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Old 12-02-2019, 02:01 PM   #121 (permalink)
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Cd 0.48

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Originally Posted by RedDevil View Post
Musk tweeted that 'with extreme effort' Cybertruck might hit a 0.30 Cd drag coefficient. 'which would be insane for a truck. Requires tweaking many small details'

Well, it takes more than small details to bring 0.48 down to 0.30.

But maybe the 0.48 model did not take this in account:

A completely flat underbody.
In Justin W. Martin's CFD presentation,he put the Cybertruck in the neighborhood of Cd 0.36.
I'd like to see an analysis with the front suspension bottomed out at 8-inch ground clearance,and the rear optimized (body raked) for lowest drag highway cruising,ala Ford Probe IV and V concept cars.

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Old 12-02-2019, 02:15 PM   #122 (permalink)
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diffuser

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The .48 model was actually questioned by another aeronautical engineer, "The underbody rear diffuser will never work so nice like in your simulation." Basically saying the .48 was giving the underside and rear exit the perfect possible design even though nobody knows how it will actually be.
If both the airdam area and diffuser are presented for approach and departure angles,there's no reason both couldn't be 'active',with the airdam lowering as Volvo and Ford have done,and an optimizing diffuser as GM did on the Epcot concept of the 1980s.
We know from Hucho,the Porsche's 914 study,and Ford's Fusion,hydrogen Bonneville LSR racer,and Ford's Probe-IV concept, what ground clearance can do for drag.
We also know from Ford's Probe-IV, what body inclination optimization can also do for drag reduction.
With the Cybertruck's active suspension,it has a few tricks it can perform,depending on specific use,all with aero implications.
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Old 12-02-2019, 02:24 PM   #123 (permalink)
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a few minutes

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He doesn't aim to get .3, he said it isn't. 3 and won't be without serious changes. I don't think they spent more than a few minutes thinking about aerodynamics on this truck, it's a whole different thing than anything else they have ever designed.
It's funny how my impression was,that they've spent more time thinking about it than any other manufacturer since 1907,when farmers began putting boxes on the back of Model-Ts.
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Old 12-02-2019, 02:39 PM   #124 (permalink)
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champfers

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Originally Posted by freebeard View Post
0.30 de-obfuscates and captures wayward periods.

The chamfers that reduce the stagnation area and the softly angled edges that reattach longitudinal vortexes, as aerohead is discussing in the other thread, suggest it is carefully reasoned. Not to mention the separation edge in the rear.
The Cybertruck caused me to dig into the S.R.Ahmed body research,1984,and that of P.W.Bearman et al,from 1982 (SAE Journals and Transactions).
Between the two,you can almost 'build' the Cybertruck.And the sharp edges return remarkable performance with a touch of 'chamfer.' It appears that separation bubbles are intentionally designed into the Tesla,in order to take advantage of what attached vortices can do.It's all hiding in plane view.Very clever.
'Honk if you have a small one!'
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Last edited by aerohead; 12-07-2019 at 02:47 PM.. Reason: spell
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Old 12-02-2019, 04:56 PM   #125 (permalink)
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Quote:
they've spent more time thinking about it than any other manufacturer since 1907,when farmers began putting boxes on the back of Model-Ts.
Like Tang, a spun-off result from the space race.

I've been forcing myself to spell chamfer without a 'p'. You're not helping.
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Old 12-03-2019, 08:04 AM   #126 (permalink)
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Quote:
Originally Posted by Hersbird View Post
He doesn't aim to get .3, he said it isn't. 3 and won't be without serious changes. I don't think they spent more than a few minutes thinking about aerodynamics on this truck, it's a whole different thing than anything else they have ever designed.
Quote:
Originally Posted by Elon Musk on Twitter
With extreme effort, Cybertruck might hit a 0.30 drag coefficient, which would be insane for a truck. Requires tweaking many small details.
You think that he just did a wild guess then?
At least someone is guessing.
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Old 12-03-2019, 09:44 AM   #127 (permalink)
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You think that he just did a wild guess then?
At least someone is guessing.
No I think artists (with basic engineering knowledge) drew up a bunch of concept sketches, Elon picked this one. Then they started modeling it sticking to the sketch and fine tuned a few things aero wise but the focus was to produce the radical concept drawing in real life. I think they literally would have made a brick if that was the drawing that inspired Musk.
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Old 12-03-2019, 10:50 AM   #128 (permalink)
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It is your good right to think that.
I think that Franz von Holzhausen started out with a couple of restrictions which did include 16" clearance, 6 seats, a 6.5' bed, flat panels etc. and excluded any trace of traditional truck design.

Then they made a simulation model in which the front and rear slope were variables, ran that through simulations to get a bunch of reasonable compromise truck designs to build and test in the wind tunnel and the one that came out best is what they've shown.

Just guessing of course. It is what I would have done if I were in that position.
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Old 12-03-2019, 01:43 PM   #129 (permalink)
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Quote:
Originally Posted by RedDevil View Post
It is your good right to think that.
I think that Franz von Holzhausen started out with a couple of restrictions which did include 16" clearance, 6 seats, a 6.5' bed, flat panels etc. and excluded any trace of traditional truck design.

Then they made a simulation model in which the front and rear slope were variables, ran that through simulations to get a bunch of reasonable compromise truck designs to build and test in the wind tunnel and the one that came out best is what they've shown.

Just guessing of course. It is what I would have done if I were in that position.
I agree with you to the point of "the one that came out best in the wind tunnel won". Just simply losing the fender flairs (the most common pickup feature on the thing) would help a ton. I also think limiting the front headroom more and using a flat panel going back to the back seat would also improve aero but at the expense of looking more normal.

I do hope one day when it doesn't matter all of Musk's secrets and thought processes are shared somehow. I mean, he's pretty good at getting stoned an opening a window on Twitter or in an interview, but it would be cool to see all the actual concept iterations over time.
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Old 12-03-2019, 02:07 PM   #130 (permalink)
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Here's a CFD comparative of the CYBRTRK and the Raptor and Ram:

https://insideevs.com/news/385397/te...m-ford-raptor/

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