Truth Table for Aero. Streamlining Templates

[aerohead]

1) ' The optimum amount of streamlining then, is that for which the sum of friction and pressure drag ( profile drag ) is a minimum.'
Fluid Mechanics With Engineering Applications, page- 297
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2) ' The smallest values of the coefficient of parasite drag so far observed are those of well-designed bodies of revolution.'
Theory of Flight, page- 104.
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3) The lowest friction and pressure drag sum and lowest coefficient of aerodynamic drag for a streamlined body of revolution occurs with a fineness ratio of 2.5:1, and Cd 0.0379.
Figure 4.119, page- 200, Hucho, 2nd-Edition ( Re: Hoerner, 1965 ).
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4) If fineness ratio is smaller, pressure drag increases.
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5) If fineness ratio is larger, friction drag increases.
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6) '[L]ow drag can only be achieved when separation at the rear is eliminated.'
Hucho, page- 16, 2nd_Ed.
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7) '[P]ressure drag is the largest component in the aerodynamic drag. Its minimization is the true objective of motor vehicle aerodynamics.'
Hucho, page- 119.
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8) '[T]he optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image - produced through reflection from the roadway.'
Hucho, page-15.
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9) The lowest coefficient of aerodynamic drag for a streamlined half-body is realized when based upon a streamlined body of revolution of fineness ratio of 2.5:1, and Cd 0.0758.
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10) The ASTs are each based upon variations within the confines of a 2.5:1 fineness ratio streamlined body of revolution, as contributed from different sources.
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11) A novel feature of the ASTs are that they all remain within their original 'reflection' , with ground clearance 'removed' from the reflected body, rather than through bifurcation and lofting above the ground plane.
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12) Overall drag of the half-body with the addition of wheels will be determined by tire width.
( see ' Tire Width Impact on Fuel Economy,' by MetroMPG, #3 permalink, 3-15-2018, ( Re: BMW 318 ).
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13) By some reporting, contemporary wheel drag of passenger vehicles is on the order of Cd 0.10.
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14) ' A closer approach to the value of the basic body without wheels is only achievable through further integration of the wheels into the body,'
Hucho, page- 201, 2nd-Edition
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15) Integration of the wheels beyond what can be accomplished through active suspension / ground clearance, is addressed in 'The Leading Edge, by Goro Tamai.
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16) Up to a 70% wheel drag reduction via Tamai's presented technology is reported.
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17) The most current AST represents, schematically, the 70% wheel drag reduction technology.
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18) The AST wheel drag reduction technology respects all SAE' approach, breakover, and departure clearance angles.
( Please see SAE Handbook ).
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19) Paul Jaray demonstrated that the peculiar quasi- axysymmetricality of the half-body is not a mandatory condition of low drag, as long as cross-sectional area-per-unit-position along the body profile does not vary, which allows for semi-circular-to- more rectangular section, as long as critical edge radii and tumblehome are respected; facilitating improved space utilization.
( and exo-duct analogue to A.S.H.R.A.E. common practice )
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20) Vehicular length requirement for ultra-low drag, with respect to 'practical' length consideration has already been investigated and active aerodynamic solutions presented, since, circa-1939, by Baron Reinhard von Koenig-Fachsenfeld and others.
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21) As off-the-shelf technology, with the attribution as an 'optimum' architecture for low drag ( Refer to (8) ) , and when applied as a simple comparative tool, it may not be inconceivable that AST profiles could be capable of generating low drag modifications without need of additional R & D, as long as body porosity, or any underbody or wheelhouse corruptions of the basic, simple conditions are accounted for; and chosen AST profile properly integrates into the vehicle's initial aft-body profile.
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22) Results from on-road, Chrysler Proving Grounds, Bonneville Speedway, and full-scale / 1/3- scale wind tunnel testing imply such capability.

[JulianEdgar]

Sure, but that does not support in any way the approach that has been taken here in applying the template. Viz:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars

What you are describing in your post is one approach to developing a low drag car from scratch. (Only one approach, because of course solar cars don't follow a lot of these rules of thumb and yet develop the lowest drag of any vehicles ever.)

But nearly all of us are modifying existing cars, not building cars from scratch. A completely different endeavour.

