Project: making a permanent Metro Kammback extension

[akcapeco]

This progress is really fun to watch.

[Katana]

Only just noticed this thread, the end look and aero results will be interesting to see, keep up the work!

Looking at that Mercedes bionic concept car, why did they base it on a fish, fish are hydrodynamic not aerodynamic. A dolphin although a water based animal seems to have that teardrop shape body that work for aerodynamics, should have used it as a template.

[lunarhighway]

@Katana

i think they mainly chose the boxfish, as it combines a boxy shape with a good drag quoefficient, and it's relative dimentions are similar to those of an mpv.

some of the most practical of todays cars, combine a big interior space with very modest exterior dimentions to aid parking etc. they achieve this by a raised roofline, so the seating position can be more upright and less legroom is required. computer designed engine bays vertually eliminate the need for a big nose section wich further enhances the boxy dimentions of those cars.

big luxury cars are often long and slender, and today, have also very good drag quoefficients. wich is easier to achieve as their relative dimentions are more akin to low drag shapes like the dolphin. also sportscars are more slender and potentionally aerodynamic, however fuel economy is not what these cars are bought for.

personally i think the only way to create a practical low drag car is to go for a trike layout with a single rear wheel, as this would allow for a massive boat tail, treardrop shape potential, without any substantial practicality problems. a well set up suspention combined with electronic traction and stability aids wich have become fairly common would eliminate any potential negative handling characteristics.... however this would require a lot of RND wich would eat away proffit... while virtually any car from the 20's till today would accept a "boxfish" bodywork

[akcapeco]

Originally Posted by lunarhighway

@Katana

personally i think the only way to create a practical low drag car is to go for a trike layout with a single rear wheel, as this would allow for a massive boat tail, treardrop shape potential, without any substantial practicality problems.

In the earlier pages of this thread, there is a terrific overview, albeit informal, of the history of automotive aerodynamic shapes, including Benz Bionic, and the Fuller Dymaxion (above)

[Tourigjm]

Originally Posted by Katana

Looking at that Mercedes bionic concept car, why did they base it on a fish, fish are hydrodynamic not aerodynamic.

funny thing about fluids, they all flow the same, some are just a little thicker than others

all fluid flow can be calculated using the navier-stokes equations... solving those equations is a totally different animal though

[riddleyo]

This project is amazing. I can't wait to see it gloss black and an A-B-A-B test!

[MetroMPG]

Hmm, will you settle for semi-gloss black? That appears to be about the best I'm going to achieve from a spray can, never mind what the label says.

The A-B-A has already been done on the first kardboard prototype - 2.3% fuel economy improvement @ 55 mph. I expect this version would perform better (longer, rounded shoulders, slightly steeper angle while retaining attached flow), but I'm not promising to A-B-A it any time soon. Lots of other projects competing for time.

Originally Posted by KJSatz

When you next take pictures with it mounted, would you mind getting one of the whole car from maybe 4:30 o'clock (12:00 being straight ahead)? I'm interested in what it looks like in the whole body's context.

One more sand & coat of black, then I'm calling it finished. Unfortunately, something reacted to the paint on this (2nd) coat, and a couple of spots bubbled/cracked. Painting a big surface like this is maddening. Wish I had a proper compressor/gun setup.

[riddleyo]

Originally Posted by MetroMPG

Hmm, will you settle for semi-gloss black?

Looks good so far!

Originally Posted by MetroMPG

Unfortunately, something reacted to the paint on this (2nd) coat, and a couple of spots bubbled/cracked

Hmm, how did you go about painting it? Did you wash the surface with soapy water and tack cloth it? Did you wetsand between coats? Spray any clearcoat on to protect it from UV rays/chipping?

Nice work though!

[Daox]

Looks very nice.

[KJSatz]

That's pretty BA!