Another Metro goes aero

[robertwb70]

No progress due to rain for the last 2 days, I'm at the point where I need to remove the glass from the hatch to continue and I have to work outside so hopefully tomorrow I can get it (mostly) finished.

The shorter cardboard version got me around 2 mpg so I'm hoping to get 3 mpg out of this one.

Couple of rough pictures

[robertwb70]

Didn't get it finished but got a good chunk of it done, new pics on my blog and in the garage here. Also updated pics of what the front looks like now.

Somehow the angle on the Kammback changed to 17 degrees, too late to change it now so I'm hoping it will be OK. The roof directly in front of the hatch is 10 degrees already so it should allow the air to stay attached at the steeper angle I'm hoping, but we'll see. Also the rear tires are smaller than the fronts and due for replacement anytime, the new tires will likely be the same as the fronts so that will decrease the angle some.

Robertwb70

[RobertSmalls]

It looks good, and it makes you wonder why Suzuki didn't give the Metro a CRX-style upper/lower glass arrangement.

You should probably tuft test it before you cut the sides to see if flow remains attached. No sense putting all this effort into something that won't work.

How well can you see through plexiglass at 73°?

If you leave the original glass in place, then your cabin is still enclosed with approved safety glazing.

[robertwb70]

Too late, I've already removed the factory glass. I could always put it back in if necessary.

As far as seeing I'm not sure since I haven't driven the car yet but I'll find out tomorrow. I did move the car a few feet today and now the angle finder says 15 degrees so apparently my slab isn't level.

I'll put some tufts on it when I find some appropriate string/yarn.

[Christ]

Originally Posted by robertwb70

Too late, I've already removed the factory glass. I could always put it back in if necessary.

As far as seeing I'm not sure since I haven't driven the car yet but I'll find out tomorrow. I did move the car a few feet today and now the angle finder says 15 degrees so apparently my slab isn't level.

I'll put some tufts on it when I find some appropriate string/yarn.

I'd definitely take a 16" 2x4 and lay it across the slab on the 2" face, then lay a level on it to make sure.

Also, don't forget now that when you load down the car (if you do), it will probably change the angle enough that you can't keep attached flow at highway speeds (45+), since the angle is already 15*. The roof slope might help you out a bit, though.

[robertwb70]

Don't know why I've never checked the slab before now but I'll definitely have to put it on the list.

I'm hoping some tuft testing will tell me if the angle is acceptable or not. I figure I'm in the car alone / no load about 95% of the time so I'm not too concerned with the other 5% of the time.

I've been searching and found that there are variations with what is considered the "optimal" angle from 10 to 15 to 22 degrees, depending on the source and the rest of the cars shape/ angles.

[Christ]

I can tell you how to level the slab very easily if it needs to be done, but you'll need a cement pump.

PM me if you need to.

[RobertSmalls]

Originally Posted by Christ

Also, don't forget now that when you load down the car (if you do), it will probably change the angle enough that you can't keep attached flow at highway speeds (45+), since the angle is already 15*. The roof slope might help you out a bit, though.

How much does the rear suspension compress when you throw a few hundred lbs on it? I don't know, but for each inch you compress the rear of a car with a 95" wheelbase (e.g. Insight), you change the angles by 0.6°.

[Christ]

Originally Posted by RobertSmalls

How much does the rear suspension compress when you throw a few hundred lbs on it? I don't know, but for each inch you compress the rear of a car with a 95" wheelbase (e.g. Insight), you change the angles by 0.6°.

There's something like 7" of compression from idle state, and it only takes something like 400 LBS or so to bottom out the rear suspension, IIRC.

I don't think it's the wheelbase that matters in that calculation, so much as the distance between the pivot point (front wheels) and the opposite end of the car.

The front wheels act as the fulcrum, the rear wheels are just providing resistance to movement (if you add weight to the back), so the final angle would be determined by the tail end of the car, if it makes a difference.

[COcyclist]

robert, It's good that your Kammback is clear. You can easily tuft test it with a quick look in the rearview mirror in real time, real world conditions, real driver in driver's seat. I made a coroplast prototype Kammback but couldn't see the tufts by myself and haven't had time to get back to the project.