Mark www.aeronutz.free-online.co.uk has a passion for rubber powered 1-cell, 1 actuator planes. The principle is very sound, take away the electric motor and add a motor that is its own power source and most of the weight as gone.
So why not explore another avenue? Take the motor out of the equation and use two actuators to power an ornithopter (flappy thing).
I offer no mechanical arrangement, if you come up with one that looks promising I'll offer to write the control algorithms.