Flat Bonneville-type spoiler
 

So we stop going off-topic in the Sedan-Kamm thread, I figured a new one should be made.

I went ahead and fitted my car with a 15" trunklid extension, modeled after the Fusion.

http://i3.photobucket.com/albums/y93...y/Picture7.jpg

The trunk and spoiler have a 2-3* downward angle, and the sides of the spoiler continue the 3-4* boattailing of the trunk. The vertical end plates meet the corners of the car at about a 10* angle. The roofline meets the end of the spoiler at about a 15-16* angle.

We'll see if this shows any noticeable effect.

AeroModder -

Good idea to make this a separate thread. We've talked about this spoiler in the past and speculated its downforce versus virtual-boattail versus hide-the-parachute functionality.

I am really really really really hoping the virtual-boattail wins because this mod looks cool.

CarloSW2

While the trunk extension will at least look 'race inspired', I think getting one for the underbody/bumper may help as well. Maybe a square with rounded corners. Have another one inside of it, that sticks out further, and see if we can duplicate the effects of a boattail with a different shape!

@AeroModder!
Now I'm curious too how that will perform! I hope you can do some coastdown tests!
Looking at your pic I can't stop to imagine a visual on people's face whom are wondering - what the **** is all that on that car? - : )
It would be pretty cool though if it showed a positive difference in drag reduction!

Barna

Data for the wiki would be nice. If it works I will make a new Mod listing for it, and your pic goes up first :)

My established coast testing starts at 45 MPH and compares speeds at set points (road signs). I'll see if there's any improvement, but I'm not sure if it'll show up at lower speeds like this. I've pretty much hit a plateau some time ago and can't get any better coasting.

Otherwise, the only other indicator is tank MPG, and that isn't the greatest measurement of single mods. It'll be at least a week before I get those numbers.

When ever you get the data will be fine. I take what I can get :)

The design seems pretty structurally sound. It's been subjected to gusty sidewinds and plenty of rain overnight and it doesn't look phased. I added a couple supports before the storm, though.

Hasn't been driven yet, but I'll be getting plenty of testing on Monday, including some freeway driving.

Update: I'll have to wait until next tank for any decent results. This tank is already shot from crosswinds and lots of rain, and bumper-to-bumper traffic for 3 miles. I already went past a quarter tank and didn't even cover 80 miles. I'll be lucky to see 26 on this one.

this is going to be an interesting test, i think you will see an improvement in FE but only a couple of miles per galleon (anythings better than nothing though)

thats my guess and im sticking with it :)

goodluck

Coastdown testing shows a slight reduction in speed, but that's also due to the fact it's getting quite cold out.

The airflow definitely reattaches onto the spoiler, and I noticed that the naturally occuring counter-rotating vorticies off the sedan shape become apparent. I was driving without VGs after realizing they're useless in crosswinds and noticed similar patterns in the dew even without them, but further down.

With the vortex generators positioned like \\\\\///// (as opposed to the standard
/////\\\\\), there were two high-pressure zones present at the base of the rear window:

(The /|\ lines show the directions of flow.)

I noticed the same spreading high-pressure pattern start about 5 inches before the edge of the decklid (at the beginning of the spoiler).


I was thinking about taking the side pieces of my partial kamm and putting those on to give the air off the sides a vertical surface to detach from, hopefully stopping the vortex generation.

Aeromodder -

You can use the "Code" wrapper ("#" symbol) to preserve spaces and use a mono-space font :

CarloSW2

Thanks, I'll remember that.

would something like this work on a crx style body as well to smooth the airflow off the passenger compartment and fromt the sides together? or would the sloped down kamback style work better?

I am not sure the flat spoiler is very easy to implement on the CRX style body. It looks to me you would have to go to a boat tail to improve on the CRX.

On the other hand, with the VW New Beetle with a steeper rear slope, Ernie Rogers effectively demonstrated the flat spoiler style works well. I am looking to duplicate his results on my Beetle.

The fuel attendant topped off the tank, so it went past the F mark by at least a gallon. The tank was around 26ish, but I'll average it in with the next couple tanks.

Testing changes at the turn of the season isn't the best way to do things.

So far, the average with the spoiler is about 27.7 MPG, and that's including some bad weather and a fair bit of city driving.

After the fillup, the needle was slightly below where it normally falls. The wierd thing was that it was about a gallon's worth lower the next time I turned the car on.

I'm starting to think seeing regular 30 tanks in this car might be a bit out of reach.

AeroModder, have you tufted your car yet ?
I'm guessing that you are having a lot more turbulence at the back glass versus the Fusion, due to the steeper angle.

Are you positive that the flow is re-attaching ? ( I'd guess yes - but that not enough of it is re-attaching to really make a big difference. )

I certainly do like the look of it !
If you're not seeing much attached flow, I wonder if it would be beneficial to raise it up several inches to where it meets the rest of that airflow.

I'm positive it reattaches. It's been a bit wet, but I'll see if I can tape on some tufts and see what the flow looks like when I take my fiancee to work.

I also found a '92 Civic VX hatch for sale for $2k... Seriously considering a trade-in.

i remember discussing the Bonneville-type spoiler almost a year ago


am really interested in any results you can muster

The results would appear to be no change, or too small to notice in tank averages.

