World Surveillance Group Inc (fka WSGI)

[Renaissance]

there are several papers written on this subject out of wright patterson. In addition, they held small competition in 2011 for land based hybrid motors.

http://www.wpafb.af.mil/news/story.asp?id=123281664


"Each of the four undergraduate engineering teams was given an all-electric, ground-based propulsion system (an electric motorcycle) and challenged to extend the range by modifying the system into a hybrid propulsion system. Two of the universities -- Colorado State University and University of California-Davis -- created an electro-chemical energy conversion hybrid system utilizing a hydrogen fuel cell. The other two teams (Brigham Young University and the University of Dayton) were challenged to tackle the problem via a thermo-chemical energy conversion approach utilizing a small 6-hp class IC engine, exploring both series and parallel hybrid approaches. The teams were able to able to develop up to a 50% increase in system range and up to a 10% reduction in system weight."

edit:
Here is a more recent article (not from W-P)

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3926242/