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Old 11-26-2020, 03:34 AM   #1 (permalink)
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Ultra low drag vehicles

I don't think I have linked to this here before.

If you're after ultra low drag and you are starting from scratch (velomobile, unique car, solar car, gravity car, unique RV) here are some things to pay attention to.


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Old 11-27-2020, 02:49 PM   #2 (permalink)
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In addition to the solar racers look at the velomobiles of the IHPVA on recumbents.com and the motorcycles at craigvetter.com. High performance sailplanes are very efficient as well.
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Old 11-27-2020, 05:33 PM   #3 (permalink)
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Questions:
  • Is the order important, i. e. attached flow and wetted areas more significant than frontal area and interference drag?
  • With an open wheel vehicle (my favorite use case) is the interference drag between the wheel/tire and the body or is it between the axle/suspension/steering linkage and those?

How well would a Dymaxion [Omni-directional Transport] with a boxed cavity truncation fare against these guidelines?
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Old 11-27-2020, 06:03 PM   #4 (permalink)
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Quote:
Originally Posted by freebeard View Post
Questions:
Is the order important, i. e. attached flow and wetted areas more significant than frontal area and interference drag?
The reference I am quoting puts them in the order of importance shown in the video.
Quote:

With an open wheel vehicle (my favorite use case) is the interference drag between the wheel/tire and the body or is it between the axle/suspension/steering linkage and those?[/LIST]
In the context of the video - neither. It refers to where different body parts join eg wheel spats to main body.

Quote:
How well would a Dymaxion [Omni-directional Transport] with a boxed cavity truncation fare against these guidelines?
You can guess that as well as I can!
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Old 11-27-2020, 07:33 PM   #5 (permalink)
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I'm in the process of re-designing my velomobile. This new design will be the third iteration.

Are there any free tools that you are aware of that will aid in the design of the shell, which will give actual charts or numbers to work with and not just a graphical representation? I'm looking for something that tells me what the air is doing as it passes over the shape, whether the flow is laminar or turbulent, whether the boundary layer is attached, what the pressure is at various points in the shape, overall drag coefficient value, coefficient of downforce/life values, ect.

This video was a good basic primer, but the 6 actual steps listed to minimize drag, little was explained regarding exactly HOW it is done.

I don't have thousands of dollars for software or tens of thousands of dollars for wind tunnel testing, nor do I want to have to make multiple iterations of the same thing as that takes hundreds of hours of work each time just to get a chance to tuft test it.
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Old 11-27-2020, 08:07 PM   #6 (permalink)
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Quote:
Originally Posted by The Toecutter View Post
I'm in the process of re-designing my velomobile. This new design will be the third iteration.

Are there any free tools that you are aware of that will aid in the design of the shell, which will give actual charts or numbers to work with and not just a graphical representation? I'm looking for something that tells me what the air is doing as it passes over the shape, whether the flow is laminar or turbulent, whether the boundary layer is attached, what the pressure is at various points in the shape, overall drag coefficient value, coefficient of downforce/life values, ect.

This video was a good basic primer, but the 6 actual steps listed to minimize drag, little was explained regarding exactly HOW it is done.

I don't have thousands of dollars for software or tens of thousands of dollars for wind tunnel testing, nor do I want to have to make multiple iterations of the same thing as that takes hundreds of hours of work each time just to get a chance to tuft test it.
The short answer is: no there isn't. If there were, car companies wouldn't spend millions on computers and aero software, and hundreds of millions on wind tunnels.

This is one occasion when copying one of the generic low-drag shapes will probably get you 90 per cent there.
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Old 11-27-2020, 08:31 PM   #7 (permalink)
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Quote:
In the context of the video - neither. It refers to where different body parts join eg wheel spats to main body.
Wouldn't spats apply to a mono-hull? I'm thinking of three or more aeroforms flying in formation, connected by gnarly beams and struts.

This is why I liked Oliver Kuttner's in-wheel suspension and steering. It would allow for a properly filleted intersection.



The Toecutter — Blender has an Export To Paper Model function that will give you a cutting pattern for an arbitrary shape, but I haven't seen convincing CFD yet.
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Old 11-28-2020, 01:16 AM   #8 (permalink)
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Quote:
Originally Posted by freebeard View Post
Wouldn't spats apply to a mono-hull? I'm thinking of three or more aeroforms flying in formation, connected by gnarly beams and struts.

This is why I liked Oliver Kuttner's in-wheel suspension and steering. It would allow for a properly filleted intersection.
As we've previously discussed, I am loath to just guess stuff. And, since I have no tech literature on this subject, and haven't personally tested it, I have little idea.
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Old 12-02-2020, 12:11 PM   #9 (permalink)
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free tools

Quote:
Originally Posted by The Toecutter View Post
I'm in the process of re-designing my velomobile. This new design will be the third iteration.

Are there any free tools that you are aware of that will aid in the design of the shell, which will give actual charts or numbers to work with and not just a graphical representation? I'm looking for something that tells me what the air is doing as it passes over the shape, whether the flow is laminar or turbulent, whether the boundary layer is attached, what the pressure is at various points in the shape, overall drag coefficient value, coefficient of downforce/life values, ect.

This video was a good basic primer, but the 6 actual steps listed to minimize drag, little was explained regarding exactly HOW it is done.

I don't have thousands of dollars for software or tens of thousands of dollars for wind tunnel testing, nor do I want to have to make multiple iterations of the same thing as that takes hundreds of hours of work each time just to get a chance to tuft test it.
The International Human Powered Vehicle Association ( IHPVA ) would probably be your best bet. They represent the international community of university engineering departments, which come together south of Battle Mountain, Nevada for land speed record attempts, on a section of state highway, intermittently closed to through traffic by state police for the event.
They run fully-enclosed streamliner bicycles, and three-wheel velomobiles.
Battle Mountain's convention center is a hive of activity during qualifications and competition.
Lot's of Cd 0.11 bikes and 85-mph on a good day! It's a real hoot to attend. It used to be $ 35/ year ( US ) to join, and receive newsletters.
Check out their website. Or attend, and take in Bonneville, during the same week.
Last time I attended, one of the amateur members did 57-mph in his Coroplast-clad 3-wheeler.
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Last edited by aerohead; 12-02-2020 at 12:15 PM.. Reason: add data
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Old 12-03-2020, 12:37 AM   #10 (permalink)
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At recumbents.com there is the shell design program that can be used to create a shell form. The file then can be used in CFD programs such as AutoDesk. The question as with all measuring devices is how good is good enough?

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