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The Fulton Skyhook May 26, 2012

Posted by peterxu422 in Science, Superheroes.
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One of the best scenes in The Dark Knight was when Batman was in Hong Kong apprehending a crime boss. He asked his tech expert, Lucius Fox, how he would be able to get back into a plane without it landing. Fox suggested Skyhook, a technique used by the CIA for getting their agents out of hotspots.

The Fulton Skyhook, as it was called, was developed by a man named Robert Edison Fulton Jr. The system works by attaching a modified weather balloon to a 500 ft nylon cable and the other end to the person or cargo to be recovered. The nose of the pickup plane is modified to have a protruding 30 ft ‘V’ that would hook onto the nylon cable as the plane flew into it, dragging the cargo with it. The back of the plane opens up where crewmen would try to reel in the cargo and bring it safely into the aircraft. More detailed information could be read here.

The article mentions an interesting test that was performed, where they tested the system on a pig.

The pig survived the test, even after it began to spin out of control while it flew through the air at 125 mph. Once the pig had its feet on the ground and regained its orientation, it began to attack the crew.

The first actual human pickup didn’t take place until 1958 when Marine Staff Sergeant Levi W. Woods was successfully hoisted in during a test of the system. The process took only 6 minutes and Wood’s avoided the spinning the pig endured simply by extending his arms and legs.

I find it interesting to note how Woods avoided the violent spinning situation by simply extending his arms and legs. In doing this, Woods increased what’s known as his moment of inertia (I), the tendency to resist rotation. The greater your moment of inertia, the less you will rotate. The reason this is true is because of nature’s tendency to conserve Angular Momentum (L), the amount of rotational motion. If your angular velocity, how fast you’re spinning, is w, then angular momentum and moment of inertia are related by the formula L=I*w. If you have a large I, then you must have a smaller w (you spin more slowly) in order to keep L the same.

The way you can increase your moment of inertia is by increasing the radius of your rotation. In Wood’s case, he did this by extending his arms and legs. The situation is exactly the same as a figure skater going into a spin. They spin faster when they pull their arms in close to their body because they have reduced their moment of inertia. To compensate, their rotation rate must increase in order to conserve angular momentum.

Here is the scene with the Skyhook in The Dark Knight. The final installment, The Dark Knight Rises, comes out July 20.

VIDEO: The dark knight plane scene

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