I remember an engine that would not extend caused by a spark plug wire stuck to the muffler! Apparently the engine had been retracted without a sufficient cooling period and spark plug wire came to rest on the muffler and melted the insulation that turned to glue when it cooled down! Oddball malfunction for sure. Also heard rumors about pilots forgetting to add oil to the fuel in 2 stroke engines and another guy that accidentally added oil twice to the same batch of fuel. Then there was the pilot that leaned out his engine for peak power and melted a cylinder on takeoff. Seems to me that electric motors are the best way forward, but self launching with a motor in the nose gives very little prop clearance. The JETA looks promising.
JJ