Originally Posted by
truefaith
Q17. When the plane goes into descent without increasing power with RPM, airspeed increases, what does the CSU do to maintain constant RPM
(a) increase the blade angle
(b) to remain covered by fuel irrespective of the aircraft attitude
(c) decrease the blade angle
(d) maintain blade angle
The key to figuring out this question is to consider what would happen to the speed of the propeller if the aircraft airspeed increased (for example, in a descent) and the propeller governor took no action - in other words, if the propeller governor did not change the blade angle as it is supposed to.
If the speed of the aircraft increases (with no change to engine power setting, as would be the case if you just nosed over into a descent) and the propeller governor took no action, the speed of the propeller would also increase.
The purpose of the propeller governor is to keep the propeller turning at a constant RPM regardless of aircraft speed. So, if the speed of the aircraft increases (and the power setting is not changed), the propeller governor will increase the blade angle of the propeller - so that the propeller 'takes a bigger bite of the air' with each turn - and the propeller speed thus remains constant at the speed that the pilot has set using the propeller RPM control.
Similarly, if you attempt to climb without changing the power setting, the aircraft will slow down a bit, and the propeller governor will reduce the propeller blade angle so that the propeller 'takes a smaller bite of the air' with each revolution, and thus maintains the speed you have set with the propeller RPM control.
Michael