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Old 12-02-2019, 01:39 PM   #81 (permalink)
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Originally Posted by Hersbird View Post
I believe you can get close with a model but you also have to scale the speed down the same. It sill will give a .05-.1 higher Cd even then. Better would simply use the real height and width as it's not a real wind tunnel but a computer simulation.

If it's already over .3 then adding wipers and mirrors is not going to get any better. Only if by "extreme" they mean ditch the fender flairs, keep the tires inside the body and maybe even flatten the roof. The roof may not change the CD much but dropping 3-4 square feet off the frontal aera will be even better.
The CFD sofware Tesla uses is full-scale,Full Navier-Stokes equation,large domain spherical vectors,millions of cells analyzed simultaneously,with over 99% accuracy compared to full-scale tunnel testing.A few years ago,with the fastest supercomputers,it took almost 2-days to run a single shape iteration.
I don't know about desktop programs.
One of the CFD online presentations demonstrated full-scale dimensions for the Cybertruck,at 39.34 meters/second velocity.They were trying for accuracy.
Wipers can be hidden below a valence,which shaves 0.005 off the Cd (DARKO)
Mirrors are an issue.My SCCA units cut drag from 0.024 down to 0.010,and frontal area,on the longer 1983 Subaru XT struts.
Again,testing velocity will be a function of dynamic similarity (varisimilitude).
It appears that Tesla is using intentional separation bubbles to sculpt inviscid flow,even captured longitudinal vortices,acting like virtual flying buttresses to actually kill attached vortices,otherwise shedding off the aeroshell portion of the body,as Space Shuttle's, Concorde's delta wings,and the NASA-Vought fly-by-wire, supercritical wing of the early 1970s; tuned with angles,tumblehome, and body rake.

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Old 12-02-2019, 02:23 PM   #82 (permalink)
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It appears that Tesla is using intentional separation bubbles to sculpt inviscid flow,even captured longitudinal vortices,acting like virtual flying buttresses to actually kill attached vortices,otherwise shedding off the aeroshell portion of the body,as Space Shuttle's, Concorde's delta wings,and the NASA-Vought fly-by-wire, supercritical wing of the early 1970s; tuned with angles,tumblehome, and body rake.
So I read up on the F-8, and the stall characteristics of the supercritical wing, but how do the Shuttle and Concorde relate?

Quantum computers are coming online right now.
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Old 12-02-2019, 02:36 PM   #83 (permalink)
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The scale won't be an issue as long as he selects a velocity which will ensure supercritical Reynolds number,and fully-turbulent boundary layer;something aerodynamicists refer to as varisimilitude.
But he didn't he just ran them all, the full scale Tesla and the toy Ford and Ram, at the same 65mph. The worst thing is there was no reason to leave the toy dimensions in the simulation and not the real, readily available dimensions on the Ford and Ram. Makes me think he is more of an amateur than me, and I'm definitely an amateur.
I would love it if a clean version of the Cybertruck can get .3 or even under. I know I can build a perfectly clean version as a fold out camper. That's my new camper design if it gets .3-.35 with fender flairs, mirrors, and wipers. Means a camper that shape without any add ons would be under .3.

Ps, actually even if it's .45 I will use that as a design, just because a bunch of Cybertruck owners would be partial to buying a matching Cybertruck trailer. I could do pure cargo, or I bet designed to even fit a Model 3 inside, or the 4 wheelers or snowmobiles, and of course a popup camper version.
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Old 12-02-2019, 03:02 PM   #84 (permalink)
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Shuttle,Concorde

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So I read up on the F-8, and the stall characteristics of the supercritical wing, but how do the Shuttle and Concorde relate?

