Volvo 240 wagon - partial Kammback prototype

[MetroMPG]

Originally Posted by edbso

It likely will leave a "pebbled" finish which may act as the dimples on a golf ball.

Just jumping in to dispel this oft-repeated myth. Golf ball-type dimpling of automotive body surfaces has no useful aerodynamic effect (other than to perpetuate the myth).

[brucepick]

Apparently the screening helps without painting to seal up the holes. However I plan to paint except near the exhaust if I do screen it. I found some white latex or acrylic primer made for aluminum/galvanized that worked very well on stainless; I'll try that first if I do screen it.

Frame is a neat idea. Build to fit between side skirts (another future project). Pop it in, pop it out.

[metroschultz]

I may be a bit late on this.
BUT.
The snow seems to have formed the perfect mold for your Kamback.
Just add fiberglass cloth over the snow and cover with resin.
How easy would that be?
You might need to mist it with water and let it freeze solid first.
Just a thought.
S.

[diesel_john]

And it even showed the difference in designing for a cross wind.

After seeing that,
i was trying figure out how to duplicate nature, with sawdust or sand or something and then just drive it to let the air design it for me.

[aerohead]

Sorry,I'm away from my resource materials,however,I don't remember that Hucho's book actually had a formula for that design.I believe it was merely a windtunnel excercise to investigate how far you could cheat on a boattail (get around someone elses' patent) and still realize some aerodynamic benefit.The flow immediately separates from the trailer then reattaches on the box,with locked-vortices captured in between.The surrounding flow is supposed to flow over the vortices as though they were solid surfaces,and then separate from the box into a wake that is somewhat sculpted into a form better approximating Mair's 22-degree boattail.Being flat surfaces,I suspect that in full-scale,such panels would be inherently weak structurally,and would have to be reinforced (added weight )to achieve the integrity of the more natural compound form they are trying to mimic.Good thing these people don't design rectal suppositories!

[brucepick]

Originally Posted by aerohead

...then separate from the box into a wake that is somewhat sculpted into a form better approximating Mair's 22-degree boattail...

Can someone elaborate on the 22-degree boattail? I should know about it but I don't. I've read of 12 and 15 degrees as recommended max angles of change. Can you have an angle of 22 degrees and still keep flow attached at highway speeds?

[roflwaffle]

Izat yer place diesel john?

[diesel_john]

I found info on this offset plate test. Reseached by Hucho[1987] in the late 1970's. Full scale test's in 1988 at Nasa's Ames Research.[Lanser et. al 1991].

The results showed that the highest drag reduction came with a plate of 0.36w and inset of 0.06w, where w is the width of the trailer. For a full sized enclosed semi-trailer this translates to a plate length of 33 inches inset at approx. 7 inches form each edge. For this configuration the researches recorded an overall drag reduction of approx. 10% over a +/- 15 degress yaw range.

interestingly the tangent of 0.06/ 0.36 = 9 1/2 degrees. vs. the 10 to 12 degrees often quoted for the smooth boatail.

[diesel_john]

Originally Posted by brucepick

Can someone elaborate on the 22-degree boattail? I should know about it but I don't. I've read of 12 and 15 degrees as recommended max angles of change. Can you have an angle of 22 degrees and still keep flow attached at highway speeds?

I think 22 degrees would be both sides 11 and 11.