I read that the fish itself had a Cd of .04. The fish also had a skin texture that resembled a series of 3-pointed stars like the Mercedes logo, but they decided not to use that on the car.
Yes, I read that, too! Their computer model of the fish is 0.06, and the clay model with covered wheels is 0.095. I think I may have to try and make a basswood model of that, and may even start my CarBŒN model over... I like the looks of the clay model (lots of hard chines!) but it looks like it has ground clearance problems.
Here's the latest drawing of the CarBŒN Concept EV Mk 2.7 -- notice the rear seats are mirrored from the previous layout, so that more weight is away from the rougher edge of the road...
Here's an overlay of the CarBŒN Mk 2.6 with the (flipped) side view of the Mercedes Bionic/Boxfish model. The front wheels are aligned, and scale of the B/B model is just by eye to match the overall size:
The differences are that the front of the B/B is shorter, and the front wheels are closer to the front. The arch of the roof on the B/B is slightly farther back, and it's wheelbase is slightly longer.
The windshield on the B/B is steeper than the CarBŒN, as well. Look how closely the undersides line up! The departure angles are very close, as well (save that "flip" on the back of the B/B).
I hear you anticipate a drag coefficient around 0.095 and a drag area of 2.5ft² for CarBEN.
Earlier I posted:
Quote:
Originally Posted by RobertSmalls
The M-B Bionic concept illustrates that a blunt front is okay, but a low drag car needs to have a very small rear. That explains a large part of the difference between the Cd=0.095 clay model and the Cd=0.20 concept car, which had a relatively large rear. The rest may be due to adding door handles, wipers, ground clearance, and panel gaps. CarBEN's rear is much larger than that of the clay model. As a percentage of frontal area, it's somewhere between that of the Cd=0.25 Insight and the Cd=0.188 EV1.
I'd like to hear your thoughts on how much drag CarBEN's vortical wake will contribute, and how you can reduce the size of that wake.
Are you interested in looking for ways to reduce your frontal area? I see room to slice a foot out of the middle of the car in plan view, and the middle foot of CarBEN is by far the draggiest foot.
I'd appreciate it if you'd spell out your project goals (low cost, min Wh/mi, seats five, fun/awesome to drive, impressive to look at, fun to design and build, etc.), to make it possible for others to contribute to this open source project, or at least to better understand it.
If you have a .DXF solid model of the latest version, I'd like a copy.
You are correct that one of the biggest reason for the "final" Bionic car having a Cd 0.19 is the larger rear/lack of major taper; but it is not the only thing. The wheel openings, the engine cooling, the higher stagnant point, and probably a less complete belly pan also contributed to the increase.
The current frontal area of the CarBŒN is a bit under 25 sq. ft. and the current trailing face is under 10 sq. ft.
My goals are many: I want CarBŒN to be an open source project, and I have shared the model and drawings with at least 5 people so far. This is important -- I do not want the process of designing an uber-efficient car to be locked up, and if I am not able to ever build it, and/or I fail to "commercialize" it, I don't want the effort already invested to go to waste. If others want to build/produce it, then great! As long as they contribute back what they have learned/fixed/designed, then that is the biggest thing I hope to accomplish.
I want to be in the same ballpark as where we anticipate the Edison2 VLCe will be: they are estimating their weight with a ~15kWh pack to be ~1,200-1,300 pounds. I think that they could be even lower than that, since their 4 seat VLC is just over 700 pounds with the ~100 pound Yamaha engine. Trade that 100 pounds for the electric motor and gearbox, and then add the battery pack, and they could be as low as 1,000 pounds with a small 12-16kWh pack.
I hope to (eventually) have a big battery pack in CarBŒN -- in the same league as the Illuminati Seven, with it's 52kWh pack (which is the same as the Tesla, as well). I'm hoping to find out from them how much their pack weighs and how big it is. I have also asked FVT for the dimensions and weight of their EiG batteries; which are prismatic, and as such have a much better chance of fitting in the floor of the CarBŒN as I've shown in the latest drawing.
As far as the frontal area goes, that is a complicated question. As you may have noticed, the frontal area of the CarBŒN (and the Mercedes B/B car) are roughly square-ish. This provides a larger volume, and therefore a more usable interior volume, for the same frontal area.
Stated another way, if I lower the roof and widen the car, and end up with the same ~25 sq ft frontal area, then interior of the car would be far smaller, and much less useful, and there is probably no way to get 5 people seated in there; let alone as comfortably as I think the current CarBŒN design does.
If I am going to build the CarBŒN myself, without any/much sponsorship then it has to be fairly low cost. I know that the Illuminati Seven cost ~$120,000 to build, and I think that about $15,000 of that was for the battery pack. I certainly hope it will be much lower cost, because I certainly cannot afford $120K. Sweat equity is where it's at!
I do need to rewrite/update my blog entry on the CarBŒN, but please refer to it for additional details, about why I am planning on the articulated wheel skirts, the rear entry hatch/doors, the surrounding safety structure, the slim and light and cool mesh seats, the video mirrors, the position of the battery pack and drive motor(s), the air ventilation intake and exhaust, the structural and insulation considerations... the list of design considerations is very long:
I need to establish a place to start building the chassis -- my 1 car garage is full of *stuff* and it needs repairs and upgrades. My neighbor who is a cabinet and furniture maker has a quite large bandsaw -- that is not currently working. I either need to help him fix it, ot buy my own (used) bandsaw. I think it is inevitable that I will cut the male ribs to form the outside shell, and these will also have the female interior cabin walls at the same time. The first CarBŒN will have those plywood ribs largely left in place in the finished car; I don't really think I can take on making "production" molds first...
Here are images of the CarBŒN Concept EV Mk 3.0; showing a heavily revised front end, with hard chined fenders, a lower stagnant point, revised sides with the windows right behind the 'A' pillars more convex, "swoopier" lines, etc.
That looks like a lower-drag body for sure, assuming flow remains attached across its entire length. How did you bring the sides in, and what was holding them out in the previous design?
Transom area as a % of frontal area looks much improved. Do you have numbers on this?
The sides have been tapered about the same amount all along -- the rear track is ~3 1/2" narrower on each side, than the front. The extra convex on the side windows is done by not tapering it in as quickly.
The frontal area is ~25 sq. ft. and the rear transom is a little under 10 sq. ft.
My hunch about the new nose is that the (apparently) lower stagnant point can help, and if the fenders are going to help wedge the air around the front wheels, then it could help. But, it might add some separation on the sides, and if it is problematic, I'll revert to something like I had before. *Hopefully* I can figure out how to get some CFD done!?
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I either need to help him fix it, ot buy my own (used) bandsaw. I think it is inevitable that I will cut the male ribs to form the outside shell, and these will also have the female interior cabin walls at the same time. The first CarBŒN will have those plywood ribs largely left in place in the finished car; I don't really think I can take on making "production" molds first...
