Propeller effect on the L/D of an aircraft (Pusher Propeller configuration) I recently performed an aerodynamic analysis of a fixed-wing UAV with a pusher propeller configuration. I found out that the L/D reduced by about 15% when compared to the body alone without propeller. I am investigating methods to mitigate this problem. 

The following are some details about the aircraft,
Wing Span = 2.5 m

Fuselage length = 2 m

MTOW = 25 kgs

Tandem wing configuration. The following image is a representative image.

Courtesy: Raytheon Coyote



Any suggestions will really be helpful.
You need to fair in the tail with a carbon fibre fairing/spinner such that the prop folds back and nests into it.  Like below.