Quantum computers are coming online right now.
For takeoff and landing,(landing only for the Space Shuttle) the builders rely on lift-due-to-vorticity enveloping the wings upper surface.
The downwards-sloped greenhouse and tumblehome of Cybertruck could be intentionally tuned to produce some magnitude of bounded edge vorticity, which would act for transverse shearing flow,as an attached transverse vortice would for longitudinal flow;providing phantom 'flying-buttress' radii, for which slow,high-pressure flank flow could bleed into the fast,low-pressure upper flow descending the 'aeroshell' downslope,without triggering massive,drag-producing longitudinal vortices.It would be invisible to the naked eye,like the nose/frunk,and roof apex vortices.
I hope Tesla's aero team will publish and talk at the SAE Congress.
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Old 12-02-2019, 03:09 PM   #85 (permalink)
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toy dimensions

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But he didn't he just ran them all, the full scale Tesla and the toy Ford and Ram, at the same 65mph. The worst thing is there was no reason to leave the toy dimensions in the simulation and not the real, readily available dimensions on the Ford and Ram. Makes me think he is more of an amateur than me, and I'm definitely an amateur.
I would love it if a clean version of the Cybertruck can get .3 or even under. I know I can build a perfectly clean version as a fold out camper. That's my new camper design if it gets .3-.35 with fender flairs, mirrors, and wipers. Means a camper that shape without any add ons would be under .3.

Ps, actually even if it's .45 I will use that as a design, just because a bunch of Cybertruck owners would be partial to buying a matching Cybertruck trailer. I could do pure cargo, or I bet designed to even fit a Model 3 inside, or the 4 wheelers or snowmobiles, and of course a popup camper version.
Ouch! Yeah,that would a heck of an oversight on their part.
If I were pulling,I'd build a deflector as AeroStealth did on his F-150,to help the air up,and around the trailer nose,as NASA did in the 1970s,and Texas Tech did in the 1980s.
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Old 12-02-2019, 05:05 PM   #86 (permalink)
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... and of course a popup camper version.
The pivot point is obvious. The walk-in entrance could be in a bullet boat tail and the flat top rotate forward up to 190-200.
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Old 12-02-2019, 10:50 PM   #87 (permalink)
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After the Model 3 was unveiled he tweeted that they were aiming for 0.21, and that car ended up at 0.23. So I read this the same as you--it isn't going to hit 0.30. (I'm also remembering Mercedes 2010 announcement that within 5 years all their cars would be at Cd 0.20. 9 years later, we're still waiting).
Tested with professional CFD software, the truck shows a .47 Cd.


https://images.app.goo.gl/Suy9Vtg6DkHQ4NxM6

The CFD software used in the pictures in this thread is from a program that was apparently created as an app for cell phones to give a very rough estimate of Cd.
It's fun to play with, but not very accurate.
I got a .41 when I tested the truck using the same software.
Adding mirrors actually decreased the Cd - I guess because the turbulence merged into the turbulence spilling over the sides and actually cleaned it up a bit.
Is that actually accurate ? Most likely a big NO.
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Old 12-02-2019, 11:05 PM   #88 (permalink)
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Here is a very detailed breakdown of the trucks' aerodynamics.
This very professional test achieved an Cd of.48

https://airshaper.com/assets/reports...cybertruck.pdf
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Old 12-03-2019, 10:40 AM   #89 (permalink)
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Here is a very detailed breakdown of the trucks' aerodynamics.
This very professional test achieved an Cd of.48

https://airshaper.com/assets/reports...cybertruck.pdf
How can anyone earn a living doing those types of reports when there are folks out there doing it for free?
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Old 12-03-2019, 01:15 PM   #90 (permalink)
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How can anyone earn a living doing those types of reports when there are folks out there doing it for free?

Who is doing it for free ?
I'd love to find out, because I'm still puzzled by the drag on the Mazda MX - 3 ( at .32 Cd ) and I'm curious how it is so aerodynamically dirty.

Right now, I'm testing the truck in three configurations : closed bed / open bed / and closed bed, but with mirrors.
The software I'm using seems to be giving figures backwards. With an open bed, the results were .47, and .52 for a closed bed.
Also, the Cd drops when tested with mirrors.
I wish i knew how to get accurate results.

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