Volvo 240 wagon - partial Kammback prototype

[brucepick]

Originally Posted by tjts1

Hey Bruce
Quick question. What kind of plastic did you use to make your airdam and more importantly where did you find it. Did you put it together with rivits, nuts and bolts. Im dreaming up an undertray for the 850. I was planning to use aluminum but that stuff is getting expensive and hard to find.
thanks for the help
Justin

I like wood. Cheap to buy and easy to work. I used approx. 1/4" plywood for the airdam and 5.4 mm. lauan plywood for the undertray. More recently I used 2.7 mm. lauan for the 'grill' panel - I like the 2.7 mm. a lot. Get lauan at Home Depot etc. 2.7 mm. is $7.xx per sheet!

Folks can joke if they want about the plywood. Even without primer protection I had no rot problems due to lots of drying airflow. However, no primer = finish paint gets wrecked fast. I used oil base house primer on the grill panel and the primer survived winter's blowing road sand and everything else. Any new wood work will get that primer. I had them mix it as dark a gray as they would go. Too much pigment = not durable. I wouldn't use latex primer. Oil base is a lot tougher. Just doing small sheets, so I use cheap foam brushes and cleanup is not an issue.

The grill's dark blue finish coat took a beating though. Black pickup bed liner paint from Duplicolor has done very well on top of the primer when I put it on the air dam and in other applications. It's tough stuff, and cheap. I'm still looking for some tough clear protective top skin. I'm sure the bed liner (comes in black only) would hold up fine on the grill but I think it looks good in dark blue.

The 1/4 inch plywood strip for the lower air dam was a bear to bend. This spring I plan to build a new one of 2.7 mm. lauan.

I got a strip of aluminum angle stock and cut it to make angle brackets. That's what attaches the undertray to the lower air dam. I used stainless screws + nuts. Rust is a PITA, stainless ain't that expensive unless you want metric.

Next time I'm considering pop rivets instead of screws + nuts. Because you have to get at the back side to hold the nut, the undertray is roughly 1/2 inch up from the air dam's lower edge (for access to the nut). Using rivets I should be able to drill thru panel + bracket and then put the rivet in. So undertray can go flush at bottom edge of lower air dam.

[tjts1]

Good info, thanks Bruce. I think I still prefer using metal or plastic but at least I know if all else fails I can rely on wood.

[diesel_john]

imho, on a blocky car, it is important that the air leaves all four sides at the rear edge of the vehicle at same time. to further define this picture, ideally the air on all four sides would have the same amount of energy, so pressures, speeds, and mass if taken all together would be equal for each surface at the back edge. simply put i wouldn't want air from say high prressure on top of the vehicle to come off the rear and plunge to a low pressure area coming from under the vehicle. so the air needs to leave the rear edge parallel to the streamlines of the vehicle. carrying this notion further fwd along the sides, the air needs to stay on the same side of the vehicle as it travels back along the car, on a square cornered car, i would put fins on the corners (they could be a on the 45) to keep the air from spilling over the sides. if the sides are angling in slightly as they come back, (11 to 15) degrees, the last couple inch should straighten out. Fins on these tapered sides have an added bonus of pressurizing the air between them slightly which causes it to speedup as it leaves. almost like squirting out the back. what do think of those wacky ideas?

[cfg83]

brucepick -

This is not as ambitious as what you want to do, but this is what I want to do :



CarloSW2

[diesel_john]

my caravan was parked yesterday facing a snow storm. i did not touch the snow. this is what the wind did. the wind was coming from the front left corner, so shows what a yaw angle would do. the two back sides are different

pics 3,4,5. are my variable grillmockup, on kitchen drawer rails.

[brucepick]

cfg83 - I had one sorta like that for a few months last summer, coroplast and duct tape. Couldn't document that mine helped but I'm sure that if its built well, it will help. Reading on the Kamm topic in wikipedia makes me think you could/should slope it down a bit steeper. The idea is to have a smaller cross section at the point where the airflow finally leaves the body. Taper it downwards a bit. Curve it down if you can, but making a curve there will probably get you a compound curve that's tough to build. Taper it in sideways too.

diesel_john - Very neat - it made its own Kamm back!

[trebuchet03]

Originally Posted by diesel_john

my caravan was parked yesterday facing a snow storm. i did not touch the snow. this is what the wind did. the wind was coming from the front left corner, so shows what a yaw angle would do. the two back sides are different

pics 3,4,5. are my variable grillmockup, on kitchen drawer rails.

Natural Selection in action

[edbso]

Originally Posted by brucepick

...What you don't see is the flat panel beneath the air dam. My added panel plus the oem belly pan together cover from the air dam to the front wheel centers. This spring I hope to add screening from there to the rear bumper.

I don't want to hijack but I am curious about the screening. Is a tight and light screening an effective way to do a full belly pan?

[brucepick]

Originally Posted by edbso

I don't want to hijack but I am curious about the screening. Is a tight and light screening an effective way to do a full belly pan?

I apologize. I'd forgotten that the screening discussion was on another board, not on EcoModders. You can see it in this link; the 5th post in the thread is where the screening discussion begins.

http://www.gassavers.org/showthread.php?t=5613
I'm interested in it but need warmer weather and to make the project a priority if I'm ever going to get around to covering Sven's underbody.

[edbso]

Thanks for the reply and the link, most interesting.
Some thoughts.
Spray with rubberized under body coating. It is inexpensive and will cover in one application. It likely will leave a "pebbled" finish which may act as the dimples on a golf ball.
They do make stainless steel screening. Stiffer and less likely to sag.
For my Matrix an actual screen frame likely will work. It will stretch, keep the screen taught and attach with fewer attachment points. Just might be easily removable to.

I also wonder if is necessary to cover the holes.
Thanks again.