A book to buy and read

[aerohead]

Originally Posted by JulianEdgar

We can very quickly see that you have not measured aero pressures on real cars on real roads (or if you have, you've forgotten what you did) when you write stuff like that!

For example, I don't know of even one road car that has a high vertical downwards force at the nose. And as for pressures at the area of the roof apex not impacting lift, well....

* The raw pressure data I'd theoretically measure would have no context, unless we had the actual axle loads.
* You'd want to take the curb-weight, plus all passengers, plus luggage / cargo, up to full-rated allowable gross weight, determine from the front/rear weight bias, the actual static axle loading, compared to any 'lift', whether positive or negative; and 'see' what that looked like.
* And it may not have registered, that a streamline half-body begins its boat-tailing at the drivers shoulder, at the roof apex.
* The boundary layer doesn't 'grow' as with conventional bodies. The velocity gradient is continuously falling, across a diminishing cross-section, while maintaining a gently-increasing pressure gradient, which the boundary layer 'loves.'
* By default, being 'streamlined', the profile cannot trigger separation. There is no pressure drag. Only friction drag, and that is at the observable minimum of all bodies, by definition.

* You might be surprised by a streamlined half-body.
* According to the airship designers, at zero-yaw, a streamline body of revolution produces zero-lift.
* 100% full, local atmospheric pressure is acting on the nose.
* At a 2.5:1 L/D ratio, perhaps as high as 91% of local barometric pressure is available over the aft-body.
* This would be the same for the half-body.
* The diffuser would counteract any rear lift.
* Hucho stated that , for passenger cars, neutral lift is a perfectly acceptable target.
* A dorsal appendage could address any crosswind / gust issues. It won't be long before roadside meteorological monitoring stations will communicate, directly, in real-time with vehicle AI, providing 'guidance' with respect to any problematic weather scenarios.

[JulianEdgar]

Originally Posted by aerohead

* September, 2020, Julian Edgar makes the comment that no ( not one! ) notchback produced since 1990 suffers separation at the end of the roof.
* In 2006, 16-years after 1990, Julian Edgar publishes, in autospeed, ' As with [many] booted sedans,... the airflow tends to separate form (sic) the body at the trailing end of the roof..... the streamline doesn't stick to the body of the roof in the roof/rear window transition but instead tends to leave at this point.'
* The statistical mean average lifespan for an automobile is 13-years.
* Statistically, 'ALL' of the 'many' notchbacks inferred by Mr. Edgar's statement would have been manufactured well beyond the 1990 cut-off date.
* Would Mr. Edgar like to address this discrepancy?

In 2006 in that article I was writing for the readers of AutoSpeed, and many of them still drove cars where yes, separation occurred at the end of the roof on notchbacks. An example is the 1986-1988 Commodore VL turbo, a car that (in modified form) was then still very popular with readers. That car had a roof / rear window angle that dated back to 1978. In fact, the VL Group A Walkinshaw remains one of the best aero specials ever built, and to achieve attached flow on the bootlid, they had to raise it massively.

The reason that I nominate 1990 as the date from which notchback airflow largely changed is that by that year, most manufacturers were producing cars that had much shallower angle rear windows. (Of course, that refers to cars first produced from that year, not carryover old models.) Here in Australia that included the VN Commodore and EA Falcon, and the same happened elsewhere.

And of course, rear window angles have got shallower, and boot lids higher, ever since - such that today, a notchback's airflow is often closer to a fastback.

There is no doubt that when old aero references (and they include more than just Hucho 2nd edition) describe notchback flow, they are usually describing something quite different to today's notchback cars - and to the vast majority of notchbacks of the last 30 years.

[JulianEdgar]

Originally Posted by aerohead

* The raw pressure data I'd theoretically measure would have no context, unless we had the actual axle loads.
* You'd want to take the curb-weight, plus all passengers, plus luggage / cargo, up to full-rated allowable gross weight, determine from the front/rear weight bias, the actual static axle loading, compared to any 'lift', whether positive or negative; and 'see' what that looked like.
* And it may not have registered, that a streamline half-body begins its boat-tailing at the drivers shoulder, at the roof apex.
* The boundary layer doesn't 'grow' as with conventional bodies. The velocity gradient is continuously falling, across a diminishing cross-section, while maintaining a gently-increasing pressure gradient, which the boundary layer 'loves.'
* By default, being 'streamlined', the profile cannot trigger separation. There is no pressure drag. Only friction drag, and that is at the observable minimum of all bodies, by definition.

* You might be surprised by a streamlined half-body.
* According to the airship designers, at zero-yaw, a streamline body of revolution produces zero-lift.
* 100% full, local atmospheric pressure is acting on the nose.
* At a 2.5:1 L/D ratio, perhaps as high as 91% of local barometric pressure is available over the aft-body.
* This would be the same for the half-body.
* The diffuser would counteract any rear lift.
* Hucho stated that , for passenger cars, neutral lift is a perfectly acceptable target.
* A dorsal appendage could address any crosswind / gust issues. It won't be long before roadside meteorological monitoring stations will communicate, directly, in real-time with vehicle AI, providing 'guidance' with respect to any problematic weather scenarios.

