What is It....

I have seen some pics of rv4's that have a second hole on the lower fuselage behind the control rod hole for the wing alerons...what is this hole for...it seems to have a flange of some type on it (viewing from the inside....)

Air vent

On my RV4 I chose to bring fresh air from under the wing into the cockpit(ala RV8) To do this I needed to install an flanged hole aft of the aileron exit hole on the left side of the fuselage.
http://img111.imageshack.us/img111/3373/00001993di.jpg