EcoModder.com

EcoModder.com (https://ecomodder.com/forum/)
-   Aerodynamics (https://ecomodder.com/forum/aerodynamics.html)
-   -   Old square sedan kammback (https://ecomodder.com/forum/showthread.php/old-square-sedan-kammback-29389.html)

Joris 07-02-2014 07:05 PM

Old square sedan kammback
 
2 Attachment(s)
I have read a lot of sedan kammback builds, most of them using newer, more rounded cars. So I need your help on this one.

I have mocked up this cardboard kammback.
http://www.mijnalbum.nl/Foto-4HXC4EP7-D.jpg

However, I think that it could turn out to have a negative result because the air 'overshoots' the trunk.

Without kammback there is lots of turbulence in the middle of the rear screen, but some reattached air on the spoiler.

The kammback can't be much longer, because then the trunk will hit it.

What do you think?
- Would the car benefit from the kammback?
- Should I leave it alone?
- Or should I make the spoiler on the trunk longer, so flow can reattach?

ecomodded 07-02-2014 10:05 PM

From my gleamed knowledge I think your trunk is to low to hope to attach the flow to. Unless your spoiler was 18" high (forget it) so you should concentrate on a kammback

Could a longer Kammback go on the outside of the trunk seam ?
If so maybe the trunk could be left operational.

MetroMPG 07-03-2014 12:23 PM

Have you confirmed you have re-attached flow on the trunk lid?

Myself, I'd look for a way to make a Kammback that is attached to the trunk or trailing edge of the roof, but can open up to preserve trunk access.

Like:

http://i282.photobucket.com/albums/k.../Image0208.jpg

from: http://ecomodder.com/forum/showthrea...ods-20741.html

Joris 07-03-2014 02:42 PM

Thanks for the answers! I have done some tuft-testing, but before I start on the kammback I should do it again (better).

http://www.mijnalbum.nl/Foto-U6DSKVA6-D.jpg

It looks like there is some reattached flow on the rubber spoiler. The back window and middle of the trunk are all turbulence. I'm I seeing this right?

I can't (will not) drill holes in the roof to secure hinges, but I just realised I might be able to use the raingutter as a mounting point. I have a spare trunk that I can hack up so I might go for the full (to the bumper) kammback and make it hinge via the raingutters.

ecomodded 07-03-2014 03:51 PM

I would spend lots of time developing the kammback before fabricating one.

You need to simplify the installation and mounting method to a point that no one could improve on it, at least without great effort & Knowledge.

Off hand I think silicone mounted would be enough, if you gave it lots of surface area to adhere to , and designed it to be self supporting (hooked in rain gutter etc.). My Aftermarket rear top of the glass roof spoiler is mounted with silicone as per instructions.

Varn 07-03-2014 04:03 PM

I did yarn testing of my VW. I put on some heavy wire masts on the back and tied a flag every 3". Once you see where the wind is not turbulent you can use that point for an "anti spoiler" What surprised me is how quickly air went from being fairly organized to a frenzy. It would only stay together a few inches past the edge of the body.

http://veloliner.com/vw/tuftest.jpg
Here is an over the shoulder pic of it a few inches behind the back window.

I used a section of cattle fencing. to hold the tufts. I know a guy who uses a fiberglass wand (fishing pole) with a bit of yarn on it. He can hold it where he wants to test.

freebeard 07-03-2014 06:36 PM

You could attach the wand to you rear window wiper. :thumbup:

/me neither.

ecomodded 07-03-2014 10:31 PM

:turtle: attach tufts on the wiper


Or.. you could get some duct tape and wool ..

aerohead 07-07-2014 05:55 PM

Kamm-back
 
From the Porsche 914,you can see what Lotus did with their Europa,with boot height and length pushing the rear out near the 'Template' for Cd 0.29.
If your Kamm addition filled in this compromised area,you'd be poised for a nice drag reduction.
http://i1271.photobucket.com/albums/...d2/06-2816.jpg
http://i1271.photobucket.com/albums/...d2/06-2828.jpg
You can see how the 1st-gen Golf/Rabbit would have the lowest drag if it's roofline had been 'filled in.''
http://i1271.photobucket.com/albums/...an01-18-14.jpg
You can also see how Chrysler lowered their Charger's drag by filling in this area.
http://i1271.photobucket.com/albums/...n12-21-133.jpg
A quick cardboard mockup would give you your fuel savings numbers.

