Low drag shape design

[JulianEdgar]

As I have often stated, in modifying cars I think by far the best approach is to measure what you have and then make specific modifications, testing each one as you proceed.

But what about a vehicle (including a trailer) that is being designed from scratch?

I think in that case the best approach is to look at the lowest drag vehicles that have ever been run on roads - and that's solar race cars.

The Leading Edge (Tamai) is I think the gold standard book - but it's also pretty complicated.



But there is one book that has an excellent, short and accessible chapter on ultra low drag aero. It's Speed of Light - the 1996 World Solar Challenge. It was published by the University of New South Wales (here in Australia) and the cheapest price I can find it for is in the link (Australian dollars).

The chapter on aero design is only 16 pages long but it covers the real essentials, including:

• attached flow
• wetted area
• boundary layers
• surface finish
• induced lift and ground interference drag
• wing tip drag
• frontal area
• interference drag
• ventilation drag
• side wind stability
• pitch stability

The chapter is by Clive Humphris, who was a Ford Australia aerodynamicist, designer of two solar race cars (including a second placegetter) and also co-designer of a world champion ultra mileage vehicle.

He summarises the best approach as series of rules, eg the second rule is that wetted area should be minimised while ensuring flow remains attached.

So if you're interested in developing a low drag vehicle from scratch (and none of the vehicles mentioned in the chapter have a Cd higher than 0.125!), this might be a book to look at.

[JulianEdgar]

[freebeard]

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

This article is about the structured design approach by architect Christopher Alexander. For other uses, see Pattern language (disambiguation).
A pattern language is an organized and coherent set of patterns, each of which describes a problem and the core of a solution that can be used in many ways within a specific field of expertise. The term was coined by architect Christopher Alexander and popularized by his 1977 book A Pattern Language.

A pattern language can also be an attempt to express the deeper wisdom of what brings aliveness within a particular field of human endeavor, through a set of interconnected patterns. Aliveness is one placeholder term for "the quality that has no name": a sense of wholeness, spirit, or grace, that while of varying form, is precise and empirically verifiable.[1] Some advocates[who?] of this design approach claim that ordinary people can use it to successfully solve very large, complex design problems.

Might have application to someone's solar home.
________________

Se also Ross Lovegrove

[Grant-53]

I have 75 technical books in my library. I would rate them on degree of difficulty. A mechanic uses arithmetic. A technician uses advanced algebra and an engineer or designer uses calculus. I have both Tamai and Katz along with a college text on fluid mechanics. A book is like a tool or a set of tools. An elegant solution is both simple and robust.

[aerohead]

Originally Posted by JulianEdgar

As I have often stated, in modifying cars I think by far the best approach is to measure what you have and then make specific modifications, testing each one as you proceed.

But what about a vehicle (including a trailer) that is being designed from scratch?

I think in that case the best approach is to look at the lowest drag vehicles that have ever been run on roads - and that's solar race cars.

The Leading Edge (Tamai) is I think the gold standard book - but it's also pretty complicated.



But there is one book that has an excellent, short and accessible chapter on ultra low drag aero. It's Speed of Light - the 1996 World Solar Challenge. It was published by the University of New South Wales (here in Australia) and the cheapest price I can find it for is in the link (Australian dollars).

The chapter on aero design is only 16 pages long but it covers the real essentials, including:

• attached flow
• wetted area
• boundary layers
• surface finish
• induced lift and ground interference drag
• wing tip drag
• frontal area
• interference drag
• ventilation drag
• side wind stability
• pitch stability

The chapter is by Clive Humphris, who was a Ford Australia aerodynamicist, designer of two solar race cars (including a second placegetter) and also co-designer of a world champion ultra mileage vehicle.

He summarises the best approach as series of rules, eg the second rule is that wetted area should be minimised while ensuring flow remains attached.

So if you're interested in developing a low drag vehicle from scratch (and none of the vehicles mentioned in the chapter have a Cd higher than 0.125!), this might be a book to look at.

Only wing-based vehicles would be associated with wetted area. Wings, as basic shapes for real passenger cars are not recommended. Single-and duel-passenger solar cars, which require the driver/passenger to be shoe-horned in, are already as large as the largest passenger cars ( 1991 Buick Roadmaster / Chevrolet Caprice ).
To make them user -friendly to a typical family, they'd have to have the dimensions of a box-truck.
Half-bodies, based on streamlined bodies of revolution ARE recommended as the basis for passenger cars.

[aerohead]

Originally Posted by JulianEdgar

Toyota offered a wing-derived 'Ra-Ra' solar car for sale in Japan, in the 1990s. I never saw one on the streets when I was over there.

[freebeard]

Single-and duel-passenger solar cars,

This explains the tail-gunner seating position.

A wing-based vehicle:

[aerohead]

Originally Posted by freebeard

This explains the tail-gunner seating position.

A wing-based vehicle:

So, now consider it expanded to accept a family of four, maybe pets, and enough luggage for holiday travel. Powertrain, offset-collision protection. Rollover roof crush standards, height limitations, bumpers, lights, etc..

[freebeard]

I still don't get how it works at all.

[aerohead]

Originally Posted by freebeard

I still don't get how it works at all.

It's just like a sailboat. Air passes over the airfoil obliquely and a net lift vector is generated, acting ahead and to the side of the vehicle. The car is impelled by the longitudinal component of the vector, attempting to 'catch' the low pressure which is forever moving ahead of it, as long as there's sufficient wind, and at an acceptable angle of attack to the foil.
This guy came through Lubbock, Texas and was pulled over for speeding on State Highway-82. He told the DPS officer that he thought '82' was the posted speed limit. The officer let him go.