What does the nitrogen driven oil accumulator allow during flight?

The nitrogen-driven oil accumulator primarily serves the function of assisting in the un-feathering of the propellers during flight. In the context of a multi-engine aircraft like the Beechcraft Travel Air BE-95, the propellers can be feathered to reduce drag and increase safety during engine failures. The accumulator provides the necessary hydraulic pressure to un-feather the propellers, allowing them to resume their normal operating position and thereby improving the aircraft's controllability and performance after an engine is lost.

This capability is crucial during a critical phase of flight, particularly during takeoff or climb, when having both propellers functioning can help maintain performance and safety. By restoring the propeller's pitch from a feathered state, the accumulator directly contributes to the aircraft's ability to fly effectively on a single engine, which is a key design feature for safety in multi-engine aircraft.

In this manner, the design of the nitrogen-driven oil accumulator directly supports the un-feathering process by providing instantly available pressure, thus facilitating necessary maneuvers in flight and enhancing operational reliability.