thinking about an underbody fairing

[lunarhighway]

last week i came across some coreoplast signs at work they where throwing out. these where swiftly transfered from the garbage to my trunk (wich sometimes isn't much difference)

initially i just wanted to make a grillblock, but i've got enough of the stuff to cover the lower end of the bumper as wel. i'd like to span the gap between the edge of the bumper and gently slope down to direct the air over the engine rather that straight onto it.

i know some people here have made similar setups so anyone willing to give some advice in welcome to do so.

what king of FE increase could i expect. i don't do a lot of highway driving but a great part of my dayly commute is between 70 and 90 km/h, a speed range where aero starts comming into play.

i just need to find a simple way to make a rigid frame to attach things to. there's nothing to attach the trailing edge of the cover to so i'll have to find something to span the length of the bumper to the rear. i was thinking in the direction of a thin wooden girder (whats a more appropriate word?) i think wood whould be lighter, stronger and cheaper than a metal tube exept aluminum maybe, of equal dimentions.... but i'll see what comes up.

hopefully i can find time soon to make this so i can start harvesting these FE gains