Normal mish mash of irrelevancies, red herrings, etc.

This was in response to Aerohead claiming:

5) all the low pressure of the suction peak can be overwhelmed by the high local static pressure acting at the nose and tail.

There is no high pressure acting downwards at the nose of any normal road car. Another example of Aerohead's weird theories crashing into reality.

[aerohead]

Originally Posted by JulianEdgar

In 2006 in that article I was writing for the readers of AutoSpeed, and many of them still drove cars where yes, separation occurred at the end of the roof on notchbacks. An example is the 1986-1988 Commodore VL turbo, a car that (in modified form) was then still very popular with readers. That car had a roof / rear window angle that dated back to 1978. In fact, the VL Group A Walkinshaw remains one of the best aero specials ever built, and to achieve attached flow on the bootlid, they had to raise it massively.

The reason that I nominate 1990 as the date from which notchback airflow largely changed is that by that year, most manufacturers were producing cars that had much shallower angle rear windows. (Of course, that refers to cars first produced from that year, not carryover old models.) Here in Australia that included the VN Commodore and EA Falcon, and the same happened elsewhere.

And of course, rear window angles have got shallower, and boot lids higher, ever since - such that today, a notchback's airflow is often closer to a fastback.

There is no doubt that when old aero references (and they include more than just Hucho 2nd edition) describe notchback flow, they are usually describing something quite different to today's notchback cars - and to the vast majority of notchbacks of the last 30 years.

What would we make of an article, also about the Mitsubishi Lancer VGs, in 2014, in which they're remarking in the year 2014, that ' One of the main reasons of aerodynamic drag for sedan vehicles is the flow separation near the vehicle's rear end.' which was published in the International Journal of Mechanical & Mechanatronics Engineering IJMME-IJENS Vol: 14 No. 02 ?

[aerohead]

Originally Posted by JulianEdgar

In 2006 in that article I was writing for the readers of AutoSpeed, and many of them still drove cars where yes, separation occurred at the end of the roof on notchbacks. An example is the 1986-1988 Commodore VL turbo, a car that (in modified form) was then still very popular with readers. That car had a roof / rear window angle that dated back to 1978. In fact, the VL Group A Walkinshaw remains one of the best aero specials ever built, and to achieve attached flow on the bootlid, they had to raise it massively.

The reason that I nominate 1990 as the date from which notchback airflow largely changed is that by that year, most manufacturers were producing cars that had much shallower angle rear windows. (Of course, that refers to cars first produced from that year, not carryover old models.) Here in Australia that included the VN Commodore and EA Falcon, and the same happened elsewhere.

And of course, rear window angles have got shallower, and boot lids higher, ever since - such that today, a notchback's airflow is often closer to a fastback.

There is no doubt that when old aero references (and they include more than just Hucho 2nd edition) describe notchback flow, they are usually describing something quite different to today's notchback cars - and to the vast majority of notchbacks of the last 30 years.

' Vast majority' does not constitute 'ALL.'

[aerohead]

Originally Posted by JulianEdgar

Normal mish mash of irrelevancies, red herrings, etc.

This was in response to Aerohead claiming:



There is no high pressure acting downwards at the nose of any normal road car. Another example of Aerohead's weird theories crashing into reality.

How do you explain the 100% atmospheric pressure acting on the nose of a 1968 Volkswagen Transporter?
I'm looking at Figure 6.8, Hucho.
How do you explain the 100% atmospheric pressure acting on the nose of the circa 1936, Jaray car, Figure 9.4, page 160, AERODYNAMIC DRAG, Horner, 1951. Hucho uses the 1960s edition of the book.
How do you explain the 100% atmospheric pressure acting on the nose of a L/D= 5.5, streamline body of revolution, depicted in the same book?
How do you explain the 100% atmospheric pressure acting on the nose of the body depicted in Figure 2.4, page 51, Hucho, ( which is 100% accurate for the first 85.5% of the body) ?
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' Normal' is a weasel word. It cannot be quantified. It has no place in a scientific conversation.

[freebeard]

How do you explain the 100% atmospheric pressure acting on the nose of a 1968 Volkswagen Transporter?
I'm looking at Figure 6.8, Hucho.

For sake of clarity, could you quantify the downward component in the Figure you point toward.

[aerohead]

Originally Posted by freebeard

For sake of clarity, could you quantify the downward component in the Figure you point toward.

all available existing pressure is acting against the nose and front bumper of the bus.

[Vman455]

Originally Posted by aerohead

all available existing pressure is acting against the nose and front bumper of the bus.

Yes, but how much of the resultant force acts on the vertical axis? That's what's in question here; if very little force is exerted in a direction parallel to the vertical axis, there's no way it can "overcome" the suction acting over the hood, roof, and rear window.

[freebeard]

Minor correction:
"there's no way it can "overcome" the suction acting over the hood, roof, and rear window.'