The parts of the airflex clutch that give the propeller shaft ahead rotation are illustrated in view A of figure 12-6. The clutch tube nearest the engine (forward clutch) is inflated to contact and drive the forward drum with the engine. The for-ward drum is keyed to the forward drive shaft, which carries the double helical forward pinion at the afterend of the gear box. The forward pinion is in constant mesh with the double helical main gear, which is keyed to the propeller shaft. By following through the gear train, you can see that, for ahead motion, the propeller must rotate in a direction opposite to the rotation of the engine. (See the directional arrows.)

Reverse Rotation

The parts of the airflex clutch that give the propeller shaft astern rotation are illustrated in view B of figure 12-6. The reverse clutch is inflated to engage the reverse drum, which is then driven by the engine. The reverse drum is keyed to the short reverse shaft, which surrounds the forward drive shaft. A large reverse step-up pinion transmits the motion to the large reverse step-up gear on the upper shaft. The upper shaft rotation is opposite to the rotation of the engine. (Note the directional arrows in view B.) The main reverse pinion on the upper shaft is in constant mesh with the main gear. By tracing through the gear train, you should see that for reverse rotation the propeller rotates in the same direc-tion as the engine.

The diameter of the main gear of the airflex clutch is approximately 2 1/2 times as great as that of the forward and reverse pinions. Thus, there is a speed reduction of 2 1/2 to 1 from either pinion to the propeller shaft.

Since the forward and main reverse pinions are in constant mesh with the main gear, the set of gears that is not clutched in will rotate as idlers driven from the main gear. The idling gears rotate in a direction opposite to their rotation when carrying the load. For example, with the forward clutch engaged, the main reverse pinion rotates in a direction opposite to its rotation for astern motion. (Note the dotted arrow in view A of fig. 12-6.) Since the drums rotate in opposite direc-tions, a control mechanism is installed to prevent the engagement of both clutches simultaneously.