Old square sedan kammback

[Sven7]

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

[freebeard]

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

[Joris]

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.


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.


For extra crosswind protection I have made some braces that go into the trunk gap.


Then came the hard part, making the side panels.


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.


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.

[renault_megane_dci]

Try coroplast, it's basically free.

[freebeard]

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]

The kammback tail is finished. Yesterday I made the two sides, much easier using aluminium.



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.


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.



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]

That's way cool !

[aerohead]

It tastes great and there's less filling!

[Joris]

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]

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