8/10/21 The styling work continues. It was interesting and educational to see the reactions to the earlier version. Naturally people try to associate new things with something they already know. A lot of references were made to the Enzo from the front and the NSX from the back. Below is the actual comparison:

The reference are understandable, and have reminded me that there are some things people find distinctive about various designs. I suppose that's the whole idea behind 'design language' - associating certain shapes with a brand identity. Not that these are bad cars to be associated with in any way, but my goal is to have the D8 stand on its own and be tied to my previous cars more than anything else.

Here is the latest - not final, but getting there.

These are the previous cars to which I want to maintain visual links (without being too constrained by them):

Of course the design has to work in real world, which dictates some compromises. This evolution very much takes that into account. The aero is now where I want it to be, at over 600 lb downforce @100 mph, with 2.2:1 L/D.

The dimensions of the car are rather compact (because I like compact cars, and because it's intended to be able to take a GT40 body if desired). Here is a size comparison with the latest Corvette.

The packaging is challenging, so occasional reality checks are a healthy thing. The goal is to accommodate people over 6'3". The modern racecar raised-feet driving position provides the most flexibility as the back can be arched and knees bent without undue discomfort.

Some quick measurements using a standard seat tilted back confirm that this will work. Note the space behind the shoulders. Obviously we'll have to create custom seats for the car, but we know how to do that.

Progress is happening every day. More updates soon.

9/6/21 I mentioned some of the D8 work in a recent D9 post, a few more updates here.

Even though I said earlier the current round of CFD was done, I can't help but come up with more questions. And the answers being readily available, it's only natural to do a few more runs and be better informed.

One example is what happens at higher rideheight. Most of the simulations so far have been run at 55mm rideheight. It's very usable on a racetrack, and even tolerable on the street with some care. But this being intended as a streetable car, I had to find out what happens at 80mm and 108mm. Not bad, actually.

At 80mm the downforce drops to 569 lbs and drag goes up to 314 lbs. At 108mm the downforce is 490 lbs and drag 334lbs. Front/rear balance is almost unchanged, closely matching the 40/60 weight distribution. I'm very happy with that.

There are three main reasons why it works so well at higher rideheights: the wing(flap)/diffuser architecture, airskirts, and the fact that the nose is shaped to supply enough air to underbody even at 108mm. This was all conceptual when I got started, but the simulations (and the related real-life testing on D2 and D4) confirm I'm on the right track.

For those interested, the following four images show the different underbody airflow components. In order, center section, tunnels/diffusers, side area between wheels, and airskirt.

The flow is very 3D so I've made the body transparent to show what it's doing. The wing/flap gets all its air topside, but interacts very strongly with underbody flow.

The front diveplanes and rear spoiler ends contribute their share as well.

When you combine all of this, you get this rather complex but fun (to me, at least) image:

The iso surfaces are by velocity and show the boundaries between regions of various airflow velocities. This is relative to the car, not ground. As I've mentioned in earlier posts, this way of looking at it is computationally convenient, but one should bear in mind that when we see air at 0 mph, this really means the car is dragging it along at 100 mph relative to the ground.

So the air is sitting there, minding its business. Along comes a 100 mph car and takes some of it for a ride. What's more, air with higher velocity than 100 mph in the simulations (all the red stuff) is actually made by the approaching car to go in the opposite direction of car travel.

This is a key thing to understand and get one's mind around. How do you get air to do that? Hurl a car at it at 100 mph and get the previously still air to dive under the car in the opposite direction? Managing pressure gradients is the simple answer, but as the images above show it's far from simple in practice.

Here are a few more iso surfaces that may be informative to some. They are at 50, 30, 15 and 5 mph (relative to car of course).

The patterns are rather unique because of the unique configuration of the car. This is not something you would normally see, and is kind of where the magic is. A while back I was debating whether to try patenting any of this, and ended up deciding not to for various reasons. So might as well make it public for all to use. Reference the source if you do :)

10/1/21 The styling is getting there. Only tweaks left now are to the parting lines and any mold construction related adjustments. Quite happy with it overall. It's been a process, including much aero and packaging work (see earlier posts). Lots learned in the process, so that is good in itself.

Now that the bodywork envelope has been defined, anothe iteration of frame and aero packaging, then actual parts can get made. Fun. :)

11/12/21 Most of this post is about additional info learned - I strive to learn as many things as I can every day. Today was a good day. But there is some of putting the learning to use, too.

