Are the boxy Tesla Cybertruck’s aerodynamics any good? An engineer found out

November 25, 2019

Tesla’s Cybertruck made quite a splash last week with its unconventional design, which raised a lot of interesting engineering questions. Among these was the question of aerodynamics. If the rest of Tesla’s vehicles use nice smooth curves to gain an aerodynamically efficient form, how does the Cybertruck move with all those hard angles?

Turns out an aerospace engineer had the same question and ran the Cybertruck through CFD software (computational fluid dynamics, a computer version of a wind tunnel) to find out whether the truck drives like a brick — or only looks like one.

Aerospace engineer Justin Martin built a model of the truck from every angle he could see in photos and video of the event. Martin says he researched photos and videos from all angles for around 24 hours before running the simulation. While not everything is perfect, the general body shape of the car is as close as he could get it.

He declined to share a Cd (coefficient of drag) number because his assumptions with the wheels and fenders could affect the result significantly, such that his results were likely conservative. Cd numbers have gotten more popular lately as a rough measure of how efficient a car is (though they don’t mean everything — cross-sectional area is also important).

Martin sent us the results of his Cybertruck aerodynamic study, which you can see below:

The results look promising, as one of the open questions was whether the truck’s hard lines would cause airflow to become separated from its surfaces.

In aerodynamics, it’s important to maintain smooth airflow along a surface. If that airflow breaks from the surface and causes turbulence, this creates drag.

The worry was that the top edge of the Tesla Cybertruck would cause a turbulent vortex over the entirety of the bed area, which is what happens in a normal pickup truck. There are some CFD photos of an F150 in this blog post, which show that turbulent area behind the cab.

But it turns out that Cybertruck’s “vault” works quite well to maintain an attached flow over the top of the car. There’s a bit of a rough point at the very peak of the truck, where airflow reaches 88 mph at a vehicle speed of 65 mph. This does result in some detached airflow (the yellow line behind the truck), but that mostly comes from A-pillar edges where the air blows off the massive windshield:

So our pain points are basically all of the edges of the massive flat windshield and the big front bumper (which is likely required to meet pedestrian safety regulations). Martin thinks the vortex coming from the A-pillars helps to push the air from the peak back down to the vault and reattach the flow.

There is also a huge area of turbulence behind the closed truck bed, but most vehicles do have some amount of drag there, especially trucks. The ideal aerodynamic shape would be a perfect teardrop with a very pointy rear end, but this is not practical (or legal, for safety reasons).

Finally, the fenders/wheels are also an open question, as Martin wasn’t able to model them accurately with the information he had.

Though there are limitations to Martin’s model here, it’s a good rough first guess. And as far as this guess goes, the truck seems to have better aero than initial visual impressions might have suggested.

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