Final answer:
The maximum structural cruising speed of an aircraft is marked on the airspeed indicator by the Vno, the upper limit of the green arc transitioning to the yellow arc.
Step-by-step explanation:
The airspeed indicator marking that identifies the maximum structural cruising speed of an aircraft is known as the Vno, which stands for 'Velocity, not to exceed.' This is indicated on the airspeed dial of an aircraft as the upper limit of the green arc and the start of the yellow arc. Operating beyond this speed is not recommended under normal flight conditions because it could lead to structural damage or failure due to excessive airframe stress, turbulence, or sudden maneuvers.
Understanding the importance of Vno is crucial for safe aircraft operation, especially during cruising when air density changes with altitude, affecting lift and drag force on the aircraft. Wind tunnel tests, similar to those conducted by NASA researchers, help to determine these critical speed limits and the overall performance characteristics of the aircraft.