Tinker71

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Which airflow model?

Grab a screenshot, please. Sometimes a picture really is a thousand words.

-Crissa
From JBee post.
1655325635243.png
 

Ogre

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Instead of copying the image, we should just use descriptive text for @Crissa to interpret.

JBee posted an image of a Cybertruck with jet thrusters blasting chemtrails out the back. The truck has clearly just pushed through a giant pile of whipped cream and is sloughing off chunks.
 

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The length of the BAW in a stowed vertical position will not add drag enough to be worth mentioning. This is because the dominant form of drag in a wheeled vehicle velocity range is "form drag" (from the shape and frontal area) and not "skin drag" (from the length of the vehicle exposed to airflow).
How much positive impact would "dimpling" the CT have on it's drag? Let's get the most out of this beast!

I've heard on golf balls it's effect is nearly double the ball flight of an otherwise equal but smooth ball. In cars I think it was tested to something like a 15% increase in MPGs, but was cosmetically unacceptable. Who give a $!#% about cosmetics, we're driving an EV truck here!
 

Crissa

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From JBee post.
1655325635243.png
Yeah, those are turbulence models of where the laminar flow is broken.

All the white stuff is where the air spins in tiny bits of low pressure. They move around based on the speed of the object through the fluid. If it were water, that's where you'd see cavitation (bubbles).

-Crissa

I'm sure someone will come along and nitpick my wording, but it's like saying the world is round. An oblate spheroid is round. It's still a sphere within a certain tolerance of error.
 
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Ogre

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How much positive impact would "dimpling" the CT have on it's drag? Let's get the most out of this beast!

I've heard on golf balls it's effect is nearly double the ball flight of an otherwise equal but smooth ball. In cars I think it was tested to something like a 15% increase in MPGs, but was cosmetically unacceptable. Who give a $!#% about cosmetics, we're driving an EV truck here!
There were some previous discussions about dimpling. We decided a dimpled skin would give the truck significant aerodynamic advantage.

Tying to decide which domain name I should buy “cyberdimple.com” or “DympleTruck.com”
 

firsttruck

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There were some previous discussions about dimpling. We decided a dimpled skin would give the truck significant aerodynamic advantage.

Tying to decide which domain name I should buy “cyberdimple.com” or “DympleTruck.com”

I mentioned before about how you pay more for new jeans that are pre-washed and torn.

Can you imaging how hard and long it is going to be for Tesla to completely dimple a 3mm cold-rolled 30x stainless steel exoskeleton Cybertruck !!!

The price for a dimpled Quad motor AWD 4WS Cybertruck with SpaceX cold thruster package will be more than a Bugatti Chiron ( $4 million).
 

Crissa

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What sort of metal would you have to have to ball-peen (assuming enough force, so some sort of robot) the dimples in? What's hard enough?

-Crissa
 

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I don't want no stinkin plain jane round dimples neither. I want the fancy angular hexagon double dimple Bridgestone e12 Contact style for my angular CT.


e12 Contact.png
 


JBee

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How much positive impact would "dimpling" the CT have on it's drag? Let's get the most out of this beast!

