Ultra low drag vehicles

[Grant-53]

The Ford Probe was an example of a low drag prototype that inspired a production vehicle.

[aerohead]

Originally Posted by freebeard

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?

1) Your 1st question isn't specific enough. We need some caveats, conditions of the vehicle specification in order to work with it.
2) The 1976 CNR project provides insight into the DYMAXION Car question.
* The Morelli body of the 'Banana' car was Cd 0.161.
* When wheels were added, the Cd jumped to Cd 0.35.
* When the wheels were 'integrated' ( Hucho's terminology ) better into the bodywork, the drag fell to Cd 0.201.
* Hucho has also written on the remarkable drag contribution of the open wheels of the Rumpler Limousine, measured at Volkswagen.
* The 1987 GM Sunraycer was reported to have a difference of Cd 0.089, and Cd 0.12 when the full wheel-fairing package was removed for the World Solar Challenge.
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As to the DYMAXION Car box cavity. Again, we'd need to know how much truncation would be performed, and then the type, and length of the box-cavity.
* Hucho depicts one type of architecture.
* United States Patent # 4,682,808, Filed July 24, 1985, by Alan J. Bilanin depicts a proper cavity. His twenty-one references date to as early as 1933.

[aerohead]

Originally Posted by freebeard

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.

I believe that we explored this situation over a decade ago. Around 1958, Mercedes-Benz published that, in spite of its significantly greater frontal area, and weight, that it's fully-enclosed Grand Prix race car had significantly less overall drag than the same car, as an open-wheeled race car.
And yes, it has to do with the interference drag of a 'mutilated' ( Frederick Lanchester's terminology ) form.

[aerohead]

Originally Posted by Grant-53

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?

The 2015, ECORUNNER - V, by Delft Technical University, may have reported the lowest extant drag for a land vehicle. Cd 0.0512.
This would have to be considered within the context of a 3.8-sq-ft frontal area vehicle, averaging 15-mph ( burn - and - coast ), on a closed-course, perhaps completely shielded from any wind, or terrestrial boundary layer.
It is a 'three-wheeler', so, it might qualify for a 'fairing' on a velomobile.
The 2006 PAC car-II is also a three-wheeler, and formally held the low-drag record at, Cd 0.07. Perhaps at a higher Reynolds number than the ECORUNNER-V.
Only you can judge how far you want to push the CdA. And under what conditions.

[aerohead]

Originally Posted by Grant-53

The Ford Probe was an example of a low drag prototype that inspired a production vehicle.

Yes, the PROBE-III. Cd 0.22. Which influenced the 4-Door, Ford Scorpio/ Merkur XR4Ti, Cd 0.34 w/o bi-wing spoiler, Cd 0.32 with.
The shorter, two-door sedans were Cd 0.33 with spoilers.
The Ford 'PROBE' production car, constructed at the joint-venture Ford / Mazda facility, took the 'PROBE' name, but none of the concept car's architecture.

[Piotrsko]

Originally Posted by aerohead

The 2015, ECORUNNER - V, by Delft Technical University, may have reported the lowest extant drag for a land vehicle. Cd 0.0512.
This would have to be considered within the context of a 3.8-sq-ft frontal area vehicle, averaging 15-mph ( burn - and - coast ), on a closed-course, perhaps completely shielded from any wind, or terrestrial boundary layer.

EXACTLY how would you shield from the terrestrial boundary layer? If it flies, it isn't a car, ditto for a vacuum.

[AeroMcAeroFace]

Originally Posted by Piotrsko

EXACTLY how would you shield from the terrestrial boundary layer? If it flies, it isn't a car, ditto for a vacuum.

What is meant by that, I think is that there is no wind across the road, the terrestrial boundary layer would be there if there is wind. It was a complicated way of saying, done on a windless day.

[aerohead]

Originally Posted by Piotrsko

EXACTLY how would you shield from the terrestrial boundary layer? If it flies, it isn't a car, ditto for a vacuum.

All one could do is not drive when there's wind, or solar convection currents present. That would limit the UK to 7-days/ year according to MIRA.
Aircraft are designed for 'flight' conditions, above Earth's TBL.
Aircraft do experience winds aloft, convective columns, Katabatic winds, the Jet Stream, clear air turbulence, and such, so they do have 'issues.'
Just not 'automotive' issues.

[The Toecutter]

Originally Posted by JulianEdgar

This is one occasion when copying one of the generic low-drag shapes will probably get you 90 per cent there.

I did that already, and it's definitely not 90% there, maybe 30% there, although I think that has a lot to do with the fact that I still have outboard open wheels. Due to the clearance issues posed with the steering geometry and suspension, wheel wells were difficult to implement. I wanted to avoid having large wheel well gaps and needed to retain access to the brake calipers and axle for maintenance/repairs(often on a sidewalk 30+ miles from home), so the first two shells had open/outboard wheels. And that is really bad for drag.

I made some farings for the front wheels out of aluminum, but they actually added drag. I didn't have them shaped right and their frontal area penalty likely outweighed any drag coefficient reduction they provided for the wheels, plus the backs of the farings seemed to act as parachutes. I over-sized the clearances for them because I did not want them to give me a flat tire, and even then there was a bit of rub that had to be corrected!

I'm working on a set of more narrow profile farings that may actually show an aerodynamic benefit. We'll see.

I think I solved how to shape the wheel wells for an inboard wheel design with an inverted half-toroid shape, which should hopefully allow operation without any tire scrubbing during cornering or over rough roads, for the next design iteration. If successful, I expect greatly reduced overall drag.

[aerohead]

Originally Posted by Piotrsko

EXACTLY how would you shield from the terrestrial boundary layer? If it flies, it isn't a car, ditto for a vacuum.

What immediately comes to mind would be a race course, buffered from ambient wind, embedded within the stadium, high crash-wall, environment. Like The Indianapolis Motor Speedway, or Phoenix International Speedway where I observed the Solar 500.
A laminar aircraft is designed for 'flight' conditions, up and away from terrestrial effects, such as Earth's boundary layer.
Hucho depicted an Urban boundary layer extending to around 525-meters AGL.
According to MIRA, there are only, on average, 7-days a year in England, free of terrestrial turbulence.