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Old 02-21-2018, 10:27 AM   #1 (permalink)
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To Wheel Or Not To Wheel ?

I know a lot was talked in this forum about ALberto Morelli's ideal aerodynamic proposal:





But this design, despite represent a 0,05 drag shape, do not consider any wheel. Aptera, based in Morelli's shape, reached 0,11 to 0,125 (varies according Aptera models) drag coefficient after add wheels, even if using streamlined covers to the wheels.



For other side the Solar Aztec car from MIT, had 0,12 drag, despite have no streamedline covers to the wheels and even a open hole in the shell near wheels:





Maybe because it was more rounded on top than Aptera, I don't know... Aptera's wheels was large, thick, and maybe it's the reason the drag raised a lot.

A third Morelli's shape car was the Solarworld No.1, but I could not find the drag coefficient for this vehicle, despite a lot of web research :







I bet Solarworld No.1 have lower drag than Aptrera and MTISolar Aztec .

But the reason I created this thread is about Ecorunner VI, with 0,048 drag coefficient already with wheels.



The earlier model, Ecorunner V, already had a drag of 0,0512 with wheels. Other vehicles with similar size and "torpedo shape style" in Shell Eco Marathon had a drag of 0,08 with wheels.
Maybe there a key point, precise calculation for aerodynamic, simulation on computer, trying to find the best shape alread with wheels (streamed covered), instead of try a shape to just later try to add wheels to it.
I just wonder what is be Ecorunner VI drag coefficient without wheel...

The hope I have it's that maybe it's possible to find a much better way to add wheel to a Morelli's basic design, and still have a drag bellow 0. or even bellow 0,91


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Old 02-21-2018, 12:29 PM   #2 (permalink)
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The most efficient design would be a torpedo shape, with 2 wheels inline, just barely poking through slits in the body. A collapsible kickstand could be deployed when the vehicle stops.
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Old 02-21-2018, 01:06 PM   #3 (permalink)
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I understand the torpedo shape to have equal air resistance all around, but does not the ground affect the air pressure of the air deflected by the bottom line of the body? Should not there be a longitudinal crease in the bottom line of the torpedo to relieve some of that higher pressure felt on the bottom?
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Old 02-21-2018, 01:09 PM   #4 (permalink)
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Like Ecomobile.



Not sure what is the drag or it.

But Monotracer (similar to Ecomobile) have a CdA of 0.18.
http://www.evo.co.uk/features/featur...onotracer.html

How convert to CD ?

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The most efficient design would be a torpedo shape, with 2 wheels inline, just barely poking through slits in the body. A collapsible kickstand could be deployed when the vehicle stops.

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Old 02-21-2018, 01:28 PM   #5 (permalink)
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And when you put wheels and full length skirts on, and lower the torpdos to where the tops are the same highth, it gets worse for the un-creased torpedo:
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Old 02-21-2018, 05:50 PM   #6 (permalink)
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The Ecorrunner V and VI remambers a lot a torppedo, but the shape have some interesting variances from top to botton, probably to create a bettert aerodynamic than a simple torpedo shape.

This is probably the reason it have (already with wheel) much better drag (0,048 for version VI) than other torpedo like vehicles (with around 0,08) or their own quite earlier version.






Old version from years ago :



If their aerodynamic engeneer could try "his best shot" on Morelli concept, to try to add wheels and keep drag low...

Have Morelli ever said his model was the best possible, or said just it was the best for a reasonable space in the front area ?
After all, a flat plate in horizontal, following the wind orientation, have even lower drag, and some solar cars try to be a flat plate with a pilot and wheels, but just got around 0.078 or so.




Quote:
Originally Posted by Angel And The Wolf View Post
I understand the torpedo shape to have equal air resistance all around, but does not the ground affect the air pressure of the air deflected by the bottom line of the body? Should not there be a longitudinal crease in the bottom line of the torpedo to relieve some of that higher pressure felt on the bottom?
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Originally Posted by Angel And The Wolf View Post
And when you put wheels and full length skirts on, and lower the torpdos to where the tops are the same highth, it gets worse for the un-creased torpedo:

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Old 02-21-2018, 06:07 PM   #7 (permalink)
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Quote:
Originally Posted by All Darc View Post

After all, a flat plate in horizontal, following the wind orientation, have even lower drag, and some solar cars try to be a flat plate with a pilot and wheels, but just got around 0.078 or so.

The higher number comes not from the flat plate, but from the wheel pods and cabin shape. Look at them alone, and you will not see a good aerodynamic
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Old 02-21-2018, 10:45 PM   #8 (permalink)
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Yeah, Imagine that. But you can't kill the driver.

Take Stella solar car (3 different models but similar in performance) :

https://en.wikipedia.org/wiki/Stella_(solar_vehicles)

One paragraphy sounded like crazy absurd or a error, perhaps the editor just forgot to say that the recharging by few minutes a day and low speed drive on sun would take a month to fully charge the battery, since it's a 15KWH battery and a 1,5KW solar cells array :

"According to the developers, "in real-world conditions, the Stella's large solar array would be able to charge the car's 15 kWh battery pack in 30 to 45 minutes of being parked, sitting in traffic, or tooling around town at low speed" "

Of course, once the battery is charged, maybe by 8 hours on sun in 2 or 3 days, if the car is not used for many hours, the car can really produce more energy in one day than what it would consume in a day.

But for drive on city, and reduced battery need, it's really a good idea. If we left the solar array in home we would need larger and much expansive batteries.

I saw threads in this forum from 3 years ago, about buy solar cells, and I saw people getting cells from ALiexpress. But ALibaba have better offer. I was surprised with Sunpower flexible solar cells that could be as little as 1,0 or1,5 dollars per cell, in a 150 cell pack.

Solar power is comming to stay.

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The higher number comes not from the flat plate, but from the wheel pods and cabin shape. Look at them alone, and you will not see a good aerodynamic

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Old 02-22-2018, 02:45 AM   #9 (permalink)
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Quote:
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After all, a flat plate in horizontal, following the wind orientation, have even lower drag, and some solar cars try to be a flat plate with a pilot and wheels, but just got around 0.078 or so.

Keep in mind that the goal is to minimize drag with these cars, not just Cd. Drag is a function of Cd x A (frontal area). Flat solar cars may sacrifice a little Cd in order to greatly reduce frontal area.
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Old 02-22-2018, 08:28 AM   #10 (permalink)
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You are right. I must said drag coefficient instead of say just drag, when refering about Morelli 0,05 otherwise I would be reffering to another thing.

Drag coefficient it's the same for a vehicle or for a scale model of the same vehicle. For other side drag force it's different.

It's easier to a torpedo shell have reduced drag coefficient, as it have reduced drag force. The drag force fights less air with a reduced frontal area to push air.

For a solar car, the drag force it's important to calculate how much the motor will need to fight the atmosphere.
And there is also CDA, that is CD x Area (frontal). Os it can be calculated by removing the A in the equation od CD:



Some designs makes me a bit confused, like how define the frontal area, if by looking at it, in some cases, we see not a very clear division. I supose it's the area in a transversal cut, like cutting a salami, right? Is the point of cut would be until the wider area before it stat to get narrow? Is the point where the "salami slice" is larger ?


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Keep in mind that the goal is to minimize drag with these cars, not just Cd. Drag is a function of Cd x A (frontal area). Flat solar cars may sacrifice a little Cd in order to greatly reduce frontal area.


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