Aeromod of a 1964 Saab 96

[JohnAh]

Here's a quite good photo (not mine) of how the rear end looks:


The fact that Saab also build airplanes is clearly seen in the design of the cars of the older days. The basic concept of model 96 was created in the late 1940's. The body shape is smooth and looks aerodynamic but in reality I think the rear part is a disaster. What could have been a perfect shape has been distorted short, or concentrated, in order to fit a practical passenger car.

Attaching a boattail/kammback would probably improve aerodynamics a lot. I have decided to do this in small but less rewarding steps to make it easier to the rest of the family but also to avoid starting up another big project I can't finnish... Starting with the rear window as an isolated module seems therefor right.

[California98Civic]

Fun idea for a project! Have you seen this thread? Take a look at the discussion others and I have been having the last couple days about these Saabs... http://ecomodder.com/forum/showthrea...tml#post437525 (note one site I found claims a 0.32 stock Cd for this car... you think that's accurate?)

[JohnAh]

Oh nice, the bronze car is "Helga", a Saab 96 V4 customized by Jari Luoma in Finland. It's absolutely fabulous! I don't know anything about it except for the looks. Probably a bit better aerodynamicks than the original but still a bit to steep slope and too round corners in the rear I think.

https://www.facebook.com/jari.luoma.1

[JohnAh]

Here's some quick-n-dirty illustrations of my aeromod plans.
The first is like a "window adaptor" that fits in the place of the original window. It'll be made of welded steel with a small oval plastic window.
The "window adaptor" will mainly give more space to my dog and protect him from being fried by the sun but it may also (with some luck) make a slight improvement to drag.

The second image is a hinged cover made of fiberglass or whatever seems best. It should be light weight and don't need to be perfectly watertight since it will only be like an extra cover over the rear end and not a replacement. The "aerobutt" needs to be lifted at least 45 degrees to give me access to the trunk. The extra space may be used for an auxillary power unit (electric or diesel) with a fifth wheel just behind the car.

[JohnAh]

Does a kammback need to have a closed rear end or can it be left open if there's no other way that airflow can enter? If left open, I guess there can be some air oscillation making the whole thing rattle. A rear wall will offcourse make the whole thing more stable. But if making something lika a half kamm-cover over the upper part just to get a slight improvement it sure could make the construction a bit easier. -Don't need extra rear lights and licence plate for example.

[renault_megane_dci]

Whow, I like this a lot.

4,5 liters is mighty impressive !
Is it a personal best or your new average ?

On most of the pic, including your sketchs with the template, I am under the impression the car is tail low when it is required to be nose diving for best aero.

I like your rear window kamm idea.

[aerohead]

Originally Posted by JohnAh

Does a kammback need to have a closed rear end or can it be left open if there's no other way that airflow can enter? If left open, I guess there can be some air oscillation making the whole thing rattle. A rear wall will offcourse make the whole thing more stable. But if making something lika a half kamm-cover over the upper part just to get a slight improvement it sure could make the construction a bit easier. -Don't need extra rear lights and licence plate for example.

If open,you'd have a sort of sculpted box-cavity.
If closed,the recirculating air of separation can strike the rear surface and impart a small degree of forward thrust,something which cannot occur in an open cavity.
One of our members in Belgium tested a tonneau cover with gate down and gate up on hie pickup truck and noticed a slight reduction in performance when the gate was down or off.

[JohnAh]

Originally Posted by renault_megane_dci

Whow, I like this a lot.

4,5 liters is mighty impressive !
Is it a personal best or your new average ?

On most of the pic, including your sketchs with the template, I am under the impression the car is tail low when it is required to be nose diving for best aero.

I like your rear window kamm idea.

My 4.5 (or actually 4.4 but as I don't like to be disappointed I adjusted the figure slightly) is a personal best from last fill-up. It's a slight improvement from the last couple of periods and even though it has been a long sloping trend for some time now I don't expect to reach even lower without some aeromods or other more extreme changes.

I's soon time for nex fill-up and I have a feeling that the result will be in the same region, even if I had some smaller errors last time.

It's definitely time to start building that fuel computer I've been dreaming of for a few years now.

Concerning the aeromods I'm still aiming for some sort of kammback extension in first hand, since it will probably be the most rewarding one mod, but also because it's the only aeromod I can explain to my family as something that will make travel more comfortable (less sunlight from rear window and more space for dogs and luggage).

My ideas have changed a bit and I'm not aiming for a two-step solution as mentioned above. Instead I', thinking about an extension "box" that will fit into both the rear window rubber seal and to the trunk hatch at the same time. I will probably weld some kind of framework from steel as I have a spare trunk hatch to start working from. Fiberglass and polyester wold be much nicer but I don't have the same skills there. Steel is also easier to modify bit by bit until I get the shape I like.

The best would be to weld a new body shape directly to the car but this will have to involve a "registration approval", M.O.T or whatever it's called in non-swedish. Such a modification will also be more permanent. When I build the extension from welded steelpipes I can also work in my garage with another Saab 96 as a template while still driving the family car. When the extension box is ready I just move it to the other car and if my family goes crazy and I fail to explain why we must have such a crazy looking car, I can easily convert the car back to something quite normal. If they know the modification is easy to undo they may also be more tolerant to it and give it a chance.

Since I plan to use the original rubber seal around the rear window and the trunk, my extension box is actually mounted against TWO holes in the car's body. This may look a bit odd but will give a trustworthy seal against rain and snow. The outside will not be as smooth as if I designed the extension to exactly follow the car's body, but I can easily fill the gaps with duct tape, sheet plastic or whatever.

[JohnAh]

I'm not skilled with the pen but I played a little with a curvature-whatever (...it's called in english) just to get a hint of what my latest ideas would look like.

The first step is to create something like a station wagon out of an old trunk hatch so it can be detacheable. The upper part of the "station wagon adaptor" will be slightly larger than the rear window to straighten out the bent roofline a bit. Since it will cover the window entirely I don't have to remove the window, but since my large dog have complaints and I don't like the idea of double rear windowns I'll most likely remove it.

The station wagon adaptor will have an entirely flat surface in the rear end, with a small door and a window to make the trunk accessible from outside. The original rear lights will be left in place, all I need to to is to modify/extend the rear fenders to give a flat surface in level with the SW-adaptor.

This modification/attachment should give some Kamm-effect superior to the sofly rounded original 96 design. To really get to the extreme I can then build a second extension that is hinged to the roof of the first extension. This part will be like a fiberglass bucket, or even be a quite massive part with a core of expanded polystyrene. To make the car easier to park I can have a mechanism that allows me to raise the tail extension over the roof, exposing the rear window/door and making the car a lot shorter. If I need to use the hitchball or go somewhere were I can't have the tail at all, it is easily detachable, exposing the original rear lights fully. With the final extension in place, the original Saab rear lights will still be partly visible, mainly from the sides, marking the width of the car seen from straight behind.

The best thing is that I can do this crazy thing in two steps, making the project less complicated.

[JohnAh]

The "step" in the rear is just me playing with shapes and design. I guess it may reduce the benefit with Kammback shapes but it doesn't need to be as deep as in the picture. When I extrapolated the different body lines of the Saab I noticed parts of nice teardrop shapes. Playing with these lines led to this particular design where the rear lights in the extension protrudes to the sides, reminding of a whale's tail or the wings of an airplane. Hmm, the guys at Saab were aircraft designers from the beginning, so...