Update: The spoiler is off, and replaced with trip wires to give the air a clean edge to separate from. Soon I'll be attaching the side supports I had for the kammback to give a vertical surface off the cabin to reduce vortex generation.

The spoiler appeared to produce some downforce. The bottom of the center support was actually bent inwards.

I took a look at the end of the roof and it's slope, and the glass is somewhat inset. The angle before the separation hits the trunk about an inch or two before the edge of the trunk.

http://i3.photobucket.com/albums/y93...y/DSCF0910.jpg

My understanding of these spoilers at Bonneville was for center or pressure.
I thought they were used to move the CoP back, ideally behind the CoG for high speed stability.
Of course they still might help for ecomodding.

thats disappointing


now i want to do some more research into flat spoilers

My first tank without it came to around 25 MPG, so it may have some effect after all. The temparatures cooled and more rain came around after I installed it, so it might have evened out the drop in FE.
I had to fill with E10, though, because the price of unblended premium is 50 cents a gallon more than E10 regular, and it's no longer cost-effective going with the premium.

I might revisit this mod later on.

what about doing something to keep the airflow from detaching from the car body and then trying to reattach to the vertical sides of the spoiler. Which in theory would create turbulence between the corners of the car and the sides of the spoiler, which would probably decrease your fe gains.

I could keep my side extensions on, which hold's the body's boattail angle out further. I took those off when I put the spoiler on.

Did you tuft it ? I was looking at a Fusion the other day thinking of this post.
I'm pretty sure you would get better results if you knew what the airflow was doing back there.
The angle of your back window is really steep.
My guess is still that you are not getting the airflow to connect.

Never got a dry day and time to tuft test, unfortunately. But I'm quite certain it's attaching. I tuft-tested the rear a long time ago, before any modding, and found that the airflow did reattach about halfway down the trunk.

I'll see if I can get a good day after I put it back on.

Aaaaaaah I really want to know if this would help.

My back window angle is rather steep, so I'm hoping a flat spoiler on the back would help the flow reattach. My only concern is that my brake lights may be obstructed from anyone with a vehicle raised higher than mine (nearly everyone)

Observations on virtual boat tails.
 

Observations from wind tunnel test pictures would indicate that with a boat tail, one can go to ~15deg, with a virtual boat tail off the back of an average sedan, ~10deg is more of the max. The 10deg number would assume there is nothing turning the air at the beginning. This would explain why small cutouts for windows, lights, etc. have less of an impact when integrated correctly on a steeper angle. I attached a picture of a sedan in a wind tunnel, and it looks like the air wants to exit at ~10deg. A re-build at 10deg may show real gains.

angles
 

You can go as steep as 22-degrees but you have to be careful how you get there.
You'll notice that the smoke traces make no abrupt changes,but rather gentle curves,beginning with zero-degrees tangent angle at the point of the roofs maximum camber location,and steepening as the flow works its way back.
I'm encouraging members and lurkers to consider 'angles' in the context of their 'position' in the aft-body.
The Aerodynamic Streamlining Template Part-C is based on this premise.All 'angles' must be viewed within a contextual environment.If you haven't seen the template,check it out.Also,in a previous thread there a few hundred additional Flow Images.

Hello -

This is the thread that aerohead is referring to :

http://ecomodder.com/forum/showthrea...rt-c-9287.html

CarloSW2

There's a '68 barracuda that has one of these. I can't find the write-up but there's a shot of it in this article: (I can't post a link because of I don't have 5 posts, ridiculous)
They don't call it a fast-back for nothing. I think they got this one down to like .19 CD.

'Blowfish' ?
 

Hot Rod Magazine recently carried a story about a 4-cyl 'cuda called 'Blowfish' with Cd 0.20 that exploded its engine during an LSR attempt at Bonneville.
Beautiful car!
Out on the salt,the trays offer traction,directional stability and clean air for the drogue-chute to catch, so as to get the main chute out better 'cause the brakes burn out pretty fast at these speeds.

George Poteet's Blowfish is an amazing car, simply stunning to look at. Powered by a turbo Dodge four cylinder, it set the F/BFCC record at 255mph.

Hot Rod article:
1969 Plymouth Barracuda Blowfish - Hot Rod Magazine

Mike

darcane -

This is my favorite picture. Check out that spoiler! :

http://image.hotrod.com/f/9349073+w7...smoke_wand.jpg

CarloSW2

Look at a similar spoiler on a modern VW Bug. If it can help reduce drag on a Bug, it should work on most anything.

Welcome to www.max-mpg.com

Pendragon, you must be my cyber doppelganger... I was just looking at these Bonneville pics and then the VW spoiler site yesterday. I agree... if it works on cars as different as the Blowfish and a production dub, then some form of the design ought to work on just about any car. Seems logical. I have been looking at pics of the Mercur XR4Ti double spoiler someone mentioned on a thread here... that's a weird and interesting example too.

There was an XR4ti that used to autocross with the local sports car club in the day. It was nicknamed "Mr. Potatohead" because of it's shape. There was a good bit of space between the multiple elements of the rear wing/spoiler. I don't know that it would clean up the airflow that much, but you never know.

Cheers

Beautiful car!