Adrian Bejan | Evolution of Helicopters, from Design in Nature
In this video, Adrian Bejan goes backward in time from today and connects the evolution of airplanes with something much simpler, the design of boats with sails, to complete your exposure to this design of how things move. In this video, Adrian Bejan promises a PDF and an article on predicting the evolution of helicopters, whose main purpose is to hover like a jellyfish or a hummingbird. In this video, Adrian Bejan explains that helicopters do not use two wings, but rather a rotor made of several wings called blades, plus a small propeller at the end that rotates in a vertical plane to keep the helicopter oriented in one direction. In this video, Adrian Bejan says the paper repeats the sequence of steps seen in the evolution of airplanes, but now the question is about the rotor radius and the overall mass, derived analytically before being compared with data from the entire helicopter industry. In this video, Adrian Bejan ends by pointing to sharp correlations and a convergent evolution in which helicopters, small and large, end up looking the same.
Adrian Bejan links the path to today with antiquity and says the people selling the boats were actually very smart. In this video, Adrian Bejan uses this connection to set up the evolution of airplanes and then helicopters.
Bejan describes the helicopter rotor and its blades, and he adds a small propeller that prevents the helicopter from rotating in the opposite direction to the rotor. In this video, Adrian Bejan frames this as the basic design for hover.
He says the paper derives results analytically and then compares them with data from the entire helicopter industry. In this video, Adrian Bejan describes relationships that link the actual work to the engine size, and the engine mass to the fuel load and the total helicopter mass.
Bejan points to very sharp correlations in the data and says this indicates principles of physics at work. In this video, Adrian Bejan mentions the Cold War, institutions working independently in secret, and how they arrived at the same conclusions, like convergent technology and drones today.
He compares the airplane wing to the rotor blade, where air creates lift, the blade bends, and the stresses are highest at the axle, where the blades are attached. In this video, Adrian Bejan says this leads to the rotor radius being proportional to body mass and to the vehicle's length scale, which matches the convergent evolution of helicopters.
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