Cybertruck is NOT aerodynamically efficient - why the shape?

[Ostrichsak]

Tesla can go full boat tail to maximize aerodynamics, but the truck would be too long for most parking spaces, probably less functional, and I imagine less appealing. I think Tesla did a good job optimizing everything.

You miss the point because they didn't optimize anything because if they did the roof would have a more gradual break, the wheel wheels would be less square and most other surfaces would be more "slippery" to the air. That's the point. The design is NOT focused on aerodynamic efficiency. Full stop.

 

[J X 3]

An airfoil has something like a 0.045Cd, an airfoil is like a plane wing. Aero is more about how you release the air than how you hit it.
The very long slope and bed cover do help and you can see that it starts just above the driver's head, that's not random.
With this vehicle, the air goes mostly over and under it. The flat underbelly should help. The pointy top, hard to say but does seem like it risks separation and hard to guess if they do anything to mitigate. Maybe they also factor in situations where the bed is not covered or the vehicle is towing something and they want to address those too. Sharp corners do make for a clean separation, it's not always a bad thing. Would be silly to try to guess Cd but trucks are not great in this area and Tesla likely does a lot better.
My guess is that they get 3 EPA miles per kWh so 100kWh pack for the 50k$ version and somewhat twice that for the 70k version.

 

[CMoZ]

Thanks for the thoughtful reply. The reality is that faceted surfaces are terrible for aerodynamic efficiency. Do you know why the F-117 Nighthawk is faceted? Because, at the time, we couldn't figure out how else to reduce radar profile of more efficient aerodynamic surfaces. The F-117 was (and is) an "unstable" aircraft because of its shape.

But whatever - it's a Tesla . . .

This is actually incorrect. there are only hard angles on this as that's a limitation to keep the 30x cold rolled Stainless Steel from becoming cost prohibitive and this combined with as someone else has pointed out is the optimal aero shape ( Streamlined body/half body) approximated with a flat faceted surface is a compromise of aero efficiency for weight/durability. The F-117 is unstable has it has to manage that on many planes not flat on the ground like a truck.

 

[omgwtfbyobbq]

You miss the point because they didn't optimize anything because if they did the roof would have a more gradual break, the wheel wheels would be less square and most other surfaces would be more "slippery" to the air. That's the point. The design is NOT focused on aerodynamic efficiency. Full stop.

I agree the wheel wells could be less efficient, and they could have used full wheel well covers, but they wouldn't do well offroad. They may also have some aerodynamic modifications up their sleeve to minimize the penalty of open wheel wells, ala the front bumper on the 3.

The roof doesn't need a flat section to prevent flow detachment. Had Tesla built a more conventional truck with a much steeper windshield, then yeah, they would have needed something flat up top to facilitate the transition between the front and back of the vehicle. They don't need that because both the front and back have relatively shallow angles.

The design isn't maximally aerodynamically efficient, like a solar car or similar low power vehicle, but odds are it'll be better than every other truck out there and most cars as well.

 

[Doc Brown]

You need to forward this ASAP to the Engineering department at Tesla and CC Elon. I don't think they have seen this. In fact, you should offer your engineering expertise.

I’m on it.

In the mean time - send me yours and I’ll send it to McLaren’s F1 team - they can put you on the faceted/square test car design team.

 

[J X 3]

In product design there are always many compromises and lots of things to consider..
Tesla had to adapt to the limitations of the manufacturing process for these load bearing "panels". Structural integrity is also a big deal especially vs costs. Then they had to maximize footprint utilization and fit 3 seats on each row, consider wheelbase vs vehicle length too. Consider driving dynamics, offroad abilities. Aero was clearly a high priority but they had to factor in lots of other things with cost being the leading factor, it starts at about the same price as a M3 SR+ or MY base while being much larger.

 

[Doc Brown]

So... if we're willing to sacrifice a little aerodynamic efficiency we could get something with the "performance of a Porsche" that also has a reduced radar profile? I can now justify redirecting some of my annual speeding-ticket budget toward paying for this thing!

Can’t argue with that. I changed my mind and ordered one.

 

[Ostrichsak]

An airfoil has something like a 0.045Cd, an airfoil is like a plane wing. Aero is more about how you release the air than how you hit it.
The very long slope and bed cover do help and you can see that it starts just above the driver's head, that's not random.
With this vehicle, the air goes mostly over and under it. The flat underbelly should help. The pointy top, hard to say but does seem like it risks separation and hard to guess if they do anything to mitigate. Maybe they also factor in situations where the bed is not covered or the vehicle is towing something and they want to address those too. Sharp corners do make for a clean separation, it's not always a bad thing. Would be silly to try to guess Cd but trucks are not great in this area and Tesla likely does a lot better.
My guess is that they get 3 EPA miles per kWh so 100kWh pack for the 50k$ version and somewhat twice that for the 70k version.

