instead of from the roofline. Would I be wasting my time to build a boat tail of that nature?

does this look right?

Looks right. I'd think such a boattail would provide effectiveness somewhere between that of a Bonneville spoiler and a full boattail.

I decided that I might as well just build a real boat tail. I have a piece of plexi that I got for free so figuring thats about the most expensive part I might as well just go all out. I Think I would like to cut it off at the 50 degree line. Any suggestions on an angle coming from the rear bumper?

hows this look....too steep for the bottom?

I think so.

scottoriou -

My earlier contribution for a 3rd-gen agrees with your center of roof camber :

http://ecomodder.com/forum/member-cf...ow-overlay.jpg

I'd go look at the aerocivic for what his choice was for the bottom angle.

CarloSW2

after an evening of staring at the back end of a saturn I decided that right now I dont want to deal with it. I see why most boat tails are done to hatch backs. Kind of an easy canvas to work from compared to a sedan. I might just go with a spoiler that reaches out and touches the overlay. any ideas on angles for that? If I did go with a boat tail I think I would just keep my sides vertical and they would look like they would come straight up out of the trunk and then straight back from there. Working around all of the goofy angles on that car is more than I want to deal with at the moment.

Anywhere from 0 (horizontal) to 30 deg up I guess. At 0 it'll stick further out the back but it should leave less trailing wake area thus be more effective. At 30 it'll stick up and get in your rearward vision but it'll intersect the template curve without sticking so far out the back- and of course it'll leave a larger trailing wake area but still be better than nothing.

scottoriou -

I made this for the other 3rd-gen owner too :

http://ecomodder.com/forum/member-cf...erlay-duck.jpg
http://ecomodder.com/forum/member-cf...verlay-mid.jpg
http://ecomodder.com/forum/member-cf...verlay-low.jpg

CarloSW2

thanks for those pictures. I think if I scaled them right that last one is about ten inches long? do you happen to know if thats correct?

scottoriou -

I don't know but I did some pixel calcs and the agree. The SC2 is 180" long and the car picture is 478 pixels wide :

478 pixels / 180 inches = 2.66 pixels per inch

The last spoiler is about 26 pixels wide :

26 pixels / 2.66 pixels per inch = 9.79" => almost 10"

CarloSW2

Check out this thread for a sedan boattail (or wingtail). The one pictured eventually blew off the car so use that as a learning experience. It gives 10 to 20% improvement in mpg.

http://ecomodder.com/forum/showthrea...-a-7489-4.html

When I finish my current boat project, I have another wingtail design in mind. With the trailer hitch receiver as the mounting point, use a "tee" welded up from 1-1/4" square tube and from that frame build up a thin plywood boattail using stitch and glue boatbuilding techniques.

that nature
 

scottoriou,there are many instances documented that show a drag decrease from just about anything which filled in some of the turbulent wake.
For lack of an official term I call it stuffing the wake.
If you begin the boat tail where you want to, you'll lose some potential energy due to the overhead turbulence but I do believe you'll see re-attachment and drag reduction,depending on length.Kinda like the difference between an Audi TT and a New Beetle.The Audi is still an aerodynamic compromise but its far and away superior to the VW.
GM did what your doing with the Impact/EV-1 and set a land speed record.It would have also extended the battery range.

So what if instead of an entire boat tail I created sort of a prius shape to the rear of the car. It would possibly increase the rear section area which could possibly hurt the performance but if clean separation was induced with sharp corners on all parts would it be helpful? here are some pictures of things i was thinking.

what if
 

This is kinda where Kamm and Korff were going with their recommendations.They realized that a full tail was 'impractical' with respect to driveways and parallel parking and such,and advocated that the tail be truncated at a point where the wake area equaled 50% of frontal area.
There's still 50% of the drag left on the table mind you ( good for another 25% mpg ), but your not strapped with an enormous cantilevered tail hanging way out there.
Adding only a foot to my CRX was good for Cd 0.235 and 60+ mpg @ 55 mph,52 @ 70.
I would not be concerned with 'burst'.Your Cd is fixed at about 20 mph and the separation point at the rear isn't moving around.That's straight from Hucho.
I would encourage you to do a shorter tail exactly on the 'Template' rather than a longer one which either falls above or below it.
--------------------------------------------------------------------------
The Renault Vesta II is an example of a "Template" car.She's good for 138 mpg @ 100 Km/h.
The Mercedes 'Boxfish' is also a "Template" car.
Both have Cd 0.19 and are very short for their Cds.They have only about 32% of aft-body.( the New Beetle,also a 32% aft-body car suffers with Cd 0.38 due to the pseudo-Jaray 'fastback' roofline,which breaks all the rules of streamlining ):o
------------------------------------------------------------------------- The other thing is, that these cars are 'plug and play.' If you want more mpg at a later date,you just plug in a longer tail.Modular!

"The Renault Vesta II is an example of a "Template" car.She's good for 138 mpg @ 100 Km/h."

Hardly, 4.25 l/100 km = 55 mpg city/83 hwy for a 1000 lb 700 cc car. mpg by French standard not EPA

But Vesta 2 was run from Bordeaux to Paris using only 1,94 l/100 km @ 100,9 km/h - that's 121 mp(US) @ 62.7 mph

Slowing down to 50 km/h or 31 mph , it used 1.6 L/100km or 147 mpg.

Imagine what it'd do with EFI and LRR tires.

Hardly
 

The first article I saw for the Vesta II had to do with the Paris/Bordeaux run,and 138 MPG.
I later wrote to Renault and they mailed me a press kit for the car.I believe they offered the same numbers as in the initial article.No mention of any EPA protocals,just steady-speed driving,two passengers and luggage.

Considering how aerodynamic that car already is I'd just get rid of the spoiler and make an airdam or belly pan.

A tail might be worth it for a van or a wagon, but this car already has a tail-- the rear bodywork.