The Norden Bomb Sight manual

Fig. 3

B. Auto- Pilot Clutch Fig. 3

a tension of 18 to 24 pounds, so that the clutch will slip before any damage is done to any of the connected units. The auto-pilot clutch is also a mechanical arrangement affording a slip connection between the horizontal gyro and the PDI brush. The auto- pilot clutch has a two fold function. (1) Without the bombsight installed, the auto-pilot clutch provides a means of transmitting directional impulses from the directional gyro to the direct- ional panel. The clutch also provides a means of stabilizing the PDI brush. (2) With the bomb- sight installed, the auto-pilot clutch is disen- gaged. Any clockwise or counter-clockwise move- ment of the auto-pilot clutch under this condition will be caused by the rotation of the turn or drift knobs (either one causes the drift gear to rotate which in turn causes the auto-pilot clutch to rotate). Rotation of the course knobs will be transmitted from the drift gear through the auto-pilot clutch connecting rod to the auto- pilot clutch. The auto-pilot clutch is adjusted to slip at a tension of 10 to 12 pounds. The adjustment is provided by a spring and turret head screw. The adjustment of this tension is important.

C. Drift Gear Clutch Fig. 4

D. Direct- ional Gyro and Cardan Fig. 5 Fig. 18 pg. 33

The drift gear clutch is a slip connection between the drift gear and the PDI brush. Its function is to prevent damage to the PDI brush by any sudden extreme rotation of the drift gear. The drift gear obtains its stabilization in azi- muth from the stabilized bombsight case (through the drift worm which is an integral part of the bombsight case and therefore stabilized by it), with the bombsight mounted, and through the drift gear clutch this stabilization is transmitted to the PDI brush and to the auto-pilot clutch. The tension of the clutch is from 6 to 8 pounds and is obtained by adjusting the tension of the spring on the screw under the drift gear. The directional gyro is a gyroscope with the spin axis mounted in a horizontal plane and pivot- ed to the cardan at the center of mass of the gyro. The purpose of the gyro is to provide and maintain an azimuth reference line. The directional gyro rotates about an approx- imately horizontal axis. It is carried by hori- zontal gudgeons working in bearings in a cardan, which cardan itself rotates in vertical gudgeons working in bearings in the stabilizer housing.