Lowest Cd of Production Car

[mpg_numbers_guy]

Does anyone know the frontal area of the XL1 or the Lightyear? CdA = Cd*A is more important than just Cd.

[Hersbird]

Originally Posted by mpg_numbers_guy

Does anyone know the frontal area of the XL1 or the Lightyear? CdA = Cd*A is more important than just Cd.

according to this the XL1 is 1.50m2 frontal aera (at 2:22). So smaller than a 1st gen Insight. Also according to ecomodder Wiki, the overall CdA is 3.00 compared to 2.98 for the Aptera. That's pretty good considering the XL1 was not just an idea of what could be.

https://www.youtube.com/watch?v=dF_GUFB5mfo

[pieter_ly]

Lightyear has sold over 120 vehicles in pre-orders. Production has yet to start. Deliveries are expected in 2021.

What's your take on Lightyears focus on energy efficiency - and as a result of that increased range? Where do see the EV market developing? Which variables are you expecting to be important?

[RedDevil]

Originally Posted by Hersbird

Who said anything about 5 seaters only?

LightYear did, as Kach22i's post kindly shows.

Let's hope the LightYear One will sell in bigger numbers that the XL1 did.
At least they aspire to, something VW never did.

I somehow have the feeling that the need to have a large flat surface for the solar panels actually (slightly) increases the air resistance. The roof line follows the template, but the sides are almost straight.
If the cabin curves / tapers inward more back and forth the Cd might be even lower.

But that would leave a smaller, more complex curved surface for the solar cells.
The use case for the LightYear is focused on its ability to harvest sunlight, so I can see how ultimately maximal solar cell area takes prevalence over getting the last 0.01 Cd reduction (and that's assuming my feeling is correct in the first place!)

All in all, nice job. If I had loads of money I'd certainly be tempted.

[Hersbird]

If you need a bunch of qualifiers it's not "the most aerodynamic car". Especially considering it not only wont have the lowest CD but it will also have probably 1.5 times the frontal aera. Overall it won't be more aerodynamic than a Gen 1 Insight.

[kach22i]

Originally Posted by mpg_numbers_guy

....... CdA = Cd*A is more important than just Cd.

Not to sidetrack the thread, or dispute the math but those old black and white pre WWII films NACA did on bi-plane aircraft bracing planted a disturbing seed in my head.

If I recall correctly what they showed was a round guy wire in tension having similar drag to teardrop shaped wing bracing of ten times the guy wire size.

If my memory is not faulty, then shape is far more important than size which runs contrary to the math quoted above.

Turn down the sound - sorry, could not find the original narration.

1935 Aerodynamics Air Flow and Flow Separation NACA 1

https://www.youtube.com/watch?v=pb38NU-fKXw

EDIT-1:

Found this......................

Dramatic drag comparison
https://ecomodder.com/forum/showthre...son-32585.html

Originally Posted by aerohead

The following is an anatomical drag comparison between a circular cylinder section and a NACA laminar wing section.
The two bodies are shown in true size relationship to one another.
The laminar wing section is 167-X longer than the cylinder.
They have identical drag.

(we don't need no stinkin' streamlining)
PS, the table is from 'Boundary Layer Theory,' by Hermann Schlicting,7th-Edition

Sorry about the blurry image - freaking Photobucket.

Originally Posted by darcane

Last two digits for NACA airfoil designations indicate maximum thickness as a percentage of chord.

21% of 167 is 35.1.

So this NACA airfoil has the same drag as the cylinder in spite of having a 35 times larger frontal area.

Not 10X, but 35X ?

Still reading that old thread.

https://ecomodder.com/forum/showthre...n-32585-2.html

Originally Posted by RedDevil

Compare this to the old video Darcane posted in this link:
http://ecomodder.com/forum/showthrea...rag-25378.html

From that, at 5:49:

A properly streamlined strut can be 10 times thicker than a wire and yet have no more drag.

Ten times. That is quite a bit less than the NACA wing shape, but the wing shape used there did not have the concave tail section.
Would that alone make for such a big difference?

EDIT-2:

Here is the link to those old films - with original narration.

2013
NCFMF Video: How to Reduce Drag
https://ecomodder.com/forum/showthre...rag-25378.html

Originally Posted by darcane

I found this very interesting video on another forum, but it is very applicable here so I thought I'd share:

There is a whole collection of these National Committee for Fluid Mechanics Films (NCFMF) videos. More here: National Committee for Fluid Mechanics Films

[kach22i]

Originally Posted by Hersbird

If you need a bunch of qualifiers it's not "the most aerodynamic car". Especially considering it not only wont have the lowest CD but it will also have probably 1.5 times the frontal aera. Overall it won't be more aerodynamic than a Gen 1 Insight.

I see your point, it can be a bit misleading. However that is marketing, and if you are not promoting in your best interest then you are not doing your job.

The claims I find very interesting are the ones on full sized pick up trucks, their power, payload and towing capacity.

Each manufacture seems to have a niche at which they can claim top prize in their respective class.

[Hersbird]

Interesting, I didn't know it wasn't just a function of a straight multiplication of the size. There must be a precise formula based on wind tunnel results. It also may be completely dependent on speeds. What's good for a jet at 600 mph is not necessarily the best for a car at 60 mph. It's hard to argue with the 250 mpg results of the XL1. That just plain blows away any other production car ever.

[botsapper]

https://www.youtube.com/watch?time_c...&v=0MuVExCsS_s

[mpg_numbers_guy]

I wonder what the battery level was before and after the 250 mpg run.

If the battery level is lower at the end than the beginning, then it gives a false impression of better MPG.

The XL1 is a PHEV..

250 MPG seems high; I would surmise closer to 125-175 mpg real world driving, and 200+ mpg only if used as a PHEV and the electricity cost is ignored. Or if you're a hypermiler.