Quote:
Originally Posted by cfd_guy
How does a diffuser over 4 degrees magically make drag, but 3 degrees don't???
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Going off memory, rear underbelly angle of inclination should be limited to 10-degrees.
This is similar to the over the body angle being limited to 22-degrees.
I think with rear diffusers with vertical strakes or fins contain the air and keeps it from wandering or rolling off to the sides.
This containment zone between the fins I believe allows for angles greater than 10-degrees to exist and function as intended for ground effects.
I would think the 3-4 degree thing may apply to the initial curvature upward and not a mandatory angle to be maintained the entire length.