A book to buy and read

[aerohead]

Originally Posted by JulianEdgar

And that's fine. But the trouble is, you refuse to acknowledge when people quote from more recent references - let alone learn from them.

So we're stuck in an era where:

• full wheel covers always gave the lowest drag
• lift was caused by separation
• airflow direction can be predicted by The Template
• rear spoilers 'reach up' to flow
• airflow separates at the end of the roof of notchbacks

.... and so on - all of which are wrong for any cars of the last 30 years.

* what is communicated to the viewer when, a multi-billion dollar multi-national corporation, which could possess/ construct, the best technology imaginable, choose MOON discs when they attempt land speed records.
* You've yet to master the Bernoulli theorem, so I advise you to keep your mouth shut until you do. Your way out of your depth. Book sales be damned!
* The 'template' is a known quantity. It provides for fully-attached flow.
* All the spoilers listed in Hucho's 2nd-Edition were immersed in turbulence. And yes, they extend upwards through what would otherwise be turbulence, allowing the flow to intercept a target which will force the flow to follow a path of less severe pressure rise; and allow reattachment once the severe positive pressure is abated. Page - 61, ' One way to generate negative lift is a rear spoiler, the decisive feature being the relative height of 'separation' in relation to the rest of the body.' Hucho.
Page-282, 'negative lift values of... negatively inclined wings... increase with clearance above the body surfaces as they enter the ' undisturbed air flow.' ( what do you think Huchos' talking about? )
* Since notchbacks are a mutilation to a streamlined contour, one attempts to minimize the damage with whatever will pass muster with the stylist, designer, and production engineer. ( A Cd 0.22 notchback is not the same as a Cd 0.09 half-body ).

[aerohead]

Originally Posted by JulianEdgar

Sorry, I don't really see it.

I am not saying the cars (ie the house) was/were wrong.

I am saying that analysing modern aerodynamics on the basis of car shapes that are often 60+ years old is not a good idea.

Nor is pretending we have learnt nothing about car aero since the 1930s/1950s/1960s/1980s.

It would be a bit like taking the contemporaneous 1960s state of the art analysis of the house that you show - and applying it today. So no IR temperature analysis, no air leakage tests, no modern insulating materials or selective coatings on solar heaters, etc. Let alone discussions of embodied energy, etc.

I have absolutely no issue with Aerohead choosing not to keep up with current car aero thinking. But I have major issues with his continually misleading people on the basis of his outdated ideas and understandings.

If he qualified his comments ("This is what I read 40 years ago and I am not sure it is still current") then that would be fine. But in fact he actively rejects any more recent references and/or tests.

And that isn't fine.

' [W]ith refinements in aerodynamics progress is towards the body of revolution.' Hucho, page 107 ( or skip the refinements and just leap-frog to the body of revolution )

[aerohead]

Originally Posted by JulianEdgar

All correct!



Incorrect - as about a million streamline pics show. Here's one:



Note the airflow wrapping around those upper curves. Note how the streamlines get closer together. Note how this indicates higher airflow speed and lower pressure.

How you can seamlessly segue from correct material to absolute rubbish is beyond me.

You're looking at the wrong part of the car!
At the rear, the streamlines are diverging, velocity dropping, pressure rising.
That high pressure is associated with the high base pressure/ low pressure drag, low total drag, no vorticity. Cd 0.19.
You can't see the forest for the trees!

[JulianEdgar]

Originally Posted by aerohead

You're looking at the wrong part of the car!
At the rear, the streamlines are diverging, velocity dropping, pressure rising.
That high pressure is associated with the high base pressure/ low pressure drag, low total drag, no vorticity. Cd 0.19.
You can't see the forest for the trees!

Never mind. I think everyone else can see the airflow wrapping over the upper surfaces, giving those low pressures where the body curves are greatest. That's what we were discussing, remember?

[JulianEdgar]

I originally wrote:


So we're stuck in [Aerohead's] era where:

• full wheel covers always gave the lowest drag
• lift was caused by separation
• airflow direction can be predicted by The Template
• rear spoilers 'reach up' to flow
• airflow separates at the end of the roof of notchbacks

.... and so on - all of which are wrong for any cars of the last 30 years.

Now what points has Aerohead answered?

Originally Posted by aerohead

* what is communicated to the viewer when, a multi-billion dollar multi-national corporation, which could possess/ construct, the best technology imaginable, choose MOON discs when they attempt land speed records.

Aerohead isn't keeping up with the literature. A good example of where he simply refuses to be guided by more recent references.

* You've yet to master the Bernoulli theorem, so I advise you to keep your mouth shut until you do. Your way out of your depth. Book sales be damned!

Typical personal abuse - and note, no answer to the point. Aerohead still apparently believes that lift is caused by separation. At least 30 years out of date with cars.

* The 'template' is a known quantity. It provides for fully-attached flow.

No doubt. But that doesn't therefore mean it can predict flow direction, as Aerohead often uses it to. Same old logical fallacy. Dogs have four legs, but not all four-legged animals are dogs.

