Quote:
Originally Posted by racprops
First need more info on Rockettail
Second my van already has vortex generators.
Third ground effects.
So bottom line how much MPG improvements can these aero mods give, in a percentage of MPG improvement.
Rich..
Here are few pictures of my van:
|
I don't think we can say definitively.
1) I know only of a Naval officer's Master's Thesis on a Dodge Pickup, which investigated an airdam as low as your's.
Extending down even with the belly returned the lowest drag.
2) Deeper than that only increased drag, however, if extended to within one inch of the pavement, it indicated the lowest drag. For racing only. Very conditional!
3) CAR and DRIVER found an airdam they tested to be most effective when it wrapped around the leading edge, extending as close as possible to the front tires, closing the gap.
4) The deep rocker panel extensions are an unknown quantity. Typically, for passenger vehicles, they extend no lower than the belly.
5) And then you have the big-rigs using deep skirts below the semi-trailer, and these are laboratory developed.
6) Extending the panels, picking up behind the rear wheels would help ,maintain a flow surface which currently does nor exist.
7) Aeronautical engineer, Gary Wheeler, who invented AIRTABs, developed them originally for a notchback car, to assist in flow reattachment. As the van has no structure behind it onto which separated flow could attach, I've never understood how they could function as installed.
8) Drag reduction is from pressure recovery. Pressure recovery is from attached flow decelerating on a diminishing cross-section in the direction of flow.
9) There's no surface like that.
10) 'pinching' the wake, if that actually happened, wouldn't have any affect on base pressure.
11) Hucho said, boat-tails and box-cavities are the only devices known to actually reduce drag.
12) No 2-D, 'aeronautical' devices ever reduced drag in 3-D flow.