On Piper Cub and C150, 152, 172 (turned off) engine can by driven by air flow - in that case drag is much more higher. During my basic trainning instructor was turning off the engine when he could. In order to get better L/D in an emergency I was teached to slow the plane and stop the propeller. My last proficiency check was performed with another FI - he didn't turn off the engine, only idle the throttle. I didn't make it to the runway...by a bit. I'm almost sure that with stopped propeller it was possible.
Sorry for my poor English, lot of work have to be done on it
