| http://www.w3.org/ns/prov#value | - bout each rotor to propel the machine by selectively increased traction of the rotors on the work, said means including a universally pivotal mounting between one of the rotors and means for applying a tilting force about said pivotal mounting; said machine having its center of gravity located near a point in the biaxial plane and midway between said rotor axes, and the operator's seat being posit
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