With extreme effort, Cybertruck might hit a 0.30 drag coefficient

The introduction of Tesla Cybertruck was a sensation, and this caused a lot of interesting technical questions, including the issue of aerodynamics.

Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case. For some classes of racing vehicles, it may also be important to produce downforce to improve traction and thus cornering abilities. Aerodynamics is extremely important to get past that limiting barrier that you go through all the time on the highway.

Automotive aerodynamics is studied using both computer modelling and wind tunnel testing. 

An airfoil-shaped body moving through a fluid produces an aerodynamic force. The component of this force perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag. Subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with a symmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the working fluid are called hydrofoils.
Let us now see how Cybertruck fits this.

Image from video Design Prototype Test /YouTube

Despite its angular shape, it fits perfectly into the airfoil. So the facts suggest that the Cybertruck will be really energy efficient. What can not be said for trucks that have a design similar to the Ford F-150. Let's get a look.

Image from video Design Prototype Test/YouTube

So, we see inconsistencies between the airfoil and the Ford. The front end does not look aerodynamic, and in general the entire truck does not correspond to a graceful curve. Also pay attention to the protruding rear edge of the cab, this is a key point. Indeed, behind this protruding element, during movement, a huge vortex appears, and it spins right behind the truck. This is extremely inefficient. You just spend a lot of fuel to push this truck on the road.

Image: Valentin/xplrcreate

Justin Martin, an aerospace engineer using CFD software (computational fluid dynamics, a computer version of a wind tunnel), tested the aerodynamics of Cybertruck.

Martin spent about 24 hours studying the exterior of Cybertruck using photos and videos, after which he built a truck model and tested it using a CFD simulation.

Source: Justin Martin/Instagram

Judging by the test the Cybertruck's vault works well and maintains an attached flow as it passes over the top of the car. A little rough point can be seen at the top of the car where airflow goes up to 88 mph when the car is doing 65 mph. Perhaps this Easter egg from Elon Musk?

Back to the Future fans will recognize the 88mph from the movie as the speed needed to activate the flux capacitor and time travel. In reality, a DeLorean’s speedometer only goes up to 85mph, which may have perplexed a couple of people in the 80’s when Back to the Future was first released to theaters. By choosing a number higher than 85, however, the movie’s creators hinted that Doc’s DeLorean was particular and that he could have altered it for time travel.

Image: nofilmschool

So, the yellow line at the back of the car shows that this leads to a detached airflow, but most of that is due to the air blowing off of the truck's huge windshield.

Almost everything sheds a vortex, as Martin pointed out to us, however, he found it interesting how it does so over the bedsides of the Cybertruck. His belief is that it perhaps helps to reattach airflow after the peak.

The biggest point of turbulence is at the back of the truck, behind the closed truck bed. This is quite normal in most trucks, though.

Also, due to the lack of information, Martin was unable to account for fenders and wheels, and that remained a question. He admitted that this is just a draft, which does not fully reflect the aerodynamic capabilities of the car. That is why Martin also decided not to specify Cd (drag coefficient). But in any case, the presence of this analysis helped answer some questions and showed that the truck is more aerodynamic than skeptics thought.

Source: Justin Martin/Instagram

The drag coefficient of an automobile impacts the way the automobile passes through the surrounding air. When automobile companies design a new vehicle they take into consideration the automobile drag coefficient in addition to the other performance characteristics. Aerodynamic drag increases with the square of speed; therefore it becomes critically important at higher speeds. Reducing the drag coefficient in an automobile improves the performance of the vehicle as it pertains to speed and fuel efficiency.

The two main factors that impact drag are the frontal area of the vehicle and the drag coefficient. The drag coefficient is a unit-less value that denotes how much an object resists movement through a fluid such as water or air. A potential complication of altering a vehicle's aerodynamics is that it may cause the vehicle to get too much lift. Lift is an aerodynamic force that acts perpendicular to the airflow around the body of the vehicle. Too much lift can cause the vehicle to lose road traction which can be very unsafe.

The deletion of parts on a vehicle is an easy way for designers and vehicle owners to reduce parasitic and frontal drag of the vehicle with little cost and effort.
Side mirrors both increase the frontal area of the vehicle and increase the coefficient of drag since they protrude from the side of the vehicle. If you have not noticed, note that Cybertruck does not have side mirrors.

The same applies to windshield wipers; they are absenton Cybertruck. And recently Tesla has submitted a patent for a Pulsed Laser Cleaning glass from debris.

Image: Tesla

The design of Cybertruck is undoubtedly perfectly thought out, which is what endows it with high characteristics. On December 1, Elon Musk tweeted that with extreme effort, Cybertruck might hit a 0.30 drag coefficient, which would be insane for a truck.

With extreme effort, Cybertruck might hit a 0.30 drag coefficient, which would be insane for a truck. Requires tweaking many small details. https://t.co/IMLJbsInmq

— Elon Musk (@elonmusk) December 1, 2019

Comparing to other cars in the range of 0.30, the Tesla Cybertruck has aerodynamics similar to a lot of sleek sportscars. 

Also, the presence of a smooth bottom Cybertruck improves its aerodynamic characteristics.

Laminar air flow due to a completely smooth bottom is underappreciated

— Elon Musk (@elonmusk) December 1, 2019

Overall shape is good for low drag coefficient. Matters a lot exactly how you trip airflow at edges & guide air around wheels, like an invisible sculpture.

— Elon Musk (@elonmusk) December 1, 2019

So, as seen in the CFD modeling,  also take into account many other facts and listening to common sense, the Cybertruck does seem to be a lot more aerodynamic than the competition.

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https://www.tesla.com/cybertruck