Wednesday, August 07, 2013

Azon Bomb

The AZON bomb was perhaps the world's first smart bomb.  AZON stood for Azimuth Only, which I'll explain. It was officially named the VB-1, the VB stood for Vertical Bomb. The whole idea of a smart bomb is that primitive explosives aren't very clever. You drop them you throw them... they detonate wherever they land when the impact, fuse or timer triggers the explosion. At some point some military minds began thinking about steering them. This is the fundamental idea behind a "smart" bomb. The  first steering mechanism of course was radio control. This was used mostly in 1944 and 1945. More here.

On this topic, I must give the hat tip to Tesla for inventing radio control in 1898. All later designs are derived from his ideas. This particular design was developed by by Major Henry J. Rand and Thomas J. O'Donnell. the word "design" there sounds like they designed a whole bomb, not so. The Azon Bomb was just a special tail fin unitbolted to a 1,000-pound GP bomb (General Purpose). While that's true, it understates what a big step this was.

With the addition of this unit, the bomb’s trajectory could be adjusted in flight via radio signals which moved the fins. But this didn't allow total control through three dimensional space. It only adjusted the yaw axis. So let's explain that. An airplane manners in 3 axis, yaw, pitch and roll. Roll is controlled by the flaps on the wings and literally could roll the airplane like a barrel. So imagine that rotation as one axis. Pitch is effectively up and down. The pilot pushes the stick forward, you dive, he pulls back you climb. It's controlled by the horizontal flaps (ailerons) on the tail. Yaw is the one you're trying to figure out. Yaw is only left/right movement controlled by the single vertical flap on the tail fin.  Here the Axon bomb is falling (a purely vertical movement) and the axon unit steers with fin adjustments. To aid steering a candela  flare was attached to the tail so a bombardier could see the bomb better for remote steering.

Four antennas wrapped around the fins and signal was tuned by a single on board radio. This was powered by a small battery with about 3 minutes of life. But three minutes was plenty. The transmitter ont eh aircraft operated at 25 watts and controlled 3 signals.  The first signal at 30-40 hertz, triggered the flare. Then two other signals controlled the flaps: one at 475 hertz for left deflection, one on 3,000 hertz for right deflection. these are extremely low frequencies.

Prior to this given good weather hitting large targets like factories was doable, but small targets like railroads, roads and bridges was difficult. But the axon could be steered onto much smaller targets.
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