Joris 07-07-2014 06:42 PM

Thank you Aerohead, I will get some pieces of cardboard and start testing (tuft-testing, coast-testing and fuel consumption testing). My neighbour has a Lotus Europe, really cool car! Incredibly small and light. Would be a perfect car to put in a small 3 cylinder engine.

But first I have to fix a dragging wheelbearing. Found out today that the front left is on its way out.

Varn 07-07-2014 07:43 PM

I used this overlay on the jetta back end. I have a composite photo of the Rabbit with drag lines, and Jetta with a prototype of the tail.

http://veloliner.com/vw/rabbitoverlaycarbontail.JPG

End the end I didn't make the whale tail wide enough. I have taken the whale tail off recently and plan on making a hinged folding tail and attaching it to the window cover.

Joris 07-09-2014 01:37 PM

I've been doing some thinking, and my brother came up with the idea of using a pvc plastic banner for the full kamback. This way the trunk can still be used. I will weld some brackets on the spare trunk I have to support the middle and end section, and use the driprails/raingutter to secure the top. Still thinking about what to do with the sides.

Maybe a little hard to understand without some pictures :)

freebeard 07-10-2014 04:04 AM

Well, have a picture then:

http://i282.photobucket.com/albums/k.../Image0208.jpg
from here

aerohead 07-10-2014 04:26 PM

1992 Volvo ECC
 
If you haven't seen it,here's a link to Volvo's 1992 Environmental Concept Car,Cd 0.23.
It's still a notchback,although you can see the direction the roofline is heading.http://pics.imcdb.org/0is438/ecc9221fg.3098.jpg

Joris 07-10-2014 05:10 PM

I had seen that concept, it has many in common with the production version (S80).

Here are some more concepts, I did not know Volvo made a electric vehicle in 77'.
Volvo Concept Cars Part of a Conscious Strategy

Joris 07-27-2014 12:05 PM

Only 8 days left until I go on a 2000 mile trip. So I started on the kammback, so far so good! I also did front wheel covers, rear wheel covers are yet to come.

http://www.mijnalbum.nl/Foto-4XZYHBXO-D.jpg

http://www.mijnalbum.nl/Foto-DXIYDC3B-D.jpg

http://www.mijnalbum.nl/Foto-KPBG4A78-D.jpg

renault_megane_dci 07-27-2014 04:51 PM

So the tail will somehow roll on the trunk when it's lifted open ?

Xist 07-28-2014 05:12 AM

It clamps onto your rain gutters?

Please tell us how you did this! :) It looks beautiful! :)

I have been trying to figure out something like this for my Civic, but I do not have gutters. Christofoo used rare earth magnets: http://ecomodder.com/forum/member-ch...back-moves.jpg

Joris 07-28-2014 09:18 AM

Yes, it clamps on the rain gutters! I wanted the kammback to be easily removable without leaving traces of it on the car and still be able to use the trunk. So this was (in my opinion) the best solution I could come up with.

I'm not sure if the photo is detailed enough. I used the clamps and protective rubbers (haha:D) of a original roofrack (the black triangles) and took some 3 mm steel plate to attach the aluminium bar to. Pretty simple actually.
http://www.mijnalbum.nl/Foto-6TQ7IWN3-D.jpg

The tail/kammback is a separate trunk, I just lift it by hand and then open the original trunk. I later found out that the bar across could be used to support the tail on the trunk while opened.

renault_megane_dci 07-28-2014 11:16 AM

Can't wait to know how much it will boost your FE !

Sven7 07-29-2014 11:54 AM

Fantastic. I vote we put this on the front page.

freebeard 07-29-2014 03:30 PM

I look forward to seeing how the sides are skinned and the fit along the fender-tops when it's closed.

Joris 07-29-2014 05:07 PM

Thanks for the kind words, it motivates me!

Today I have painted the frame after adding some extra braces to stiffen it up a bit.
http://www.mijnalbum.nl/Foto-WWGTN4QT-D.jpg

While I was waiting for the paint to dry, I made some brackets to secure the rear of the tail to the car. Together with some cheap straps the tail is tightened down to the trunk.
http://www.mijnalbum.nl/Foto-RTFEPASO-D.jpg

For extra crosswind protection I have made some braces that go into the trunk gap.
http://www.mijnalbum.nl/Foto-EOSMTCOJ-D.jpg

Then came the hard part, making the side panels.
http://www.mijnalbum.nl/Foto-64GQ4RBL-D.jpg

Besides from not being easy to cut, acrylsheets do not want to bend very easy. I had convinced myself that it would work after I had nicely bended a small piece.
Unfortunately I was wrong.
http://www.mijnalbum.nl/Foto-T3FYYN4S-D.jpg

It looks horrible, and since I'm already over the budget I had set to myself I think I will just get some nice aluminium sheets to cover the sides with. Can't leave it looking this horrible.
http://www.mijnalbum.nl/Foto-P6UHOJJK-D.jpg

renault_megane_dci 07-29-2014 06:13 PM

Try coroplast, it's basically free.

freebeard 07-30-2014 02:23 PM

The bracing is a good idea, and the tabs in the trunklid gap is a neat trick.

