Neil's News

Airship Tails

16 December 2011

Our team at Google got the opportunity to fly in a Zeppelin yesterday. This is the first Zeppelin to fly in the US since the Hindenburg. I had been looking forward to this flight for several years. The photos are spectacular.

One of the many difference between the new Zeppelin NT and the airships of the early 20th century is the tail. The new airship (above) has three fins arranged at 120°. The old airships (below) had four tail fins arranged at 90°: two vertical rudders for yaw (left-right), and two horizontal elevators for pitch (up-down).

The obvious advantage of having just three fins is the significant weight savings. Another advantage is the lack of a fin pointed straight down, which routinely sustained damage during ground operations. However, unlike the four fin system, three fins cannot be controlled by a human. To turn left, the top fin needs to be deflected, while the two angled fins need to be deflected by an amount which can only be computed by the sine and cosine of 2π/3 radians times the deflection of the top fin. Turning while climbing becomes even more complicated. The Zeppelin NT boasts fly-by-wire technology where computer interprets the pilot's joystick inputs and computes the correct angles for the flight control surfaces.

As much as I love digital computers, they actually aren't necessary for this task. The computation need not be done electronically -- it could be done mechanically. I threw together this mock-up of a three-encoder joystick which shows how the Graf Zeppelin and Hindenburg could have been controlled with just three tail fins. Here's a video:

The same joystick design could also be used for computer-less control of a trianguar omni-wheeled robot or a hexacopter.

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