I've heard on golf balls it's effect is nearly double the ball flight of an otherwise equal but smooth ball. In cars I think it was tested to something like a 15% increase in MPGs, but was cosmetically unacceptable. Who give a $!#% about cosmetics, we're driving an EV truck here!
Yeah dimpling would probably help a bit, but there's a couple of constraints on their effectiveness.
  • About 30% of the CT surface is glass and mostly needs to be clear to look out of. Except the rear roof. So you won't be able to dimple that.
  • The rest you could probably dimple with a thick textured car wrap
  • Dimples help a golf ball fly because it's also rotating while it travels through the air. This also helps it's aerodynamics and creates lift, and also makes it turn when you slice it. It's not really possible to make parts of the CT rotate it's dimples, so the dimpling effect will be limited.
  • The other issue with dimpling it that it will only work within a certain speed range and then tapers off as it gets slower, hence the sudden turns it makes at the end of the shot, where the air starts to "grab" as soon as the surface microturbulence is overwhelmed by forward airflow. You could design the size and depth to work in certain speed ranges but as always, any aero improvements will have the most effect at higher speeds as drag increases exponentially, meaning if you double the vehicle speed you quadruple the drag. So adding dimpling might not improve range by much if you don't use higher speeds much like on the highway.
"If" you wanted to improve the CT aerodynamics and range, in particular at higher average travel speeds then the fastest and most cost effective way would be to:
  • Attach a rear mounted luggage box to the rear of the CT, that is flush with the sides and top, to extend the length by probably 2-3ft, and bring the Kammback design down to a smaller tailgate area. You could do this by having a hitch connected carrier that snuggles up to the CT tailgate, or you could probably make something that sits on and encompasses the tailgate and sits snug to the sides etc. you would need to plug in some lights into the trailer connector, and you'd also get a decent expansion of luggage volume, should you for example need the bed space for camping or other gear. Even for weight this will work quite well because of the CT's long wheelbase, compared to say a F150. You could actually go out 5-6ft without running into the 60% of wheelbase overhang rule, but it might look a bit silly.
  • Make the CT as low as possible using the suspension and front and rear body spoilers, use fairly flat wheels or covers, get some air curtain producing body panels for the wheel arches (I haven't seen any yet on the CT unlike many other ICE/EVs)
  • Possibly add a poly bull bar to the front with aero enhancement features as above
  • Smooth that roof apex out with a ridged curved body panel add-on to direct airflow as you want it
Of course if you wanted to go really serious you could do some active aero, which not many cars have at all. Most cars are just ignore low speeds because it doesn't matter much and optimise for cruise speeds. Which is fair enough for your run of the mill jalopy, but airflow is not always in the direction of travel and is impacted by other vehicles in front of you too. The first thing would be able to monitor airflow with body sensors and then next to use body panels or aero surfaces, maybe even inflatable skins, to modify air flow according to the incoming air. At some point though you might end up with a negative feedback loop where the weight of the parts decrease you range from rolling resistance, but that can be overcome with some other enhancements.

Like many mechanical things, cars a very dynamic beasts and have various forces they have to contend with. in the case of drag though, there's also the option to reduce rolling resistance by using the "drag" component for lift without an energy penalty. This then becomes lift induced drag, but with the side benefit that it actually reduces rolling resistance produced by the vehicle mass, by using the airflow you have anyway to lift it. There's also something called in ground effect, where two surfaces in close proximity to each other causes lift, (Look up WIG on youtube) a bit like a hovercraft.

At first it may seem counterintuitive, in that lift also means less traction on the wheels, which in turn means less deceleration to brake or acceleration to go around a corner etc. But this is where active aero comes in, similar to the rather rudimentary F1 DRS, in that depending on the state of the car, and the dynamic change that needs to accelerate/decelerate it in a different trajectory, the active aero would either increase or even decrease the lift. A simple way to visualize this is to think of the Red Bull X1 design where they use a fan to modulate lift. In the straight aways the vehicle has virtually no down force meaning that all propulsion power can be used to accelerate to max velocity using conventional aero, but when the corner comes the fan sucks the car down as soon as the brakes are engaged (or regen) giving the vehicle more traction to slow down and turn, to the point it could technically drive upside down around the corner.

Obviously, having the fan on all the time would use excessive amounts of energy, but only having it on when you need it doesn't. Similarly the opposite is also true, in that using lifting body/surfaces in such a way using lift, they reduce consumption, without impacting on safety because they can be modulated to fit the requirements in realtime.

I remember a few decades or so ago when Mercedes was experimenting with radar cruise control. There they were using it to get vehicles to tailgate eachother whilst going down the autobahn. The impacts were quite large and I'm still hoping that at least Teslas will be able to do this with FSD in the future via a software upgrade and some regulatory approval. Even if they could only tailgate a Teslas that would be fine, but imagine getting 20-30% more range because you switch tailgating Teslas along the way. Obviously you'd be nice and switch tailgating with the car in front, but in the end you aren't really impacting the car in front much or at all, so it's more about being polite and fair.

Woops went over the Twitter character quota a bit. :cool:

 

 
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