I'm not arguing exact Cd specs but you can't look at that truck and logically tell me that it wouldn't have a lower Cd if that roof line break weren't so harsh and the wheel well arches weren't more curved that the leading and trailing faces. Regardless of exact wind tunnel Cd numbers that fact can't be disputed. This is exactly the point of the conversation and yet some here who know nothing of aerodynamics aren't even questioning the motive because Tesla can do no wrong and everything they do is right.

This leads to the current state of the conversation being that we can't even bring up the "why" of the design when some people are still convinced that it's 100% for aerodynamics. It's simply not. Once we can admit that we can get into the why and I think that once these same people realize that we could have a more "normal" looking truck that is even more efficient in terms or energy use and aerodynamics we can have a more intelligent conversation about which they prefer. Many right now are stuck on stupid though and convinced that function is coming before form with this design and those of us who want different are choosing form over function which simply isn't the case.

 

[CMoZ]

Basically back of the napkin 2d approximation but it's really actually not that bad

 

[Ostrichsak]

I agree the wheel wells could be less efficient, and they could have used full wheel well covers, but they wouldn't do well offroad. They may also have some aerodynamic modifications up their sleeve to minimize the penalty of open wheel wells, ala the front bumper on the 3.

The roof doesn't need a flat section to prevent flow detachment. Had Tesla built a more conventional truck with a much steeper windshield, then yeah, they would have needed something flat up top to facilitate the transition between the front and back of the vehicle. They don't need that because both the front and back have relatively shallow angles.

The design isn't maximally aerodynamically efficient, like a solar car or similar low power vehicle, but odds are it'll be better than every other truck out there and most cars as well.

I don't like wheel well covers and actually prefer the slight loss in Cd to get something that looks better. I never was trying to say that all that mattered was aerodynamics was the single most important element. All I'm saying is that those who claim they designed it with aerodynamics being the most critical aspect and that's the sole explanation for the final design are wrong. They think that you have to have a butt ugly truck in the name of aerodynamics. What I'm saying is what we're looking at is a butt ugly truck that is also sacrificing aerodynamics for that "styling" if you want to call it that.

The Model S is insanely aerodynamic and also looks amazing. Is it too much to ask for something that looks amazing and performs well? I thought that was kind of Tesla's whole thing but now I see that they're almost entirely abandoning the virtues they previously held important.

 

[Ostrichsak]

Basically back of the napkin 2d approximation but it's really actually not that bad

I never said it was awful. What I"m saying is that they actually made small decreases here and there in Cd to make it look like that. This is contrary to endless people on the internet who seem to think that it's these weird little things that make it MORE aerodynamic.

 

[omgwtfbyobbq]

I don't like wheel well covers and actually prefer the slight loss in Cd to get something that looks better. I never was trying to say that all that mattered was aerodynamics was the single most important element. All I'm saying is that those who claim they designed it with aerodynamics being the most critical aspect and that's the sole explanation for the final design are wrong. They think that you have to have a butt ugly truck in the name of aerodynamics. What I'm saying is what we're looking at is a butt ugly truck that is also sacrificing aerodynamics for that "styling" if you want to call it that.

The Model S is insanely aerodynamic and also looks amazing. Is it too much to ask for something that looks amazing and performs well? I thought that was kind of Tesla's whole thing but now I see that they're almost entirely abandoning the virtues they previously held important.

I don't disagree about the S looking great, but to be fair it doesn't have a bed hanging off the back, and it has less reference area as well, so it can afford to have a higher drag coefficient.

Is it the lines that bug you or the proportions? If it's the lines, then I agree completely. Tesla could have made something much smoother with the same proportions and it would have been just as aerodynamic. I think the lines are mostly a function of the manufacturing/design choices they made to keep costs down. The proportions on the other hand are mostly for aerodynamics are far as I can tell.

I wouldn't be surprised if it had a drag coefficient that's significantly lower than the S, mostly because it has much greater reference area, so drag coefficient is the only thing they can reduce to keep range up. I guess they could increase pack size too, but that's more money and fewer trucks built if they continue to have cell supply constraints going forward.

The interior is also spartan like the 3, so it seems to me like they're really trying to optimize costs with the truck to keep prices down and affordability up.

