The Norden Bomb Sight manual

depending upon which way the motor is rotating. When the shaft rotates and the roller presses against the ridge of the bail, a precessional force is applied to the gyro. The direction of the force depends upon the direction the roller is rotating. The precessional force will cause the gyro and cardan to rotate in azimuth. This would force the auto-pilot clutch against the stop until slippage occurred. Any movement of the auto- pilot clutch when flying on AFCE causes the plane to turn. NOTE: Precession motor no longer used.

H. PDI System Fig. 7

The Pilot Direction indicator is a double acting voltmeter. With the switch turned "on", when the circuit is equalized, or when the sta- bilized brush is centered, the pointer (of the pilot indicator) stands in the middle of the scale. When the stabilized brush is off center, the circuit now being unbalanced, the pointer of the PDI moves to one side to indicate the dir- ection which the airplane must turn. The PDI system in the stabilizer consists of a resistance coil and a stabilized brush. It is connected to an indicator in the pilot's com- partment in such a manner as to indicate the approximate amount of turn, and the direction of the turn necessary, at any time when the circuit is energized. The brush is stabilized by the directional gyro through either the auto-pilot clutch or by the bombsight clutch, when the bomb- sight is installed.

I. PDI Wiring

As previously stated the pilot's direction indicator is an instrument operating as a double acting voltmeter. The action taking place in the stabilizer is as follows: The current passes from the PDI switch to the coil, through the coil, and back to number one pole. The signal from the coil is picked up by the brush and passes through poles five and six (see stabilizer wiring diagram) to the PDI instrument in the pilot's cockpit. The brush is stabilized by the directional gyro. When the plane turns left the coil moves right under the brush and the signal or reading on the PDI indicates that a right turn is required to bring the plane back to straight flight, or to center the PDI brush. If the plane turns right the coil moves to the left under the stabilized brush and the PDI indicates that a left turn is required to center the PDI brush.