Independent Cybertruck Drag Coefficient Analysis Yields 0.34 Cd

[Diehard]

Won't any aerodynamic lift also be accompanied by more aerodynamic drag?

F150 already has the drag. Having the drag is inevitable. The question is if this shape in addition to reducing the drag has other benefits (like lift).

 

[Crissa]

More like Friction reduction. If the lift works against the weight, theortetically there would be less contact. It would be like having more air in the tire or smaller economical tire. Bothe of those usually result in better gas millage.

Sure, but it's less friction because the wheels are operating under less force of gravity. ^-^

-Crissa

 

[Diehard]

Sure, but it's less friction because the wheels are operating under less force of gravity. ^-^

-Crissa

We are on the same page. I just didn’t want to say yes to avoid someone getting on my case saying the force of gravity does not change since mass of earth and CT remains the same. Otherwise we are both talking about the same thing.

Other than decades ago messing with some elementary FEA software, I don’t have any experience with aerodynamics. It would be fun to put this thing in a wind tunnel and keep tweaking stuff to see what happens. It is hard to conduct any experiments on a highway with so many variables and especially in my area a high likelihood of a lawyers driving behind me.
.

 

[jerhenderson]

Do you guys think CT is lighter at higher speed due to having less air pressure on top like aircraft wings? Or you think the impact is negligible because there is a lot less surface area and speed?

it wouldn't be lighter because its mass or density won't be reduced - you're talking about lift . Planes aren't lighter at higher speed.

 

[CappyJax]

I probably should have worded it better. The question is, would it reduce energy consumption due to reduced stress (and may be contact area) on the tires?

Not on pavement. Any reduction of rolling friction would be countered by more aerodynamic drag from the lift. If you were on gravel or dirt, I suspect you would see a significant benefit.

 

[Jhodgesatmb]

We are on the same page. I just didn’t want to say yes to avoid someone getting on my case saying the force of gravity does not change since mass of earth and CT remains the same. Otherwise we are both talking about the same thing.

Other than decades ago messing with some elementary FEA software, I don’t have any experience with aerodynamics. It would be fun to put this thing in a wind tunnel and keep tweaking stuff to see what happens. It is hard to conduct any experiments on a highway with so many variables and especially in my area a high likelihood of a lawyers driving behind me.
.

When I was in school we had some miniature wind tunnels and I put some tent designs (made of balsa wood) in them. I bet some students would get a kick out of running some truck designs in the small tunnels (cross section about 25 square inches) as a class project. Alternatively, maybe one of the Tesla freaks working at NASA Ames (etc) could get after hours access to a small tunnel (I really have no idea how the tunnel access works over there so it might be quite impossible without funding) to do some testing.

 

[mlee168]

I would love to see how towing a trailer would affect aerodynamics compare to a F150. With a trailer, the aerodynamics could be the same as a F150 or worse when towing a trailer.

 

[FutureBoy]

I would love to see how towing a trailer would affect aerodynamics compare to a F150. With a trailer, the aerodynamics could be the same as a F150 or worse when towing a trailer.

Probably has a lot to do with the exact shape of the trailer. Some shapes/sizes work better on one or the other.

 

[CyberJoel]

The truck wont get lighter due to speed as the front is a giant wedge, as are the fenders. The fun part of tires though is that they get larger as you speed up therefore reducing the contact patch. Look up videos of top fuel dragsters. The effect is not as much on cars and trucks but if Tesla requests a special tire they will get one that is affected by centripetal force more and will get taller and reduce the contact patch, and therefore the rolling resistance and therefore the Force needed to push it forward. The tires would be a tad more aerodynamic too.

You could get this to happen above 60mpg only.

 

[soonerdy]

Doesn't sound like he's talking about lift to me at all, sounds like he's talking about reduced top pressure. Sure, that means less counter-pressure to any lifting force, but isn't lift itself.

I have a question, would it have made sense for the tailgate to have angled in corners to improve high speed stability? I imagine the swirling air behind a vehicle may not slow it down, but does it contribute to vibration and instability?

 

[Albern]

Something I just noticed; on the night of the Semi reveal, Elon stated that the CD of the Semi would be 0.36. Given that this model is predicting a CD of 0.34, how isthe difference of 0.02 explained by the greater frontal area of the Semi vs the Cybertruck?

Is Elon sandbagging again?

 

[Mr.Dee]

Something I just noticed; on the night of the Semi reveal, Elon stated that the CD of the Semi would be 0.36. Given that this model is predicting a CD of 0.34, how isthe difference of 0.02 explained by the greater frontal area of the Semi vs the Cybertruck?

Is Elon sandbagging again?

Cd is independent from frontal area, or cross sectional area as a more appropriate term.

When calculating total drag, cross sectional area is determined by size while the coefficient of drag is determined by shape.

Image if you had two semi trucks of the same design, but truck "A" is larger and has twice the cross sectional area as truck "B". Even though the area is larger, they both have the same shape, and therefore the same Cd. Assuming all else equal, drag would be calculated by Cd x Area. If you apply this to both trucks, truck A will have 2x the drag as truck B.

Think of Cd as a "modifier" to the area. You could have a bullet and a brick of the same size, but the bullet has a more aerodynamic shape and thus, a smaller Cd, or modifier multiplied to the area.

 

[Albern]

Cd is independent from frontal area, or cross sectional area as a more appropriate term.

When calculating total drag, cross sectional area is determined by size while the coefficient of drag is determined by shape.

Image if you had two semi trucks of the same design, but truck "A" is larger and has twice the cross sectional area as truck "B". Even though the area is larger, they both have the same shape, and therefore the same Cd. Assuming all else equal, drag would be calculated by Cd x Area. If you apply this to both trucks, truck A will have 2x the drag as truck B.

Think of Cd as a "modifier" to the area. You could have a bullet and a brick of the same size, but the bullet has a more aerodynamic shape and thus, a smaller Cd, or modifier multiplied to the area.

Ah that makes things much more clear, thanks so much.