 

[CMoZ]

I'm not arguing exact Cd specs but you can't look at that truck and logically tell me that it wouldn't have a lower Cd if that roof line break weren't so harsh and the wheel well arches weren't more curved that the leading and trailing faces. Regardless of exact wind tunnel Cd numbers that fact can't be disputed. This is exactly the point of the conversation and yet some here who know nothing of aerodynamics aren't even questioning the motive because Tesla can do no wrong and everything they do is right.

This leads to the current state of the conversation being that we can't even bring up the "why" of the design when some people are still convinced that it's 100% for aerodynamics. It's simply not. Once we can admit that we can get into the why and I think that once these same people realize that we could have a more "normal" looking truck that is even more efficient in terms or energy use and aerodynamics we can have a more intelligent conversation about which they prefer. Many right now are stuck on stupid though and convinced that function is coming before form with this design and those of us who want different are choosing form over function which simply isn't the case.

Well you're right that it's not 100% for aerodynamics you're wrong that "we could have a more "normal" looking truck that is even more efficient in terms or energy use" ( aerodynamic efficiency is redundant here as that feeds energy efficiency )

The following are considerations it appears Tesla worked towards

- Durability or toughness

- Range

- Power ( or towing capacity for this conversation )


So to break these down into the design decisions that feed each

-Durability or toughness
-- SpaceX alloy - Using this alloy necessitates the angular panels as it's prohibitively expensive to put in compound bends as you can't stamp it at the thickness they're using as well bending could introduce weakness into the panels

-Range
--Weight reduction by moving to the exoskeleton necessitating the triangular shape and rear sail panels
--Retractible tonneau cover to prevent the bed from catching air
--Aero - within the bounds of the material using "most optimal" shape ( low triangular shape)

-Power
--Weight reduction as above
--Exoskeleton design for body rigidity and make space for higher forward leaning dual stack battery pack
--Adjustable Air suspension


I'm inevitably missing some things here but you couldn't achieve a standard design with the range, power, weight and towing capacity the cybertruck has with existing tech. You'd have to sacrifice something

Example the R1T

- Towing Capacity 11,000lbs
- $69000 starting they haven't even release prices for the mid and high end one
- Range 200mi, 300mi or 400mi ( and the top end one has reduced HP to hit that range)
- Fastest one is 0-60 in 3s

 

[CMoZ]

Also something to consider is the drag coefficient of paint vs stainless steel. I believe bare stainless steel is actually quite a bit lower than regular automotive paint. I know in aerospace they use specialized paints to control it

 

[Troyrod]

The F-117

Will the Cybertruck be stealth to police radar?

 

[jerry33]

I don't like wheel well covers and actually prefer the slight loss in Cd to get something that looks better. I never was trying to say that all that mattered was aerodynamics was the single most important element. All I'm saying is that those who claim they designed it with aerodynamics being the most critical aspect and that's the sole explanation for the final design are wrong. They think that you have to have a butt ugly truck in the name of aerodynamics. What I'm saying is what we're looking at is a butt ugly truck that is also sacrificing aerodynamics for that "styling" if you want to call it that.

The Model S is insanely aerodynamic and also looks amazing.

The Model S looks like every other car in it's class. Sure Tesla had to do that because the conservative purchasers wouldn't buy anything that broke new grounds. The Cybertruck looks great, once you get over the fact that it looks different, far batter than any other truck on the market (I have a Model S, it's a great car, but it only has ho-hum looks).

 

[mspohr]

Basically back of the napkin 2d approximation but it's really actually not that bad

Your video shows the problem well. It's the "breakaway" of laminar flow which causes drag at the tailgate. One solution that people are using is to put vortex tabs at the breakaway zone to shape the air into more coherent flow.

Airtab | Aerodynamic Fuel Savers | Welcome

 

[CMoZ]

Your video shows the problem well. It's the "breakaway" of laminar flow which causes drag at the tailgate. One solution that people are using is to put vortex tabs at the breakaway zone to shape the air into more coherent flow.

I think you're being a bit too exact with my video.

1) even in the video the separation is minimal compared to similarly sized conventional pickups

2) my video is not a complete 3 dimensional analysis of the truck it's a polygon in the rough profile shape I drew up and uploaded to a modelling web app ( as well the underside is completely imagines as we have no pictures of that) you can even see the white triangles outside the profile interacting with the flow so this may show a more negative flow than reality

3) As I mentioned before this may be offset by the overall lower drag coefficient of a bare stainless steel vs painted surface as there is an improvement there

In any event the primary design decision here wasn't around aerodynamics although it was ( and is always ) PART of the consideration it was around limitations of the material

 

[mikes_fsd]

Saw this on Twitter, so do not have a link to original FB source...

 

[Mysta]

Obviously only gives an idea but someone did a cfd.
Justin Martin