Making a more efficient, aerodynamic soapbox gravity race car

[orengomotors]

Originally Posted by aerohead

From the table below,we find the drag minimum at the bottom of the curve's 'bucket',at a chord to thickness ratio of 3.92:1

ok, so 3.92 it will be!

and the body shape?
whats the optimal body shape for this car?

the subsonic land speed record cars are a good inspiration?





why are those cars so long? the optimal shape of 3.92:1 is shorter.
i'm imagining a car like that but with open wheels. what do you think?

[orengomotors]

i found some interesting short videos:

https://www.youtube.com/watch?v=qt7G...ature=youtu.be

https://www.youtube.com/watch?v=LO5ZKSka91c

https://www.youtube.com/watch?v=vk7i...ature=youtu.be

https://www.youtube.com/watch?v=q540...ature=youtu.be

https://www.youtube.com/watch?v=1hEV...ature=youtu.be

https://www.youtube.com/watch?v=c-07...ature=youtu.be

[darcane]

Originally Posted by orengomotors

the subsonic land speed record cars are a good inspiration?

why are those cars so long? the optimal shape of 3.92:1 is shorter.
i'm imagining a car like that but with open wheels. what do you think?

Good inspiration, but they have different goals than you and because of this, their designs may be challenging to apply to your build.

Aero is the hugely important in land speed racing (LSR). The streamliners tend to be long because they have a lot of stuff to pack in the car (parachutes, fire suppression system, robust cage, drivetrain, etc) while minimizing frontal area. They also want to separate the center of pressure and center of mass to improve stability, and adding length and a vertical wing to the rear of the streamliner helps there.

For the streamliners, I think the most forward thinking designs are a series of cars called the Nebulous Theorem. Costella & Yacoucci's tiny little streamliner, Nebulous Theorem, set a record of 352.525 mph (567km/h) with a 1520cc 4 cylinder.
Worlds Fastest 4 Cylinder Nebulous Theorem II
Jack Costella's Official Website

[botsapper]

Originally Posted by orengomotors

ok, so 3.92 it will be!

and the body shape?
whats the optimal body shape for this car?

the subsonic land speed record cars are a good inspiration?





why are those cars so long? the optimal shape of 3.92:1 is shorter.
i'm imagining a car like that but with open wheels. what do you think?

Landspeed legend Breedlove, created an open-wheeled dragster for aerodynamic demo purposes. NHRA used wheel pants for while but deemed it sketchy after several crashes, but drivers swear it did not affect their safety and was not dangerous. http://www.nhra.com/blog/popup.aspx?...PictureId=7769

[orengomotors]

Originally Posted by darcane

Good inspiration, but they have different goals than you and because of this, their designs may be challenging to apply to your build.

Aero is the hugely important in land speed racing (LSR). The streamliners tend to be long because they have a lot of stuff to pack in the car (parachutes, fire suppression system, robust cage, drivetrain, etc) while minimizing frontal area. They also want to separate the center of pressure and center of mass to improve stability, and adding length and a vertical wing to the rear of the streamliner helps there.

For the streamliners, I think the most forward thinking designs are a series of cars called the Nebulous Theorem. Costella & Yacoucci's tiny little streamliner, Nebulous Theorem, set a record of 352.525 mph (567km/h) with a 1520cc 4 cylinder.
Worlds Fastest 4 Cylinder Nebulous Theorem II
Jack Costella's Official Website

Thank you, you have taught some things to me!
i thought that because LSR aero is focused on reducing drag and improving stability that it was a good idea to apply their shape.
i don't have any idea of how the shape has to be, looking LSR cars i see lots of different shapes, noses and boat tails.

[freebeard]

Nice.


http://www.nhra.com/blog/popup.aspx?AssetGalleryId=984&PictureId=7769



Make this an open-wheeler and you're back to a belly tank, with it's problematic ground interactions. Better to start here:


http://www.vmmv.org/tanktk/me262/me262.htm

Not quite a half-body. The bottom is flat for good ground interaction, but the top has a more Gothic than Romanesque arch. Maybe a Gaudi Parabolic arch? Wouldn't this would reduce crosswind lift and improve directional stability.

The question is how you get there from your rectangular chassis. I suggest a look at the Ford Indigo: https://en.wikipedia.org/wiki/Ford_Indigo


http://i.forbesimg.com/images/2002/06/10/indigo_415x275.jpg

[orengomotors]

Originally Posted by botsapper

Landspeed legend Breedlove, created an open-wheeled dragster for aerodynamic demo purposes. NHRA used wheel pants for while but deemed it sketchy after several crashes, but drivers swear it did not affect their safety and was not dangerous. http://www.nhra.com/blog/popup.aspx?...PictureId=7769

i had never seen a dragster with wheel pants! wow

[orengomotors]

Originally Posted by freebeard

Nice.


http://www.nhra.com/blog/popup.aspx?AssetGalleryId=984&PictureId=7769



Make this an open-wheeler and you're back to a belly tank, with it's problematic ground interactions. Better to start here:


http://www.vmmv.org/tanktk/me262/me262.htm

Not quite a half-body. The bottom is flat for good ground interaction, but the top has a more Gothic than Romanesque arch. Maybe a Gaudi Parabolic arch? Wouldn't this would reduce crosswind lift and improve directional stability.

But the first image triumph is very close to ground, there aren't any ground interaction? why adding wheels will cause ground interactions? what are and how they work?
You know Gaudi? it is a very famous architect here!
The soapbox has an hexagonal shape, when seen from front, its an hexagonal "extrusion"

[freebeard]

That's the reason I mention his name. I also admire the Spanish anarchists in the 30s and think Catalonian independence might bring that back.

It isn't the added wheels, it the rounded bottom. aerohead has a chart. Starting from a hexagon section you could add curved lower skirts and get the Indigo shape going. Open front wheels and enclosed back wheels. Maybe with more boat tail.

Edit: Gaudi rant: The world-famous architect did a little-known (until 1956) project for New York city, the Hotel Attraction:


https://en.wikipedia.org/wiki/Hotel_Attraction

On the proposed site, the cabal erected a building in the shape of the number 11, with an unusual skin-and-core design almost intended for deconstruction. The site was cleared in September of 2011. The Gaudi design was proposed as an replacement, but instead 'they' chose the Freedom Tower as it more correctly propagandizes 'our freedumbs'. The Gaudi design was a masonry shell that would deflect or crush an airplane, like the Empire State building did in 1945.
[/rant]

[orengomotors]

Originally Posted by freebeard

That's the reason I mention his name. I also admire the Spanish anarchists in the 30s and think Catalonian independence might bring that back.

It isn't the added wheels, it the rounded bottom. aerohead has a chart. Starting from a hexagon section you could add curved lower skirts and get the Indigo shape going. Open front wheels and enclosed back wheels. Maybe with more boat tail.

well, catalonian independence is a big problem now, it is always on Tv and it is a constant battle Barcelona-Madrid. Catalonia only did a democratic votations to kwon how many catalans wanted independence and how many not. And from madrid they see that like a criminal act. But this is another subject

going back to aerodynamics, the rounded bottom causes the ground interactions?
so the triumph LSR "motorbike" isn't optimal? So whats best flat bottom with rounded edges or flat bottom with squared edges?

the bottom has to be flat? it can have a diffuser? what angle?