I expected the side pieces to be your big challenge, but the result looks like you used a heat gun. Right? The cost for aluminum sheet would be similar to new plastic. Try cold rolling [either] before you attach the pieces, or even trim the final shape. The tool would be two rollers on the bottom, with a third that you can press down from the top incrementally as you push and pull the sheet through. The roll would start on a line from the top front to lower rear corners.

Given the size of the pieces you might want to just take that step to a sheet metal shop.

Joris 07-31-2014 04:10 PM

The kammback tail is finished. Yesterday I made the two sides, much easier using aluminium.
http://www.mijnalbum.nl/Foto-LMUUWW4H-D.jpg
http://www.mijnalbum.nl/Foto-W7FVHLFQ-D.jpg

Then came the task of making the big acryl window on top. And just like the side panels, it went horrible. When I wanted to drill, bend or secure the panel, cracks were forming and pieces eventually broke off. So lesson learned, I will never use acryl again. Looks nice, but a pain to work with.
http://www.mijnalbum.nl/Foto-A8KU387T-D.jpg

So in the end I've should have gone straight for the aluminium panels. Works easy, looks good and they are lighter. I added a rubber strip to prevent cutting myself (or someone else) on the sharp edge of the sheet. And between the hinge where it attaches to the car. Also added a little handle to allow easy opening.
http://www.mijnalbum.nl/Foto-4HESHUAT-D.jpg
http://www.mijnalbum.nl/Foto-O8XHDV43-D.jpg

Couple of things I still have to do.
Weigh the tail, hoping it will be under 10 kg.
Possibly paint the whole thing white, cooler in the sun and less reflection for other drivers.
And tonight when the roads are calmer I plan on doing some coast down tests.

renault_megane_dci 07-31-2014 05:41 PM

That's way cool !

aerohead 07-31-2014 07:27 PM

new tail
 
It tastes great and there's less filling!:D

Joris 07-31-2014 09:31 PM

So, 2 AM and I have the results from the coast-down test. There is a hill nearby and I used both sides of it. B is with kammback, A is without. Started with the kammback because that was easier. Then took it off, did some runs and then some more runs with the kammback on. Starting speed was 100 KM/H. And roadsigns where used as speedtraps. No wind as far as I could feel.

Route North.
B1; 100 - 95 - 81
B2; 100 - 97 - 82

A1; 100 - 92 - 80
A2; 100 - 93 - 80

B1; 100 - 98 - 82
B2; 100 - 96 - 82


Route South
B1; 101 - 61 - 50
B2; 100 - 59 - 48

A1; 100 - 58 - 45
A2; 100 - 58 - 45

B1; 100 - 60 - 50
B2; 100 - 60 - 49
B2; 100 - 60 - 49


It looks like the kammback is doing it's job. The road wasn't really sutable for faster testing, but that would have been better I think.

Next thing is tuft-testing, but that will have to wait until after the 2000 mile trip.

backpacker3 07-31-2014 10:25 PM

Wow. Just wow. I would love to do something like that with my car.

tvbd56 07-31-2014 10:39 PM

I would imagine your vision is blocked partially by the aluminum, as long as you're comfortable and safe with it that's what counts:) It looks amazing!

renault_megane_dci 08-01-2014 06:12 AM

Quote:

Originally Posted by Joris (Post 437993)
So, 2 AM and I have the results from the coast-down test. There is a hill nearby and I used both sides of it. B is with kammback, A is without. Started with the kammback because that was easier. Then took it off, did some runs and then some more runs with the kammback on. Starting speed was 100 KM/H. And roadsigns where used as speedtraps. No wind as far as I could feel.

Route North.
B1; 100 - 95 - 81
B2; 100 - 97 - 82

A1; 100 - 92 - 80
A2; 100 - 93 - 80

B1; 100 - 98 - 82
B2; 100 - 96 - 82


Route South
B1; 101 - 61 - 50
B2; 100 - 59 - 48

A1; 100 - 58 - 45
A2; 100 - 58 - 45

B1; 100 - 60 - 50
B2; 100 - 60 - 49
B2; 100 - 60 - 49


It looks like the kammback is doing it's job. The road wasn't really sutable for faster testing, but that would have been better I think.

