Final answer:
When a pilot decreases power in an airplane with a constant speed propeller during a stabilized cruise, the propeller governor enters an underspeed condition, temporarily adjusting the propeller pitch to maintain the set RPM.
Step-by-step explanation:
When the pilot of an airplane with a constant speed propeller decreases power in a stabilized cruise for a descent, the propeller governor temporarily enters a condition of underspeed. The governor's job is to adjust the blade pitch to maintain a certain RPM. When power is reduced, RPM drops, signaling the governor to decrease the pitch of the propeller blades to try to maintain the set RPM. This is analogous to cruise control in cars, which keeps the vehicle at a steady speed.
In the context of aircraft and helicopters, understanding rotational kinetic energy is crucial. Just like helicopters must not allow their blades to slow below a critical velocity to maintain lift, airplanes must manage the propeller speed to ensure efficient flying conditions. The propeller governor automates this process, adjusting the pitch in response to changes in power settings. The gravitational potential energy in a descending helicopter can be used to increase the rotational kinetic energy of the blades, but if a plane's propeller falls off, it will no longer be able to generate thrust.