3d Shape with lowest drag coefficient subsonic ground level

AI Thread Summary
The discussion focuses on identifying the 3D shape with the lowest drag coefficient for a motorcycle at subsonic speeds and ground level. A symmetrical airfoil with a truncated tail is suggested, though concerns are raised about increased drag from truncation. The NACA 0021 airfoil is considered, but challenges arise in modifying it to meet specific dimensions while maintaining optimal drag characteristics. The ideal fineness ratio for ground performance is noted as 5:1, with aspirations to achieve a drag coefficient below 0.1 for speeds around 200 kph. Ultimately, the NACA 0021 remains a strong candidate, but its adaptability and testing limitations are acknowledged.
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Hello,

What shape has the lowest drag coefficient at ground level and at subsonic speeds (0-150kph) with the following dimensions?

Width 60cm (at 45%)
Height 120cm (at 45%)
Length 220cm

These dimensions will fit my motorcycle (not too narrow and not too long).

I am thinking it would be a symmetrical airfoil with a truncated tail but I do not know for sure. That is why I am asking.

The shape will have 10-20cm ground clearance.

Thank you for your time, this stuff is way over my head.
 
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A teardrop shape would likely be pretty close to ideal. Truncating the tail would likely increase drag.
 
I'd have to agree with you there.

I have been looking at airfoiltools.com.

Stretching the naca 0021 airofoil to 128.7% gives the required 60cm thickness with a 220cm chord. However the widest point is at 30% length not 45% length. It is impossible to change this. Also the changed airfoil cannot be tested to determine it's drag coefficient.

The same naca0021 airfoil would be stretched vertically to double the thickness to reach the required height of 120cm. However this is impossible to create and impossible to test.

Considering that a naca0021 airfoil with a fineness ratio of 3:1 is perfect in the air and 5:1 ratio on the ground I definitely want to get as close to the latter ratio.

Using the perfect shape of the naca 0021 airfoil I should be able to achieve sub 0.1 drag coefficient and reach speeds of around 200kph at 10kw.

It is unknown if there is a shape better than the naca 0021.
 

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