08/28/21 Everything I do is connected, in countless ways. So while there may seem to be little direct work on the D9 recently, the things happening with D8 and other cars are advancing this project as well.

One of those things is the aero work. I've already posted quite a bit of it on the D8 blog - the airskirt, the wing as a flap and its interaction with the spoiler, and so on. The D9 will use all of these concepts.

Couple days ago we did another of our ORP test days, this time outfitting Valerie's D4 with a spoiler to see the effect it has. The results were impressive - a little bit of carbon enabled her to go from a personal best of 1:58 to a 1:51 in just two sessions. Neil drove the car as well and confirmed the difference.

Of course the spoiler by itself is not all that significant - it's the effect it has on the rest of the systems, and in particular the underbody, that makes all the difference. It was interesting to see the difference in the dust being kicked up by the D4 vs the D1 that doesn't have a spoiler yet, even though the wings and underbody are the same. Yes, the D1 will get a spoiler next.

It's always fun to be out at ORP - this time I camped in the van overnight and did a few laps on the bike in each direction at the start of the day (I keep the bike in our garage at the track). Having the track literally to myself, in perfect weather, is living the dream. Didn't take video this time, but here is one from another of our days a couple weeks ago. Tough work, but someone's gotta do it.

The physical testing serves to validate all the SolidWorks CFD I've been doing - literally hundreds of runs.

Another way of validating is comparing simulations with other cars in the same setup, and same car in other setups. As a result of a discussion on a FB aerodynamics group, I downloaded the aero model for the Reynard Inverter and ran it on the same setup as a comparison. The Inverter is somewhat smaller than the D8 and runs at 35mm rideheight vs 55mm for the D8 in lowest setting.

A couple people on the group also ran the Inverter in Open Foam CFD. Learned quite a few things from all this. Found a small glitch in my setup and another in the spreadsheet I am using to post-process the results. Fixed both. Interestingly, despite the higher rideheight the D8 gets virtually the same downforce numbers as the Inverter (a bit over 620 lbs at 100 mph), albeit with higher drag (290 lbs vs 240) which is to be expected if you look at the overlaid comparison. The airskirt is a big reason why, but of course it works with the diffuser, the spoiler, the wing and all that.

I was also (and again) impressed with how effective SolidWorks is as a development tool, when you have it set up right. The adaptive meshing and the fast, usable results that correlate well with real world enable rapid iterations. This in turn enables evaluating many radical what-if scenarios and figuring out what does what. Where a 'lightweight' model like the Inverter takes about 15 minutes for a full run in SolidWorks on a single-CPU Ryzen, the same model in Open Foam takes a couple days on a dual-20-core-CPU machine. The numbers end up being very similar, with SolidWorks being less optimistic than Open Foam and showing more turbulent flow. Based on my real-world correlation, I think SoliWorks is the more accurate setup. Amusingly, some on the group claim the flow in my simulations is 'idealized', while refusing to post images of what non-idealized flow should look like. Human nature never ceases to fascinate me.

As a further reality check I asked Arron, a friend who is in charge of aerodynamics at one of the major F1 teams, to look it over. He had some good suggestions which I'm implementing now and already seeing incremental gains.

So I'm pretty excited about applying all of this to the D9. For now, the D8 continues to be the immediate focus. But a few D9 specific things are getting done as well. The drivetrain uses the Cascadia integrated motor/inverter unit and the same chain drive AWD system that is used in the D1 and D4. This requires a reduction unit that can handle 500 lb-ft of torque at 12K RPM input speed, while being light and compact. Naturally such a thing does not exist, so I have to design it and have it made. The design is almost complete now, just need to finish up the details and start cutting metal.

And all the while, great progress is happening with the ModBatt modular batteries that will power both the D8 and D9. Yes, everything is connected. More on all fronts soon.

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