taps mic is this thing on?
Hello! Long time no see. Sorry about the extended absence... I intended to cover the 2019 World Solar Challenge the way I did in 2015 and 2017, but life got in the way. This year I'm headed back to outback... Even though I haven't been blogging in the lead up to the race, I wanted to get some thoughts down before the start.
So for starters: What are the significant changes to the regs since 2019?
1) Ground clearance/approach angles/etc. WSC continues to try to force teams to drive their cars on and off the highway and the start/end of the race day, rather getting lifted onto the highway and sitting stationary in the lane at the start of the day and parking on the highway to get lifted off to the shoulder at the end. Rather than just stating that "cars must be able to drive off a 50mm vertical drop" as in 2019, now we have a minimum 100mm ground clearance, minimum approach and departure angles, a minimum hump that cars must be able to drive over without high-centering, etc.
2) Wheel count. For the first time since 2011, WSC is allowing three-wheeled Challenger class cars (Cruisers still need 4 wheels). On the one hand, all the cars that I ever worked on were three-wheelers and I was disappointed when WSC started to require four wheels in 2013. On the other hand, given how many off-road excursions happened in 2019, I was very surprised to see this change... it's only going to make the modern skinny monohulls even less stable. WSC *has* added a static stability requirement - cars must be able to be tilted 45 degrees across any two adjacent tire contact patches - but I haven't seen any evidence of a tilt table at scrutineering...
3) No more gallium arrays; allowed solar collectors sizes are only called out for Silicon (unchanged at 4sqm). If a team want to propose using something different, "the materials should have low environmental toxicity; this precludes the use of GaAs, CdTe and CuInSe2".
4) Here's an interesting one: For the first time (as far as I can tell), WSC is requiring cars to have automatic battery protection systems, not just battery monitoring systems - peep the language changes in reg 2.5.9. I'm assuming Nuna 10 burning down on the finish line in 2019 might have had something to do with this? I guess it's one thing when non-competitive teams burned down outside of Darwin every other race, but a star team burning down in front of news vans outside Adelaide was different matter.
5) License Plate. No more shenanigans with it being inside the canopy and hard to see, NOTHING can be aft of the license plate within a defined cone. I was interested to see if any teams tried shenanigans here, never underestimate a determined aerodynamicist! But the rule is extremely clear and so far I haven't seen anything questionable. Most teams have a very clear location to mount the plate, as seen for example on the back of Twente's car below:
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| Photo: Ⓒ Solar Team Twente (image source) |
6) Occupant Space. This is the first year that WSC will be using a test fixture that they call "PVC Pat" to inspect the size of the interior.
7) Rear steer: forbidden this year. No using a rear steering system that only operates at extreme steering lock to meet the U-turn reg, no rear steering system to "crab" the car into crosswinds and reduce aerodynamic drag. I'm told that this is in a bid to reduce car speeds - apparently several teams were sailing VERY effectively in 2019. But notably movable aerodynamic devices are not banned...
8) 3.24.6: "If a solar car rolls onto its side or roof then the team must withdraw immediately." It'll be interesting to see how this reg intersects with the three-wheel reg potentially reducing the stability of the cars. Twente apparently already put the car on its side during pre-race testing.
OK regs talk over, let's talk about cars.
The main way these regs seem to be influencing the teams is: More monohull/bullet cars: fully 3/4 of the Challenger entries this year are monohulls. The modern monohull trend started in 2017: that was the first year of the 4sqm array formula, and we saw highly competitive monohulls finish in 2nd and 4th place overall. This result apparently inspired teams - about half the field was in monohulls in 2019, and the vast majority of the "good" teams were, with 7 out of the top 8 finishers being monohulls. But! Until Twente wrecked out and Vattenfall (formerly Nuon, now Brunel) burned down, the three fastest cars were all catamarans, and the overall winner was a catamaran from Agoria. Given that result, why are teams committing further to the monohull concept (including the winning team from 2019)? I think it's mostly down to the 3-wheel rule.