I came across a post about Williams F1 team inadvertently releasing 3D model of their car in a phone app, and some clever people extracting the info and running CFD on it. Naturally I had to follow up on that.

I've always been curious about how effective the hugely complicated F1 aero is. And, I'm always looking for reality checks on my own work.

In this case I just got the front wing and nose - an admittedly limited experiment, but one that can answer many questions. Getting it into SolidWorks was a bit of an exercise and I learned some stuff just from that. With some help, I was successful.

Next came the initial runs, just using default settings, and knowing it will be 'off'.

The initial mesh is about 500K cells, very coarse. It basically disregards the slot gap flow and ends up treating the wing as a single element, effectively. The results are consistent with what you'd expect for a single element wing of this size - at 50 m/s (112 mph), it reports 174 lb downforce and 77 lb drag. It took 4 minutes to run on a 16-core PC.

The feedback from my collaborator is that it's 'low' on downforce. So I enabled the mesh refining and tweaked some other settings. The resultant mesh (over 8M cells, second image) is below, compared to non-refined (first image).

The simulation now produces very different results. Compare the pressure distributions and flow lines with the earlier image.

So it turns out, the fancy F1 geometry IS extremely effective. How effective? The new simulation reports 428 lb downforce and 84 lb drag. This is compared to 420 lb downforce and 62 lb drag reported by a much more sophisticated, weeks-long effort in STAR-CCM+. Mine took 1.5 hours.

The key thing is that both the initial pass and the refinements were 'run in SolidWorks'. Same computer, same data, same tools. Just a matter of figuring out how to use it. The result is dramatically different. It is the carpenter, not the hammer. But a power hammer makes a skilled carpenter much more productive.

Below are some images that have been very educational to me, hope they are to you. The level of refinement of the design is truly impressive. Obviously the rest of the car is not present and would affect things significantly, but there is much to be learned even without that if you're willing.

All this mostly refines my understanding of aero and gives an addtional reality check on the tools I'm using. Confidence added.

In the meantime, the detail work on bodywork, chassis, ModBatt battery modules, and everything else is ongoing. Even managed to get 7th ModBatt patent ready for filing. Next 4 already planned.

11/24/21 In the final stretches of chassis and bodywork design. Of course everything is connected to everything else. ModBatt module design updates change packaging opportunities, which in turn change chassis, which allows better aero, and so on.

The chassis for the electric version is nearly final. Will need lots of brackets and detail stuff, but getting close to having tubes ready to order. The whole thing weighs 235 lbs according to SolidWorks, so about 250 when all said and done. Main roll strucutre is 1.75" OD, 0.095" wall chromoly tube. The rest is a mix of 1.5" OD and 1.0" OD, 0.065" wall.

The battery pack is 60KWh, 800V nominal, 600KW continuous / ~800KW peak. 20 ModBatt modules.

The following pix show the relationships of the major components.

One of the many challenges is ergonomics. I am chopping 6" off D2's height (46" to 40") and reducing the wheelbase by 9" (104" to 95"). Also providing room for airskirt and tunnels, neither of which the D2 had. And still accommodating drivers over 6'4". Impossible? No, just challenging. The difference between D2 and D8 can be seen in the following image:

The D2 was designed as a street car primarily. So it's actually quite 'tall', relatively speaking, and the driver position is relatively upright. The D8 is more hardcore. Still, the driver has to be effectively connected to the car if he/she is to control it. The modern feet-raised position is key. All that said, reality check is in order.

With the seat removed and a 4" block to raise my heels next to the pedals - this works! Oddly, even without a seat it's not uncomfortable. I'm 5'11" but the pedals are adjusted 2" in, and plenty of room to bend knees. Gives good reference for lines of sight, control positions and such. It's good to not be starting from zero.

There is of course another level of complicaton - as some may recall, this is primarily an electric platform but with options for gas and hybrid configurations as well. So I had to test that out. Many of the tubes will need to be different aft of the firewall. But it all fits, and since each car is built to order anyway, we can do this.

The engine is LT1 e-rod, and transmission is Sadev SL-90. It works.

Now, the next steps. Detailed CAD for the bodywork mold patterns, brackets, bolts, linkages, hinges, and so on. It's amazing how complex a car is. A 20-dimensional puzzle. That is what makes it so satisfying to solve.

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