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Glenn’s Computer Museum

The museum is incomplete: the last change was on 9/11/2014. A change log is here.

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Norden Bombsight

One of the most famous devices of WW II is the Norden bombsight, often mentioned along with radar and the atomic bomb as the most umportant technologies in winning the war. There is lots of good reference material on the web, including this great site about for bombsights.

We are fortunate to have a complete Norden bombsight (with the optional X-1 reflex sight). A large part of the bombsight consists of two stabilization gyroscopes. The actual analog computing element (called the rate end) is the upper right portion. On the left is a diagram from the Bombardiers Information File (BIF), dated 1944 showing the major components. This very informative document is available from our site here (warning: this is a 50MB file). Below this diagram is is a closer view of the top portion. Using the knobs on the right side that connect into the rate end, the bombardier enters the altitude, airspeed, turn and drift rate of the plane, and the drag factor (“trail”) for the type of bomb to be dropped. Several other alignment controls must be set. The target is sighted through the telescope that looks down through the bombsight.

The rate end unit performs continuous calculations (as the sight angle to the target changes or new inputs are made) of when to release the bomb and the course the plane should fly. Near the end of the “bomb run”, the plane’s autopilot is connected to the bombsight and it actually steers the plane. The bomb release can be controlled directly by the computer.

Fortunately, we also have a separate (and never used) rate end (the computer component). On the right it is taken apart so you can see the analog computing mechanism. Note the disk and wheel integrator assembly: the wheel is on a splined shaft just below the middle of the left half and the disk is sticking vertically out of the right half.

In addition to the bombsight, the BIF, and the extra rate end, we have the maintenance manual that which contains a wealth of detail on how the bombsight works.

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