* All the spoilers listed in Hucho's 2nd-Edition were immersed in turbulence. And yes, they extend upwards through what would otherwise be turbulence, allowing the flow to intercept a target which will force the flow to follow a path of less severe pressure rise; and allow reattachment once the severe positive pressure is abated. Page - 61, ' One way to generate negative lift is a rear spoiler, the decisive feature being the relative height of 'separation' in relation to the rest of the body.' Hucho.
Page-282, 'negative lift values of... negatively inclined wings... increase with clearance above the body surfaces as they enter the ' undisturbed air flow.' ( what do you think Huchos' talking about? )

What was Hucho talking about? Well, self evidently, cars that mostly had a lot of separated flow! That is not the case with any car of basically the last 30 years.

* Since notchbacks are a mutilation to a streamlined contour, one attempts to minimize the damage with whatever will pass muster with the stylist, designer, and production engineer. ( A Cd 0.22 notchback is not the same as a Cd 0.09 half-body ).

Meaningless stuff, I am afraid. Just go and talk to a professional car aerodynamicist about "mutilation to a streamlined contour". They'll just say: WTF?

[aerohead]

Originally Posted by JulianEdgar

Never mind. I think everyone else can see the airflow wrapping over the upper surfaces, giving those low pressures where the body curves are greatest. That's what we were discussing, remember?

1) the nose and tail are part of the upper surface.
2) in side elevation view it's impossible for the streamlines not to be crowded together, it's an element of Bernoulli's relationship between displacement, velocity, and pressure.
3) I'd be surprised if you could find a member here at the aero forum that doesn't already firmly understand that.
4) that area near the roof apex does not govern lift. It doesn't matter how low the pressure is at that location. It's as if you were saying that our Hoover Dam could never be a success due to the high hydrostatic pressure out in the middle of the span, as if ignoring the countering force where the dam is anchored to the canyon walls.
5) all the low pressure of the suction peak can be overwhelmed by the high local static pressure acting at the nose and tail.
6) and no discussion about lift can ignore the underbody pressure distribution.
--------------------------------------------------------------------------------------
My # 9 comment is scientifically correct.

[aerohead]

Originally Posted by JulianEdgar

I originally wrote:


So we're stuck in [Aerohead's] era where:

• full wheel covers always gave the lowest drag
• lift was caused by separation
• airflow direction can be predicted by The Template
• rear spoilers 'reach up' to flow
• airflow separates at the end of the roof of notchbacks

.... and so on - all of which are wrong for any cars of the last 30 years.

Now what points has Aerohead answered?



Aerohead isn't keeping up with the literature. A good example of where he simply refuses to be guided by more recent references.



Typical personal abuse - and note, no answer to the point. Aerohead still apparently believes that lift is caused by separation. At least 30 years out of date with cars.



No doubt. But that doesn't therefore mean it can predict flow direction, as Aerohead often uses it to. Same old logical fallacy. Dogs have four legs, but not all four-legged animals are dogs.



What was Hucho talking about? Well, self evidently, cars that mostly had a lot of separated flow! That is not the case with any car of basically the last 30 years.



Meaningless stuff, I am afraid. Just go and talk to a professional car aerodynamicist about "mutilation to a streamlined contour". They'll just say: WTF?

I'm quite pleased to learn that every automobile sold in the last 30-years had Cd 0.09. That would be the reality of separation-free automobiles.
Hummer H-1s weren't really Cd 0.70. And Ariel Atoms weren't really Cd 0.68.
And Dodge Viper ACRs weren't really Cd 0.56. And Silverados weren't Cd 0.412. Pontiac Solstice wasn't Cd 0.45. Chevy Malibu Maxx wasn't Cd 0.37. Certainly todays' Nissan Versa notchback can also defy the laws of physics.
I'm glad also that the Tesla Model X now has 178 mpg-e at 70-mph, with a range of over 525-miles, even without the new 54% power density increase mentioned on the 22nd. ( 808-miles ).
No more dirt accumulating behind vehicles. Porsche Taycan Turbo Ss at 195-mph. We've finally achieved Hucho's limit.
Like driving on the Moon.

[freebeard]

2) in side elevation view it's impossible for the streamlines not to be crowded together, it's an element of Bernoulli's relationship between displacement, velocity, and pressure.
3) ....
4) that area near the roof apex does not govern lift. It doesn't matter how low the pressure is at that location. It's as if....

Cybertruck. One-dimensional apex with massive tumblehome.

Longitudinal vortexes work for free.

[JulianEdgar]

Originally Posted by aerohead

1)
4) that area near the roof apex does not govern lift. It doesn't matter how low the pressure is at that location. It's as if you were saying that our Hoover Dam could never be a success due to the high hydrostatic pressure out in the middle of the span, as if ignoring the countering force where the dam is anchored to the canyon walls.
5) all the low pressure of the suction peak can be overwhelmed by the high local static pressure acting at the nose and tail.

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....

[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?