This was one model of my entry for the TRIPLE contest, hosted by www.eurobricks.com.
More about the contest here:
-working contra-flapping wings
-wind up propulsion
-part count: 414
-size: 46 x 41 x 10,5 cm
The winding-up works by pulling an axle which makes the wind-up gear mash with the gear of the main drive shaft. Rotating the axle adds energy to the pullback motor. By pushing the axle back, the wind-up gear releases the main drive shaft and the model starts moving.
More pictures can be found here