Next thing is tuft-testing, but that will have to wait until after the 2000 mile trip.

I'll dig out a conversion to turn those in % improvement cos someone nice made it for me in my bike thread

Joris 08-01-2014 06:23 AM

Quote:

Originally Posted by tvbd56 (Post 438006)
I would imagine your vision is blocked partially by the aluminum, as long as you're comfortable and safe with it that's what counts:) It looks amazing!

You're right, it is blocking the rear view. I can see about 20-30 meter behind the car. Best would be an open view to the back, but that is not possible. So I will have to do with it. Parking is no problem this way.

But, I sometimes have to drive a van for work. And those vans also don't have a rear window. So I am a bit used to not using the rear view mirror.

@ Renault_Megane_DCI

That would be great!

Do you know if driving in France with something like this on my car will get me pulled over? Are you allowed to have shiny aluminium sheets on your car there?

RedDevil 08-01-2014 06:32 AM

You probably don't need a full size rear window, a half size would give you a clear view straight back from the center rear view mirror.

Maybe you can use what's left of your acrylic kammback.
I've cut my acrylic upper grill block (not fitted yet) with a Dremel (like) mini tool and its small disc blade cutter. The acrylic will melt (and stink! Do it outside) but not shatter.

You need a lot of patience though and a steady hand.
I shattered the little disc just before finishing the cut and was too lazy to replace it and continue. Well it is too hot now for a full grill block anyway...

MetroMPG 08-01-2014 09:59 AM

Quote:

Originally Posted by Joris (Post 437993)
So, 2 AM and I have the results from the coast-down test.

Thanks for posting your testing efforts.

MetroMPG 08-01-2014 10:09 AM

Quote:

Originally Posted by Sven7 (Post 437500)
Fantastic. I vote we put this on the front page.

Added to home page after testing!

renault_megane_dci 08-01-2014 11:40 AM

Quote:

Originally Posted by Joris (Post 438040)
Do you know if driving in France with something like this on my car will get me pulled over? Are you allowed to have shiny aluminium sheets on your car there?

It is my personnal opinion that it looks factory enough to help you through scutinity.
That and the fact law enforcement might fear to have a chat with a foreigner.

I would add a paint stripping and a brand marking to help with this scenario.

But you know, **** happens ...

If you get pulled over, stick to dutch :confused::confused::confused:

renault_megane_dci 08-01-2014 11:56 AM

http://ecomodder.com/forum/showthrea...t-21853-2.html

Quote:

Originally Posted by renault_megane_dci (Post 307574)
Today was coast down test day.

We rode to the "quiet back road" my colleague mentionned.
It was rather windy ...
So I went for a ride, trying to pass his parked car at 100 Km per hour, pulling the clutch and then cheking the speed at a distance, namely a sign on the side.

With the kammback : two attempt showed 62 ish Km per hour

Without the kammback, the bike was easier to maintain at speed (probably more throttle, maybe less wind) and I got a consistant 60 ish Km per hour.

Then I fitted the kammback back but we didn't do more attempts.

All in all : waste of gas ...

I don't know the distance from point A to point B either just the tiny difference in speed

Can I work out something out of it ?
:confused:

Quote:

Originally Posted by janvos39 (Post 307644)
The kinetic energy at 100 km/hr is 0.5*m*v*v and that is with a bike+rider of for instance 250 kg 0.5*250*27.77*27.77=96450 in both tests
This kinetic energy at 60 km/hr is 0.5*250*16.66*16.66=34722
So without the tail enengy consummed by air and roll resistance is 96450-34722=61728

Now with the tail. Energy left at 62 is 0.5-250*17.22*17.22=37076
So energy consummed in this case is 59374. (so approx. 4% less)


Joris 08-01-2014 02:45 PM

Wil do some maths tonight, thank you!

Today I swapped the fuel filter, differential oil and made some last additions to the kammback to make it a real 'Kammback'.

http://www.mijnalbum.nl/Foto-TM6D3W7T-D.jpg
http://www.mijnalbum.nl/Foto-J4EYD4CF-D.jpg
http://www.mijnalbum.nl/Foto-FGQ4XWXO-D.jpg

Should be good now! I have decided that I won't paint it, but maybe put on some graphics.

Thanks for putting me on the homepage, really pleased with that!

whatmaycome14 08-01-2014 06:40 PM

Impressive and inspiring!


All times are GMT -4. The time now is 08:18 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com