[aerohead]

Originally Posted by JulianEdgar

Sure, but that does not support in any way the approach that has been taken here in applying the template. Viz:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars

What you are describing in your post is one approach to developing a low drag car from scratch. (Only one approach, because of course solar cars don't follow a lot of these rules of thumb and yet develop the lowest drag of any vehicles ever.)

But nearly all of us are modifying existing cars, not building cars from scratch. A completely different endeavour.

Since these four 'bullets' were also at the 'Hucho's 'templates' thread, I responded to them there.
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As to the solar cars, they do produce low drag as well.
I've attended three solar car competitions, plus an all-day visit with the SolarWorld GT team, at Texas Christian University, as they were traveling the world with their racer.
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1) One takeaway is that these cars can be as large as the largest production automobiles made in the recent past ( Chevrolet Caprice Classic, Buick Roadmaster, Cadillac Deville ).
2) As large as they are, typically, they seat a single occupant.
3) If they seat two, it's in tandem.
4) The driver/passenger are typically in a recumbent seating orientation.
5) The cars have terrific tumblehome requirements.
6) Pretty awful interior space utilization.
7) Part of their low drag is associated with the Bridgestone ECOPIA EP80, or Schwalbe Energizer-S electric vehicle, slick, racing tires of very narrow section. ( 57mm for the ECOPIA ) operating @ 800 KPa ( 116 psi ).
8) 'Knife-edge' trailing surfaces are typically chosen ( difficult to mount a license plate or DOT taillamps).
9) Frontal areas may range from 7.5-sq ft, to 14.2-sq-ft.
10) While I would 'jump' at the chance to commute in one, I'm uncertain if the rest of the world is ready.
11) 5-Star Safety ratings are very popular in the marketplace.
12) 'Scaling up' to more family-friendly frontal areas is a non-starter.
I love 'em, but seems like they'd be a hard sell, if not impossible.
Just thinking out loud.

[JulianEdgar]

Originally Posted by aerohead

Since these four 'bullets' were also at the 'Hucho's 'templates' thread, I responded to them there.
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As to the solar cars, they do produce low drag as well.
I've attended three solar car competitions, plus an all-day visit with the SolarWorld GT team, at Texas Christian University, as they were traveling the world with their racer.
--------------------------------------------------------------------------------------
1) One takeaway is that these cars can be as large as the largest production automobiles made in the recent past ( Chevrolet Caprice Classic, Buick Roadmaster, Cadillac Deville ).
2) As large as they are, typically, they seat a single occupant.
3) If they seat two, it's in tandem.
4) The driver/passenger are typically in a recumbent seating orientation.
5) The cars have terrific tumblehome requirements.
6) Pretty awful interior space utilization.
7) Part of their low drag is associated with the Bridgestone ECOPIA EP80, or Schwalbe Energizer-S electric vehicle, slick, racing tires of very narrow section. ( 57mm for the ECOPIA ) operating @ 800 KPa ( 116 psi ).
8) 'Knife-edge' trailing surfaces are typically chosen ( difficult to mount a license plate or DOT taillamps).
9) Frontal areas may range from 7.5-sq ft, to 14.2-sq-ft.
10) While I would 'jump' at the chance to commute in one, I'm uncertain if the rest of the world is ready.
11) 5-Star Safety ratings are very popular in the marketplace.
12) 'Scaling up' to more family-friendly frontal areas is a non-starter.
I love 'em, but seems like they'd be a hard sell, if not impossible.
Just thinking out loud.

Since you didn't respond, I'll say it again.

What you are describing in your post is one approach to developing a low drag car from scratch.

But nearly all of us are modifying existing cars, not building cars from scratch. A completely different endeavour.

[aerohead]

Originally Posted by JulianEdgar

Since you didn't respond, I'll say it again.

What you are describing in your post is one approach to developing a low drag car from scratch.

But nearly all of us are modifying existing cars, not building cars from scratch. A completely different endeavour.

Yes, and it's gone on long enough. We're done discussing it, you and I.
I never knew I'd experience a black hole.

[freebeard]

But nearly all of us are modifying existing cars, not building cars from scratch.

It hasn't been the same since ecomodder.com: Remove my membership