Given a free hand in the design, his team developed a continuously variable transmission system that allows the petrol engine and electric motor to work separately or in tandem.
The B-1B has a "variable-geometry" or swing-wing design: The wings are swept forwards, almost at right angles to the body, for take-off and landing and cruising.
My last conversation with Adrian Bejan ended on the notion that if design in nature is a universal principle of the material world, then freedom is the key variable that determines how efficiently designs can evolve over time.