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Old 07-25-2022, 03:47 PM   #18 (permalink)
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behind the rear axle

Originally Posted by JRMichler View Post
I took photos of the underside. The first photo is under the front bumper looking to the rear.

There is no air dam, except for a spat in front of each front tire. The underside is belly panned from the front bumper back to the rear axle, with gaps for the front suspension and exhaust system. This truck is front wheel drive, and the hybrid does not have a four wheel drive option. Ford did not leave space for a drive shaft to the rear axle in this vehicle.

The next photo is under the rear bumper looking forward.

The belly pan stops at the rear axle. There is no rear diffuser underneath, just an open area. But that open area is above the belly pan, so does not have high velocity air hitting things. This is consistent with a figure from Aerodynamics of Road Vehicles by Hucho:

The largest drag reduction comes from belly pans extending from the front bumper back to the rear axle, with only minimal benefit from belly pans after the rear axle.

I do not intend to experiment with front air dams or belly pans on this truck. Ford did too good a job, and I see no opportunity to make a noticeable improvement in this area.
In Hucho's 2nd-Edition underbody research, for the Audi 100-III, all the forward belly panels allowed for the rear panel, which provided as much drag reduction as the forward panel.
If a 2.8-degree upswept 'diffuser' took the place of the 'level' rear panel, the Audi would experience an additional 20% drag reduction.
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