Underbody spoilers vs bellypan

[Sunwapta]

Same as my post earlier today on spoilers vs full wheel skirts - would two or three spoilers mounted across a vehicle's frame work as well as a full bellypan?

I noted in the post below that if front air dams work to some degree why not put a couple more under the vehicle to reduce drag (but not vertical air dams but appropriately angled air deflectors.) ie at some distance behind the air dam I imagine turbulence increases due to the frame and drivetrain components. Would a spoiler help streamline the airflow under those components.

Does reducing ground clearance REALLY reduce drag?

Originally Posted by SteveP

OK, just to confuse things further, here's something I ran across late today. It's from an SAE paper, 951906, "Vehicle Design Strategies to Meet and Exceed PNGV Goals" by Timothy C. Moore and Amory B. Lovins, found here

https://www.rmi.org/images/PDFs/Tran...nStategies.pdf

The following comes from page 11:

"Rather than smooth the underbody and attempt to tuck chassis
components up out of the flow, the industry strategy has
tended towards air dams below the front bumper to force much
of the flow around the vehicle rather than under. This needlessly
increases frontal area and leads to the erroneous notion
that achieving very low aerodynamic drag requires extremely
low ground clearance[5]."

Footnote [5] says:

"If chassis components are streamlined or otherwise covered
by a smooth floorpan to prevent interference drag, there is
little reason, beyond the limited exposure of more of the tires’
frontal area, to prevent the airflow from passing under the car
(P. MacCready, AeroVironment, personal communication,
April 1995). Allowing the airflow to pass under the car can
actually aid in eliminating lift-induced drag."


In case you are not familiar with "P. MacCready" or AeroVironment, see

Paul MacCready - Wikipedia, the free encyclopedia

--Steve

[FastPlastic]

From what I understand you can use this trick with decent results. This is similar to an arrangement I'm working on with my Jeep. You would probably need more then two or three for a car for it to work well. The big thing is getting them spaced/angled correctly to work optimally.

[aerohead]

I have no data for undercar multiple spoilers,so I'm worthless to you on that one.----------------- With respect to ground clearance,I would infer from the really low-drag concept-cars,that limiting ground clearance is good for mpg,even with cars which have completely smooth undersides.Active suspension is always involved,and lowering only occurs at speed,and never on surface streets or arterials.