What causes car drag?

[JulianEdgar]

Originally Posted by freebeard

I think the delivery is fine, but the room acoustics are 'boomy'. Could you hang some drapery behind the camera to absorb some reverb?

It's just because I have cleaned up my office!

[freebeard]

The acoustic signature of a rectangular box.

(Wouldn't happen in a dome)

[JulianEdgar]

Originally Posted by freebeard

The acoustic signature of a rectangular box.

(Wouldn't happen in a dome)

Yes, that's right - it wouldn't.

And I am using just that technique in my spherical speakers - that just happen to be in my home office!



(And the speakers certainly sound a lot brighter since I cleared away the junk.)

[aerohead]

' Aero is more about the rear of the car than the front.'
Freeman Thomas, Director, Strategic Design, Ford Motor Company, 2008 Los Angeles Auto Show

[freebeard]

But the front and rear have to accommodate each other. Airdam/spoiler coupling?

[aerohead]

Once the forebody detail optimization achieves ' saturation,' the 'front' of a streamlined vehicle constitutes less than 6% of the overall vehicle drag, compared to almost 73% at the 'base,' behind the car. This is why the aft-body is so important to drag reduction. Why the GOODYEAR airships are shaped the way they are.
With Kamm's, simple, prismatic wind tunnel model, removing the aft-body created a jump in drag, from Cd 0.21, to Cd 0.70.
Kosin & Lehmann's fuselage went from Cd 0.066, to Cd 0.384.
W. A. Mair's 16% thickness, boat-tail research model went from Cd 0.066, to Cd 0.204.
From bio-mimicry, consider that the Peregrine falcon can achieve 255-mph vertically, on 1.5-pounds of thrust.
Or the 1929, ZMC-2, Metalclad airship,( 'Tin Bubble' ), by the Detroit Aircraft Company, pushing 2,108-square-feet of frontal area through the air, at 70-mph, with 299- horsepower.

[freebeard]

en.wikipedia.org/wiki/ZMC-2#Assembly

It's a fascinating story. The assembly procedure, in Alclad, sounds very similar to the current operations in Boca Chica by SpaceX. I'd bet Elon Musk could spring for a ZMC-2 clone in stainless steel.

Getting the Helium inside at the end was non-trivial.

[JulianEdgar]

Originally Posted by aerohead

Once the forebody detail optimization achieves ' saturation,' the 'front' of a streamlined vehicle constitutes less than 6% of the overall vehicle drag, compared to almost 73% at the 'base,' behind the car. This is why the aft-body is so important to drag reduction. Why the GOODYEAR airships are shaped the way they are.
With Kamm's, simple, prismatic wind tunnel model, removing the aft-body created a jump in drag, from Cd 0.21, to Cd 0.70.
Kosin & Lehmann's fuselage went from Cd 0.066, to Cd 0.384.
W. A. Mair's 16% thickness, boat-tail research model went from Cd 0.066, to Cd 0.204.

But, as you so often do, you move the goal posts wildly and then pretend we're still talking about the same thing.

We're talking about what causes the various proportions of drag on current cars, not talking about cutting off the back half of a 1930s model and pretending that the change in drag is somehow analogous to the topic.

If you want to be on the topic, why not discuss the drag/thrust pattern shown on the Jaguar, or the centreline pressures on the Hyundai?

[aerohead]

Yeah, seems like pocket change, in a relative sort of way.
The ZMC, although low drag, was reported to induce air sickness for the crews on occasion. As an aerial reconnaissance or weapons platform it might be a bust.
The 1961- 2020 Hughes / McDonnel Douglas, OH-6 Cayuse, LOACH, MD Defender, Quiet Defender ( UFO ), is of even lower fineness ratio, 2.33:1, for the main fuselage, however the rear rotor boom would greatly improve the 'ride quality.'
They swarm by AeroStealth's at night sometimes. Ya never know they're there until they're THERE ! No lights. Wicked.

[aerohead]

Originally Posted by JulianEdgar

But, as you so often do, you move the goal posts wildly and then pretend we're still talking about the same thing.

We're talking about what causes the various proportions of drag on current cars, not talking about cutting off the back half of a 1930s model and pretending that the change in drag is somehow analogous to the topic.

If you want to be on the topic, why not discuss the drag/thrust pattern shown on the Jaguar, or the centreline pressures on the Hyundai?

Correct me if I'm mistaken, but ' What causes car drag' does not encompass the specificity with which you speak.
' Current cars' is ex post facto.
And since most of the drag of modern cars remains a function of what's NOT there, it's a perfect segue into what I posted.
Automotive drag is about pressure drag.
Pressure drag is an artifact of flow separation on the aft-body.
Separation is a function of aft-body shape.
An introduction to known shapes, devoid of separation would be fundamental to any meaningful understanding of 'car drag.'
If you want to be on topic, then discuss the highest attainable centerline aft-body pressures recognizable. You won't find them on any Jaguar or Hyundai product.