One of the major disadvantages of the 2017/19 4-wheel monohulls over their catamaran counterparts is that the wider monohull has a much larger surface area close to the road - the entire region bounded between the wheels is basically flat against the ground, in relatively dirty airflow. The body also has to stay wide all the way to the rear wheels and can only start to aerodynamically close behind them. The skinny catamaran pontoons can be much shorter front-to-back, minimizing the parts of the car that are down low. But with only three wheels, a monohull's body can start to sweep inward and upward immediately aft of the front pair of wheels, reducing the area of the car that has to be near the ground. Clearly teams think that this is a big enough change to tip the balance in favor of monohulls... Both Twente and Innoptus (formely Agoria, the 2019 winner) have switched from catamarans to monohulls for 2023.
The big outlier is Brunel (formerly Vattenfall, formerly Nuon): Nuna 12 is a three-wheeled "outrigger" catamaran. It has the driver against one side of the car with a wheel fore and aft of the driver as on previous four-wheel cars, but only a single wheel centrally located on the side opposite the driver.
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| Photo: Ⓒ Brunel Solar Team (image source) |
I am genuinely excited about this car, I feel like the sport has been waiting for this design for over a decade. Nuon themselves thought about the idea when the change from laydown cars to upright seating happened with the WSC 2007 regs, you can see an outrigger catamaran concept peeking out in the back of this photo (they ended up choosing the middle concept, setting the tone for the 2007/09/11 generation of cars):
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| Photo: Ⓒ Brunel Solar Team (image source) |
And prior to the mid-2012 regs release mandating 4-wheel cars, I was seriously proposing to my old team that they field a design like this for WSC 2013 - and I know that I wasn't the only person doing do!
Of course, the same can be said for Twente and Innoptus - they clearly believe in monohulls now, despite being at the top of the field in 2019 with catamarans. That Moroccan race in 2021 that Brunel finished in 3rd with their first outrigger catamaran? Twente won that race with their first monohull car, and Innoptus came in second with their first monohull. Both of those teams have brought new second-generation monohulls to WSC this year as well.
It's going to be a really fascinating race between these teams this year. We also can't forget Michigan, one of the originators of the modern monohull concept back in 2017 and bringing another good looking monohull. Similar to the teams above, Michigan hasn't been resting over the WSC pandemic break - they also built a non-WSC car over the pandemic (although it didn't race anywhere), so the team has worked to keep their skills fresh.
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| Photo: Ⓒ University of Michigan Solar Car Team (image source) |
Worth noting, since you're going to see it on a lot of the monohulls - see the raised nose? It's a very distinctive change from previous monohull designs, and one that is featured on a LOT of the cars this year. I was puzzling over why - maybe there's an aerodynamic reason, but how did every team land on the same aerodynamic feature at the same time? - but then I realized that this is a consequence of the 10° approach angle rule!
This post is getting longer than I planned, so very briefly: All the other teams from the top grouping in 2019 - Tokai, Top Dutch, Sonnenwagen, Kogakuin - are back, with monohulls. Kogakuin of course has some very interesting suspension concepts that I will hopefully be able to get pictures and post about. NITech and Antakari were unable to make it, but Blue Sky, Eclipse, and JU are all back as well. Notably Eclipse is the only WSC 2019 finisher that's coming back with a catamaran, and JU is bringing the only monohull that doesn't have the driver canopy protruding over the solar array. WSU is also back with a monohull - hopefully they won't have a repeat of their very rough 2019 race.
On the Cruiser side of the competition, the big news is that neither Endhoven nor Bochum are attending this year! Eindhoven won all four previous Cruiser classes 2013-2019, and Bochum has historically been a strong competitor. Without the two of them, Minnesota, Sunswift, and Sophie are likely the three strongest competitors in the class this year, although I'm also keeping my eyes on Apollo. There's also a very interesting rule that the teams must upload telemetry about solar energy collected and energy used from the battery at each of the control stops, I'm very curious to see what that data looks like.
OK - time to stop typing. See ya later, folks.
Good to have you back! Looking forward to excellent updates and discussions about the event.
ReplyDeleteNice to read and great that you are back with your sharp, highly detailed analysis of the WSC!
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