Ground Clearance vs Aerodynamic Drag

[Piotrsko]

Ah yes I remember the turnaround at Bob's big boy and Pershing drive fondly.

Question: is an airgap required to reduce high pressure formed under the belly pan?

[aerohead]

Originally Posted by California98Civic

So for the Schlor' about 3.5" ground clearance was best.

The graph did not show any test points lower than 9.13-inches,but does show a drag increasing trend line with reduced ground clearance as if they did test with compressed suspension.
So I'd have to say the the 'factory' clearance showed the lowest 'practical' Cd.

[aerohead]

Originally Posted by Piotrsko

Ah yes I remember the turnaround at Bob's big boy and Pershing drive fondly.

Question: is an airgap required to reduce high pressure formed under the belly pan?

For production,street driven automobiles,the airgap would provide the ground clearance necessary to prevent the chassis from striking the ground when ascending or descending driveway ramps or traversing railroad crossings,and providing some clearance during major rain events which might sweep a vehicle away in moving water.
Other than that,some ground clearance would maintain a separation from road and the bellys boundary layer which is thickening as the flow moves ever further under the car.
If the boundary layer were to reach the road,then it would choke the flow,leading to a pressure rise and instability.

[freebeard]

Flat plate at a rake or underbody tunnels?

[skyking]

I got the stock tires on the truck which will lower the area, and it also raises cruise RPM.
I also removed some steel blocks at the rear axles for another 1.25" at the back. Now the truck sits level with no rake at all.
I looked into lowering up front again, and I will call on the cost of some custom springs. I need to keep at least 1.5" for hard hits.
I can drop the rear easily with shackles. Still have to make a dam.
I take a long trip Monday to get a new used 5th wheel, so I might toss something together for just this trip.

[gone-ot]

Here in Arid-zona, back in the late 1950's-early 1960's, the police used a "pack of cigarettes" to test if your hotrod car was lowered too much. If the pack "fit" upright, you were OK; but if it didn't, you got a repair-order ticket (the first time).

[freebeard]

In California it was the center of the headlight. Famously captured on Hot VWs original Cal Look cover:


VW Forum - VZi, Europe's largest VW, community and sales - View Single Post - Greg aroson cal look beetle

Edit: Maybe it's worth pointing out that the car I was driving in those years (as shown on my avatar)—had it been lowered—would have been immune to such harassment.

[aerohead]

Originally Posted by freebeard

Flat plate at a rake or underbody tunnels?

Sorry for late response,just now caught your question.
Since there's such little published information I'm gonna guess that:
*tunnels would only be for record cars on a closed track,where downforce would be helpful around the banked curves.
*otherwise,a flat belly,and maybe raked,as Ford did with their Probe-IV

As we get closer to 2025,we may see some research papers on this sort of thing as carmakers attempt to reach 50+ mpg fleet average.

[aerohead]

Here is an image I adapted from the SAE Handbook which illustrates what manufacturers design to as to approach,ramp breakover,and departure angles,which will prevent a groundstrike when the vehicle is fully loaded.

[freebeard]

Sorry for late response,just now caught your question.

I had to think for a moment about what I was asking.





Bucky Fuller put his 'air keel' in the front, but I think he was going for rear end lift.

My thinking with the magic trumpet is that it would channelize the air—sort of give it someplace to go. This could be put into a wind tunnel with an L-shaped blocking plate for A-B testing.